NOVEL METHOD OF MANUFACTURE OF METAL NANOPARTICLES AND METAL SINGLE-ATOM MATERIALS ON VARIOUS SUBSTRATES AND NOVEL COMPOSITIONS
20210252486 · 2021-08-19
Inventors
Cpc classification
C23C16/4417
CHEMISTRY; METALLURGY
B01J37/0219
PERFORMING OPERATIONS; TRANSPORTING
B01J37/0217
PERFORMING OPERATIONS; TRANSPORTING
B01J21/063
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J21/06
PERFORMING OPERATIONS; TRANSPORTING
B01J23/46
PERFORMING OPERATIONS; TRANSPORTING
B01J35/00
PERFORMING OPERATIONS; TRANSPORTING
B01J37/02
PERFORMING OPERATIONS; TRANSPORTING
Abstract
The present invention discloses a novel method and novel compositions comprising well-dispersed particulate metal materials, including metal nanoparticles and/or metal single-atom materials, on various substrates, said method comprising the use of atomic layer deposition (ALD) and optimization of the metal precursor dose time and the number of ALD cycles. Illustrative of the metals are Fe, Ni, Co, Ru, Rh, Ir, Os, Pt, Pd, and the like; and illustrative of the various substrates are carbon nanotubes (CNTs) (including multi-walled carbon nanotubes (MWCNTs), SiO.sub.2, TiO.sub.2, alumina, CeO.sub.2, ZnO, ZrO.sub.2, activated carbon, CuO, Fe.sub.2O.sub.3, MgO, CaO, graphene, and the like. The density of the dispersed metals on the substrates is significantly higher than the metal density
Claims
1. A method for depositing a metal onto a substrate by using ALD in a suitable reactor, to provide a well-dispersed metal/substrate composition, said method comprising one or more of the following steps: (a) obtaining a premeasured amount of a suitable metal precursor; (b) obtaining a premeasured amount of a suitable substrate; (c) making ready an excess amount of one or more suitable precursor gas; (d) degassing the substrate at a temperature ranging between about 100° C. and about 200° C. for a period of time ranging between about 5 hours and about 15 hours; (e) loading the degassed substrate into the reactor; (f) raising the temperature of the reactor to between about 100° C. and about 500° C.; (g) fluidizing the substrate particles in the reactor by using flowing inert gas; (h) loading the metal precursor into a bubbler heated to between about 40° C. and about 280° C.; (i) carrying the metal precursor particles into the reactor by using flowing inert gas; (j) feeding the one or more precursor gas separately into the reactor through a distributor plate to react with the metal precursor and produce the metal particles; (k) subjecting the reactor to vibration from vibrators to enhance particle fluidization during the ALD coating process; (l) continuing the reaction of the metal precursor and the one or more precursor gas in the reactor for a suitable dose time, and for suitable number of cycles, to result in deposition of the metal particles onto the substrate particles; (m) flushing the reactor with inert gas to remove unreacted metal precursor and precursor gas and any byproducts; (n) evacuating and cooling to ambient temperature; (o) obtaining the well-dispersed metal/substrate composition; wherein the suitable metal precursor and the one or more precursor gas are selected to be reactive with each other to produce metal particles; and wherein the suitable reactor is selected from a fluid bed reactor (FBR) or a viscous flow reactor or any other suitable flow types of reactors known in the art; and wherein said well-dispersed metal/substrate composition comprises metal nanoparticles and/or metal single atoms on said substrate
2. The method of claim 1, wherein the weight ratio of the suitable metal precursor to suitable substrate is in the range between about 0.05 and about 1.
3. The method of claim 2, wherein the weight ratio of the suitable metal precursor to suitable substrate is in the range between about 0.08 and about 0.15.
4. The method of claim 1, wherein in step (d) the degassing temperature is about 150° C.
5. The method of claim 1, wherein in step (d) the degassing period of time is about 10 hours.
6. The method of claim 1, wherein in step (f) the reactor temperature is about 400° C.
7. The method of claim 1, wherein in steps (g) and (i) the gas flow rate is controlled by mass flow controllers.
8. The method of claim 1, wherein in step (h) the bubbler is heated to about 115° C.
9. The method of claim 8, wherein the well-dispersed metal/substrate composition is a metal nanoparticle/substrate composition.
10. The method of claim 8, wherein the well-dispersed metal/substrate composition is a single metal/substrate composition.
11. The method of claim 1, wherein the metal is selected from Fe, Ni, Co, Ru, Rh, Ir, Os, Pt, and Pd.
12. The method of claim 1, wherein the suitable substrate is selected from inorganic non-metallic materials, metal oxides, and carbon materials.
13. The method of claim 12, wherein the suitable substrate is selected from carbon nanotubes (CNTs), SiO.sub.2, TiO.sub.2, alumina, CeO.sub.2, ZnO, ZrO.sub.2, activated carbon, CuO, Fe.sub.2O.sub.3, MgO, CaO, and graphene.
14. The method of claim 13, wherein when the suitable substrate is a carbon nanotubes substrate it is a multi-walled carbon nanotubes substrate.
15. The method of claim 1, wherein when the metal is Fe, Ni, or Co, the suitable metal precursor is ferrocene, nickelocene, or cobaltocene, respectively, and the suitable precursor gas is hydrogen gas.
16. The method of claim 1, wherein when the metal is Ru, the suitable metal precursor is selected from 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium, RuCp.sub.2, Ru(EtCp).sub.2, (EtCp)Ru(Py), and (MeCp)Ru(Py), and the suitable precursor gas is selected from O.sub.2 gas and O.sub.2/H.sub.2.
17. The method of claim 1, wherein when the metal is Rh, the suitable metal precursor is rhodium (III) acetylacetonate, and the suitable precursor gas is selected from O.sub.2 gas and O.sub.2/H.sub.2.
18. The method of claim 1, wherein when the metal is Ir, the suitable metal precursor is selected from Ir(acac).sub.3, (EtCp)Ir(COD), (MeCp)Ir(CHD), and IrF.sub.6, and the suitable precursor gas is O.sub.2/H.sub.2.
19. The method of claim 1, wherein when the metal is Os, the suitable metal precursor is OsCp.sub.2, and the suitable precursor gas is O.sub.2/H.sub.2.
20. The method of claim 1, wherein the suitable metal precursor is a mixture of two or more different suitable metal precursors of the same metal.
21. The method of claim 1, wherein the suitable metal precursor is a mixture of two or more different suitable metal precursors of two or more different metals.
22. The method of claim 1, wherein the suitable substrate is a mixture of two or more different suitable substrates.
23. The method of claim 1, wherein the metal in the obtained well-dispersed metal/substrate composition is selected from nanoparticulate metal, sub-nanoparticulate metal, and single metal atoms.
24. The method of claim 1, wherein the metal in the obtained well-dispersed metal/substrate composition has a higher density than metal densities obtained in other published methods.
25. The method of claim 1, wherein the metal in the obtained well-dispersed metal/substrate composition has well-defined and uniform dispersion on the substrate, whose dispersion ranges between 70% and 100%.
26. The method of claim 1, wherein the obtained well-dispersed metal/substrate composition exhibits more than six-fold enhancement of catalytic activity in the photocatalytic degradation of methylene blue over pure substrate alone.
27. The method of claim 26, wherein the metal is Fe and the substrate is TiO.sub.2.
28. The method of claim 1, wherein the obtained well-dispersed metal/substrate composition exhibits catalytic activity towards CO oxidation that is more than two orders of magnitude higher than that of reported literature catalysts.
29. The method of claim 28, wherein the metal is Fe and the substrate is SiO.sub.2.
30. A composition comprising metal nanoparticles and/or metal single atoms on a substrate, said composition obtained by a novel method for depositing a metal onto a substrate by using ALD in a suitable reactor, wherein said method comprises one or more of the following steps: (a) obtaining a premeasured amount of a suitable metal precursor; (b) obtaining a premeasured amount of a suitable substrate; (c) making ready an excess amount of one or more suitable precursor gas; (d) degassing the substrate at a temperature ranging between about 100° C. and about 200° C. for a period of time ranging between about 5 hours and about 15 hours; (e) loading the degassed substrate into the reactor; (f) raising the temperature of the reactor to between about 100° C. and about 500° C.; (g) fluidizing the substrate particles in the reactor by using flowing inert gas; (h) loading the metal precursor into a bubbler heated to between about 40° C. and about 280° C.; (i) carrying the metal precursor particles into the reactor by using flowing inert gas; (j) feeding the one or more precursor gas separately into the reactor through a distributor plate to react with the metal precursor and produce the metal particles; (k) subjecting the reactor to vibration from vibrators to enhance particle fluidization during the ALD coating process; (l) continuing the reaction of the metal precursor and the one or more precursor gas in the reactor for a suitable dose time, and for suitable number of cycles, to result in deposition of the metal particles onto the substrate particles; (m) flushing the reactor with inert gas to remove unreacted metal precursor and precursor gas and any byproducts; (n) evacuating and cooling to ambient temperature; (o) obtaining the composition comprising metal nanoparticles and/or metal single atoms on the substrate; wherein the suitable metal precursor and the one or more precursor gas are selected to be reactive with each other to produce metal particles; and wherein the suitable reactor is selected from a fluid bed reactor (FBR) or a viscous flow reactor or any other suitable flow types of reactors known in the art.
31. The composition of claim 30, wherein in the novel method the weight ratio of the suitable metal precursor to suitable substrate is in the range between about 0.05 and about 1.
32. The composition of claim 31, wherein in the novel method the weight ratio of the suitable metal precursor to suitable substrate is in the range between about 0.08 and about 0.15.
33. The composition of claim 30, wherein in step (d) of the novel method the degassing temperature is about 150° C.
34. The composition of claim 30, wherein in step (d) of the novel method the degassing period of time is about 10 hours.
35. The composition of claim 30, wherein in step (f) of the novel method the reactor temperature is about 400° C.
36. The composition of claim 30, wherein in steps (g) and (i) of the novel method the gas flow rate is controlled by mass flow controllers.
37. The composition of claim 30, wherein in step (h) of the novel method the bubbler is heated to about 115° C.
38. The composition of claim 30, wherein the obtained composition is a metal nanoparticle/substrate composition.
39. The composition of claim 30, wherein the obtained composition is a metal single atom/substrate composition.
40. The composition of claim 30, wherein the metal is selected from Fe, Ni, Co, Ru, Rh, Ir, Os, Pt, and Pd.
41. The composition of claim 30, wherein in the novel method the suitable substrate is selected from inorganic non-metallic materials, metal oxides, and carbon materials.
42. The composition of claim 41, wherein in the novel method the suitable substrate is selected from carbon nanotubes (CNTs), SiO.sub.2, TiO.sub.2, alumina, CeO.sub.2, ZnO, ZrO.sub.2, activated carbon, CuO, Fe.sub.2O.sub.3, MgO, CaO, and graphene.
43. The composition of claim 42, wherein in the novel method when the suitable substrate is a carbon nanotubes substrate it is a multi-walled carbon nanotubes substrate.
44. The composition of claim 30, wherein in the novel method when the metal is Fe, Ni, or Co, the suitable metal precursor is ferrocene, nickelocene, or cobaltocene, respectively, and the suitable precursor gas is hydrogen gas.
45. The composition of claim 30, wherein in the novel method when the metal is Ru, the suitable metal precursor is selected from 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium, RuCp.sub.2, Ru(EtCp).sub.2, (EtCp)Ru(Py), and (MeCp)Ru(Py), and the suitable precursor gas is selected from O.sub.2 gas and O.sub.2/H.sub.2.
46. The composition of claim 30, wherein in the novel method when the metal is Rh, the suitable metal precursor is rhodium (III) acetylacetonate, and the suitable precursor gas is selected from O.sub.2 gas and O.sub.2/H.sub.2.
47. The composition of claim 30, wherein in the novel method when the metal is Ir, the suitable metal precursor is selected from Ir(acac).sub.3, (EtCp)Ir(COD), (MeCp)Ir(CHD), and IrF.sub.6, and the suitable precursor gas is O.sub.2/H.sub.2.
48. The composition of claim 30, wherein in the novel method when the metal is Os, the suitable metal precursor is OsCp.sub.2, and the suitable precursor gas is O.sub.2/H.sub.2.
49. The composition of claim 30, wherein in the novel method the suitable metal precursor is a mixture of two or more different suitable metal precursors of the same metal.
50. The composition of claim 30, wherein in the novel method the suitable metal precursor is a mixture of two or more different suitable metal precursors of two or more different metals.
51. The composition of claim 30, wherein in the novel method the suitable substrate is a mixture of two or more different suitable substrates.
52. The composition of claim 30, wherein the metal in the obtained composition is selected from nanoparticulate metal, sub-nanoparticulate metal, and single metal atoms.
53. The composition of claim 30, wherein the metal in the obtained composition has a higher density than metal densities obtained in previously published methods.
54. The composition of claim 30, wherein the metal in the obtained composition has well-defined and uniform dispersion on the substrate, whose dispersion ranges between 70% and 100%.
55. The composition of claim 30, wherein the obtained composition exhibits more than six-fold enhancement of catalytic activity in the photocatalytic degradation of methylene blue over pure substrate alone.
56. The composition of claim 55, wherein the metal is Fe and the substrate is TiO.sub.2.
57. The composition of claim 30, wherein the obtained composition exhibits catalytic activity towards CO oxidation that is more than two orders of magnitude higher than that of previously reported literature catalysts.
58. The composition of claim 57, wherein the metal is Fe and the substrate is SiO.sub.2.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
[0016]
[0017]
[0018]
[0019]
[0020]
[0021]
[0022]
[0023]
[0024]
[0025]
[0026]
[0027]
[0028]
[0029]
[0030]
[0031]
[0032]
[0033]
[0034]
[0035]
[0036]
[0037]
[0038]
[0039]
[0040]
DETAILED DESCRIPTION
[0041] Before the present methods, implementations and systems are disclosed and described, it is to be understood that this invention is not limited to specific components, specific methods, specific implementation, or to particular compositions, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular implementations only and is not intended to be limiting. Neither are mechanisms which have been provided to assist in understanding the disclosure meant to be limiting.
[0042] In one embodiment, disclosed herein are novel compositions comprising well-dispersed metal nanoparticles (NPs) and/or metal single atoms on various substrates. These compositions are obtained via a novel method for depositing metals on said various substrates. In one aspect, the density of the metals on the substrates achieved by this novel method is significantly higher than the metal density in previously reported methods. Stated another way, a key differentiator of this method, as compared to prior art methods, is that it provides a higher number of atoms per given surface area, and consequently, a higher density of active sites on the substrate. The method disclosed herein allows deposition of a metal onto a substrate by using ALD in a reactor designed for carrying out ALD, such as, illustratively, a fluidized bed reactor (FBR) or a viscous flow reactor or other flow types of reactors known in the art, to provide a well-dispersed metal/substrate composition of the invention, wherein said method comprises one or more of the following steps: [0043] (a) obtaining a premeasured amount of a suitable metal precursor; [0044] (b) obtaining a premeasured amount of a suitable substrate, wherein the weight ratio of the amount of suitable metal precursor to suitable substrate is in the range between about 0.05 and about 1, preferably between about 0.08 and 0.15; [0045] (c) making ready an excess amount of one or more suitable precursor gas; [0046] (d) degassing the substrate at a temperature ranging between about 100° C. and about 200° C., preferably at about 150° C., for a period of time ranging between about 5 hours and about 15 hours, preferably about 10 hours; [0047] (e) loading the degassed substrate into the FBR; [0048] (f) raising the temperature of the FBR to between about 100° C. and about 500° C., preferably to about 400° C.; [0049] (g) fluidizing the substrate particles in the FBR by using flowing N.sub.2 gas with the gas flow rate controlled by mass flow controllers; [0050] (h) loading the metal precursor into a bubbler heated to between about 40° C. and about 280° C., preferably at about 115° C. (depending on the metal); [0051] (i) carrying the metal precursor particles into the FBR by using flowing N.sub.2 gas with the gas flow rate controlled by mass flow controllers; [0052] (j) feeding the one or more precursor gas separately into the FBR through a distributor plate to react with the metal precursor and produce the metal particles, such as metal NPs or single metal atoms, such that the precursor gas flow rate ranges between about 3 sccm and about 30 sccm, preferably between about 6 sccm and about 10 sccm; [0053] (k) subjecting the FBR to vibration from vibrators or suitable other methods known in the art (e.g., stirring) to enhance particle fluidization during the ALD coating process; [0054] (l) continuing the reaction of the metal precursor and the one or more precursor gas in the FBR for a suitable dose time, and for suitable number of cycles, to result in deposition of the metal NPs or single metal atoms onto the substrate particles; [0055] (m) flushing the FBR with inert gas (e.g., N.sub.2 gas, and the like) to remove unreacted metal precursor and precursor gas and any byproducts; [0056] (n) evacuating and cooling to ambient temperature; [0057] (o) obtaining the well-dispersed metal/substrate composition of the invention (i.e., metal NPs or single metal atoms/substrate composition);
wherein the suitable metal precursor and the one or more precursor gas are selected to be reactive with each other to produce metal particles, such as metal NPs or single metal atoms.
[0058] In another embodiment of the method of the invention, the metal may be selected from a broad variety of metals, illustratively including Fe, Ni, Co, Ru, Rh, Ir, Os, Pt, Pd, and the like. In another embodiment of the method of the invention, a broad variety of suitable substrates may be used in the method of the invention, including inorganic non-metallic materials, metal oxides, carbon materials, and the like, such as, illustratively, carbon nanotubes (CNTs) (including multi-walled carbon nanotubes (MWCNTs)), SiO.sub.2, TiO.sub.2, alumina, CeO.sub.2, ZnO, ZrO.sub.2, activated carbon, CuO, Fe.sub.2O.sub.3, MgO, CaO, graphene, and the like. In another embodiment of the method of the invention, a broad variety of suitable metal precursors may be used, such as, illustratively, ferrocene and the like, nickelocene and the like, cobaltocene and the like, respectively, along with hydrogen gas as the additional precursor; 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru (DER) and O.sub.2, or tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium [Ru(thd).sub.3] and O.sub.2, or RuCp.sub.2, Ru(EtCp).sub.2, (EtCp)Ru(Py), or (MeCp)Ru(Py), and the like, along with O.sub.2/H.sub.2; rhodium (III) acetylacetonate and the like, along with O.sub.2 or O.sub.2/H.sub.2; any one of Ir(acac).sub.3, (EtCp)Ir(COD), (MeCp)Ir(CHD), or IrF.sub.6, and the like, along with O.sub.2/H.sub.2; OsCp.sub.2 and the like, along with O.sub.2/H.sub.2.
[0059] It is understood that, if desired, instead of using only one suitable metal precursor in the method of the invention, two or more different suitable precursors of the same metal may be used. Also, as contemplated herein, two or more different suitable precursors of two or more different metals may be used together, in which case a composition comprising two or more well-dispersed different metals on the same substrate would be obtained. Likewise, if desired, instead of using only one suitable substrate in the method of the invention, two or more different suitable substrates may be used together, to provide a composition comprising one or more well-dispersed metal on two or more different substrates.
[0060] Another embodiment of the invention provides a general ALD strategy to prepare compositions comprising well-dispersed metal on a substrate, such as nanoparticulate metal atoms, sub-nanoparticulate metal atoms, and single metal atoms, on various substrates, via the ALD-mediated reaction of a suitable metal precursor with a precursor gas, through optimizing dose time of the metal precursor and the number of metal ALD cycles. In one aspect, the compositions obtained by the method include a higher density of well-dispersed, non-aggregated metal relative to the density of metal obtained in published methods.
[0061] While the novel technology herein has been illustrated and described in detail in the foregoing description, and in the following examples and the figures herein, the same is to be considered as illustrative and not restrictive in character. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.
EXAMPLES
[0062] The following examples further illustrate specific embodiments of the invention. However, the following examples should not be interpreted in any way to limit the invention.
[0063] EXAMPLE 1. General method for preparing metal single atoms via ALD. Generally, the following steps may be used to prepare single atoms via ALD: (a) putting certain amount of substrates ranging between about 1 g to 20 g in the reactor (e.g., FBR is used in this example for illustration); (b) fluidizing the substrate particles in the FBR by using flowing inert gas (e.g., N.sub.2 gas) with the gas flow rate controlled by mass flow controllers ranging between about 3 sccm and about 20 sccm, preferably about 7 sccm; (c) degassing the substrate at a temperature ranging between about 100° C. and about 200° C., preferably at about 150° C., for a period of time ranging between about 5 hours and about 15 hours, preferably about 10 hours; (d) raising the temperature of the FBR to between about 100° C. and about 500° C., preferably to between about 300-400° C.; (e) loading certain amount of the metal precursor ranging between about 0.2 g and about 2 g, into a bubbler heated to between about 40° C. and about 280° C., preferably at about 115° C.; (f) carrying the metal precursor into the FBR by using flowing gas (e.g., N.sub.2 gas) with the gas flow rate controlled by mass flow controllers ranging between about 3 sccm and about 20 sccm; (g) feeding the one or more precursor gas separately into the FBR through a distributor plate to react with the metal precursor and produce the metal particles, such as metal nanoparticles or single atom metal particles; (h) continuing the reaction of the metal precursor and the another precursor gas (e.g., H.sub.2) in the FBR for a suitable dose time ranging between about 10 s and about 600 s, and for a suitable number of cycles ranging between about 1 and about 30 cycles, preferably about 5 cycles, to result in deposition of the metal nanoparticles or single metal atoms onto the substrate particles; (i) flushing the FBR with inert gas (e.g., N.sub.2 gas) to remove unreacted metal precursor and precursor gas and any byproducts for a certain time ranging about 60 s and 1200 s; (j) evacuating and cooling to ambient temperature; (k) obtaining the composition comprising the metal/substrate material (i.e., the material comprising the metal NPs or single metal atoms deposited onto the substrate).
[0064] EXAMPLE 2. Methods. Preparation of Catalysts. The following is a representative, non-limiting example using Fe as the metal being deposited on three different supports. Fe single atoms were deposited on MWCNTs (US Nano Inc), SiO.sub.2 NPs (20-30 nm, US Nano Inc), and TiO.sub.2 NPs (DT 51, 100% anatase, ˜80 m.sup.2/g, Cristal Inc) by ALD using ferrocene and hydrogen (H.sub.2, 99.9%, Airgas) as precursors in a fluidized bed reactor, as schematically shown in
[0065] EXAMPLE 3. Characterization. The Fe mass fractions of prepared Fe samples with different Fe ALD cycles were measured by ICP-AES. The crystal structure of TiO.sub.2 was detected by XRD. The Fe supported on MWCNTs, SiO.sub.2, and TiO.sub.2 NPs were directly observed by FEI Tecnai F30 HRTEM. HAADF-STEM analysis was performed by Nion UltraSTEM 100. XAS was applied to verify the composition of Fe on the TiO.sub.2 nanoparticles. Raman spectra of TiO.sub.2 and Fe/TiO.sub.2 samples were obtained using a Horiba-Jobin Yvon LabRam spectrometer. The PL spectra were recorded with a HORIBA FL3-22 spectrometer (HORIBA, Edison, N.J.) to investigate the recombination of photo-generated e.sup.−/h.sup.+ pairs in the samples. UV-visible DRS of Fe/TiO.sub.2 samples were obtained with a UV-visible spectrophotometer (Varian Cary 5) and BaSO.sub.4 was used as an absorbance standard in the UV-visible absorbance experiment. The details of characterization are as follows:
[0066] XRD analysis. The crystal structure of TiO.sub.2 and Fe/TiO.sub.2 samples was detected by X-ray diffraction (XRD) with filtered Cu Kα radiation (λ=1.5406 Å). The scanning range was 2θ from 20° to 80°, with a scanning rate of 0.025°/s. The Scherrer equation was applied to estimate the average crystallite sizes of TiO.sub.2 and Fe/TiO.sub.2 samples:
where B is the half-height width of the diffraction peak of anatase, K=0.89 is a coefficient, 0 is the diffraction angle, λ is the X-ray wavelength corresponding to the Cu Kα irradiation (1.5406 Å) and D is the average crystallite size of the powder sample.
[0067] Raman analysis. Raman spectra of TiO.sub.2 and Fe/TiO.sub.2 samples were recorded using a Horiba-Jobin Yvon LabRam spectrometer, equipped with a 17 mW He—Ne laser. Spectra were collected using a 10× objective lens over a wavenumber range of 200-1200 cm.sup.−1. The reported spectra were generated from 10-20 scans of the respective wavenumber range, each taking ten seconds.
[0068] Band gap calculation. The UV-visible diffuse reflectance spectra (DRS) were used to evaluate the band gap of TiO.sub.2 and Fe/TiO.sub.2 samples by plotting [F(R)*hv].sup.1/2 against hv, where hv is the energy of the incident photon and F(R) is the reflection in Kubelka-Munk function (see: George, S., et al., Journal of the American Chemical Society, 133(29):11270-11278 (2011)). The linear part of the curve was extrapolated to zero reflectance and the band gap energy was derived.
[0069] XAS analysis. XAS, including extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near edge structure spectroscopy (XANES), was conducted at bending magnet beamline 9-BM at the Advanced Photon Source (APS), Argonne National Laboratory. The XAS spectra were recorded in transmission mode with the ionization chamber optimized for maximum current with a linear response (see: Lei, Y., et al., Chemistry of Materials, 24(18):3525-3533 (2012)). Spectra at the Fe K edge (7.0-7.7 keV) were acquired for the 5c-Fe/TiO.sub.2 and 5c-Fe/TiO.sub.2-300 samples. Fe foil was used to calibrate the monochromator. Standard procedures based on Athena software were used to fit the XAS data.
[0070] EXAMPLE 4. Photocatalytic activity measurement. Methylene blue (MB) solution was used to evaluate the photocatalytic activity of TiO.sub.2 and Fe/TiO.sub.2 particles, as described in detail previously (see: Wang, X., Nanotechnology, 28(50): Article No. 505709 (2017)). Briefly, 0.1 g of sample was added in a 100 mL, 10 ppm MB solution in a suitable solvent, e.g., de-ionized water, and the like. First, the suspension solution was stirred in the dark for 60 min to achieve adsorption/desorption equilibrium. Then a UV lamp was used for 360 nm UV irradiation, and ˜1 mL test samples were taken from the main solution for analysis at a 664 nm wavelength at certain time intervals. The change in concentration of MB in the main solution was recorded over a period of reaction time.
[0071] EXAMPLE 5. A general ALD strategy to deposit well dispersed Fe single atoms on various substrates (e.g., MWCNTs, SiO.sub.2, and TiO.sub.2) is described. Through optimizing dose time of ferrocene (Fe(Cp).sub.2, precursor of Fe) and the number of Fe ALD cycles, Fe single atoms were deposited on different supports via Fe ALD. All prepared Fe samples are named and listed in Table 1. The formation of Fe single atoms was verified by X-ray absorption spectroscopy (XAS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The photocatalytic activity of Fe/TiO.sub.2 catalysts was evaluated by photocatalytic degradation of methylene blue (MB), as one application example of Fe/TiO.sub.2. The results showed that 2 cycles of Fe ALD deposited TiO.sub.2 catalyst presented the highest activity and had a more than six-fold enhancement of photocatalytic activity over pure anatase TiO.sub.2 nanoparticles (NPs).
TABLE-US-00001 TABLE 1 Label of samples and sample description. Ferrocene Label of Sample Sample description dose time (s) 1 2c-Fe/MWCNTs 2 cycles of Fe ALD on MWCNTs 300 2 5c-Fe/MWCNTs 5 cycles of Fe ALD on MWCNTs 300 3 8c-Fe/MWCNTs 8 cycles of Fe ALD on MWCNTs 300 4 3c-Fe/SiO.sub.2 3 cycles of Fe ALD on SiO.sub.2 300 5 10c-Fe/SiO.sub.2 10 cycles of Fe ALD on SiO.sub.2 300 6 5c-Fe/SiO.sub.2-600s 5 cycles of Fe ALD on SiO.sub.2 600 7 1c-Fe/TiO.sub.2 1 cycle of Fe ALD on TiO.sub.2 300 8 2c-Fe/TiO.sub.2 2 cycles of Fe ALD on TiO.sub.2 300 9 5c-Fe/TiO.sub.2 5 cycles of Fe ALD on TiO.sub.2 300 10 10c-Fe/TiO.sub.2 10 cycles of Fe ALD on TiO.sub.2 300 11 20c-Fe/TiO.sub.2 20 cycles of Fe ALD on TiO.sub.2 300 12 25c-Fe/TiO.sub.2 25 cycles of Fe ALD on TiO.sub.2 300
[0072] EXAMPLE 6. Results. Preparation of Fe single atoms. Firstly, different cycles (2-8 cycles) of Fe ALD were deposited on 3 g of MWCNTs in a fluidized bed reactor (
[0073] Fe single atoms were also deposited on TiO.sub.2 via ALD to prove that Fe ALD is a universal method to synthesize Fe single-atom materials on various substrates. 1-25 cycles of Fe ALD were applied on TiO.sub.2 NPs with 300 s of Fe(Cp).sub.2 dose time. As shown in
TABLE-US-00002 TABLE 2 Valence state of Fe in 2c-Fe/TiO.sub.2 and 5c-Fe/TiO.sub.2 samples. Fe.sup.0 Fe.sup.2+ Fe.sup.3+ 2c-Fe/TiO.sub.2 0 12.8% 87.2% 5c-Fe/TiO.sub.2 0 14.6% 85.4%
[0074]
[0075] ALD is a surface-controlled process based on self-limiting surface reactions. Through making use of the unique advantage of ALD, Fe single atoms deposited on MWCNTs, SiO.sub.2, and TiO.sub.2 by controlling the Fe(Cp).sub.2 dose time and the number of ALD cycles. Therefore, Fe ALD has been demonstrated to be a general method and can be used in preparation of Fe single-atom materials on various supports, including inorganic non-metallic materials, metal oxides, and carbon materials. Moreover, it was demonstrated that ALD is likewise useful in preparation of other metal single-atom materials, including Ni, Co, Ru, Rh, Ir, Os, Pt, Pd and the like, on various substrates.
[0076] EXAMPLE 7. Photocatalytic performance of Fe/TiO.sub.2. The photocatalytic activity of TiO.sub.2 and Fe/TiO.sub.2 catalysts were evaluated in terms of degradation of MB under irradiation of UV light.
[0077] As shown in
TABLE-US-00003 TABLE 3 Comparison of the photocatalytic activity of various Fe/TiO.sub.2 samples. Preparation Sample method Pollutant k.sub.app(sample):k.sub.app(pure TiO.sub.2).sup.[a] Reference 2c-Fe/TiO.sub.2 ALD Methylene blue 6.46 This work 0.5% Fe/TiO.sub.2 Wang et al..sup.[b] Formaldehyde 3 .sup.[c] 4% Fe/TiO.sub.2 Sol-gel method Methyl orange 2.0-2.5 .sup.[d] 0.25 at. % Fe/TiO.sub.2 Ultrasonic method Acetone 1.75 .sup.[e] 0.002% Fe/TiO.sub.2 Sol-gel method Methyl orange 1.62 .sup.[f] 1.8 at. % Fe/TiO.sub.2 Sol-gel method Salicylic acid 1.18 .sup.[g] 0.1% Fe/TiO.sub.2 Hydrothermal Methylene blue <1 .sup.[h] method .sup.[a]k.sub.app is the apparent first order constant. .sup.[b]Wang, C. -y., et al., Chem. Commun., 2000(16): 1539-1540. .sup.[c] Dukes, F. M., et al., Langmuir, 28(49): 16933-16940 (2012). .sup.[d] Sonawane, R., et al., Materials Chemistry and Physics, 85(1): 52-57 (2004). .sup.[e] Zhou, M, et al., Journal of Hazardous Materials, 137(3): 1838-1847 (2006). .sup.[f] Liu, S., et al., Catalysis Communications, 10(6): 894-899 (2009). .sup.[g] Popa, M., et al., Journal of materials science, 44(2): 358 (2009). .sup.[h] Li, Z., et al., Journal of Hazardous Materials, 155(3): 590-594 (2008).
[0078] The much higher photoactivity of 2c-Fe/TiO.sub.2 than that of TiO.sub.2 may possibly be due to the following several factors. Firstly, Fe.sup.3+ ions could improve the intensity of absorption in the UV-visible light region and make a red shift in the band gap transition of 2c-Fe/TiO.sub.2 sample. This can induce more photo-generated e.sup.− and h.sup.+ to participate in the photocatalytic reactions (see: Zhou, M., et al., Journal of Hazardous Materials, 137(3):1838-1847 (2006)). In order to verify the hypothesis, UV-visible diffuse reflectance spectra (DRS) for pure TiO.sub.2 and Fe/TiO.sub.2 catalysts were recorded and the band gap was calculated. As presented in
[0079] Secondly, Fe.sup.3+ can work as an e.sup.−/h.sup.+ pair traps to suppress the recombination of e.sup.−/h.sup.+ pairs and enhance lifetimes of e.sup.− and h.sup.+, which can improve the photocatalytic activity of Fe/TiO.sub.2 samples as well. In order to investigate the recombination rate of e.sup.−/h.sup.+ pairs in all catalysts, Raman and photoluminescence (PL) were performed. As shown in
[0080] Moreover, the atomic size and uniform dispersion of Fe on TiO.sub.2 surface is another important factor influencing photocatalytic efficiency. Fe ALD took full advantage of the high surface area of TiO.sub.2 and Fe single atoms (˜0.2 nm) were highly dispersed on TiO.sub.2. Thus, Fe.sup.3+ ions worked as e.sup.−/h.sup.+ traps as much as possible in Fe/TiO.sub.2 samples, which leads to the fact that the recombination of e.sup.− and h.sup.+ decreased and the photocatalytic activity improved drastically. In addition, according to XRD analysis, the TiO.sub.2 in all samples remained anatase structure after Fe ALD and no peak corresponded to the reflections from Fe, which indicates that the crystal structure did not affect the improvement of photocatalytic activity for 2c-TiO.sub.2 sample (
[0081] Lastly, the defect sites on the surface of TiO.sub.2 would be decorated by Fe single atoms because Fe atoms preferred to deposit and grow on defect sites during the ALD process based on ALD mechanism (see: George, S. M., Chemical Reviews, 110(1):111-131 (2010)), which can be called “defect healing”. As reported before (see: Zhang, D., Transition Metal Chemistry, 35(8):933-938 (2010)), a large surface area can enhance the photocatalytic performance of samples. However, powders with a large surface area are usually associated with large amounts of crystalline defects, which favor the recombination of photo-generated e.sup.− and h.sup.+ leading to a poor photoactivity (see: Carp, O., et al., Progress in Solid State Chemistry, 32(1):33-177 (2004); Ohtani, B., et al., The Journal of Physical Chemistry B, 101(19):3746-3752 (1997)). In the Fe ALD process, Fe was deposited on defect sites preferentially and overcame this problem. All factors mentioned above worked collectively and resulted in improved photocatalytic activity of 2c-Fe/TiO.sub.2.
[0082] In summary, Fe single atoms were deposited on MWCNTs, SiO.sub.2, and TiO.sub.2 NPs by Fe ALD. HAADF-STEM and XAS analysis proved the existence of Fe single atoms on MWCNTs and TiO.sub.2 NPs, respectively. Ferrocene dose time and the number of ALD cycles are two dominating factors in the preparation of Fe single atoms on substrates. 2c-Fe/TiO.sub.2 catalyst showed the highest photocatalytic activity and had a more than six-fold photocatalytic activity enhancement over pure TiO.sub.2 for the degradation of MB due to the fact that Fe.sup.3+ ions played a role as e.sup.−/h.sup.+ pair traps and consequently reduced e.sup.−/h.sup.+ pair recombination rate. The uniform dispersion of Fe and the effect of “defect healing” were another two factors to enhance the activity of samples. Fe ALD is a universal strategy to prepare Fe single-atom materials on various kinds of substrates. Moreover, the ALD method has been expanded to synthesize other metal single-atom materials, without limitation regarding supports, through optimization of corresponding precursor dose time and the number of ALD cycles.
[0083] The following Examples provide additional experimental details of the disclosed invention, particularly as applied to the catalytic oxidation of carbon monoxide (CO) in the presence of metal on various supports prepared via ALD deposition. It is to be understood that oxidation of CO is but one representative example of the catalytic power of the ALD-prepared metal/supports of the invention, and that, as contemplated herein, the invention can be used to catalyze advantageously other reactions known to those skilled in the art. It is likewise understood that although in the following Examples Fe/SiO.sub.2 is used as a representative catalyst/support, other metals/supports are contemplated herein to provide similar catalytic activity as well.
[0084] EXAMPLE 8: Highly active and stable Fe/SiO.sub.2 catalyst synthesized by ALD for CO oxidation. CO is a strongly toxic gas. Vehicle emission is the largest anthropogenic source of CO in the United States. (e.g., see: Biabani-Ravandi, A., et al., Chemical Engineering Science, 94:237-244 (2013); N. R. Council, The ongoing challenge of managing carbon monoxide pollution in Fairbanks, Ak., National Academies Press, 2002). Among numerous methods of CO removal, catalytic oxidation is one of the most efficient approaches (e.g., see: Gac, W., Applied Catalysis B: Environmental, 75:107-117 (2007)). Since the temperature of exhaust gas produced in the vehicles is very high (400-800° C.), a long-term thermally stable catalyst is needed for such applications. Many kinds of catalysts have been reported to remove CO, including noble metal catalysts, e.g., Au (see: Li, X.-N., et al., Journal of the American Chemical Society, 136:3617-3623 (2014)) and Pt (see: Qiao, B., et al., Nature Chemistry, 3:634-641 (2011)), and transition metal oxides, e.g., CeO.sub.2 (see: Mock, S. A., et al., Journal of Colloid and Interface Science, 466:261-267 (2016)) and Fe.sub.2O.sub.3 (see: Smit, G., et al., Journal of Molecular Catalysis A: Chemical, 252:103-106 (2006)). However, either high cost of noble metals or low stability limits their practical applications (e.g., see: Biabani-Ravandi, A., et al., Chemical Engineering Science, 94:237-244 (2013); Li, P., et al., Applied Catalysis B: Environmental, 43:151-162 (2003)). Fe, an earth-abundant metal, is a potential and proper catalyst for CO oxidation reaction due to its unique properties. Several theoretical investigations have demonstrated that Fe is suitable as a catalyst in the CO oxidation (e.g., see: Li, F., et al., The Journal of Physical Chemistry C, 116:2507-2514 (2012); Wu, P., et al., Physical Chemistry Chemical Physics, 17:1441-1449 (2015); Y. Tang, Y., et al., RSC Advances, 6:93985-93996 (2016)). However, few experimental studies were performed.
[0085] The novel atomic ALD process disclosed herein was used to prepare a low-cost and long-term stable Fe/SiO.sub.2 catalyst for CO oxidation reaction. Thus, highly dispersed Fe NPs were deposited on SiO.sub.2 NPs via ALD, as described in the foregoing. Application of the obtained Fe/SiO.sub.2 catalyst in the oxidation of CO showed a high catalytic activity and an excellent long-term stability. It is believed that this is the first time to synthesize Fe NPs using ALD and to utilize these Fe NPs for CO oxidation reactions.
[0086] The Fe mass fraction of Fe/SiO.sub.2 NPs was 1.98 wt. % after 5 cycles of Fe ALD and the BET surface area was 95 m.sup.2/g, which was lower than that of SiO.sub.2 NPs (143 m.sup.2/g, Table 4).
TABLE-US-00004 TABLE 4 BET surface areas of SiO.sub.2 NPs and Fe/SiO.sub.2 samples. Sample Surface area, m.sup.2/g SiO.sub.2 143 As-prepared Fe/SiO.sub.2 95 Fe/SiO.sub.2 after 4 cycles of CO oxidation reaction 97 Fe/SiO.sub.2 after 300 hr of CO oxidation reaction 122
[0087] Thus, the color of Fe/SiO.sub.2 was light yellow instead of white (
[0088]
TABLE-US-00005 TABLE 5 Comparison of catalytic activity for CO oxidation on different Fe-based catalysts. T.sub.10.sup.[a], T.sub.50.sup.[b], T.sub.100.sup.[c], Specific rate.sub.T100.sup.[d], Sample CO:O.sub.2 ° C. ° C. ° C. mL.sub.CO g.sub.Fe.sup.−1s.sup.−1 Fe/SiO.sub.2 1:10 355 370 410 33.67 FeO.sub.x-200 .sup.[e] 1:10 167 240 307 0.48 Fe.sub.2O.sub.3.sup.[f] 1:10 210 290 420 0.48 Fe.sub.2O.sub.3 nanorods .sup.[g] 1:10 230 289 370 0.2 Fe.sub.2O.sub.3 nanocubes.sup.[g] 1:10 300 378 580 0.2 Fe.sub.2O.sub.3 nanotubes.sup.[g] 1:10 270 400 640 0.2 Fe.sub.2O.sub.3 large cube .sup.[h] 1:16 300 470 >500 0.12 Fe.sub.2O.sub.3 large rod.sup.[h] 1:16 190 240 280 0.12 Fe.sub.2O.sub.3-430.sup.[i] 1:20 110 230 253 0.07 .sup.[a]Temperature (° C.) for 10% CO conversion, .sup.[b]Temperature (° C.) for 50% CO conversion, .sup.[c]Temperature (° C.) for 100% CO conversion, .sup.[d]Volume per second of CO oxidized over per gram of Fe at the temperature for 100% CO conversion, .sup.[e] G. {hacek over (S)}mit, et al., Journal of Molecular Catalysis A: Chemical, 252: 103-106 (2006). .sup.[f] A. Biabani-Ravandi, et al., Chemical Engineering Journal, 219: 124-130 (2013). .sup.[g] Q. -X. Gao, et al., Catalysis Science & Technology, 1: 574-577 (2011). .sup.[h] X. Liu, et al., Catalysis Communications, 12: 530-534 (2011). .sup.[i] L. Cui, et al., Journal of Solid State Chemistry, 247: 168-172 (2017).
[0089] The recycle and reuse ability of catalysts is one of the key factors in practical applications. In order to evaluate the reproducibility of the Fe catalysts disclosed herein, cycling tests were performed. As shown in
TABLE-US-00006 TABLE 6 Comparison of long-term stability of different catalysts for CO oxidation. Decrease of CO Sample Temperature, ° C. Time, hr conversion, % References Fe/SiO.sub.2 550 >300 0 This disclosure Pd/graphene 120 24 0 Li et al..sup.(3) Au@CeO.sub.2 120 70 0 Qi et al..sup.(4) Pd—Au alloy 80 10 2 Xu et al..sup.(5) Nanoporous Au 30 24 4 Xu et al..sup.(6) Au—Cu/TiO.sub.2 20 24 10 Sandoval et al..sup.(7) Co.sub.3O.sub.4 (LCP-300) 25 9 20 Wang et al..sup.(8) Au/Zeolite Y 25 70 27 Chen et al..sup.(9) Au—Ir/TiO.sub.2—S 23 20 60 Gómez-Cortés et al..sup.(10) .sup.(3)Li, Y.; et al., Applied Catalysis B: Environmental 2012,125, 189-196. .sup.(4)Qi, J.; et al., Energy & Environmental Science 2012, 5, 8937-8941. .sup.(5)Xu, J.; et al., Journal of the American Chemical Society 2010,132, 10398-10406. .sup.(6)Xu, C.; et al., Journal of the American Chemical Society 2007,129, 42-43. .sup.(7)Sandoval, A.; et al., Applied Catalysis B: Environmental 2013,140, 363-377. .sup.(8)Wang, Y. -Z.; et al., Catalysis Letters 2008, 125, 134-138. .sup.(9)Chen, Y. -H.; et al., Applied Catalysis B: Environmental 2017. .sup.(10)Gómez-Cortés, A.; et al., The Journal of Physical Chemistry C 2009, 113, 9710-9720.
[0090] Since both metallic and oxidized Fe (Fe, FeO, and Fe.sub.2O.sub.3) existed in the Fe/SiO.sub.2 catalyst disclosed herein, it was important to figure out which one played a dominating role in the CO oxidation. As shown in
[0091] Therefore, Fe.sub.2O.sub.3 was the dominate factor in the Fe/SiO.sub.2 sample to oxidize CO to CO.sub.2, since the conversion still remained 100% after 300 hr reaction, though more Fe changed to Fe.sub.2O.sub.3 during the long-term reaction. Generally, the catalytic CO oxidation over Fe.sub.2O.sub.3 can be divided into two steps. Firstly, Fe.sub.2O.sub.3 loses one oxygen atom and catalyzes CO to form CO.sub.2, then the produced FeO is oxidized by O.sub.2 soon (see: Li, P., et al., Applied Catalysis B: Environmental, 43:151-162 (2003)). When the concentration of O.sub.2 in the gas stream was high, more O.sub.2 could be used for FeO oxidation and more Fe.sub.2O.sub.3 would catalyze CO oxidation. Thus, 100% of CO conversion reached at a relatively low temperature with the CO:O.sub.2 ratio of 1:10, as shown in
[0092] It is also noted that according to the XRD analysis, the Fe.sub.2O.sub.3 crystal size was around 30 nm for Fe/SiO.sub.2 sample after 300 hr reaction, and it was much larger than that of as-prepared Fe NPs (1.5 nm). It indicates that Fe NPs aggregated during the long-term reaction process. In order to verify this, HRTEM and EDX mapping were applied for the Fe/SiO.sub.2 catalyst after 300 hr of CO oxidation reaction. As shown in
[0093] In summary of the foregoing example, highly dispersed Fe NPs were deposited on SiO.sub.2 NPs by ALD successfully, and the average size of the Fe NPs was 1.5 nm. The Fe/SiO.sub.2 catalyst showed a high activity and an excellent long-term stability at high temperature in the reaction of CO oxidation. Fe.sub.2O.sub.3 played a vital role in catalytic CO oxidation. Due to their high efficiency, excellent stability, and low cost, it is a potential catalyst for CO removal in large-scale applications, such as treatment of exhaust gas.
[0094] EXAMPLE 9. Preparation of Fe/SiO.sub.2. Fe ALD was carried out using ferrocene (99% purity, Alfa Aesar) and hydrogen (H.sub.2, 99.9%, Airgas) as precursors in a fluidized bed reactor. All of the chemicals were used as received without any treatment. Total five cycles of Fe ALD were applied on SiO.sub.2 nanoparticles (NPs) (20-30 nm). For a typical run, 3 g SiO.sub.2 NPs was loaded into the reactor. The reaction temperature was 400° C. During the ALD process, the solid ferrocene was loaded into a heated bubbler and carried by nitrogen (N.sub.2, 99.9%, Airgas) into the reactor. Ferrocene and H.sub.2 were fed separately. The particle substrates were fully fluidized and gas flow rates were controlled by mass flow controllers. The reactor was also subjected to vibration from vibrators to improve the quality of particle fluidization during the ALD process (see: Patel, R. L.; et al., Ceramics International 2015, 41, 2240-2246; Wang, X.; et al., Catalysis Letters 2016, 146, 2606-2613). N.sub.2 was used as a flush gas to remove unreacted precursors and any byproducts during the reaction. A typical coating cycle involved the following steps: ferrocene dose (900 s), N.sub.2 purge (900 s), evacuation (10 s); H.sub.2 dose (1200 s), N.sub.2 purge (900 s), evacuation (10 s).
[0095] Characterization. The Fe mass fractions of Fe/SiO.sub.2 NPs were measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Raman spectra of SiO.sub.2 NPs and Fe/SiO.sub.2 samples were obtained using a Horiba-Jobin Yvon LabRam spectrometer. A Quantachrome Autosorb-1 was used to obtain nitrogen adsorption and desorption isotherms of SiO.sub.2 NPs at −196° C. The BET surface areas of the SiO.sub.2 NPs and Fe/SiO.sub.2 samples before and after CO oxidation tests were calculated using the BET method in a relative pressure range of 0.05-0.25. TEM and EELS analysis of the Fe/SiO.sub.2 catalyst before and after CO oxidation reaction was characterized by a FEI Tecnai F30 TEM operated at 300 kV. Samples were directly supported on holey-carbon Cu grids. At least 200 particles were randomly measured to determine the average diameter of Fe NPs.
[0096] H.sub.2-temperature programmed reduction (H.sub.2-TPR) was applied to analyze the Fe/SiO.sub.2 catalyst. TPR experiments were performed using a Micromeritics AutoChem 2920 instrument. For a typical run, 50 mg of sample was loaded in a U-tube quartz reactor. Then, the sample was reduced in a flow of H.sub.2—Ar mixture (containing 10 vol. % H.sub.2), and the sample temperature increased to 900° C. at a rate of 10° C./min and held at 900° C. for 30 min. TPR patterns were obtained by recording the thermal conductivity detector (TCD) signal with respect to temperature.
[0097] The crystal structure of Fe/SiO.sub.2 sample before and after CO oxidation was detected by XRD with filtered Cu Kα radiation (λ=1.5406 Å). The scanning range was 20 from 20° to 80°, with a scanning rate of 0.025°/s. The Scherrer equation was applied to estimate the average crystallite sizes of Fe/SiO.sub.2 samples:
where B is the half-height width of the diffraction peak of anatase, K=0.89 is a coefficient, θ is the diffraction angle, λ is the X-ray wavelength corresponding to the Cu Kα irradiation (1.5406 Å) and D is the average crystallite size of the powder sample.
[0098] The XPS spectra of Fe/SiO.sub.2 samples before and after CO oxidation reactions were recorded with a Kratos Axis 165 X-ray photoelectron spectrometer using a monochromatic Al Kα radiation (hv=1486.6 eV), at a take-off angle of 0°. The survey scan spectra and Fe 2p core level spectra were recorded at a pass energy of 160 eV and 20 eV, respectively. All binding energy values were corrected to C 1s signal (284.5 eV).
[0099] General procedure for CO oxidation. The CO oxidation reactions were carried out in a fixed bed quartz reactor with quartz wool supporting the catalysts. In a typical run, 50 mg Fe/SiO.sub.2 or SiO.sub.2 NPs was used for the reactions. A gas mixture, with 4% CO, 4% O.sub.2, and 92% N.sub.2 of a total flow rate of 50 mL/min (sccm), was introduced into the reactor for CO oxidation reaction. MKS® mass flow controllers were used to control the gas flow rate. Reaction temperature ranged from 200° C. to a temperature at which the CO conversion reached 100%. Reaction products were analyzed by an online gas chromatograph (SRI 8610C) equipped with a 6 foot HAYESEP D column, a 6 foot MOLECULAR SIEVE 13× column, and a FID detector. After reaction, the Fe/SiO.sub.2 catalyst was directly used for the following cycling tests when applicable. In addition, CO oxidation reactions over the Fe/SiO.sub.2 catalyst were performed with different molar ratios of CO to O.sub.2 (1:1, 1:5, and 1:10) to investigate the effect of oxygen amount on the reaction. Moreover, in order to verify the long-term stability of the Fe/SiO.sub.2 sample, the CO oxidation reaction over Fe/SiO.sub.2 (50 mg) was performed for more than 300 hrs at 550° C.
[0100] As can be easily understood from the foregoing, the basic concepts of the present invention may be embodied in a variety of ways. The invention involves numerous and varied embodiments of producing and characterizing the compositions described herein. As such, the particular embodiments or elements of the invention disclosed by the description or shown in the figures or tables accompanying this application are intended to be exemplary of the numerous and varied embodiments generically encompassed by the invention or equivalents encompassed with respect to any particular element thereof. In addition, the specific description of a single embodiment or element of the invention may not explicitly describe all embodiments or elements possible; many alternatives are implicitly disclosed by the description and figures.
[0101] It should be understood that each element of a composition or an apparatus or each step of a method may be described by a composition term, an apparatus term or method term. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this invention is entitled. As but one example, it should be understood that all steps of a method may be disclosed as an action, a means for taking that action, or as an element which causes that action. Similarly, each element of a composition or apparatus may be disclosed as the physical element or the action which that physical element facilitates.
[0102] In addition, as to each term used, it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood to be included in the description for each term as contained in the Random House Webster's Unabridged Dictionary, second edition, each definition hereby incorporated by reference.
[0103] All numeric values herein are assumed to be modified by the term “about”, whether or not explicitly indicated. For the purposes of the present invention, ranges may be expressed as from “about” one particular value to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value to the other particular value. The recitation of numerical ranges by endpoints includes all the numeric values subsumed within that range. For example, a numerical range of one to five includes the numeric values 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, and so forth. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint and independently of the other endpoint. When a value is expressed as an approximation by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” generally refers to a range of numeric values that one of skill in the art would consider equivalent to the recited numeric value or having the same function or result. Similarly, the antecedent “substantially” means largely, but not wholly, the same form, manner or degree and the particular element will have a range of configurations as a person of ordinary skill in the art would consider as having the same function or result. When a particular element is expressed as an approximation by use of the antecedent “substantially,” it will be understood that the particular element forms another embodiment.
[0104] It is to be understood that, as used herein, the grammatical conjunction “and/or” refers throughout to either or both of the stated possibilities.
[0105] The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.”
[0106] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
[0107] Moreover, for the purposes of the present invention, the term “a” or “an” entity refers to one or more of that entity unless otherwise limited. As such, the terms “a” or “an”, “one or more” and “at least one” can be used interchangeably herein.
[0108] As used herein, the term “composition” generally refers to any product comprising the specified ingredients in the specified amounts, as well as any product which results, directly or indirectly, from combinations of the specified ingredients in the specified amounts. It is to be understood that the compositions described herein may be prepared from isolated compounds described herein or from salts, solutions, hydrates, solvates, and other forms of the compounds described herein. It is also to be understood that the compositions may be prepared from various amorphous, non-amorphous, partially crystalline, crystalline, and/or other morphological forms of the compounds described herein. It is also to be understood that the compositions may be prepared from various hydrates and/or solvates of the compounds described herein. Accordingly, such compositions that recite compounds described herein are to be understood to include each of, or any combination of, the various morphological forms and/or solvate or hydrate forms of the compounds described herein.
[0109] For the purpose of this invention, it is to be understood that terms such as “gel and/or aerogel composition”, “gel and/or aerogel material”, “gel and/or aerogel”, and related terms used herein, may be used interchangeably, unless clearly indicated by the context.
[0110] The background section of this patent application provides a statement of the field of endeavor to which the invention pertains. This section may also incorporate or contain paraphrasing of certain United States patents, patent applications, publications, or subject matter of the claimed invention useful in relating information, problems, or concerns about the state of technology to which the invention is drawn toward. It is not intended that any United States patent, patent application, publication, statement or other information cited or incorporated herein be interpreted, construed, or deemed to be admitted as prior art with respect to the invention.
[0111] The claims set forth in this specification are hereby incorporated by reference as part of this description of the invention, and the applicants expressly reserve the right to use all of or a portion of such incorporated content of such claims as additional description to support any of or all of the claims or any element or component thereof, and the applicants further expressly reserve the right to move any portion of or all of the incorporated content of such claims or any element or component thereof from the description into the claims or vice-versa as necessary to define the matter for which protection is sought by this application or by any subsequent application or continuation, division, or continuation-in-part application thereof, or to obtain any benefit of reduction in fees pursuant to, or to comply with the patent laws, rules, or regulations of any country or treaty, and such content incorporated by reference shall survive during the entire pendency of this application including any subsequent continuation, division, or continuation-in-part application thereof or any reissue or extension thereon.
[0112] Additionally, the claims set forth in this specification are further intended to describe the metes and bounds of a limited number of the preferred embodiments of the invention and are not to be construed as the broadest embodiment of the invention or a complete listing of embodiments of the invention that may be claimed. The applicants do not waive any right to develop further claims based upon the description set forth above as a part of any continuation, division, or continuation-in-part, or similar application.
[0113] While the disclosure has been illustrated and described in detail in the figures and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only selected embodiments have been shown and described and that all changes, modifications and equivalents that come within the spirit of the disclosures described heretofore and/or defined by the following claims are desired to be protected. It will be apparent to one of ordinary skill in the art that various changes and modifications can be made to the claimed invention without departing from the spirit and scope thereof. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein. In addition, all publications cited herein are indicative of the level of skill in the art and are hereby incorporated by reference in their entirety as if each had been individually incorporated by reference and fully set forth.