Method for preparation of nanoceria supported atomic noble metal catalysts and the application of platinum single atom catalysts for direct methane conversion

Abstract

Described are methods for converting methane to olefins, aromatics, or a combination thereof using a single atom catalyst comprising CeO.sub.2 nanoparticles impregnated with individual atoms of noble metals including Pt, Pd, Rh, Ru, Ag, Au, Ir, or a combination thereof. These single atom catalysts of the present invention are heated with methane to form olefins and aromatics.

Claims

1. A single atom catalyst comprising: CeO.sub.2 nanoparticles impregnated with individual noble metal atoms; and wherein an atomic ratio of a Ce.sup.4+ oxidation state to a Ce.sup.3+ oxidation state is 1.188.

2. The single atom catalyst of claim 1 wherein the noble metal atoms are selected from the group consisting of Pt, Pd, Rh, Ru, Ag, Au, Ir, and a combination thereof.

3. The single atom catalyst of claim 2, wherein the noble metal atoms consist of Pt.

4. The single atom catalyst of claim 3, wherein the platinum is present only in a Pt.sup.2+ oxidation state.

5. The single atom catalyst of claim 3, wherein a content of Pt is from about 0.42 wt % to about 0.50 wt % of a total weight of the single atom catalyst.

6. The single atom catalyst of claim 3, wherein the Pt is in an oxidized form.

7. The single atom catalyst of claim 1, wherein the single atom catalyst has a particle size of from about 15 nm to about 40 nm.

8. The single atom catalyst of claim 1, comprising a specific surface area in the range of 5 m.sup.2/g to 40 m.sup.2/g.

9. The single atom catalyst of claim 1, comprising binding energies in a range of 50 eV to 90 eV.

10. A single atom catalyst comprising: CeO.sub.2 nanoparticles impregnated with individual platinum atoms; and binding energies in a range of 50 eV to 90 eV; and wherein an atomic ratio of a Ce.sup.4+ oxidation state to a Ce.sup.3+ oxidation state is 1.188.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A-1F. Representative (a) TEM and (b-d) HAADF-STEM images of the Pt.sub.1@CeO.sub.2 catalyst with 0.5 wt % of Pt. (e, f) Intensity profiles associated with the line scans marked in (d).

(2) FIG. 2A-2D. XPS spectra collected on the (a, b) Pt.sub.1@CeO.sub.2 and (c, d) PtNPs/CeO.sub.2 catalysts at the (a, c) Pt 4f and (b, d) Ce 3d edges.

(3) FIG. 3A-3B. DRIFTS of CO chemisorption at different CO partial pressures on (a) Pt.sub.1@CeO.sub.2 and (b) PtNPs/CeO.sub.2.

(4) FIG. 4A-4D. Catalytic performance for the nonoxidative CH.sub.4 conversion evaluated at 6 L/(g.sub.cat.Math.h). (a) Catalytic activities and selectivities of the Pt.sub.1@CeO.sub.2 catalyst as functions of the reaction temperature. Black squares represent CH.sub.4 conversion, and the colored histograms for product distributions. Here the light olefins are categorized as C.sub.2 (ethane, ethylene and acetylene) and C.sub.3 (propane, propylene and propyne) hydrocarbons, with further breakdown of the C.sub.2 products shown in (b). (c) Comparison of methane conversion and product distributions at 975° C. over the two catalysts and the controls. (d) Stability test of the Pt.sub.1@CeO.sub.2 catalyst performed at 975° C.

(5) FIG. 5. Representative TEM image of the Pt-impregnated porous CeO.sub.2 nanospheres synthesized for the preparation of Pt.sub.1@CeO.sub.2.

(6) FIG. 6A-6B. Representative TEM images of (a) porous CeO.sub.2 nanospheres synthesized without adding PtCl.sub.4 and (b) CeO.sub.2 nanoslabs obtained by calcination of the porous CeO.sub.2 nanospheres at 1000° C.

(7) FIG. 7A-7F. (a) Representative TEM image of Pt nanoparticles. (b-e) Representative TEM images of PtNPs/CeO.sub.2. (f) Size distribution of Pt nanoparticles in the PtNPs/CeO.sub.2 catalyst.

(8) FIG. 8. XRD patterns of CeO.sub.2 nanoslabs, PtNPs/CeO.sub.2 and Pt.sub.1@CeO.sub.2.

(9) FIG. 9. N.sub.2 adsorption and desorption isotherms for Pt.sub.1@CeO.sub.2.

(10) FIG. 10. N.sub.2 adsorption and desorption isotherms for PtNPs/CeO.sub.2.

(11) FIG. 11. Hydrogen contents derived from the methane conversion reaction over Pt.sub.1@CeO.sub.2: (blue) calculated from mass balance versus (red) measured from the reactor effluents.

(12) FIG. 12. Estimated proportions of carbon species deposited as coke during the methane conversion over blank reaction tube, bare CeO.sub.2 support, PtNPs/CeO.sub.2 and Pt.sub.1@CeO.sub.2 at 975° C.

(13) FIG. 13. DRIFTS of CO chemisorption of other single atom noble metal catalysts supported on CeO.sub.2, which include Pd, Rh, Ru, Ag, Au and Ir.

DETAILED DESCRIPTION OF THE INVENTION

(14) The inventors have discovered the synthesis of ceria (CeO.sub.2)-supported atomic Pt catalysts for direct conversion of methane into light hydrocarbons. Pt has been widely used to active the C—H bond in hydrocarbons, but carbon coking usually takes place on the conventional catalysts composed of Pt clusters or nanoparticles at high temperatures (e.g., >800° C.), which has limited the application of Pt-based catalysts for methane conversion. In this study, nanoceria-supported atomic Pt catalysts were synthesized by calcination of Pt-impregnated porous CeO.sub.2 nanoparticles at high temperature (ca. 1,000° C.) (see Methods/Examples). The obtained Pt.sub.1@CeO.sub.2 catalyst was characterized by using HAADF-STEM and XPS, and the absence of Pt ensembles was further confirmed by DRIFTS analysis using CO as a molecular probe. The Pt.sub.1@CeO.sub.2 catalyst was then evaluated for the methane conversion reaction, and the catalytic performance was further compared to the control catalyst prepared by depositing Pt nanoparticles on similar CeO.sub.2 substrates.

(15) FIG. 1a shows the representative transmission electron microscopy (TEM) image of the as-synthesized Pt.sub.1@CeO.sub.2 catalyst. The catalyst particles exhibit a slab-like morphology with the size varying from ˜15 to ˜40 nm. HAADF-STEM images reveal that the obtained catalyst possesses atomic Pt dispersed on CeO.sub.2 nanoslabs (FIGS. 1 b-d). In these images, individual Pt atoms are exhibited as bright dots with higher contrast than the surrounding CeO.sub.2 lattice (FIGS. 1 e, f). The slab-like nanocrystals exhibit lattice fringes with the spacing measured to be ca. 0.31 nm, which can be assigned to the (111) planes of CeO.sub.2 in the fluorite phase (FIG. 1b). X-ray diffraction (XRD) pattern collected for the Pt.sub.1@CeO.sub.2 catalyst only shows the CeO.sub.2 peaks in the fluorite (Fm3m) phase (FIG. 8), where the absence of Pt-phase peaks is consistent with the atomic dispersion of Pt as observed in the STEM images.

(16) As a control, 3 nm Pt nanoparticles were synthesized and deposited on similar CeO.sub.2 nanoslabs at the same loading (denoted as PtNPs/CeO.sub.2) (FIG. 7). The loadings of Pt on the Pt.sub.1@CeO.sub.2 and PtNPs/CeO.sub.2 catalysts were measured to be ca. 0.42 and 0.60 wt %, respectively, using inductively coupled plasma-mass spectrometer (ICP-MS). Brunauer-Emmett-Teller (BET) analysis shows that the Pt.sub.1@CeO.sub.2 catalyst has a specific surface area of 20.2 m.sup.2/g, versus 7.9 m.sup.2/g for PtNPs/CeO.sub.2 (FIGS. 9 and 10).

(17) Oxidation state of Pt in the catalysts was characterized by using XPS (FIG. 2). The spectrum collected for Pt.sub.1@CeO.sub.2 shows two peaks at the Pt 4f edge with binding energies of 73.7 eV and 76.9 eV, which are assigned to the 4f.sub.7/2 and 4f.sub.5/2 states of Pt.sup.2+, respectively (FIG. 2a). For PtNPs/CeO.sub.2, the Pt 4f doublet exhibits downshift by ˜1 eV in binding energy (FIG. 2c). Deconvolution analysis reveals the presence of two additional peaks at 72.2 and 75.7 eV, in addition to the aforementioned two peaks associated with Pt.sup.2+, which can be assigned to the same spin-orbital split of metallic Pt (Pt). The atomic ratio between Pt.sup.2+ and Pt.sup.0 was estimated to be ˜1.5 in the PtNPs/CeO.sub.2 catalyst, with the oxidized Pt likely coming from surface oxidation of the Pt nanoparticles during calcination.

(18) The XPS spectra collected at the Ce 3d edge are shown in FIGS. 2 b and d for the two catalysts. As we showed in previous studies, the spectra can be deconvoluted on the basis of two multiplets that correspond to the 3d.sub.3/2 and 3d.sub.5/2 core holes of Ce (denoted as u and v, respectively) and have a spin-orbit splitting of ˜18.6 eV. A total of ten peaks can be identified in the present analysis and assigned to five different energy states: u.sup.0 (898 eV) and v.sup.0 (880 eV) for Ce(3d.sup.94f.sup.1)-O(2p.sup.6), u (901 eV) and v (882 eV) for Ce(3d.sup.94f.sup.2)-O(2p.sup.4), u.sup.I (904 eV) and v.sup.I (885 eV) for Ce(3d.sup.94f.sup.2)-O(2p.sup.5), u.sup.II (906 eV) and v.sup.II (889 eV) for Ce(3d.sup.94f.sup.1)-O(2p.sup.5) and u.sup.III (916 eV) and v.sup.III (897 eV) for Ce(3d.sup.94f.sup.0)-O(2p.sup.6). The states marked with u.sup.0/v.sup.0 and u.sup.I/v.sup.I are features of Ce.sup.3+, which was estimated to occupy ˜46% and 33% of the Ce species in the Pt.sub.1@CeO.sub.2 and PtNPs/CeO.sub.2 catalysts, respectively (Table 1).

(19) TABLE-US-00001 TABLE 1 Pt and Ce oxidation states derived from the XPS analyses for the Pt.sub.1@CeO.sub.2 and PtNPs/CeO.sub.2 catalysts. Sample Pt.sup.0 % Pt.sup.2+ % Ce.sup.3+ % Ce.sup.4+ % Pt.sub.1@CeO.sub.2 0 100 45.7 54.3 PtNPs/CeO.sub.2 40.4 59.6 32.6 67.4
These results indicate that the CeO.sub.2 nanoslabs employed as support here are rich in Ce defects and oxygen vacancies, which is likely a result of oxygen evolution during the high-temperature (1000° C.) treatment.

(20) The XPS analysis shows that, in the Pt.sub.1@(CeO.sub.2 catalysts, Pt was dispersed on the CeO.sub.2 support in the oxidized form (Pt.sup.2+). It was reported that Pt can be emitted as volatile PtO.sub.x above 800° C. in air,.sup.14 which could then re-condense and deposit on the CeO.sub.2 support. Ce(III) and oxygen vacancies enriched on the CeO.sub.2 substrate represents coordinatively unsaturated, electrophilic sites, which could have attracted and stabilized atomic platinum oxides, e.g., in the form of planar Pt.sup.2+O.sub.4 clusters..sup.36 Thereby Pt was favorably dispersed as single-atom species on the CeO.sub.2 support.

(21) To gain a more extensive evaluation of the atomic dispersion of Pt, the inventors have further performed diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis of CO adsorption on the Pt.sub.1@CeO.sub.2 catalyst. This method has previously been demonstrated to be effective in identification of single Pt atoms on oxide supports. FIG. 3a shows the absorption spectra recorded on the Pt.sub.1@CeO.sub.2 catalyst with CO pre-adsorbed at different partial pressures. Only one peak was observed at 2,089 cm.sup.−1, which can be assigned to the linearly bonded CO (CO.sub.L) on Pt.sup.δ+..sup.13 In contrast, the PtNPs/CeO.sub.2 catalyst exhibits two additional peaks at 2,078 cm.sup.−1 and 1,991 cm.sup.−1, in addition to the CO.sub.L peak at 2,089 cm.sup.−1 (FIG. 3b). In this case, the peak at 2078 cm.sup.−1 can be assigned to CO.sub.L on the Pt nanoparticles, with the different peak position from that for the Pt.sub.1@CeO.sub.2 catalyst due to the different coordination numbers or oxidation state of surface Pt atoms. The other peak at 1991 cm.sup.−1 is ascribed to the bridge bonded CO (CO.sub.B) on Pt, which is another feature of Pt ensembles with continual surfaces. The absence of the CO.sub.B peak thereby confirms the isolation of Pt sites in the Pt.sub.1@CeO.sub.2 catalyst.

(22) The Pt.sub.1@CeO.sub.2 catalyst was evaluated for nonoxidative conversion of methane at 900-1000° C. with a space velocity of 6 L/(g.sub.cat.Math.h). FIG. 4a summarizes the methane conversion and product distributions in dependence of the reaction temperature. The methane conversion increased with temperature and reached 23.1% at 1,000° C. The selectivity of C.sub.2 hydrocarbons exhibited gradual decrease from 98.4% at 900° C. to 66.7% at 1,000° C. The amount of C.sub.3 product was rather small and always <10% throughout the investigated temperature range. At temperatures ≥950° C., aromatic products started to appear and the selectivities increased with temperature, achieving 26.6% for benzene and 2.1% for naphthalene at 1,000° C. It is noticed that the amount of hydrogen generated from the methane conversion matches well with the concentrations calculated from the reaction stoichiometries and mass balance by taking the various hydrocarbon products into account (FIG. 11).

(23) The performance of the Pt.sub.1@CeO.sub.2 catalyst is noticeably different from the previously reported atomic Fe@SiO.sub.2 catalyst, albeit with similar methane conversion (e.g., 12.7% for Pt.sub.1@CeO.sub.2 versus ˜8% for Fe@SiO.sub.2 at 950° C.). The atomic Pt catalyst reported here gave rise to much higher C.sub.2 product selectivity, with 84.3% compared to ˜47% by Fe@SiO.sub.2 at 950° C. In the latter case, the rest products were mainly aromatics (consistently ˜50% in total independent of the reaction temperature) and nearly equally distributed between benzene and naphthalene. While the Pt.sub.1@2CeO.sub.2 catalyst produced all the three kinds of C.sub.2 species, ethylene was the only C.sub.2 product from the Fe@SiO.sub.2 catalyst. These differences suggest that the Pt.sub.1@CeO.sub.2 catalyst may possess distinct catalytic mechanisms, particularly in the C—C coupling steps, from the Fe@SiO.sub.2 catalyst where multi-carbon species were believed to form from gas-phase methyl (.CH.sub.3) radicals via noncatalytic, thermodynamic equilibrium processes.

(24) Breakdown of the C.sub.2 product distributions is further elucidated in FIG. 4b. At relative low temperatures, ethylene and ethane were the two dominant products, with the selectivity measured to be 51.1% and 43.6% at 900° C., respectively. At elevated temperatures, acetylene became more abundant and its selectivity achieved 41.7% at 1,000° C., whereas only 19.8% of ethylene and 5.1% of ethane were left at this temperature. These trends indicate that the C.sub.2 products may undergo further dehydrogenation after their formation, the equilibrium of which favors the generation of acetylene at higher temperatures. It is also in line with the observed production of more hydrogen from the methane conversion at higher temperatures (FIG. 11). The atomic Pt catalyst is much superior to its nanoparticulated counterpart for the methane conversion reaction. FIG. 4c provides the comparison of methane conversion and product selectivity for the Pt.sub.1@CeO.sub.2 and PtNPs@CeO.sub.2 catalysts at 975° C., together with the control in the cases of blank reaction tube and bare CeO.sub.2 support. The amount of coke formed during the methane conversion was estimated by the mass balance analysis, with the occupying ratio of carbon species presented separately in the Supporting Information (FIG. 12). It is noticed that even in the blank reaction tube, CH.sub.4 had a conversion of 1.1% at this temperature due to the non-catalytic, thermal activation and dehydrogenation, but no hydrocarbons were detected at significant amounts (albeit with some ethane at 3.2% selectivity), suggesting that the converted methane mostly became coke and deposited on the tube wall. The bare CeO.sub.2 support exhibited somewhat higher (6.9%) CH.sub.4 conversion, but coke was still the dominant (88.3%) product. The PtNPs@CeO.sub.2 catalyst raised the CH.sub.4 conversion to 9.7% and the selectivities toward ethylene and acetylene reached 8.3% and 6.3%, respectively; however, 79.8% of the carbon atoms ended up in coke which was not quite different from the situation with bare CeO.sub.2 support. Both the catalytic activity and selectivity were substantially improved with the Pt.sub.1@CeO.sub.2 catalyst, achieving 14.4% of methane conversion and 98.5% selectivity toward hydrocarbons. Herein the hydrocarbon products were dominated by ethylene (33.2%) and acetylene (35.1%). The coke formation was suppressed to be only ˜1.5% proportion of the carbon atoms derived from methane in this case, which could be ascribed to the carbon deposition on tube wall and/or the CeO.sub.2 substrate.

(25) From the above observations, it can be seen that the CeO.sub.2 substrate may play an active role in activating methane, as indicated by the considerable conversion of methane on the bare CeO.sub.2 substrate. Compared to the bare CeO.sub.2 substrate, the incorporation of Pt nanoparticles made insignificant changes to the product distributions, albeit having slightly raised the methane conversion. This finding is consistent with the reported situation on the conventional catalysts with ensembles of Pt atoms, where further oligomerization of the C—C species becomes inevitable on continuous metal surfaces and causes coking. It is only on the Pt.sub.1@(CeO.sub.2 catalyst that methane is selectively converted into light olefins and aromatics, highlighting the importance of having atomically dispersed active sites in suppression of carbon coking.

(26) Ultimately, durability of the Pt.sub.1@CeO.sub.2 catalyst was examined by performing prolonged operations of the conversion reaction. It was found that both the conversion and product selectivities were sustainable and did not exhibit any discernible drop after 40 h of reaction at 975° C. (FIG. 4d). The high durability does not only confirm the suppression of carbon coking, but also indicates great potential of the nanoceria-supported atomic Pt catalyst for implementation in practical plants.

Methods/Examples

(27) The following Methods/Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Methods/Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter. The following Methods/Examples are offered by way of illustration and not by way of limitation.

(28) 1. Materials and Methods

(29) Chemicals. Platinum(IV) chloride (>99.99%), Cerium(III) nitrate hexahydrate (>99.999%), Propionic acid (ACS reagent, ≥99.5%), Ethylene glycol (anhydrous, 99.8%), Borane tert-butylamine (97%), Oleylamine (≥98%) were purchased from Sigma Aldrich. Platinum(II) acetylacetonate (98%) was purchased from ACROS Organics. These chemicals were used as-received without further purification. Deionized water (18.2 MΩ) was collected from an ELGA PURELAB flex apparatus.

(30) Synthesis. For the preparation of Pt.sub.1@CeO.sub.2, Pt-impregnated porous CeO.sub.2 nanospheres were first synthesized by modifying the method reported in the literature..sup.1 Typically, 1.0 g Ce(NO.sub.3).sub.3.6H.sub.2O with 6.90 mg of PtCl.sub.4 was dissolved in 1 mL deionized water. To this solution 1 mL of propionic acid and 30 mL of ethylene glycol were added with stirring. The formed uniform solution was sealed in an autoclave and heated at 160° C. for 3 hours. The product was collected by centrifugation (10000 rpm, 10 minutes) and washed thoroughly with DI water and dry ethanol. It was dried at 110° C. in air for 5 h and at 300° C. for another 2 h to remove any residual water or organics. The obtained porous nanospheres (FIG. 5) were then calcined in air at 1000° C. for 2 h, which converted the nanospheres into crystalline nanoslabs with atomically dispersed Pt (see the TEM images shown in the main text, FIG. 1). CeO.sub.2 nanoslabs were synthesized in a similar way without adding the Pt salt (FIG. 6).

(31) PtNPs/CeO.sub.2 was also prepared as a control to the atomic Pt catalyst (FIG. 7). Pt nanoparticles were synthesized in an organic solution phase by following the reported method..sup.2 Basically, 0.2 mmol of Pt(acac).sub.2 was dissolved in 15 mL of oleylamine, stirred at 800 rpm in Ar atmosphere. The solution was first raised to 70° C. and kept at this temperature for 10 min, to which a mixture of borane tert-butylamine complex (BTB) (0.4 mmol) and oleyamine (2 mL) was injected. The solution was further stirred at 70° C. for 30 min and then cooled down to room temperature. The product was collected by adding 250 mL of methanol and centrifugation, which was re-dispersed in 20 mL of hexane. To deposit the Pt nanoparticles onto CeO.sub.2, 1 g of CeO.sub.2 nanoslabs and the 5.03 mg of Pt nanoparticles were mixed in 50 mL of ethanol. The obtained mixture was rigorously stirred for 45 min at room temperature. After that, the solvent was removed by using a rotary evaporator. The obtained solid was dried in vacuum and then calcined at 300° C. in air for 2 h.

(32) Characterizations. X-ray diffraction (XRD) patterns were obtained from a PANalytical X'Pert.sup.3 X-ray diffractometer equipped with a Cu Kα radiation source (λ=1.5406 Å). Nitrogen adsorption measurements were measured on a Micromeritics ASAP 2010 instrument with the samples degassed under vacuum at 300° C. for 4 h. Specific surface area (SSA) was calculated using the Brunauer-Emmett-Teller (BET) theory. The Pt contents were determined by inductively coupled plasma mass spectrometry (ICP-MS) using a PerkinElmer Elan DRC II Quadrupole ICP-MS after dissolution of the materials in the mixture of aqua regia and hydrogen peroxide.

(33) TEM images were recorded on a Philips EM 420 worked at 120 kV. The HAADF images were acquired using a 22-mrad-probe convergence semi-angle and a 90-mrad inner-detector angle at 200 KV, using an aberration-corrected JEOL JEM-ARM200CF STEM. The average particle size and distribution were determined by ImageJ software. The average particle size and distribution were determined by ImageJ software.

(34) X-ray photoelectron spectroscopy (XPS) data were obtained on a Shimadzu/Kratos Axis Ultra Dld spectrometer with Al Kα radiation as the excitation source. The adventitious carbonaceous C 1s line (284.6 eV) was used to calibrate the binding energy (BE). The XPS spectra were deconvoluted using Origin 9.0 software with Shirley background subtraction and a Gaussian-Lorentzian functions.

(35) FTIR spectra for CO adsorption were recorded on a Nicolet 6700 spectrometer equipped with a mercury cadmium telluride (MCT) detector cooled by liquid N.sub.2. The in situ cell was fitted with ZnS windows and a heating cartridge. Before CO adsorption, samples were evacuated at 200° C. for 2 h, and then cooled to 25° C. for CO adsorption. Spectra were collected at 25° C. with a resolution of 4 cm.sup.−1 and accumulation of 100 scans for each sample.

(36) Catalytic studies. Catalytic nonoxidative conversion of CH.sub.4 was conducted in a fixed-bed flow reactor at atmospheric pressure..sup.3 Before reaction, a pretreatment was applied: 0.2 g catalyst (40-60 mesh) was loaded into a microflow quartz reactor (7 mm i.d.), heated to 110° C. at a rate of 5° C./min under He (50 mL/min), and held at 110° C. for 1 h. After pretreatment, the temperature was increased to 900° C. under He and the gas flow was then switched to 1% CH.sub.4/He (20 mL min.sup.−1, space velocity=6 L/(g.sub.cat h)). The reaction temperature was increased stepwise from 900° C. to 1000° C., and the reaction was carried out at each temperature until the conversion reached constant. To determine the conversions of reactants and the formation of products, a gas chromatograph (GC-2010 plus, Shimadzu) equipped with a SH-Rt-Q-BOND column and a BID detector were employed. All of the lines between the reactor outlet and GC sampling loop inlet were heat-traced to 90° C. to prevent product condensation. Methane conversion, hydrocarbon product selectivity, coke deposition selectivity and H.sub.2 concentrations were calculated according to the mass balance, following previously reported methods..sup.4,5

(37) All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(38) The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(39) Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.