Catalysts and related methods for photocatalytic production of H.SUB.2.O.SUB.2 .and thermocatalytic reactant oxidation

Abstract

Catalysts, catalytic systems and related synthetic methods for in situ production of H.sub.2O.sub.2 and use thereof in reaction with oxidizable substrates.

Claims

1. A method for concomitant H.sub.2O.sub.2 production and reaction using a catalyst composition comprising: a particulate TiO.sub.2 core component, the particulate TiO.sub.2 core component having a surface; a SiO.sub.2 shell component coupled to and partially coating the surface of the particulate TiO.sub.2 core component; and transition metal moieties coupled to the SiO.sub.2 shell component, wherein TiO.sub.2 surface areas of the particulate TiO.sub.2 core component are exposed through the SiO.sub.2 shell component, the method comprising: exposing the catalyst composition to a reaction medium comprising O.sub.2, a proton donor, and an alkene; and irradiating the reaction medium with ultra-violet light to induce the photocatalytic oxidation of the proton donor and the formation of H.sub.2O.sub.2, whereby the H.sub.2O.sub.2 and the alkene undergo an oxidation reaction to form an oxidation product, wherein the oxidation of the proton donor and the oxidation reaction are both catalyzed by the catalyst composition.

2. The method of claim 1, wherein the proton donor is an alcohol.

3. The method of claim 1, wherein the proton donor is a linear alkene.

4. The method of claim 1, wherein the transition metal moieties comprise V, Ti, Cr, Mn, Co, Cu, Zn, Mo, Nb, Ta, W, Os, Re, Ir, Sn, or a combination thereof.

5. The method of claim 1, wherein the transition metal moieties comprise Ti.

6. The method of claim 5, wherein the alkene is propylene, and the oxidation product is propylene oxide.

7. The method of claim 2, wherein the alcohol is isopropanol.

8. The method of claim 7, wherein the photocatalytic oxidation of the isopropanol produces acetone.

9. The method of claim 8, further comprising hydrogenating the acetone to regenerate the isopropanol.

10. The method of claim 1, wherein the oxidation reaction is an epoxidation reaction.

11. The method of claim 10, wherein the alkene is a cycloalkene.

12. The method of claim 11, wherein the cycloalkene is cyclooctene.

13. The method of claim 11, wherein the proton donor is an alcohol.

14. The method of claim 1, wherein the irradiation is intermittent.

Description

DETAIL DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: TEM image of SiO.sub.2@TiO.sub.2 core-shell material, in accordance with certain non-limiting embodiments of this invention.

(2) FIG. 2: N.sub.2 adsorption isotherms for TiO.sub.2 core (.box-tangle-solidup.) and SiO.sub.2@TiO.sub.2 (.circle-solid.) materials. In the region below P/P.sub.0=0.06 there is less than monolayer coverage for the core-shell material, indicating the presence of microporosity. This adsorption phenomenon is absent for the TiO.sub.2 core material.

(3) FIG. 3: TEM images of the SiO.sub.2@TiO.sub.2 material with silica shell thickness between 1.9 and 3.0 nm.

(4) FIG. 4: Epoxide yields after 2 hours for control reactions for the combined photo-/thermo-catalytic system and TiSiO.sub.2@TiO.sub.2 catalyst: (A) standard conditions (isopropanol, O.sub.2, UV light and 65 C.), (B) standard conditions except at room temperature, (C) standard conditions except no UV illumination, (D) standard conditions except using dodecane as solvent (i.e., less effective proton donor and hole scavenger than IPA for H.sub.2O.sub.2 synthesis), (E) standard conditions except N.sub.2 is bubbled to remove O.sub.2, and (F) standard conditions using TiSiO.sub.2 material only, showing that it does not respond to the 365-nm UV light.

(5) FIG. 5: Epoxide yields vs. time for the thermocatalytic epoxidation of cis-cyclooctene on TiSiO.sub.2 for (.circle-solid.) 3.5 mmol H.sub.2O.sub.2 (50 wt %, aq.) added at once at the beginning of the reaction and () 0.2 mmol H.sub.2O.sub.2 (4.0 M dry in MeCN) added continuously at a rate of 0.1 mmol h.sup.1 over the course of the reaction, mimicking the in situ H.sub.2O.sub.2 production of the combined photo-/thermo-catalytic system. The yields for the combined photo-/thermo-catalytic system is also shown ().

(6) FIG. 6: Catalytic activity over an extended period of time, as shown through cis-cyclooctene () and cyclooctene epoxide (.diamond-solid.) production, epoxide selectivity () and mass balance (.circle-solid.). Yields are reported per gram of photocatalyst.

(7) FIG. 7: UV light affect on reaction, as shown through Acetone (), cyclooctene epoxide () and H.sub.2O.sub.2 (, right axis) production per gram of photocatalyst.

(8) FIG. 8: Combined photo- and thermo-catalytic system for hydrogen peroxide production on SiO.sub.2@TiO.sub.2 (left) and subsequent consumption via alkene epoxidation on TiSiO.sub.2 (right). Note that the TiSiO.sub.2 site may exist on the surface of the SiO.sub.2@TiO.sub.2 material, as in TiSiO.sub.2@TiO.sub.2.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(9) As relates to one or more non-limiting embodiments of this invention, reference is made to FIG. 8. A TiO.sub.2 surface is partially coated with silica (hereon referred to as SiO.sub.2@TiO.sub.2), and the resulting material is used to synthesize H.sub.2O.sub.2 photocatalytically from O.sub.2 (in the air) and a proton donor/hole scavenger. In this case protons are generated and photo-generated holes are scavenged by the concurrent photocatalytic oxidation of isopropanol to acetone, but this can be achieved using many other sources, including other alcohols. If desired, the co-product acetone could be reduced with H.sub.2 in a second step using existing art, thereby recycling the proton source and hole scavenger. The H.sub.2O.sub.2 generated in situ then migrates to an epoxidation site (e.g., either on the same or another catalyst particle) for use as an oxidant in alkene epoxidationfor instance, either, cis-cyclooctene to cyclooctane oxide or 1-octene to octane oxide. An example of such an epoxidation catalyst is TiSiO.sub.2. Alternatively, the components necessary for performing these tasks can be combined onto a single catalyst particle by first overcoating a TiO.sub.2 core with silica, then grafting dispersed Ti sites onto the silica (hereon referred to as TiSiO.sub.2@TiO.sub.2).

(10) Performing H.sub.2O.sub.2 synthesis and epoxidation in such a combined photo/thermo system offers the following advantages over conventional H.sub.2O.sub.2 synthesis and epoxidation reactions: (i) SiO.sub.2@TiO.sub.2 is a more active photocatalyst than TiO.sub.2 for H.sub.2O.sub.2 synthesis, (ii) the H.sub.2O.sub.2 does not need to be purified and concentrated, (iii) the H.sub.2O.sub.2 is not diluted with H.sub.2O (as is commercial H.sub.2O.sub.2), which is known to inhibit the epoxidation step, (iv) the epoxidation occurs at higher rates than the case where excess aqueous H.sub.2O.sub.2 is added at the start of the reaction.

(11) Performance of the present invention is demonstrated through the following comparisons (Table 1, below, summarizes the catalytic performance of the materials):

(12) SiO.sub.2@TiO.sub.2 gives higher yields of H.sub.2O.sub.2 at a given time than the TiO.sub.2 core. Table 1 entry 1 gives the performance of the TiO.sub.2 core material, while entry 2 gives the performance of SiO.sub.2@TiO.sub.2. SiO.sub.2@TiO.sub.2 yields 14 times greater H.sub.2O.sub.2 than the TiO.sub.2 core alone. This is unexpected because the SiO.sub.2 shell covers part of the active TiO.sub.2 surface. The net H.sub.2O.sub.2 production on SiO.sub.2@TiO.sub.2 is equivalent to 21 mM H.sub.2O.sub.2 h.sup.1, which is 6 times greater than the best-performing previously reported photocatalysts for H.sub.2O.sub.2 synthesis (3.4 mM H.sub.2O.sub.2 h.sup.1). A TEM image of the SiO.sub.2@TiO.sub.2 catalyst is shown in FIG. 1, which shows that the catalyst comprises a TiO.sub.2 core with a 2 nm SiO.sub.2 shell.

(13) Addition of TiSiO.sub.2 to a reactor with SiO.sub.2@TiO.sub.2 provides a catalyst system that can perform the thermocatalytic epoxidation reaction using in situ generated H.sub.2O.sub.2, as illustrated in FIG. 8. Entry 3 of Table 1 demonstrates that this physical mixture greatly increases the epoxide yield (compared to entries 1 & 2). Consequently, the H.sub.2O.sub.2 yield is reduced due to consumption of H.sub.2O.sub.2 by the epoxidation reaction. Producing the H.sub.2O.sub.2 in situ means that it does not need to be produced elsewhere, purified, concentrated, diluted, and finally transported to the reactor responsible for epoxidation. Instead, the H.sub.2O.sub.2 is not only produced on site, it is synthesized in the very same reactor as the epoxidation reaction.

(14) The photo/thermo-catalytic system with in situ H.sub.2O.sub.2 production leads to higher rates of epoxidation when compared to conventional methods of epoxidation. Entry 4 of Table 1 displays the catalytic performance of TiSiO.sub.2 for a conventional thermocatalytic epoxidation reaction, when an excess of aqueous H.sub.2O.sub.2 is added at the beginning of the reaction and there is no photocatalytic cycle taking place to produce H.sub.2O.sub.2. The epoxide yield for the photo/thermo-catalytic system (entry 3) is 7 times greater than the conventional epoxidation system (entry 4). This is unexpected because the conventional system contains a much higher instantaneous concentration of H.sub.2O.sub.2 (3.5 mmol) than is measured in the combined photo/thermo-catalytic system (0.42 mmol, using the H.sub.2O.sub.2 yield from entry 2).

(15) The photo/thermo-catalytic system with in situ H.sub.2O.sub.2 productions is active for other epoxidations. Table 1 entry 5 displays the catalytic performance for the combined system using 1-octene as the substrate. The rates of 1-octene epoxidation are 20 times higher for the combined photo/thermo-catalytic system than for a conventional thermocatalytic reaction (entry 6). 1-octene is a model reaction for the epoxidation of propylene, which is currently practiced at industrial scale over TiSiO.sub.2 catalysts with added H.sub.2O.sub.2 by various industrial concerns.

(16) The separate features of the SiO.sub.2@TiO.sub.2 photocatalyst and TiSiO.sub.2 thermocatalyst can be combined onto a single catalyst particle to perform tandem photo- and thermo-catalytic functions. By grafting Ti onto the silica-overcoated TiO.sub.2 core, a material capable of performing both catalytic reaction cycles can be obtained. Table 1 entry 7 displays the performance of single component catalyst TiSiO.sub.2@TiO.sub.2. While not achieving epoxide yields as high as the combined photo-/thermo-catalytic system (entry 3) this material still yields more epoxide than either TiO.sub.2 or SiO.sub.2@TiO.sub.2, due to addition of tetrahedral Ti on the silica shell. The performance of this material may be improved by optimizing the TiO.sub.2 morphology, the shell structure, or the Ti loading.

(17) This system is not limited to TiSiO.sub.2 as the epoxidation catalyst. Table 1, entries 8 and 9 display catalytic results for the combined photo-/thermo-catalytic system when using TaSiO.sub.2 and NbSiO.sub.2 as the thermocatalysts, respectively. As would be understood by those skilled in the art and made aware of this invention, most catalysts that use conventional H.sub.2O.sub.2 can also be utilized herewith.

(18) TABLE-US-00001 TABLE 1 Product yields after 2 hours of reaction in photo-/thermo-catalytic system for various catalysts. Acetone H.sub.2O.sub.2 Epoxide Entry Photocatalyst Thermocatalyst .sup.ammol g.sup.1 .sup.ammol g.sup.1 .sup.ammol g.sup.1 .sup.bmmol g.sup.1 1 TiO.sub.2 core 42 3 0.4 .sup.en/a 2 SiO.sub.2@TiO.sub.2 22 42 0.5 .sup.en/a 3 SiO.sub.2@TiO.sub.2 TiSiO.sub.2 37 16 12 7 .sup.c4 TiSiO.sub.2 .sup.dn/a .sup.dn/a .sup.dn/a 0.8 .sup.f5 SiO.sub.2@TiO.sub.2 TiSiO.sub.2 42 9 3 2 .sup.c,f6 TiSiO.sub.2 .sup.dn/a .sup.dn/a .sup.dn/a 0.1 .sup.g7 TiSiO.sub.2@TiO.sub.2 n/a 14 13 3 .sup.en/a 8 SiO.sub.2@TiO.sub.2 TaSiO.sub.2 48 25 14 3 9 SiO.sub.2@TiO.sub.2 NbSiO.sub.2 32 6 8 6 Conditions: 5 mg photocatalyst (if present), 15 mg thermocatalyst (if present), 10 mL isopropanol, 1.15 mmol cis-cyclooctene, 65 C., 365 nm UV, O.sub.2 bubbled every 30 minutes .sup.aYield per gram of photocatalyst material. .sup.bYield per gram of thermocatalyst material. .sup.c3.5 mmol H.sub.2O.sub.2 (aq) added. .sup.dNot applicable; no photocatalyst used. .sup.eNot applicable; no separate thermocatalyst used. .sup.f1-octene as alkene substrate g TiSiO.sub.2@TiO.sub.2 acting as thermocatalyst and photocatalyst

(19) Table 2 summarizes physical characterization data from the materials examined. All of the TiO.sub.2 based materials have edge energies of 3.2 eV, indicating that the addition of a silica shell does not change the photo-response of the TiO.sub.2 core material. The edge energy of TiSiO.sub.2 of 3.7 eV indicates that this material contains predominantly isolated Ti cations, with some clustered, non-tetrahedral Ti sites. Addition of the silica shell increases the surface area of the TiO.sub.2 core, likely due to the formation of micropores, as indicated from the N.sub.2 isotherm (FIG. 2). The crystal size does not significantly change with the addition of the silica shell. TEM images confirm the formation of a thin silica shell (FIG. 3). Taken together the characterization data show that the core-shell materials comprise a crystalline anatase TiO.sub.2 core with a transparent 2 nm microporous silica shell.

(20) TABLE-US-00002 TABLE 2 Physical characterization data of materials Surface Crystallite E.sub.g.sup.a Area.sup.b size.sup.c Material eV m.sup.2 g.sup.1 nm TiO.sub.2 core 3.2 43 23 core-shell 3.2 57 27 Ti-core-shell 3.2 56 27 Ti-SiO.sub.2 3.7 589 .sup.aEstimated from DRUV-visible spectra transformed with a tauc plot. .sup.bEstimated from N.sub.2 physisorption using the BET method. .sup.cEstimated from XRD; only anatase TiO.sub.2 is observed

(21) As illustrated by Table 1 entries 1-3, addition of the silica shell unexpectedly enhances H.sub.2O.sub.2 production, while addition of Ti to the shell surface increases the epoxidation activity. To prove that the reaction proceeds as illustrated in FIG. 8, several control reactions were performed with the combination TiSiO.sub.2@TiO.sub.2 catalyst (FIG. 4). Removing any component of the combined photo-/thermo-catalytic system reduces or eliminates production of epoxide, confirming that the reaction proceeds through the photocatalytic production of hydrogen peroxide from isopropanol and the subsequent epoxidation of cis-cyclooctene via hydrogen peroxide. Comparing the combined photo/thermocatalytic systems for both alkenes (entries 3 and 5 from Table 1) to conventional thermocatalytic reactions (entries 4 and 6 from Table 1) shows that epoxidation rates for the combined system are unexpectedly 7 times greater for cis-cyclooctene and 20 times greater for 1-octene. Finally, FIG. 5 shows that slowly adding dry H.sub.2O.sub.2 over the course of the reaction increases epoxide yields vs. the case where H.sub.2O.sub.2 is added all at once, but still does not reach the productivity of the combined photo-/thermo-catalytic system. Thus, without limitation to any one theory or mode of operation, a combined photo-/thermo-catalytic system may improve epoxide yields by slowly synthesizing H.sub.2O.sub.2 in parallel with its consumption. Further, and also without limitation, comparing yields of H.sub.2O.sub.2 and acetone, the SiO.sub.2@TiO.sub.2 material may be improving H.sub.2O.sub.2 yields by inhibiting the unproductive, subsequent decomposition of H.sub.2O.sub.2, as opposed to accelerating the production of H.sub.2O.sub.2.

(22) Accordingly, the present invention describes catalytic materials and method(s) for the photocatalytic production of H.sub.2O.sub.2 in the same reactor as the subsequent consumption of H.sub.2O.sub.2 in a useful chemical transformation (e.g., alkene epoxidation). Such methods avoid H.sub.2O.sub.2 purification and transport, and greatly simplify the total production process. A representative photocatalyst described herein for H.sub.2O.sub.2 synthesis exhibits significantly higher synthesis rates than those previously reported, and the epoxidation rates for a combined system are higher than those observed for a conventional system, due to the intimate coupling of H.sub.2O.sub.2 generation and consumption.

EXAMPLES OF THE INVENTION

(23) The following non-limiting examples and data illustrate various aspects and features relating to the catalyst materials and/or methods of the present invention, including unitary photo- and thermocatalytic nanoparticles, as are available through the synthetic methodologies described herein. In comparison with the prior art, the present methods and catalyst materials provide results and data, which are surprising, unexpected and contrary thereto. While the utility of this invention is illustrated through the use of several catalyst materials, proton donor and reactant components which can be used therewith, it will be understood by those skilled in the art that comparable results are obtainable with various other catalyst materials, proton donor and reactant components, as are commensurate with the scope of this invention.

Example 1

(24) Synthesis of SiO.sub.2@TiO.sub.2 core-shell. Anatase TiO.sub.2 nanoparticles were used as received from Sigma-Aldrich (<25 nm particles, TiO.sub.2 core). 2 g of the TiO.sub.2 core, 50 mL ethanol (KOPTEC, 200 proof), 3.2 mL NH4OH solution (56.6 w/w %) were added to a plastic container, sonicated for 30 minutes to disperse the oxide particles and equilibrate the pH. The mixture was transferred to a shaker plate, shaking at 200-250 rpm, and 1 mL of tetraethoxyorthosilicate (TEOS, Sigma-Aldrich) was added in 0.1 mL increments every 20 minutes while shaking the vial in between. The mixture was allowed to shake overnight then centrifuged to collect solids. The solids were resuspended in 50 mL of 18 M deionized water then centrifuged to wash away excess TEOS and NH.sub.4OH. This washing step was repeated 5 times. Finally the solids were collected and dried in a drying oven at 150 C. for 12 to 15 hours.

(25) Various other methods for SiO.sub.2@TiO.sub.2 synthesis can be utilized, including the use of other core materials, SiO.sub.2 precursors, and deposition conditions, as would be understood by those skilled in the art.

Example 2

(26) Synthesis of TiSiO.sub.2@TiO.sub.2. The core-shell material of Example 1 was dried under vacuum (<200 mTorr) at 200 C. for 12 to 15 hours to remove physisorbed water. In a separate round-bottomed flask titanocene dichloride (C.sub.10H.sub.10Cl.sub.2Ti, Aldrich 97%) was dissolved in freshly-distilled anhydrous toluene. In an Ar-filled glovebox the dried core-shell support was added to the round-bottomed flask and sealed. The round-bottomed flask was then removed from the glovebox and attached to a condenser and refluxed under N.sub.2 for 48 hours. The reflux occurred without stirring to avoid grinding the core-shell particles. The material was then collected via vacuum filtration where it was washed with 200 mL toluene, 400 mL acetonitrile, and allowed to dry at room temperature overnight.

(27) Various other methods of adding Ti to SiO.sub.2@TiO.sub.2 can be utilized, including the use of other precursors and deposition methods as would be understood by those skilled in the art. Likewise, as would be understood in the art, other catalytically active cations can be coupled to the SiO.sub.2 surface, such as thermocatalytic transition metals of the sort described elsewhere herein, through use of, for instance, corresponding metallocene starting materials.

Example 3

(28) Synthesis of TiSiO.sub.2. Mesoporous silica (SiO.sub.2, Selecto, 540 m.sup.2 g.sup.1, 2.2 nm average pore radius, 100-200 m particles) was dried under vacuum (<200 mTorr) at 500 C. for 12 to 15 hours and stored under N.sub.2 before use. 4-tert-butyldimethoxycalix[4]-arene (C.sub.46H.sub.60O.sub.4, CxMe.sub.2) was synthesized by methylating 4-tert-butylcalix[4]arene (C.sub.44H.sub.56O.sub.4, Cx, Sigma-Aldrich) with methyl iodide, following a literature procedure. Titanium-tert-butyl-calix[4]-arene chloride (TiCx) was synthesized by adding TiCl.sub.4 (1.0 M in tolene, Sigma-Aldrich) to a solution of CxMe.sub.2 in toluene and refluxed for 48 hours. The dried silica was then added to the TiCx solution in an Ar-filled glovebox, then removed from the glovebox and refluxed in toluene for >72 hours. During reflux N.sub.2 was continuously bubbled through the reaction solution and vented through the top of the condenser to remove HCl. The TiCx-SiO.sub.2 material was collected via vacuum filtration and repeatedly washed with toluene until the filtrate was clear (approximately 400 mL per g of material). The material was washed further with THF then water and dried at room temperature under vacuum. The final titanium loading was 200 mol g.sup.1 or 1 wt % Ti, as determined by ICP-AES.

Example 4

(29) Synthesis of TaSiO.sub.2. Mesoporous silica (SiO.sub.2, Selecto, 540 m.sup.2 g.sup.1, 2.2 nm average pore radius, 100-200 m particles) was dried under vacuum (<200 mTorr) at 500 C. for 12 to 15 hours and stored under N.sub.2 before use. To obtain tantalum-tert-butyl-calix[4]-arene (TaCx), TaCl.sub.5 was refluxed in toluene with 1 equivalent of Cx to form TaCx. The dried silica was then added to the TaCx solution in an Ar-filled glovebox, then removed from the glovebox and refluxed in toluene for >72 hours. During reflux N.sub.2 was continuously bubbled through the reaction solution and vented through the top of the condenser to remove HCl. The TaCx-SiO.sub.2 material was collected via vacuum filtration and repeatedly washed with toluene until the filtrate was clear (approximately 400 mL per g of material). The material was washed further with THF then water and dried at room temperature under vacuum.

Example 5

(30) Synthesis of NbSiO.sub.2. Mesoporous silica (SiO.sub.2, Selecto, 540 m.sup.2 g.sup.1, 2.2 nm average pore radius, 100-200 m particles) was dried under vacuum (<200 mTorr) at 500 C. for 12 to 15 hours and stored under N.sub.2 before use. To obtain niobium-tert-butyl-calix[4]-arene (NbCx), NbCl.sub.5 was refluxed in toluene with 1 equivalent of Cx to form NbCx. The dried silica was then added to the NbCx solution in an Ar-filled glovebox, then removed from the glovebox and refluxed in toluene for >72 hours. During reflux N.sub.2 was continuously bubbled through the reaction solution and vented through the top of the condenser to remove HCl. The NbCx-SiO.sub.2 material was collected via vacuum filtration and repeatedly washed with toluene until the filtrate was clear (approximately 400 mL per g of material). The material was washed further with THF then water and dried at room temperature under vacuum.

(31) As indicated above, various other thermocatalysts can be utilized, including most transition metal cations supported on SiO.sub.2, and many other materials useful in catalytic oxidation with H.sub.2O.sub.2.

Example 6

(32) Catalytic reactions. Prior to all catalytic reactions, the materials described above were calcined at 600 C. for 2 hours in static air. For the combined photo-/thermo-catalytic reaction system 5 to 10 mg of photocatalyst (TiO.sub.2 core, SiO.sub.2@TiO.sub.2 or TiSiO.sub.2@TiO.sub.2) and 0 to 70 mg of thermocatalyst (TiSiO.sub.2, TaSiO.sub.2 or NbSiO.sub.2) were added to a 20 mL reaction vial with 10 mL isopropanol, 1.15 mmol alkene (cis-cyclooctene or 1-octene) and 150 uL dodecane as an internal standard. A hole was punched into the reaction vial septum to allow the fitting of a quartz test tube to hold the 365 nm pen-ray UV lamp. Prior to reaction the reaction mixture was sonicated for 5 minutes to disperse any aggregated particle and then allowed to heat up to 65 C. for 30 minutes. The UV lamp was allowed to warm-up for 30 minutes prior to starting the reaction. O.sub.2 was bubbled through the reaction solution for 5 minutes prior to starting the reaction, and then for 1 minute at each sampling interval (0, 30, 60, 90, 120 minutes).

(33) The reaction was started by introducing the pen-ray lamp to the reaction mixture and the vessel was agitated using a Glas-Col shaker plate. 150 L aliquots were collected into GC vials with 1 mg Ag powder to decompose any H.sub.2O.sub.2 and avoid overoxidation. Acetone, cis-cyclooctene and cyclooctene oxide were quantified by GC-FID. H.sub.2O.sub.2 was quantified by iodometry (see below). For thermal reactions, 10 to 30 mg of thermocatalyst were added to a 20 mL reaction vial with 10 mL isopropanol, 1.15 mmol alkene, 150 uL dodecane as internal standard, sonicated for 5 minutes, allowed to heat up to 65 C. for 30 minutes, and then 3.5 mmol H.sub.2O.sub.2 (either from aqueous 50 wt % H.sub.2O.sub.2 or 4.0 M H.sub.2O.sub.2 in MeCN dried via MgSO.sub.4) is added to initiate the reaction. Alternatively, in one control reaction H.sub.2O.sub.2 (dried, in MeCN) is added at a rate of 100 mol h.sup.1 continuously over the course of the reaction with a syringe pump.

Example 7

(34) Catalyst activity can be demonstrated through extended reaction. A physical mixture of SiO.sub.2@TiO.sub.2 photocatalyst and TiSiO.sub.2 thermocatalyst was run with 60 mM cyclooctene in isopropanol. With reference to FIG. 6, conversion of alkene reaches 79% after 60 hours with 98% selectivity towards cyclooctene epoxide (97% mass balance, shown in black, where mass balance is ([Alkene].sub.t+[Epoxide].sub.t)/[Alkene].sub.initial). O.sub.2 is bubbled through periodically.

Example 8

(35) Reaction can be affected via the illumination source. With reference to Example 1, reaction conditions were as follows: 5 mg SiO.sub.2@TiO.sub.2, 15 mg TiSiO.sub.2, 10 mL isopropanol, 1.15 mmol cis-cyclooctene, 65 C., 365 nm UV (between 0-1, 2-3, 4-5 hours, etc.); O.sub.2 bubbled every 30 minutes. As shown in FIG. 7, periods of illumination produce hydrogen peroxide and acetone. Hydrogen peroxide is consumed during dark periods, while no acetone is produced. As long as sufficient hydrogen peroxide is present, cyclooctene epoxide formation continues during light and dark cycles.

Example 9

(36) In accordance with certain embodiments of this invention, hydrogenation can be used to regenerate a starting alcohol proton donor, as shown in Scheme 1.

(37) ##STR00001##

(38) Acetone hydrogenation was performed to demonstrate the recovery of isopropanol from the photocatalytic oxidation system. A reaction solution was prepared with 1.1 mmol acetone, 0.4 mmol cyclooctene oxide, and dodecane as internal standard in 50 mL isopropanol. Prior to hydrogenation, Pt on activated carbon (Pt/C, 1 wt % Pt, Aldrich) was heat treated to 400 C. for 4 hours under flowing He, 1 mL min in a u-tube reactor. The Pt/C catalyst was sealed within the u-tube until use for hydrogenation. The reaction solution and 230 mg of Pt/C was loaded and sealed into a high-pressure Parr reactor, de-gassed with N.sub.2, then charged with 10 bar H.sub.2. Hydrogenation occurred at 10 bar H.sub.2, 50 C., with stirring at 600 rpm. After 18 hours the reactor was cooled, de-pressurized, and an aliquot was collected for GC analysis: no epoxide was consumed under these conditions, whereas 100% of the acetone was hydrogenated.

Example 10

(39) Iodometric titration of H.sub.2O.sub.2. H.sub.2O.sub.2 was quantified by iodometry adapting previously described literature techniques. After 2 hours of reaction 200 L aliquots were added to 1 mL of 50 v/v % H.sub.2SO.sub.4 and N.sub.2 was bubbled through the solution for 10 minutes to remove O.sub.2. Then 1 w/w % KI (aq) was added to form I.sub.2, which was a yellow solution. The solution was titrated with 0.1 mM Na.sub.2S.sub.2O.sub.3 until the solution color was faintly yellow, then 0.1 mL starch indicator was added, forming a dark purple color, and the solution was further titrated until colorless. The Na.sub.2S.sub.2O.sub.3 titrant was standardized with solutions of KI.sub.3.

Example 11

(40) Characterization. All catalyst samples were calcined for 2 hours at 600 C. prior to characterization.

(41) TEM images were obtained using a JEOL 2100F transmission electron microscope. Catalyst samples were suspended in methanol, sonicated for 5 minutes, then platinum TEM grids were dipped into the suspension and dried at room temperature before imaging.

(42) Diffuse-reflectance UV-visible spectra were collected with a UV-3600 Shimadzu spectrophotometer with a Harrick Praying Mantis accessory for powder measurements and polytetrafuoroethylene as the baseline reference. Reflectance spectra were converted with the Kebulka-Munk transformation and edge energies were taken from Tauc plots of the spectra.

(43) N.sub.2 physisorption measurements were performed on a Micromeritics ASAP 2010. Prior to analysis, powder samples were dried at 200 C. under vacuum (<5 m Hg). Surface areas were calculated by the BET method.

(44) X-ray diffraction (XRD) spectra were collected with a Rigaku X-ray diffractometer from 20 to 60 2, with Cu K radiation. The slit width, dwell time and slit widths were kept constant for all materials. Crystallite sizes were estimated using the Scherrer equation for the (101) anatase reflection at a Bragg angle of 25.2 2, assuming a shape factor of 0.9 with a lower detection limit of approximately 5 nm.

(45) H.sub.2O.sub.2 is widely used as a green oxidant for chemical synthesis, because it is efficient, selective, and has only water as a byproduct. In situ H.sub.2O.sub.2 generation for selective oxidation has long been a goal of catalysis, specifically so for propylene epoxidation. As demonstrated, above, this invention provides an excellent catalyst for H.sub.2O.sub.2 production from O.sub.2 and a proton donor. In addition, H.sub.2O.sub.2 production can be coupled to a thermocatalyst for epoxidation, thus preventing the need to purify, concentrate, then dilute H.sub.2O.sub.2 for sale and transport. This invention also demonstrates oxidation of 1-octene, a model substrate for epoxidation of linear alkenes, indicating to those skilled in the art, broader applicability to other synthetic processes, including the production of propylene oxidation.