Method for coupling alkenes and carboxylic acids

Abstract

Disclosed are methods of making an alkenyl carboxylate ester i.e., alkene acetoxylation, comprising combining an alkene, a carboxylic acid, and a bimetallic single-atom alloy catalyst comprising platinum atoms and copper atoms, at a pressure and a temperature, the catalyst further comprising an oxide support such as silicon dioxide. Catalytic activity is further enhanced by adding alkali promoters e.g., potassium acetate.

Description

[0001] METHOD FOR COUPLING ALKENES AND CARBOXYLIC ACIDS

[0002] RELATED APPLICATION

[0003] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 638,681, filed April 25, 2024.

[0004] Government Support

[0005] This invention was made with government support under grant 2045675 awarded by the National Science Foundation. The government has certain rights in the invention.

[0006] Background of the Invention

[0007] Vinyl acetate (VA) is a high-value chemical with a current market value of $10b / yr that is expected to increase. The current method for the synthesis of VA involves vapor-phase oxidative coupling of ethylene and acetic acid on palladium-based catalysts, typically alkali promoted bimetallic Pd-Au nanoparticles on inert supports containing SiCE. These catalysts are prone to losing activity and precious metal content due to leaching under the corrosive effects of acetic acid in oxidative conditions.

[0008] Summary of the Invention

[0009] Disclosed is a method of making an alkenyl carboxylate ester, comprising combining in a reaction vessel an alkene; a carboxylic acid; and a catalyst comprising a plurality of platinum atoms and a plurality of copper atoms; at a pressure and a temperature.

[0010] Brief Description of the Drawings

[0011] Fig. 1. Reactivity of monometallic catalysts, (a) Experimental VA formation rate, (b) experimental VA selectivity, and (c) DFT-derived computational formation energies showing ethylene versus acetate binding strengths for (111) surfaces of Pd and its neighboring elements in the periodic table. The binding strengths in a PtCu single-atom alloy near an isolated Pt atom in Cu(l l l) are also shown in (c). The rates and selectivity in (a, b) were measured at 160 °C on 0.3-2.5g catalysts with metal loadings of 0.5wt.% (Ir) or lwt.% (others) on SiCE, and 40 cm3 / min flow rate at atmospheric pressure with 40 kPa ethylene, 10 kPa acetic acid, 5 kPa oxygen, and balance helium in a quartz reactor.

[0012] Fig. 2. Effect of PtCu bimetallic composition on rate and selectivity, (a) VA formation rate and (b) VA selectivity on lwt.% Cu / SiCE, 1.5wt.%Pto.iCu / Si02, 1.5wt.%Pto.3Cu / Si02, 1.5wt.%Pto.sCu / Si02, and lwt.% Pt / SiCE at 160 °C on 0.5-2.5g catalysts, and 40 cm3 / min flow rate at atmospheric pressure with 40 kPa ethylene, 10 kPa acetic acid, 5 kPa oxygen, and balance helium in a quartz reactor. The subscript x in PtxCu reflects the Pt:Cu atomic ratio.

[0013] Fig. 3. Comparison of co-impregnated and physical mixture catalysts. VA formation rates (left axis) and selectivities (right axis) for co-impregnated 1.5 wt.% Pto.aCu / SiCh and physical mixtures of lwt.% Pt / SiCE and 4wt.% Cu / SiC in 0.3 Pt:Cu atomic ratio at 160°C, 40 cm3 / min total reactant flow, 40 kPa C2H4, 10 kPa CH3COOH, and 5 kPa O2 at ambient pressure in a quartz reactor.

[0014] Fig. 4. Effect of reaction conditions, (a) VA formation rate and (b) VA selectivity as a function of O2 / C2H4 pressure ratio on 1.5wt.% Pto.aCu / SiCE catalysts at 150-160 °C, 1 atm total pressure in a quartz reactor with 30-40 cm3 / min total flow rate, and reactant pressures shown in kPa. C2H4 conversion < 5% for O2 / C2H4 < 1 and <30% for O2 / C2H4 >= 1. Dashed lines are added for clarity.

[0015] Fig. 5. Comparison of PtCu and Pd catalysts, (a) VA formation rate (per Pd or per Pt atom in the catalyst) and (b) VA selectivity as a function of time on stream for 1.5 wt.% Pto.aCu / SiCE, 1 wt.% Pd / SiO2, 30 cm3 / min total flow rate, 150°C temperature, ethylene Conv. < 10% 30 kPa O2, 30 kPa HOAc, 25-40 kPa C2H4 at 1 atm pressure in a quartz reactor.

[0016] Fig. 6. Catalyst performance in a high-pressure stainless- steel reactor. VA formation rates (columns) and selectivities (hollow points) on 1.5 wt.% PtojCu / SiCE catalysts at 150 °C at 1 atm and 6.5 atm total pressure in a stainless-steel reactor. Feed fractions of CH3COOH and O2 were 11% and 7.5%, respectively, and C2H6 was used as the inert carrier gas.

[0017] Fig. 7. Effect of alkali promotion. VA formation rate (filled) and selectivity (hollow) for unpromoted PtCu (triangles) and PtCu promoted with 5 wt.% K (circles). Collected on 1.5 wt.% PtojCu / SiCE with 40 cm3 / min total reactant flow, 40 kPa C2H4, and 10 kPa CH3COOH at 160 °C and 1 atm total pressure in a quartz reactor. C2H4 conversion < 5%. Helium was used as the inert carrier gas.

[0018] Fig. 8. Catalyst stability at atmospheric pressure and high pressure. Time on stream effects for (a) VA formation rate on 1 wt.% Pd / SiCE, 1.5 wt.%Pto.3Cu / Si02 and 4 wt.%Pdo.o3Cu / Si02 at atmospheric pressure in a quartz reactor, and (b) VA formation rate and selectivity on 1.5 wt.%Pto.3Cu / Si02 at 6.5 atm in a stainless-steel reactor. Data collected at 40 cm3 / min total flow, with 40% C2H4, 10% (a) or 5% (b) CH3COOH, and 5% O2 at 160 °C (a) or 150 °C (b).

[0019] Fig. 9. Comparison of the performance of an alkali promoted PdAu catalyst with PtCu catalysts prepared using different methods (samples 1-7). All measurements were performed at 150 °C. Sample 1 was measured at 1 atm, 40% ethylene, 30% acetic acid, and 30% oxygen in a quartz reactor. All other samples were measured at 7 atm, 60% ethylene, 5% oxygen, 13 or 16% acetic acid and balance ethane in a stainless-steel reactor.

[0020] Detailed Description of the Invention

[0021] Vinyl acetate (VA) monomer is an important chemical reagent used for manufacturing adhesives, paints, and coatings. Its market value is roughly $10b / yr and is expected to increase to $ 16b / yr in the next decade.1VA is typically produced by an oxidative ethylene acetoxylation reaction (oxidative coupling of ethylene and acetic acid) on catalysts containing palladium.2'15This oxidative process improves upon earlier processes based on non-oxidative reaction of acetylene and acetic acid.16The state-of-the-art catalyst for VA synthesis oxidative ethylene acetoxylation consists of PdAu bimetallic nanoparticles dispersed on a high surface area support and promoted by adding potassium acetate.17'19

[0022] Extensive research has been conducted to understand the mechanism of operation of VA synthesis catalysts,19'23improve performance through optimization of the process design,15,24catalyst composition (Pd, Au, alkali promoter, support)4 19,22’25and preparation method.11 12The operation of PdAu catalysts involves 6-10 atm pressure and a feed involving a large excess of ethylene and an inert hydrocarbon (ethane) along with acetic acid and oxygen. The oxygen feed is limited by flammability limits, which results in low single-pass conversions of ethylene (< 10%) and acetic acid (-30%) and large recycles of unreacted feed, which imposes an energy demand for chemical separation and requires significant process optimization for efficient operation.

[0023] A significant drawback of the PdAu catalyst is the dissolution of active metal atoms in thin liquid films near the catalyst surface that form under high-pressure conditions and the dynamics of catalyst involving dissolution and re-deposition of metal. Such dynamics have been studied in detail, and they also imply the potential for leaching of the metal and loss of catalytic activity over time.17 19,22This issue is partially mitigated by using narrow reactor tubes several meters long24to ensure a long path for mobile species before they exit the reactor. The catalyst and process features highlight the issues with the stability of the current VA synthesis catalyst, including the loss of precious metals (Pd and Au).

[0024] Despite these challenges and extensive research, to date, PdAu remains the prominent catalyst used in industrial VA synthesis. Most literature studies focus on PdAu or monometallic Pd and on the effects of alkali promotion and carbon deposition. Some studies describe the use of Pd as a dilute species in the Au matrix,20,26in contrast to Pd-rich PdAu used in the industry, while a few studies probe bimetallic systems involving Pd with other metals (Cu, Sn).27,28Although some patents mention a general list of group 8 metals4,7or use Pt to hydrogenate acetic acid to acetaldehyde in alternative approaches,2we are not aware of studies that focus on Pd-free compositions as promising catalysts for oxidative acetoxylation of ethylene. The development of alkene acetoxylation catalysts free of Pd and Au is important due to the high cost and the known stability issues and process condition challenges.

[0025] Unexpectedly, density functional theory calculations led to the identification of bimetallic catalysts containing platinum (Pt) and copper (Cu) with Pt:Cu atomic ratios below unity as promising new catalysts, which were subsequently found to be highly active, selective, and stable for vinyl acetate synthesis in experimental studies. This discovery is unique and unexpected because not many density functional theory predictions lead to working catalysts due to the complexity of real experimental reaction conditions. The catalytic activity is further enhanced by adding alkali promoters (e.g., potassium acetate). These catalysts have been tested at, (i) 1 atm pressure in a quartz reactor, and (ii) pressures up to 7 atm in a stainless-steel reactor with feed compositions relevant to industrial processes. In both cases, the PtCu catalyst is highly active, selective, and stable. This result is very surprising and counter-intuitive because both Pt and Cu are very poor catalysts for vinyl acetate synthesis.

[0026] The PtCu catalyst will be useful in industrial VA synthesis, boosting the performance of current processes due to improved catalyst activity, selectivity, stability and lower cost of Cu and Pt than Pd and Au. Furthermore, the stable high selectivity of PtCu over broad reaction conditions offers unique advantages for next-generation VA synthesis processes.

[0027] EXAMPLES

[0028] The above-mentioned challenges with current VA synthesis processes and Pd-based catalysts mean Pd-free catalysts are desirable. Rates and selectivities for VA synthesis on monometallic catalysts involving Pd and its neighboring metals in the periodic table were measured and the binding strengths of important reactive species (bound acetate and ethylene molecules) were calculated using density functional theory (DFT). The results of these measurements and calculations are shown in Figure 1. As expected, all other metals exhibit much lower VA synthesis rates and selectivities than Pd at identical conditions. For example, the rates on Pt and Ir are more than an order of magnitude lower [Fig. la 0.09 Ireks'1and 0.075 Pt^ks’1vs. 1.1 Pd^ks’1; M^ks'1= mol VA / (mol M. 1000 s)]. Furthermore, the VA selectivity on Ir and Pt are below 20%, in contrast to > 60% selectivity for Pd (Fig. lb). Rh, Cu and Ni exhibit 2-5 orders of magnitude lower rate than Pd. To understand the origin of these trends, binding strengths of acetate and ethylene on these metals were computed (Fig. lc; more negative values indicate stronger binding). The computational results show that Cu, Ag, and Au exhibit a much weaker ethylene binding in comparison to Pd, while Ni, Rh and Ir exhibit a much stronger acetate binding, and Pt exhibits a much stronger ethylene binding. These results suggest that the reactivity trends are at least in part determined by the Sabatier principle, which states that for maximum rates the reactants should bind neither too strongly nor too weakly to the catalyst.

[0029] It was hypothesized that Pd is more active and selective because it exhibits appropriate binding strengths for both reactants, and that there may be bimetallic compositions even closer to the Sabatier maximum than Pd. To find better alloy catalysts, acetate and ethylene binding strengths on single-atom alloys (SAA) containing isolated active metals in Cu, Ag and Au host metals were calculated. The analysis revealed that the PtCu SAA exhibits binding strengths close to Pd in a gap between it and the other metals (Fig.lc), indicating that it may be a promising catalyst. Since VA synthesis conditions are known to leach metal atoms out of catalyst nanoparticles, alloy stability can be an important factor in the ability to resist such leaching. The calculations of alloy stability in Table 1 indicate that PtCu alloys are the most stable among the compositions studied, suggesting that the strong mutual affinity of Pt and Cu atoms can resist loss of these atoms to oxidation and reaction with acetic acid. Taken together, these results suggest that PtCu is a promising candidate as an active and stable VA synthesis catalyst.

[0030] Table 1. Relative stability of single atom alloys based on DFT-derived energy differences between three-layer 4x4 monometallic (111) surface slabs and slabs with one isolated Pt group atom in Cu(lll), Ag(lll) and Au(lll) (e.g., AE= Epticu47 - 47 / 48EcU4s - l / 48Ept4s). Encouraged by these properties of the PtCu catalyst composition, the catalysts with different Pt:Cu ratios were prepared as shown in Figure 2. The VA synthesis rates and selectivity on these catalysts are much higher than monometallic Pt and Cu, consistent with improved activity of bimetallic sites. The rates per Pt are insensitive to Pt:Cu ratio in 0.1-0.5 range suggesting that a range of compositions in the dilute limit are active. However, the selectivity passes through a maximum at Pto.aCu. Therefore, this composition is used for subsequent measurements.

[0031] It was found that physical mixtures of Pt / S i O2 and Cu / SiCF give similar high rate and selectivity as the physical mixture (Figure 3), which is consistent with recent work on PdCu catalyst demonstrating that the VA synthesis conditions significantly restructure the catalyst to form alloys from physical mixtures of monometallic catalysts.29

[0032] Figure 4 shows effects of reactant partial pressures on VA synthesis rate and selectivity on the Pto.aCu catalyst (total pressure is atmospheric). These rates and selectivity exhibit complex sensitivity to pressure ratios, but generally increase with O2 and acetic acid pressure, but decrease with ethylene pressure. The selectivity increases with all three pressures except at very high oxygen pressures where combustion starts to be significant. Crucially, at 30 kPa pressure of all three reactants in Figure 4, the rate is about six times higher than the value reported for monometallic Pd in Figure 1 (~7 Pt^ks'l vs. ~1 Pd^ks'1). Previous work has shown that rates on monometallic Pd decreases at Chiethylene ratios beyond 0.5 and remains below 2.5 Pd- 1ks- 1at all atmospheric pressure conditions.23The PtCu catalyst shows a high selectivity over a very broad range of conditions in contrast to a much narrower range for monometallic Pd. Thus, Pto.aCu surpasses the Pd catalyst in both rate and selectivity over a broader range of conditions. These details are further confirmed in Figure 5 by a direct comparison of Pd and Pto.aCu at two different ethylene pressures showing higher rates and consistently higher and stable selectivities for the latter catalyst. The high selectivity values near 90% are consistent with process design studies that require selectivity optimization for maximum profitability.24

[0033] To further test the performance of PtCu catalyst under more industrially relevant conditions, measurements were performed in a stainless-steel reactor with walls coated with an inert a-Si material as shown in Figure 6. In this reactor, with other conditions being equal, the rate and selectivity increased with the increase in total pressure, and the selectivities became higher than 90%, indicating that the results from the atmospheric pressure studies can be further enhanced by industrially relevant high-pressure conditions. The effect of adding alkali promotors on rates in the atmospheric pressure quartz reactor measurements was also tested, as shown in Figure 7. The results show that for a range of O2 pressures the alkali promoted Pto.aCu sample exhibits about 4 times higher rate than the unpromoted sample. Thus, the alkali promotion can further improve Pto.aCu, which is much better than monometallic Pd even without the alkali promotion.

[0034] The stability of a PtCu catalyst was tested and compared to Pd and PdCu at atmospheric pressure conditions in a quartz reactor, as shown in Figure 8. This test indicates that the PtCu catalyst retains its activity for >20 h (Fig. 8a). This catalyst also fully retains activity and selectivity at high pressure conditions in the stainless-steel reactor in a ~15h test (Fig. 8b). In contrast, the Pd and PdCu catalysts lose activity rapidly during the initial time on stream, followed by somewhat improved stability, but losing at least 30% activity after lOh (Fig. 8a). It should be noted that stability can be further enhanced in industrial reactors using tubular reactors that are typically several meters long and increase the path length of the leached metal species.

[0035] Figure 9 compares the VA formation rate, VA selectivity, and space time yield (STY) of VA on potassium promoted PdAu catalysts with those on different PtCu catalysts. A 1.5 wt.%Pd2Au / SiO2 catalyst (1.5wt.% total metal loading with 2:1 Pd:Au atomic ratio) was prepared using incipient wetness impregnation of silica gel with mixed aqueous solution of Pd and Au precursors, drying, washing with Na2COa solution, thermal treatment in flowing helium, and addition of CH3COOK (5 wt .% potassium) by incipient wetness impregnation with aqueous solution. Samples 1-7 are co-impregnated PtCu catalysts with different metal and promoter loadings and procedures of their incorporation. Sample 1 through 5 are 1.5 wt.% Pto.aCu / SiCh while samples 6 and 7 are 5 wt.% PtojCu / SiCh. Sample 1 contains no promoter, while the promoter amount is 2.5 wt.% potassium in sample 4 and 5wt.% in other samples. Sample 2 contains 5wt.% potassium promoter added using aqueous solution of CH3COOK while samples 3 through 7 contain promoter added using CH3COOK dissolved in CH3COOH. In samples 5 and 7, the promoter is added after first treating the catalyst under VA synthesis conditions (160°C, 1 atm, 40 kPa C2H4, 10 kPa CH3COOH, 5kPa O2 at 40 cm3 / min flow for 4h) and reducing under hydrogen environment. In contrast, in samples 2-4 and 6 the promoter is added after drying and reducing under hydrogen environment without treatment under VA synthesis conditions.

[0036] Among 1.5 wt.% Pto.3Cu / Si02 catalysts (samples 1-5), the activity increases with promoter addition compared to the unpromoted catalyst (sample 1), and promoter addition in CH3COOH gives higher activity than promoter addition in water (sample 2 vs. 3). The higher promoter amount gives a higher rate but lower selectivity (sample 3 vs. 4), and a VA treatment before promoter addition gives higher rate (Sample 3 vs. 5). Higher weight loading in samples 6 and 7 (5 wt.% Pto.3Cu / Si02) gives lower rates per Pt atom, but higher space time yield due to the higher metal amount packed in the same catalyst volume. These higher weight loading samples also show higher rates when VA treatment is performed prior to promoter addition (sample 6 vs. 7).

[0037] To summarize, a combined experiment- and theory-based approach was used to discover a promising Pd-free heterogenous catalyst for VA synthesis. This new catalyst greatly surpasses the activity, selectivity, and stability of monometallic Pd, and its performance can be further enhanced by alkali promotors and tuning total metal loading, support, and optimization of process conditions. Due to its high Cu content, the PtCu catalyst significantly lowers precious metal use compared to the industrial standard and exhibits very high stability, which can help overcome the limitations of the current VA synthesis process. PtCu / SiCh exhibits high selectivity over a broad range of conditions, which offers opportunities for significantly enhanced efficiency and longevity as compared to current catalysts. The direct comparison of PtCu catalyst samples with an alkali promoted PdAu catalyst under industrially relevant high pressure conditions shows that PtCu catalysts can lead to similar or better rates and selectivity and shows what compositions and synthesis methods can lead to best performance.

[0038] Methods for Catalyst Synthesis and Rate and Selectivity Measurements

[0039] SiO2 powder (Davisil Grade 643, pore volume: 1.15 cm3g-1, 99%, particle size: 35-70 pm, specific surface area: 300 m2g-1, Sigma-Aldrich) was washed in a 0.5 M nitric acid solution, rinsed with deionized water, and dried overnight at 100°C. Precursor compounds were dissolved in deionized water and added drop wise to SiCh until incipient wetness. Pd(NO3)22H2O (99.8%, Sigma-Aldrich), Pt(NH3)4(NO3)2 (99.995%, Sigma- Aldrich), CU(NO3)2'2.5H2O (99.8%, Sigma- Aldrich), IrCl3-xH2O (Alfa Aesar, 51.94% Ir basis), Rh(NO3)3-xH2O (Sigma Aldrich) Ni(NO3)2 6H2O (Sigma Aldrich), and HAuC14-3H2O (Sigma Aldrich) were used as precursor compounds. The resulting wet solid was held in a closed beaker for 3 h, then dried for 12 h, either at 110 °C and ambient pressure or at 45°C under vacuum. The resulting powder was treated in flowing helium 400 °C for 4 h for Pt, and PtCu samples and at 450°C for 4 h other samples. Potassium promoters were added to PtCu / SiO2catalysts in the form of potassium acetate (CH3COOK, > 99.0%, Sigma-Aldrich) dissolved in deionized water and added via incipient wetness impregnation to a final concentration of 2.5 or 5 wt.% K. Before reaction measurements, catalyst samples were treated in flowing H2 at 400 °C for 1 h to reduce them to the metallic form. Analogous procedures were used for preparing Ir, Rh, and Ni catalysts using IrCh’xthO (Alfa Aesar, 51.94% Ir basis), Rt^NCh ’xEhO (Sigma Aldrich) and Ni(NO3)2 6H2O (Sigma Aldrich), respectively, as precursor compounds.

[0040] VA formation rates and selectivities at ambient pressure were measured in a U-shaped quartz tube (14” outer diameter) with a bulb and a quartz frit designed for holding catalyst samples as vertical fixed beds under the flow of gaseous reactants. Measurements above ambient pressures were carried out in a 316 stainless steel reactor tube (outer diameter %”) with vertical catalyst beds held in place with quartz wool. The inner wall of the steel reactor was coated with inert amorphous Si using chemical vapor deposition (SilcoTek SilcoNert 2000), or with an inert SiCh layer via sol-gel formation using acid-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) followed by calcination in air at 200 °C. The reactor was heated using a resistive furnace with ceramic insulation (National Element, FA120). Temperature was measured with an Omega K-type thermocouple and controlled using a Watlow EZ-Zone temperature controller.

[0041] Gaseous reactants were introduced using electronic mass flow controllers (Porter 601 CV Series II). Gases were H2 (99.9999%, supplied by a Parker-Balston hydrogen generator), C2H4 (99.5%, Airgas; or 5% in He, Airgas), O2 (ultra-high purity, Airgas; or 25% in He, Airgas), C2H6 (technical grade, Airgas), and He (99.999%, Airgas). Using C2H6 as an inert carrier gas instead of He showed no substantial effects on rates, selectivity to VA, or product distribution, but reduces the explosive composition range of the reactant mixture. Liquid CH3COOH was evaporated into the flowing reactant gas mixture using a Cole-Parmer model 100 syringe pump. Transfer lines were heated above 100 °C to prevent liquid condensation.

[0042] Reactant and product concentrations were measured by gas chromatography (Agilent 1890B). Hydrocarbons and oxygenates (C2H4, C2H6, CH3COOH, CH3CHO, CH3COOC2H3) were separated using an HP-PLOT Q capillary column (30 mm x 0.32 mm x 20.00 pm) and detected with a flame ionization detector (FID). O2, CO2, and CO were separated using a Carboxen- 1000 packed column and detected with a thermal conductivity detector (TCD). VA formation rates are reported as number of VA molecules formed per molecules of active metal (M) present in the catalyst per kilosecond [TVA; (mol VA) (mol M)'1ks'1, abbreviated to M'1ks"1]. Selectivities are reported as the number of carbon atoms in VA relative to the total number of product carbon atoms. Acid-washed SiO2 did not generate a detectable amount of VA. Synthesis Protocols for Samples 5 and 7

[0043] The most active samples (sample 5 in Figure 9 for 1.5wt.% Pto.aCu, and sample 7 in Figure 9 for 5 wt.%Pto.3Cu) were prepared by a process requiring (i) a treatment of the catalyst under VA synthesis reaction conditions after the PtCu impregnation step and before the CH3COOK promoter addition step, and (ii) dissolution of the promoter in acetic acid instead of water before adding it to the catalyst. To prepare these samples, desired amounts of Pt(NH3)4(NO3)2 (99.995%, Sigma- Aldrich) and Cu(NO3)2-2.5H2O (99.8%, Sigma- Aldrich) were dissolved in deionized water to form the catalyst precursor solution. This solution was added dropwise to acid-washed SiCh powder (silica gel, Davisil, Sigma Aldrich) until incipient wetness. The resulting wet solid was held in a closed beaker for 3 h and then dried for 12 h at 45°C in a vacuum oven. The dried powder was treated in flowing helium 400 °C for 4 h. This sample was loaded in a U-tube quartz reactor and treated under VA synthesis conditions (at 160°C, 1 atm, 40 kPa C2H4, 10 kPa CH3COOH, 5kPa O2 at 40 cm3 / min flow) for 4h. Then, the sample was treated in flowing hydrogen at 300°C for Ih to reduce Pt and Cu to metallic form. The reduced sample was cooled to room temperature, removed from the reactor, and CH3COOK dissolved in CH3COOH was added drop wise to the sample until incipient wetness. The wet solid was held in a closed beaker for 3 h, then dried for 12 h at 45°C in a vacuum oven. The amount of promoter added corresponds to 5 wt.% of K atoms (potassium) in the dried solid for both samples 5 and 7. This process led to samples with combined 1.5wt.% (sample 5) or 5 wt% (sample 7) of Pt and Cu atoms with Pt:Cu atomic ratio of 0.3, and 5wt.% of K atoms in SiCh.

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[0083] Miller, E. C. H. Sykes, P. Deshlahra, Single- Atom Alloy Formation via Reaction Driven Catalyst Restructuring, unpublished results. Incorporation by Reference

[0084] All U.S. patents and U.S. and PCT patent application publications mentioned herein are hereby incorporated by reference in their entirety as if each individual patent or patent application publication was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.

[0085] Equivalents

[0086] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

What is claimed is:

1. A method of making an alkenyl carboxylate ester, comprising combining in a reaction vessel an alkene; a carboxylic acid; and a catalyst comprising a plurality of platinum atoms and a plurality of copper atoms; at a pressure and a temperature.

2. The method of claim 1, wherein the molar ratio of the platinum atoms to the copper atoms in the catalyst is about 0.001 to about 2.

3. The method of claim 2, wherein the molar ratio of the platinum atoms to the copper atoms in the catalyst is about 0.1 to about 1.

4. The method of claim 3, wherein the molar ratio of the platinum atoms to the copper atoms in the catalyst is about 0.2 to about 0.4.

5. The method of any one of claims 1-4, wherein the combined amount of Pt and Cu in the catalyst is about 0.1 wt.% to about 50 wt.%.

6. The method of claim 5, wherein the combined amount of Pt and Cu in the catalyst is about 0.5 wt.% to about 5 wt.%.

7. The method of claim 6, wherein the combined amount of Pt and Cu in the catalyst is about 1 wt.% to about 2 wt.%.

8. The method of any one of claims 1-7, wherein the catalyst further comprises one or more promoters comprising potassium, chlorine, or palladium.

9. The method of claim 8, wherein the promoter comprises potassium.

10. The method of any one of claims 1-9, wherein the catalyst further comprises an oxide support.

11. The method of claim 10, wherein the oxide support comprises SiCh, AI2O3, aluminosilicate, TiCh, Z1O2 and / or CcCh.

12. The method of claim 11, wherein the oxide support comprises SiCh.

13. The method of any one of claims 1-12, wherein the catalyst further comprises metal nanoparticles.

14. The method of any one of claims 1-13, wherein the alkene is a linear or branched C2- C10 alkene.

15. The method of claim 14, wherein the alkene is ethylene.

16. The method of any one of claims 1-15, wherein the carboxylic acid is acetic acid.

17. The method of any one of claims 1-16, wherein the alkenyl carboxylate ester is vinyl acetate.

18. The method of any one of claims 1-17, wherein the pressure is about 0.1 atm to about 20 atm.

19. The method of claim 18, wherein the pressure is about 1 atm to about 10 atm.

20. The method of claim 19, wherein the pressure is about 4 atm to about 7 atm.

21. The method of any one of claims 1-21, wherein the temperature is about 50 °C to about 300 °C.

22. The method of claim 21, wherein the temperature is about 100 °C to about 200 °C.

23. The method of claim 22, wherein the temperature is about 130 °C to about 180 °C.

24. The method of any one of claims 1-23, further comprising oxygen.

25. The method of claim 24, wherein the alkene is about 1% to about 80% of the total pressure of alkene, oxygen and carboxylic acid in the reaction vessel.

26. The method of claim 24 or 25, wherein the oxygen is about 1% to about 50% of the total pressure of alkene, oxygen and carboxylic acid in the reaction vessel.

27. The method of claim 24, 25, or 26, wherein the carboxylic acid is about 1% to about 50% of the total pressure of alkene, oxygen and carboxylic acid in the reaction vessel.

28. The method of claim 24, 25, 26, or 27, wherein the pressure ratio of oxygen to alkene is about 0.1 to about 5 in the reaction vessel.

29. The method of any one of claims 1-28, further comprising an inert carrier gas.

30. The method of claim 29, wherein inert carrier gas is selected from helium, methane and ethane.

31. A method of making a catalyst, comprising the steps of:(i) contacting a support material with a source of platinum atoms and a source of copper atoms;(ii) contacting the support material with an alkene;(iii) contacting the support material with a reducing agent; and(iv) contacting the support material with a source of promoter atoms.

32. The method of claim 31, wherein the support material is silica.

33. The method of claim 31 or 32, wherein the source of platinum atoms comprises a solvent.

34. The method of claim 33, wherein the solvent comprises water.

35. The method of any one of claims 31-34, wherein the source of platinum atoms comprises Pt(NH3)4(NO3)2.

36. The method of any one of claims 31-35, wherein the source of copper atoms comprises a solvent.

37. The method of claim 36, wherein the solvent comprises water.

38. The method of any one of claims 31-37, wherein the source of copper atoms comprises Cu(NO3)2.

39. The method of any one of claims 31-38, wherein the support material is contacted with the source of platinum atoms and the source of copper simultaneously.

40. The method of any one of claims 31-39, wherein step (i) further comprises drying the support material after contacting with the source of platinum and the source of copper.

41. The method of claim 40, wherein the drying is conducted at a temperature of about 40 - 600 °C.

42. The method of claim 41, wherein the drying is conducted at a temperature of about300 - 500 °C.

43. The method of any one of claims 31-42, wherein the alkene is ethylene.

44. The method of any one of claims 31-43, wherein step (ii) further comprises contacting the support material with a carboxylic acid.

45. The method of claim 44, wherein the carboxylic acid is acetic acid.

46. The method of any one of claims 31-45, wherein step (ii) further comprises contacting the support material with an oxidizing agent.

47. The method of claim 46, wherein the oxidizing agent is oxygen.

48. The method of any one of claims 43-48, wherein the alkene and the carboxylic acid are in the gas phase.

49. The method of any one of claims 31-48, wherein step (ii) is conducted at a temperature of about 50 - 300 °C.

50. The method of any one of claims 31-49, wherein step (ii) is conducted at a temperature of about 100 - 200 °C.

51. The method of any one of claims 31-50, wherein the reducing agent is hydrogen.

52. The method of any one of claims 31-51, wherein step (iii) is conducted at a temperature of about 100 - 500 °C53. The method of any one of claims 31-52, wherein step (iii) is conducted at a temperature of about 250 - 350 °C.

54. The method of any one of claims 31-53, wherein the promoter atoms are alkali metal atoms.

55. The method of any one of claims 31-54, wherein the alkali metal atoms are potassium atoms.

56. The method of any one of claims 31-55, wherein the source of promoter atoms comprises potassium acetate.

57. The method of any one of claims 31-56, wherein the source of promoter atoms comprises a solvent.

58. The method of claim 57, wherein the solvent comprises a carboxylic acid.

59. The method of claim 58, wherein the carboxylic acid is acetic acid.

60. The method of any one of claims 31-59, wherein step (iv) is conducted at room temperature.

61. The method of any one of claims 31-60, wherein the molar ratio of platinum atoms to copper atoms in the catalyst is about 0.1 to about 1.

62. The method of any one of claims 31-61, wherein the molar ratio of platinum atoms to copper atoms in the catalyst is about 0.2 to about 0.4.

63. The method of any one of claims 31-62, wherein the combined amount of platinum and copper in the catalyst is about 0.1 wt.% to about 50 wt.%.

64. The method of any one of claims 31-63, wherein the combined amount of platinum and copper in the catalyst is about 0.5 wt.% to about 5 wt.%.

65. The method of any one of claims 31-64, wherein the combined amount of platinum and copper in the catalyst is about 1 wt.% to about 2 wt.%.

66. A catalyst made by the method of any one of claims 31-65.

67. A catalyst comprising a silica support material, and platinum, copper and potassium atoms, wherein: the molar ratio of platinum atoms to copper atoms is about 0.3; the combined amount of Pt and Cu in the catalyst is about 1 wt.%; and the amount of potassium in the catalyst is about 5 wt.%.

68. A catalyst, comprising a silica support material, and platinum, copper and potassium atoms, wherein: the molar ratio of platinum atoms to copper atoms is about 0.3; the combined amount of Pt and Cu in the catalyst is about 5 wt.%; and the amount of potassium in the catalyst is about 5 wt.%.

69. The catalyst of any one of claims 66-68, wherein the catalyst is capable of catalyzing the oxidative coupling of ethylene and acetic acid to form vinyl acetate.

70. The catalyst of claim 69, wherein the vinyl acetate is formed with a molar selectivity of at least about 40%, wherein the molar selectivity is defined as the percentage of carbon atoms in vinyl acetate relative to the total number of carbon atoms in product molecules.

71. The catalyst of claim 69, wherein the vinyl acetate is formed with a molar selectivity of at least about 50%, wherein the molar selectivity is defined as the percentage of carbon atoms in vinyl acetate relative to the total number of carbon atoms in product molecules.

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