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Abstract Developing improved catalysts for sustainable chemical processes often involves understanding atomistic origins of catalytic activity, selectivity, and stability. Using density functional theory and steady‐state kinetic analyses, we probe the elementary steps that form decomposition products that limit selectivity in vinyl acetate (VA) synthesis on Pd surfaces covered with acetate species. Acetate formation and coupling with ethylene control the VA formation catalytic cycle and steady‐state coverage, but acetate and ethylene can separately decompose to form CO2. Both decompositions involve initial C−H activations at acetate vacancies, followed by additional C−H activations and eventual C−O formations and C−C cleavages involving reactions with molecular oxygen. Acetate decomposition paths with non‐oxidative kinetically‐relevant steps exhibit similar free energy barriers to oxidative paths. In contrast, the non‐oxidative ethylene path involving an ethylidyne intermediate exhibits a much lower barrier than paths with oxidative kinetically‐relevant steps. Ethylene decomposition is very facile at low coverages but is more coverage‐sensitive, leading to similar decomposition and VA formation barriers at coverages accessible at steady state, which is consistent with moderate VA selectivity in measurements and ethylene vs. acetate decomposition contributions assessed from regressed kinetic parameters. These insights provide a detailed framework for describing VA synthesis rates and selectivity on metallic catalyst surfaces.
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Ethane dehydrogenation performance and high temperature stability of silica supported cobalt phosphide nanoparticles
A series of Co–P materials with varying P : Co ratio from 0 to 4 supported on SBA-15 were evaluated for ethane dehydrogenation (EDH) performance. In comparison to monometallic Co, the Co–P materials have improved ethylene selectivity from 41% for Co to 88–90% for Co–P, which was attributed to the segregation of Co atoms and the formation of partial positive Co δ + sites in the Co–P materials due to charge transfer. Among the Co–P materials studied, an optimum in stability was observed in those containing a P : Co ratio in the range 1 to 2. Below this range, limited P is available to adequately separate Co atoms. Above this range, the excess P promotes coke formation through possible acid catalyzed pathways. The stability of two of the Co–P materials containing the Co 2 P and CoP phase, respectively, were further tested for EDH at 700 °C. Under these conditions, the ethylene selectivity was 98%, and both materials remained active with little to no deactivation for over 4 h. In comparison to a Pt–Sn reference, both Co–P materials showed vastly improved stability. Additionally, both Co–P materials showed no signs of sintering after EDH at 700 °C and maintained their respective Co 2 P and CoP phases. These results demonstrate the catalytic improvement with P incorporation and highlights the high stability of Co–P, and possibly other metal phosphides, as high temperature EDH catalysts.
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- Award ID(s):
- 1647722
- PAR ID:
- 10431114
- Date Published:
- Journal Name:
- Catalysis Science & Technology
- Volume:
- 12
- Issue:
- 3
- ISSN:
- 2044-4753
- Page Range / eLocation ID:
- 976 to 985
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1CY01737C
