CAREER: Understanding Effects of Surface Coverage and Catalyst Composition on Vinyl Acetate Synthesis

职业：了解表面覆盖率和催化剂成分对醋酸乙烯合成的影响

• 批准号: 2045675
• 负责人: Prashant Deshlahra
• 金额: $ 53.7万
• 依托单位: Tufts University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2045675&HistoricalAwards=false
• 关键词: CAREER; Understanding; Effects; Surface; Coverage

The majority of chemical processes worldwide utilize catalysts that promote the efficient manufacturing of chemicals and fuels, while also lowering energy costs and environmental footprint. Advances in catalyst technology depend, in turn, on understanding how a catalyst’s performance is determined by the properties of its surface and of the reacting molecules. This project focuses on developing such understanding for the catalytic reaction involved in the synthesis of vinyl acetate (VA). VA is a high-value chemical produced in large volumes by the coupling of ethylene and acetic acid molecules on expensive palladium-based catalysts. It is an important component of many polymers and consumer products. However, current VA manufacturing processes have several limitations. The project addresses those limitations through research aimed at developing more efficient catalysts consisting of atomically dispersed precious metal atoms on inexpensive copper matrices. The project integrates research with educational and outreach activities aimed at middle- and high-school students.High surface coverages prevail in many catalytic reactions at practical conditions. Rigorous incorporation of the effects of coverage in the analysis of experimental data, as well as incorporation in simulation models, is challenging, however. Thus, few studies exist focusing on the design of catalysts to operate efficiently under high-coverage conditions. Coverage plays an important role in VA synthesis via oxidative coupling of acetic acid and ethylene. In this reaction, crowding of the surface with acetate species promotes C-O coupling and inhibits dissociative steps in ways that influence both reactivity and selectivity. Mechanistic understanding of this reaction has emerged from surface science and density functional theory (DFT), but essentially all past work has focused solely on supported palladium (Pd) or palladium-gold (PdAu) catalysts that are unstable at practical conditions without alkali stabilizers that tend to deplete over long times. This project is aimed at, (i) understanding (using kinetics and DFT) the mechanistic aspects pertaining to steady-state catalysis, (ii) assessing how the very different strengths of lateral interactions for active atoms dispersed in an Au versus Cu matrix influence rate and selectivity, and (iii) leveraging such insights to design more efficient VA synthesis catalysts. The project builds on preliminary experimental and computational results for monometallic Pd catalysts obtained by the investigator in collaboration with colleagues at his institution. The Pd work has provided significant insights on how coverages impose changes in rate liming steps when reactant pressures change in steady-state catalysis. DFT studies will build on these insights and probe, on a range of single atoms dispersed on Cu and Au matrices, how (i) enhanced lateral interactions imposed by the smaller lattice constant of Cu can promote C-O coupling, and (ii) how combined effects of coverage and composition influence catalytic performance. These results will further guide the preparation and structural-functional characterization of single atom alloy catalysts with potential for better activity, selectivity, and stability in VA synthesis catalysis. The data generation, catalyst characterization, and analysis methods employed in the study – combined with the resulting insights from VA synthesis - will carry over to other catalytic reactions that operate under conditions of high surface coverage of adsorbed species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

世界上大多数化学过程都使用催化剂来促进化学品和燃料的高效制造，同时也降低了能源成本和环境足迹。反过来，催化剂技术的进步取决于了解催化剂的性能是如何由其表面和反应分子的性质决定的。本项目的重点是发展对醋酸乙烯酯（VA）合成催化反应的理解。VA是一种高价值的化学品，通过在昂贵的钯基催化剂上将乙烯和乙酸分子偶联而大量生产。它是许多聚合物和消费品的重要组成部分。然而，目前的VA制造工艺有一些局限性。该项目通过研究开发更有效的催化剂来解决这些限制，催化剂由原子分散的贵金属原子组成，并放置在廉价的铜基体上。该项目将研究与针对初高中学生的教育和推广活动结合起来。在实际条件下，高表面覆盖率在许多催化反应中普遍存在。然而，在实验数据分析中严格结合覆盖的影响，以及在模拟模型中结合，是具有挑战性的。因此，很少有研究关注在高覆盖条件下高效运行的催化剂设计。覆盖层在乙酸与乙烯氧化偶联合成VA过程中起着重要作用。在该反应中，表面与醋酸物质的拥挤促进了C-O偶联，并以影响反应活性和选择性的方式抑制解离步骤。表面科学和密度泛函理论（DFT）对该反应的机理理解已经出现，但基本上所有过去的工作都集中在负载钯（Pd）或钯金（PdAu）催化剂上，这些催化剂在实际条件下不稳定，没有碱稳定剂，会在很长一段时间内耗尽。该项目旨在(i)理解（使用动力学和DFT）与稳态催化有关的机制方面，（ii）评估分散在Au和Cu基质中的活性原子的横向相互作用的不同强度如何影响速率和选择性，以及（iii）利用这些见解来设计更有效的VA合成催化剂。该项目建立在单金属钯催化剂的初步实验和计算结果的基础上，研究人员与他所在机构的同事合作获得了这些结果。Pd工作提供了重要的见解，当反应物压力在稳态催化中发生变化时，覆盖率如何影响速率限制步骤的变化。DFT研究将建立在这些见解和探索的基础上，在分散在Cu和Au基体上的一系列单原子上，如何(i) Cu的较小晶格常数所施加的增强的横向相互作用可以促进C-O耦合，以及（ii）覆盖和组成的综合效应如何影响催化性能。这些结果将进一步指导单原子合金催化剂的制备和结构功能表征，这些催化剂在VA合成催化中具有更好的活性、选择性和稳定性。研究中使用的数据生成、催化剂表征和分析方法——结合从VA合成中得到的见解——将延续到在吸附物质的高表面覆盖率条件下进行的其他催化反应中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Cobalt-Molybdenum Oxides for Effective Coupling of Ethane Activation and Carbon Dioxide Reduction Catalysis

• DOI: 10.1021/acscatal.2c02525
• 发表时间: 2022-09
• 期刊: ACS Catalysis
• 影响因子: 12.9
• 作者: Rui Yao;Jayson Pinals;Roham Dorakhan;J. Herrera;Minhua Zhang;P. Deshlahra;Y. Chin