乙酸乙烯酯合成中覆盖层选择性限制的机理认识。

IF 7.5 2区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY ChemSusChem Pub Date : 2024-11-03 DOI:10.1002/cssc.202401911
Gregory L Novotny, Prashant Deshlahra
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引用次数: 0

摘要

为可持续化学过程开发改良催化剂通常需要了解催化活性、选择性和稳定性的原子起源。利用密度泛函理论和稳态动力学分析,我们探究了醋酸乙烯(VA)在覆盖醋酸酯物种的钯表面合成时形成限制选择性的分解产物的基本步骤。醋酸酯的形成以及与乙烯的耦合控制着醋酸乙烯酯形成的催化循环和稳态覆盖率,但醋酸酯和乙烯可分别分解形成二氧化碳。这两种分解都涉及醋酸空位的初始 C-H 活化,随后是额外的 C-H 活化以及最终的 C-O 形成和涉及与分子氧反应的 C-C 裂解。具有非氧化动力学相关步骤的醋酸盐分解路径显示出与氧化路径相似的自由能障。相比之下,涉及乙炔中间体的非氧化乙烯分解路径所表现出的自由能垒要比具有氧化动力学相关步骤的路径低得多。乙烯分解在低覆盖率下非常容易,但对覆盖率更为敏感,导致在稳态下可接触到的覆盖率下,乙烯分解和醋酸乙烯酯形成障碍相似,这与测量中适度的醋酸乙烯酯选择性以及根据回归动力学参数评估的乙烯与醋酸乙烯酯分解贡献是一致的。这些见解为描述金属催化剂表面的醋酸乙烯酯合成速率和选择性提供了一个详细的框架。
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Mechanistic Insights on Coverage-Dependent Selectivity Limitations in Vinyl Acetate Synthesis.

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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来源期刊
ChemSusChem
ChemSusChem 化学-化学综合
CiteScore
15.80
自引率
4.80%
发文量
555
审稿时长
1.8 months
期刊介绍: ChemSusChem Impact Factor (2016): 7.226 Scope: Interdisciplinary journal Focuses on research at the interface of chemistry and sustainability Features the best research on sustainability and energy Areas Covered: Chemistry Materials Science Chemical Engineering Biotechnology
期刊最新文献
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