Crossley-Lewis Joe, Dunn Josh, Hickman Isabel F, Jackson Fiona, Sunley Glenn J, Buda Corneliu, Mulholland Adrian J, Allan Neil L
Centre for Computational Chemistry, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Applied Sciences, bp Innovation and Engineering, BP plc, Saltend, Hull, HU12 8DS, UK.
Phys Chem Chem Phys. 2024 Jun 12;26(23):16693-16707. doi: 10.1039/d3cp05987a.
Methyl carboxylate esters promote the formation of dimethyl ether (DME) from the dehydration of methanol in H-ZSM-5 zeolite. We employ a multilevel quantum method to explore the possible associative and dissociative mechanisms in the presence, and absence, of six methyl ester promoters. This hybrid method combines density functional theory, with dispersion corrections (DFT-D3), for the full periodic system, with second-order Møller-Plesset perturbation theory (MP2) for small clusters representing the reaction site, and coupled cluster with single, double, and perturbative triple substitution (CCSD(T)) for the reacting molecules. The calculated adsorption enthalpy of methanol, and reaction enthalpies of the dehydration of methanol to DME within H-ZSM-5, agree with experiment to within chemical accuracy (∼4 kJ mol). For the promoters, a reaction pathway an associative mechanism gives lower overall reaction enthalpies and barriers compared to the reaction with methanol only. Each stage of this mechanism is explored and related to experimental data. We provide evidence that suggests the promoter's adsorption to the Brønsted acid site is the most important factor dictating its efficiency.
羧酸甲酯促进了H-ZSM-5沸石中甲醇脱水生成二甲醚（DME）的反应。我们采用多级量子方法来探究在有和没有六种甲酯促进剂存在的情况下可能的缔合和解离机制。这种混合方法将用于完整周期性体系的密度泛函理论（带有色散校正，即DFT-D3），与用于代表反应位点的小团簇的二阶Møller-Plesset微扰理论（MP2），以及用于反应分子的单、双和微扰三重取代耦合簇理论（CCSD(T)）相结合。计算得到的甲醇吸附焓以及H-ZSM-5中甲醇脱水生成DME的反应焓，与实验结果在化学精度范围内（约4 kJ·mol）相符。对于促进剂而言，与仅甲醇反应相比，缔合机制的反应途径给出了更低的总反应焓和势垒。我们探究了该机制的每个阶段，并将其与实验数据相关联。我们提供的证据表明，促进剂在布朗斯台德酸位点上的吸附是决定其效率的最重要因素。
