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Transient and Steady-State Kinetic Studies of Formaldehyde Alkylation of Benzene to Form Diphenylmethane on HZSM-5 Catalysts
ACS Catalysis ( IF 11.3 ) Pub Date : 2020-08-18 , DOI: 10.1021/acscatal.0c02991 Brandon L. Foley 1 , Aditya Bhan 1
ACS Catalysis ( IF 11.3 ) Pub Date : 2020-08-18 , DOI: 10.1021/acscatal.0c02991 Brandon L. Foley 1 , Aditya Bhan 1
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A combined steady-state and transient kinetic study on the mechanism of diphenylmethane (DPM) formation in HZSM-5 from HCHO and benzene revealed two kinetically relevant steps—the alkylation of benzene by HCHO and the deprotonation of a diphenylmethane benzenium ion (DPM+) to form DPM. The functional dependence of the rate of each of these reactions was determined by observing the transient rate after a step-change in reactant partial pressures, specifically whether the rate was discontinuous through a step-change in partial pressure. Steady-state isotopic switching experiments revealed that a persistent surface intermediate with two aromatic rings, likely DPM+, is formed and has a fractional coverage ranging from sparse (near-zero) to complete (near-one) that varies with process conditions. Reaction orders obtained from steady-state rate measurements suggest that HCHO, C6H6, and H2O competitively adsorb on acid sites and that DPM+ deprotonation is first-order in C6H6, implying that deprotonation is assisted by the presence of aromatics. Herein, we propose a complete mechanism for the condensation between HCHO and C6H6 to form DPM, and from this mechanism, a six-parameter (three kinetic/thermodynamic parameters, three apparent activation/thermodynamic energies) kinetic model is derived that quantitatively describes the transient and steady-state rates and steady-state fractional coverages of DPM+.
中文翻译：
HZSM-5催化剂上苯甲醛烷基化生成二苯甲烷的瞬态和稳态动力学研究
对HCHO和苯中的HZSM-5中二苯甲烷（DPM）形成机理的稳态和瞬态动力学组合研究揭示了两个动力学上相关的步骤-HCHO对苯进行烷基化和二苯甲烷苯离子（DPM +）的去质子化形成DPM。通过观察反应物分压的阶跃变化后的瞬时速率，特别是通过分压的阶跃变化，该速率是否不连续，来确定每个反应速率的功能依赖性。稳态同位素转换实验表明，具有两个芳香环的持久表面中间体，可能是DPM +形成，其覆盖范围从稀疏（接近零）到完整（接近一），随过程条件的不同而不同。从稳态速率测量获得的反应阶数表明HCHO，C 6 H 6和H 2 O竞争性吸附在酸性位点上，并且DPM +脱质子化在C 6 H 6中是一阶的，这意味着存在下辅助了质子化芳香剂。在这里，我们提出了一个完整的机制，用于HCHO和C 6 H 6之间的缩合。形成DPM，并从该机理中，得出一个六参数（三个动力学/热力学参数，三个表观活化/热力学能量）动力学模型，定量地描述了DPM +的瞬态和稳态速率以及稳态分数覆盖率。
更新日期：2020-09-20
中文翻译：
HZSM-5催化剂上苯甲醛烷基化生成二苯甲烷的瞬态和稳态动力学研究
对HCHO和苯中的HZSM-5中二苯甲烷（DPM）形成机理的稳态和瞬态动力学组合研究揭示了两个动力学上相关的步骤-HCHO对苯进行烷基化和二苯甲烷苯离子（DPM +）的去质子化形成DPM。通过观察反应物分压的阶跃变化后的瞬时速率，特别是通过分压的阶跃变化，该速率是否不连续，来确定每个反应速率的功能依赖性。稳态同位素转换实验表明，具有两个芳香环的持久表面中间体，可能是DPM +形成，其覆盖范围从稀疏（接近零）到完整（接近一），随过程条件的不同而不同。从稳态速率测量获得的反应阶数表明HCHO，C 6 H 6和H 2 O竞争性吸附在酸性位点上，并且DPM +脱质子化在C 6 H 6中是一阶的，这意味着存在下辅助了质子化芳香剂。在这里，我们提出了一个完整的机制，用于HCHO和C 6 H 6之间的缩合。形成DPM，并从该机理中，得出一个六参数（三个动力学/热力学参数，三个表观活化/热力学能量）动力学模型，定量地描述了DPM +的瞬态和稳态速率以及稳态分数覆盖率。
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