School of Chemistry and Chemical Engineering, State Key Laboratory of Separation Membranes and Membrane Processes, Tiangong University, Tianjin 300387, P. R. China.
Phys Chem Chem Phys. 2021 May 5;23(17):10395-10401. doi: 10.1039/d0cp06523d.
Proton transfer from Brønsted acid sites (BASs) to alcohol molecules ignites the acid-catalyzed alcohol dehydration reactions. For aqueous phase dehydration reactions in zeolites, the coexisting water molecules around BASs in the zeolite pores significantly affect the alcohol dehydration activity. In the present work, proton transfer processes among the BASs of H-BEA zeolites, the adsorbed cyclohexanol and surrounding water clusters with different sizes up to 8 water molecules were investigated using ab initio molecular dynamics (AIMD) simulations combined with the multiple-walker well-tempered metadynamics algorithm. The plausible proton locations and proton transfer processes were characterized using two/three-dimensional free energy landscapes. The strong proton affinity makes the protonated cyclohexanol stable species until a water trimer is formed. The proton either is shared between protonated cyclohexanol and the water trimer or remains with the water trimer (H7O3+). With a further increase in water concentrations, the proton prefers to remain with the water clusters.
布朗斯特酸位（BAS）向醇分子的质子转移引发了酸催化的醇脱水反应。对于沸石中的水相脱水反应，沸石孔中 BAS 周围共存的水分子显著影响醇的脱水活性。在本工作中，使用从头算分子动力学（AIMD）模拟结合多行走者-well-tempered 元动力学算法，研究了 H-BEA 沸石的 BAS、吸附的环己醇和周围水簇（多达 8 个水分子）之间的质子转移过程。使用二维/三维自由能景观来描述可能的质子位置和质子转移过程。强质子亲合性使质子化环己醇成为稳定的物种，直到形成三聚水。质子可以在质子化环己醇和三聚水之间共享，也可以与三聚水（H7O3+）共存。随着水浓度的进一步增加，质子更倾向于与水簇共存。
