吸附
沸石
密度泛函理论
微晶
从头算
化学物理
催化作用
化学
分子
离子
分子动力学
计算化学
从头算量子化学方法
物理化学
结晶学
有机化学
作者
Jérôme Rey,Pascal Raybaud,Céline Chizallet
出处
期刊:Chemcatchem
[Wiley]
日期:2017-05-09
卷期号:9 (12): 2176-2185
被引量:32
标识
DOI:10.1002/cctc.201700080
摘要
Abstract The acidity at the external surface of protonic zeolites, because of the finite size of crystallites, has been questioned strongly for decades. We used density functional theory (DFT) calculations to propose atomistic models for the external surface of zeolite Beta, which show that bridging Si−(OH)−Al groups still exist at the pore mouth in what we call open micropores (pores that emerge at the external surface). However, at the outermost surface (no emerging micropores), water molecules adsorbed on Al atoms [Al−(H 2 O)] prevail. The local structure of those surface Al atoms depends on the temperature and water partial pressure. A detailed vibrational study of adsorbed CO helps in the assignment of the different sites and reveals a generalized vibrational Stark effect. Proton‐transfer ability was quantified by the adsorption of isobutene. Carbenium ions appear to be stabilized on the bridging Si−(OH)−Al groups located on the open micropores of the external surface in a similar way as in the bulk of zeolite Beta. By contrast, the outermost surface is not able to stabilize carbenium ions and promotes the existence of alkoxides. This work brings new atomic‐scale insights into the concept of pore‐mouth catalysis and provides the molecular architecture of potential active sites located in open micropores.
科研通智能强力驱动
Strongly Powered by AbleSci AI