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Investigating the Surface Structure of γ-Al2O3 Supported WOX Catalysts by High Field 27Al MAS NMR and Electronic Structure Calculations
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-10-04 00:00:00 , DOI: 10.1021/acs.jpcc.6b09060 Chuan Wan 1, 2 , Mary Y. Hu 1 , Nicholas R. Jaegers 1, 3 , Dachuan Shi 1 , Huamin Wang 1 , Feng Gao 1 , Zhaohai Qin 2 , Yong Wang 3 , Jian Zhi Hu 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-10-04 00:00:00 , DOI: 10.1021/acs.jpcc.6b09060 Chuan Wan 1, 2 , Mary Y. Hu 1 , Nicholas R. Jaegers 1, 3 , Dachuan Shi 1 , Huamin Wang 1 , Feng Gao 1 , Zhaohai Qin 2 , Yong Wang 3 , Jian Zhi Hu 1
Affiliation
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The metal–support interaction in γ-Al2O3 supported WOX catalysts is investigated by a combination of high field quantitative single pulse (SP) 27Al MAS NMR spectroscopy, 2D MQMAS, 1H–27Al CP/MAS, and electronic structure calculations. NMR allows the observation of at least seven different Al sites, including a pentahedral Al site (AlP), three different tetrahedral Al sites (AlT), and three octahedral Al sites (AlO). It is found that the AlP site density decreases monotonically with an increased WOX loading, the AlO site density increases concurrently, and the density of AlT sites remains constant. This suggests that the AlP sites are the preferred surface anchoring positions for the WOX species. Importantly, the AlP site isotropic chemical shift observed for the unsupported γ-Al2O3 at about 38 ppm migrates to the octahedral region with a new isotropic chemical shift value appearing near 7 ppm when the AlP site is anchored by WOX species. Density functional theory (DFT) computational modeling of the NMR parameters on proposed WOX/γ-Al2O3 cluster models is carried out to accurately interpret the dramatic chemical shift changes from which the detailed anchoring mechanisms are obtained. It is found that tungsten dimers and monomers are the preferred supported surface species on γ-Al2O3, wherein one monomeric and several dimeric structures are identified as the most likely surface anchoring structures.
中文翻译：
调查的表面结构的γ-Al 2 ö 3支持的WO X催化剂由高场27的Al MAS NMR和电子结构计算
通过高场定量单脉冲（SP）27 Al MAS NMR光谱，2D MQMAS，1 H– 27 Al CP / MAS和电子技术的组合，研究了γ - Al 2 O 3负载的WO X催化剂中金属与载体的相互作用结构计算。NMR允许观察至少七个不同的Al位点，包括五面体Al位点（Al P），三个不同的四面体Al位点（Al T）和三个八面体Al位点（Al O）。据发现，在Al P位点密度与增加WO单调减小X装载，使Al Ò位密度同时增加，并且Al T位的密度保持恒定。这表明，Al P位点是WO X物种的首选表面锚固位置。重要的是，Al的P站点各向同性化学位移为不支持的观察到的γ-Al 2 ö 3在约38ppm的迁移到八面体区域与出现近7ppm的一个新的各向同性化学位移值当Al P网站由WO锚定X物种。密度泛函理论（DFT）上提出的NMR参数的计算建模WO X /γ-Al系2 ö 3进行聚类模型以准确解释剧烈的化学位移变化，从而从中获得详细的锚固机理。据发现，钨二聚体和单体上的γ-Al优选支承表面物质2 ö 3，其中一种单体和几个二聚结构被确定为最有可能的表面锚定结构。
更新日期：2016-10-04
中文翻译：
调查的表面结构的γ-Al 2 ö 3支持的WO X催化剂由高场27的Al MAS NMR和电子结构计算
通过高场定量单脉冲（SP）27 Al MAS NMR光谱，2D MQMAS，1 H– 27 Al CP / MAS和电子技术的组合，研究了γ - Al 2 O 3负载的WO X催化剂中金属与载体的相互作用结构计算。NMR允许观察至少七个不同的Al位点，包括五面体Al位点（Al P），三个不同的四面体Al位点（Al T）和三个八面体Al位点（Al O）。据发现，在Al P位点密度与增加WO单调减小X装载，使Al Ò位密度同时增加，并且Al T位的密度保持恒定。这表明，Al P位点是WO X物种的首选表面锚固位置。重要的是，Al的P站点各向同性化学位移为不支持的观察到的γ-Al 2 ö 3在约38ppm的迁移到八面体区域与出现近7ppm的一个新的各向同性化学位移值当Al P网站由WO锚定X物种。密度泛函理论（DFT）上提出的NMR参数的计算建模WO X /γ-Al系2 ö 3进行聚类模型以准确解释剧烈的化学位移变化，从而从中获得详细的锚固机理。据发现，钨二聚体和单体上的γ-Al优选支承表面物质2 ö 3，其中一种单体和几个二聚结构被确定为最有可能的表面锚定结构。
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