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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopic and Structural Characterization of Chlorine Loading Effects on Mo/Si :Ti Catalysts in Oxidative Dehydrogenation of Ethane
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Spectroscopic and Structural Characterization of Chlorine Loading Effects on Mo/Si :Ti Catalysts in Oxidative Dehydrogenation of Ethane

机译：乙烷氧化脱氢中Mo / Si：Ti催化剂中氯负载量的光谱和结构表征

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摘要

The structural changes induced in a silica-titania mixed-oxide support (1:1 molar ratio) by chlorine addition at different loading levels,their relation to the structural characteristics of supported MoO_x species over the support,and their correlation with ethane oxidative dehydrogenation (ODH) activity have been examined.The molybdenum and chlorine precursors are incorporated into the Si/Ti support network as it forms during gelation by using a "one-pot" modified sol-gel/coprecipitation technique.In situ X-ray diffraction during calcination shows the Si/Ti 1:1 mixed-oxide support is in a state of nanodispersed anatase titania over amorphous silica.With the addition of molybdenum and chlorine modifier,this anatase feature becomes more pronounced,indicating a decreased dispersion of titania.The effective titania surface area on the chlorine-doped Si:Ti support obtained from 2-propanol temperature-programmed reaction supports this observation.Raman spectra of dehydrated samples point to an enhanced interaction of MoO_x species with silica at the expense of titania.X-ray photoelectron spectroscopic results show that,without forming a molybdenum chloride,the presence of chlorine significantly alters the relative surface concentration of Si vs Ti,the electronic structure of the surface MoO_x species,and the oxygen environment around supported MoO_x species in the Si/Ti network.Secondary ion mass spectrometry detected the existence of SiCl fragments from the mass spectra,which provides molecular insight into the location of chlorine in Mo/Si:Ti catalysts.The observed increase in ethane ODH selectivity with chlorine modification may be ascribed to the MoO_x species sharing more complex ligands with silica and titania with the indirect participation of chlorine.Steady-state isotopic transient kinetic analysis (SSITKA) is used to to examine the oxygen insertion and exchange mechanisms.The catalysts show very little oxygen exchange with the gas phase in the absence of a reaction medium.During the steady-state ODH reaction,lattice oxygen appears to be the primary source of oxygen in the formation of water and CO_2.
机译：硅-二氧化钛混合氧化物载体（摩尔比为1：1）在不同的负载水平下加入氯引起的结构变化，它们与载体上负载的MoO_x物种的结构特征有关，以及与乙烷氧化脱氢的关系（通过使用“一锅法”改进的溶胶-凝胶/共沉淀技术，将胶凝过程中形成的钼和氯前体掺入到Si / Ti载体网络中。煅烧过程中的原位X射线衍射表示Si / Ti 1：1混合氧化物载体处于无定形二氧化硅上的纳米分散的锐钛矿型二氧化钛状态。通过添加钼和氯改性剂，该锐钛矿特性变得更加明显，表明二氧化钛的分散性降低。通过2-丙醇程序升温反应获得的掺氯Si：Ti载体的表面积支持了这一观察结果。脱水样品的拉曼光谱指向X射线光电子能谱分析结果表明，在不形成氯化钼的情况下，氯的存在显着改变了硅与钛的相对表面浓度，从而改变了表面的电子结构。 MoO_x物种以及Si / Ti网络中支持的MoO_x物种周围的氧环境。二次离子质谱法从质谱图中检测到了SiCl碎片的存在，这提供了分子了解Mo / Si：Ti催化剂中氯的位置。观察到的经过氯改性的乙烷ODH选择性增加可能归因于MoO_x物种与二氧化硅和二氧化钛共享更复杂的配体，而氯间接参与其中。稳态同位素瞬态动力学分析（SSITKA）用于检查氧的插入在没有反应的情况下，催化剂与气相的氧交换非常少在稳态ODH反应期间，晶格氧似乎是水和CO_2形成过程中的主要氧气来源。

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