Surface Science Studies of Model Supported Vanadia Catalysts

9712774宾夕法尼亚大学教授约翰·M·沃斯将研究以二氧化钛、二氧化铈、氧化锆单晶和氧化镁为载体的模型钒催化剂的结构和反应活性。这项基础研究与各种工业过程有关，如烃和醇的选择性氧化和氨氧化，氨和烃还原氮氧化物，以及杂芳烃的加氢处理。HREELS，Auger，RBS，XPS，Leeds，STM/AFM，甲醇、甲酸、水、氨和乙胺的TPD，甲醇常压氧化的反应动力学，以及NH3还原NOx将是表征结构和反应活性的主要技术。这项研究的显著特点是气相沉积均匀的(可能是外延的)钒覆盖层，并测定载体-O-V键的强度--负载钒的选择性通常归因于此。这种强度将与局部结构和探针分子的反应性相关，并将随载体的组成和结构而变化。用光谱分辨率低至8厘米-1的HREELS技术将测定负载型钒和化学吸附的探针分子的振动特性。此外，作者还将研究比V=O模式更能反映载体相互作用的表面-O伸缩模式和O-V-O弯曲模式。表面物种(羟基、氨基、亚硝基、甲氧基)将通过化学吸附产生，并通过TPD解吸。稳态反应(甲醇氧化或NOx SCR与NH3)将在侧面微反室内进行，样品可以在没有空气暴露的情况下转移到该室内。

Abstract - Vohs 9712774 Professor John M. Vohs, of University of Pennsylvania, will investigate the structure and reactivity of model vanadia catalysts supported on single crystal titania, ceria, zirconia, and magnesia. This fundamental research is of relevance to various industrial processes, such as selective oxidation and ammoxidation of hydrocarbons and alcohols, reduction of nitrogen oxides by ammonia and hydrocarbons, and hydrotreatment of heteroaromatics. HREELS, Auger, RBS, XPS, LEEDS, STM/AFM; TPD of methanol, formic acid, water, ammonia and ethylamine; reaction kinetics of the atmospheric pressure oxidation of methanol; and reduction of NOx with NH3 will be the primary techniques to characterize structure and reactivity. The distinctive feature of this investigation is the vapor deposition of uniform (possibly epitaxial) vanadia overlayers and the determination of the strength of the support-O-V bonds -- to which the selectivity of supported vanadia is usually attributed. Such strength will be correlated with local structure and probe molecule reactivity, and will be varied by the composition and structure of the support. The vibrational characteristics of both supported vanadia and chemisorbed probe molecules will be determined with an HREELS technique having spectral resolution as low as 8 cm-1. In addition, the author will study the surface-O stretching modes, and the O-V-O bending modes, which are more indicative of support interaction than the V=O mode. Surface species (hydroxyl, amino, nitrosyl, methoxy) will be produced by chemisorption and desorbed by TPD. The steady state reactions (methanol oxidation or NOx SCR with NH3) will be carried out on a side microreactor chamber to which samples can be transferred without air exposure.