Surface Analysis of Catalysts by Low-Energy Ion Scattering

摘要

The characterization of catalyst surfaces using Low Energy Ion Scattering (LEIS)is described. The structure of a catalyst is generally described in conjunction with the different spectroscopic techniques used to characterize them. LEIS is discussed in detail. The importance of the different mechanisms for a number of elements is discussed and related to the total shape of a LEIS spectrum. The consequences for quantitative surface composition analysis are addressed. The absence of signals for tetragonally coordinated cations in the surface of gamma Al2O3 is argued to be due to the preferential exposure of crystallographic planes which contain exclusively octahedral sites. The insight makes it possible to propose a detailed model for the surface structure of gamma Al2O3 and the position of deposited metaloxides there upon. The location of molybdenum strongly depends on the amount deposited and the calcination temperature. The addition of lanthanum making gamma Al2O3 more thermostable is investigated. A series of silica supported molybdenum oxide catalysts is investigated toexplain the remarkable behavior to the selective oxidation of ammonia.