Nano Catalyst Design and Application in Sustainable Chemistry

Abstract

Heterogenous catalytic process is a complex art of surface, the surface properties, especially the properties of active sites such as geometric structure and chemical environment would drastically influence the reaction performance. Traditionally, most studies for catalyst surface properties rely on the ex situ characterisation which examines catalysts out of reaction condition. However, considering most of the heterogenous catalytic reactions are carried out under a harsh condition, i.e. elevated temperatures and pressures, the surface dynamic change over catalyst under reaction condition is generally not negligible and dominating the reaction performance. Thus, for understanding the real catalyst surface behaviour, we must observe the catalyst during reaction condition. Three different catalytic systems were selected in this research and the combined in situ microscopy and spectroscopy techniques, including in situ TEM, in situ EELS spectroscopy and in situ DRIFTS spectroscopy, were implemented to investigate the catalyst behaviour during the reactions. The first reaction is the oxidative methane coupling reaction over Li/MgO. Then followed by the oxidative methane coupling over La/MgO and ammonia synthesis over Ru/MgO. The in situ TEM provides the information of surface geometric change while the in situ EELS and DRIFTS give the chemical information of catalyst surface as well as adsorbed intermediates. Combined with ex situ characterisation results, the more comprehensive pictures for the mechanism of the investigated reactions can be depicted. The outcome of this thesis bridged the gap between surface geometric-chemical change over catalysts active sites and the reaction performance over heterogenous catalyst, which might even be the guidance for heterogenous catalyst development in the similar systems.