Structure sensitivity in CO2 methanation over CeO2 supported metal catalysts

Abstract

The CO2 methanation reaction often attracts attention in the energy sector, since combined water electrolysis and methanation can store the surplus renewable electrical energy into chemical energy. This reaction was first introduced in 1902 and has been studied extensively since then. A catalyst is required to obtain a better efficiency of CO2 methanation reaction. It has been established that Ni and Ru are the best performing metals in terms of activity, selectivity, and stability. Highly dispersed nanoparticles of these metals on support (usually, thermally stable metal oxide) are generally used during the reaction. There are two types of supports, namely reducible supports, and non-reducible supports. Reducible supports (e.g. CeO2, TiO2) are more active than non-reducible supports (e.g. Al2O3, SiO2) since they provide additional sites for CO2 activation. CeO2 can easily switch between 4+ and 3+ oxidation without phase change, which results in the formation of abundant oxygen vacancies. As a result of this unique property, CeO2 supported catalysts show excellent activity for CO2 methanation reaction compared to other supported catalysts. In the last decade, significant research was done in studying the CeO2 nano-shapes, with wellcontrolled crystal planes, such as rods, cubes, and octahedra. Variation in the shape of CeO2 results in variation in properties and activities of these materials. Previous publications reporting on the effect of CeO2 morphology on the activity for CO2 methanation, as well as other reactions, often neglected the effect of metal particle size. Therefore, this study reports the effect of metal (Ni and Ru) particle size on the activity of catalysts. Moreover, we also studied the morphology effect of CeO2 nano-shapes by keeping identical metal particle size on all three supports. The thesis is mainly divided into two parts, studying the morphology and particle size effects using Ru/CeO2 (chapter 2 and 3) and Ni/CeO2 (chapter 4) catalysts.