Synthesis and characterisation of mesoporous transition metal ion modified silica-zirconia and silica-sulfated zirconia materials towards NOx catalysis

Abstract

The purpose of this work is to design and investigate mesostructured material as a potential support for the reaction of the methane with surface NOx species. Several objectives have been pursued in achievement of the goals. The first objective is to develop a facile procedure for the synthesis of mesoporous silica-zirconia mixed oxide supports that are modified with the sulphate (SO4 2-), cobalt (Co2+) and palladium (Pd2+) ions. The support with requisite catalytic properties was obtained through the adjustment of the synthetic steps and optimisation of the composition. The second objective is to explore the effect of cobalt and zirconia loading in the reaction of the NOx species with methane over the Co-, Pd-, and Co-Pd-silica-sulfated zirconia (Si-SZr). A one-pot synthesis procedure has been developed to prepare the mesoporous silica-zirconia (Si-Zr), Si-SZr supports and the supermicroporous Co(II) incorporated Si-SZr catalysts with a wide range of zirconia loadings. Introduction of the Co(II) active sites by various post-synthesis methods leads to the modification of the surface, whereas the direct (co-precipitation) techniques have provided the modification of both surface and bulk of the supports. The palladium ions were introduced by the conventional impregnation methods onto the calcined solid materials. The detailed analysis of the materials has revealed that the silica and zirconia are well mixed in the framework, whereas the cobalt and sulfate ions are uniformly dispersed on the internal surface of the silica-zirconia supports. The materials prepared in this thesis possess sufficient stability, requisite catalytic properties, as well as good Bronsted and Lewis acidity. However, the high cobalt loading renders the catalytic performance of the Pd-Si-SZr catalysts. Among the investigated catalysts, the interaction of the NOx species with the CH4 takes place at the lowest temperature over the Co-, Pd-, Co-Pd-supported zirconia rich (Zr/Si = 28) Si-SZr catalysts.