Metal phosphate and precious metal catalysts for selective oxidation

Abstract

The main objective researched in this thesis involves the selective oxidation of methanol to formaldehyde, using metal phosphate based catalysts. Molybdenum and vanadium phosphate based catalysts have been prepared, thoroughly characterised and tested as active catalysts for the selective oxidation of methanol to formaldehyde. Initial investigations highlighted the relatively low activity of both metal phosphate catalysts, however, significant enhancements in the catalytic activity and formaldehyde selectivity of both materials have been achieved in this research, primarily by supporting molybdenum phosphate catalysts using a range of supports, and also promoting both molybdenum and vanadium pyrophosphates with transition metals. It was discovered that a catalyst of 10 wt% (MoO2)2P2O7 supported on SiO2 containing 1 mol% vanadium (as a promoter) achieved significantly higher formaldehyde per pass yields (>20 %) than MoO3 supported on SiO2 (reported in the literature) and comparable activity to that of the commercial iron molybdate catalyst. Due to the promotional effect of vanadium, and the known activity of V2O5 catalysts for the oxidation of methanol to formaldehyde, molybdenum promoted (VO2)2P2O7 catalysts were tested for this reaction and reported for the first time. Catalytic studies revealed that there is a direct correlation between molybdenum content and catalytic activity, indicating a synergistic effect of the two transition metals. The penultimate chapter of this thesis involves the use of supported mono- and bi-metallic gold(palladium) catalysts and their use in both CO oxidation and selective methanol oxidation. A novel method of maintaining considerably small Au(Pd) nanoparticle size (unlike the standard thermal treatment method) has been discovered by the Hutchings group at Cardiff Catalysis Institute, involving the removal of stabilising IV ligands with a solvent extraction method. Using high resolution microscopy and a range of characterization techniques, the nanoparticle size was attributed to the surprisingly high activity achieved for both CO oxidation and methanol oxidation to methyl formate, at low temperatures which, particularly in the case of methanol oxidation, is a remarkable discovery.EThOS - Electronic Theses Online ServiceGBUnited Kingdo