Characterization of NiMo catalysts with noble metal promoters

Sammanfattning: To be able to face the challenges brought on by climate change there is an urgent need to reduce the heavy dependence on fossil fuels. Bio-oil is one such renewable and carbon-neutral replacement that has shown promising potential. A key step in making bio-oil commercially feasible is improvements of the upgrading processes of the bio-oil. One such upgrading process is catalytic hydrodeoxygenation (HDO), which has been developed using mainly molybdenum sulfide (MoS2) catalysts. One method to further develop the process is to improve the catalyst performance by the addition of promoters. Nickel and cobalt has commonly been used as promoters for MoS2 catalysts, but there is potential for further improvement of the catalysts by addition of noble metals as promoters. In this study the promoting effects of adding the noble metals iridium, palladium and platinum using two different impregnation methods were investigated. This was done by studying the reduction characteristic of the new catalysts using Temperature Programmed Reduction (TPR), together with chemical characterization using Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDX). All the studied noble metals induced a significant change of the reduction characteristics of the catalysts, by lowering the reduction temperature of the Ni-Mo oxide. Two different promoting mechanisms could be identified. The addition of iridium resulted in a separate reduction of IrO2 with a subsequent promoting of Ni-Mo oxide, while the addition of platinum and palladium gave rise to simultaneous reduction of the noble metal and the surrounding Ni-Mo oxide. One possible mechanism for the promoting by iridium is hydrogen spillover. The differing behaviours of palladium and platinum could indicate a different behavior, for example the ability to be dissolved in the Ni-Mo oxide structure, creating nucleation sites for the reduction process. The formulation method used was found to have the largest effect on the iridium catalysts, where co-impregnation improved the promoting abilities. No significant changes were found for palladium and platinum. Overall this study has found promising results in the use of noble metals as promoter for Ni-Mo catalysts, and further studies are warranted.