Methanol Catalysts from Single Crystals to Nanoparticles

Methanol, a versatile chemical feedstock and potential energy carrier, has been proposed as a key candidate in reducing greenhouse gas emissions. A new method of producing methanol from renewable hydrogen and captured carbon dioxide (CO₂) has shown promising reductions in CO₂ emissions compared to conventional methods. However, further development in low-pressure and low-temperature methanol catalysts is still needed to fully utilise this new technology.

This thesis explores powder catalysts, thin film catalysts and single crystal catalysts for the conversion of carbon dioxide (CO₂) to methanol.

The copper catalyst promoted with germanium had been predicted to have high activity for methanol synthesis from hydrogen and CO₂. Multiple powder samples were synthesised for testing this prediction. New synthesis methods using ammonia evaporation synthesis for the creation of a phyllosilicate structure providing additional stability, and tested in a plug flow reactor at 10 bar. The catalyst was further characterised with in-situ X-ray diffraction to investigate the evolution of the catalyst under different conditions.

The δ-Ni5Ga3 thin film catalyst was synthesised via magnetron sputtering to ensure phase purity and subsequently characterised to elucidate its catalytic behaviour. Thin film formats enabled the use of advanced characterisation techniques not applicable to powders, such as X-ray reflectometry. Near ambient pressure X-ray photoelectron spectroscopy combined with density functional theory, provided new insights into the activation, reaction, and deactivation mechanisms of the δ-Ni5Ga3 catalyst. 

A major focus of this work is the design and implementation of a state-of-the-art ultra-high vacuum setup for measuring turnover frequencies on single crystal surfaces. Key considerations and challenges in the development of such a system are highlighted. The setup includes a high-pressure cell integrated without air exposure, enabling catalytic activity measurements under 1 bar conditions. Using this system, the turnover frequency of a zinc-promoted copper surface, proposed as the most active for methanol synthesis, was determined, offering valuable data for the future optimisation of copper-zinc catalysts.