Copper Catalysts for Synthesis Gas Conversion - Promoter and Support Effects

Abstract

Catalysts have been used for decades to produce various materials on a large scale. A good catalyst contributes to a reduction in energy consumption and waste streams. The starting point in this thesis is the copper catalyst: active copper nanoparticles, supported on a high-surface-area material (a support). The catalyst activity is usually enhanced by adding a component such as zinc oxide (a promotor) to the catalyst. This catalyst is industrially used to produce methanol, but the exact catalyst structure during high-temperature and pressure operation is not yet fully understood. This thesis describes the structure of various promotors (zinc oxide, manganese oxide, and cobalt) and their contribution to the catalytic performance of supported copper catalysts, as well as how the support material (carbon or silica) plays a role in this. The catalysts were tested for the conversion of syngas (a mixture of hydrogen and carbon monoxide) under high temperature and pressure conditions. Promotion by zinc oxide and CO2 enrichment of the syngas feed have been studied simultaneously using graphite as model support. The two factors show a complex synergy. The relevant fraction of the zinc oxide promoter is completely reduced and alloyed with copper particles during operation: an effect that is not observed on a commonly used silica support. Reversible CO2 adsorption occurs on the manganese oxide, making it a fundamentally different promoter for copper particles than zinc oxide. Finally, this thesis describes the preparation of supported bimetallic copper–cobalt particles, which can lead to the formation of longer alcohol molecules.