Capturing the attributes of reducible oxides for steam reforming and methanation reactions

Catalyst supports are known for their influence on the behaviour and performance of the metal phase supported. This is especially applicable to reducible oxides which interchangeable oxidation states offer many interesting surface chemistry attributes. Titanium dioxide (TiO2) is one of the most studied metal oxides for its ‘strong metal-support interaction’ properties while oxides of cerium have also garnered significant attention. Both these oxides have therefore been chosen as the support material for nickel catalysts and their performance for steam reforming of methane (SRM) and methanation investigated. For this purpose, TiO2-supported nickel was studied for its SRM performance at 400 – 500 oC. Different TiO2-supported-nickel species were found to have different roles in low temperature SRM. The more weakly interacting species contribute to hydrogen production via the water-gas shift reaction whereas the more strongly interacting fractions are crucial for the low temperature activation of methane. This was confirmed when a performance comparison was made against silica-supported nickel which provided a system with weaker metal-support interaction. Following these findings, the addition of cerium to titanium oxide supports was investigated. In this section of work, the support oxides were synthesised with varied compositions. Two synthesis techniques (sol-gel and flame spray pyrolysis) were used to manipulate the support features and their impact on low temperature SRM. It was found that while the Ni-loaded sol-gel oxides displayed improved methane conversion upon enriching the support with cerium, the effect differed for the flame-made equivalents. Despite a higher support surface area and better dispersion of surface nickel, the poor support crystallinity of the flame-made catalysts ultimately translated to poor stability during SRM. The last section of the investigation explored the use of sol-gel-synthesised ceria-titania mixed oxide supported nickel catalysts for their proficiency in photothermal CO2 methanation. The findings revealed that the support plays an instrumental role in maintaining the reduced state of supported nickel with the metallic state being important for photothermal activation. Moreover, the relative stability of the reduced surface cerium states in the presence of titanium oxide also facilitated adsorption of the CO2 reactants and contributed to improved CO2 conversions