STRUCTURE AND METANOL ACTIVATION - NIOBIA PROMOTED PT AL2O3 CATALYSTS/

Distinction between geometric and ligand effects has been studied by t he infrared study of CO chemisorption on four catalyst samples modifie d by niobia. According to earlier studies the metal-support interface plays a crucial role in the CH3OH + D2 reaction. Platinum and niobia c ontent, oxidative-reductive treatment and chloride content gas a great influence of the niobia decorating Pt surface. High temperature reduc tion does not effect niobia-free sample, while niobia addition decreas es the bridged/linear ratio of the adsorbed CO, especially in the SMSI state. Simultaneously the peak positions are shifting towards higher frequencies. Both geometric effect of decoration and ligand effect are observed. The observed effect has been further supported by XRD data for the platinum crystallite sizes and a quantitative parameter for th e characterization of SMSI is proposed.