Structure and methanol activation: niobia promoted Pt/Al₂O₃ catalysts

Distinction between geometric and ligand effects has been studied by the infrared study of CO chemisorption on four catalyst samples modified by niobia. According to earlier studies the metal-support interface plays a crucial role in the CH₃OH + D₂ reaction. Platinum and niobia content, oxidative-reductive treatment and chloride content has a great influence of the niobia decorating Pt surface. High temperature reduction does not effect niobia-free sample, while niobia addition decreases 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 the characterization of SMSI is proposed.