Immobilization and Characterization of SiO₂-supported Ir-complex Catalyst for Practical Hydrogen Generation from Formic Acid

Abstract

Hydrogen generation via dehydrogenation of formic acid using an immobilized Ir-complex catalyst, which combines the catalytic ability of the homogeneous catalyst and ease in handling of the heterogeneous catalyst, was investigated. The immobilization process was analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption measurement. Analytical methods for the heterogeneous catalyst remained appropriate for immobilized catalyst analysis. Hydrogen generation using the immobilized catalyst showed the same activation energy (Ea = 72.5 kJ mol⁻¹) as the analogous homogeneous catalyst (Ea = 72.1 kJ mol⁻¹). However, the reaction rate for the immobilized catalyst was 70 % of that achieved for the homogeneous catalyst because of the reduced collision frequency. The ζ potential measurement implied that immobilized catalyst did not form a stable dispersion during the catalytic reaction. Effective agitation control is needed for efficient dehydrogenation reaction using immobilized catalyst. Immobilization of the homogeneous catalyst represents a new technology for practical hydrogen generation.