Kinetic studies of ionic substituted copper catalysts for catalytic hydrogen combustion

Ionic substituted Cu catalysts in the reducible supports (SnO2, CeO2) and non-reducible supports (Al2O3, ZrO2) were synthesized by a single step solution combustion method and characterized by BET, XRD, TEM and XPS techniques. The catalytic activity of these compounds was investigated by performing the hydrogen combustion reaction. Due to the ionic substitution of aliovalent Cu ions, lattice oxygen was activated in these supports and all catalysts showed high rates and low activation energy. Cu substituted SnO2 catalyst showed the highest activity with 98% conversion at 320 °C whereas Cu substituted ZrO2 was the least active among the studied catalysts with 98% conversion at 480 °C. At 300 °C, the rates of the reaction over Cu substituted SnO2 and Cu substituted ZrO2 were 8.7 and 1.94 μmol/g/s. The reaction mechanisms were proposed based on an analysis of the surface mechanism and spectroscopic insights. The mechanism utilizing the oxide ion vacancies for O2 and H2 dissociation was proposed to describe the kinetics of the reaction over the reducible oxides SnO2 and CeO2. A mechanism based on the interaction of adsorbed H2 and O2 through the hydroxyl group was proposed for the reaction over non-reducible supports ZrO2 and Al2O3. These models were able to predict the rate of formation of H2O reasonably well.