Catalytic combustion of propane and natural gas over Cu and Pd modified ZSM zeolite catalysts

Copper-exchanged ZSM-5, ZSM-11 and ZSM-48 as well as Pd-ZSM-5 zeolite catalysts were prepared and tested for their light-off and conversion behaviour in complete oxidation of propane and natural gas. Metal modified ZSM zeolite catalysts were found to be superior to the Pd and Cu/alumina catalysts prepared for comparison. Cu-ZSM-5 (Cu, 1.3 wt.-%) appeared to be the most active of the Cu-containing ZSM catalysts exhibiting combustion efficiencies of 97.6 and 94.8% for propane and natural gas, respectively, The method of introducing Pd into the zeolite was found to affect the catalysts activity strongly. Pd-ZSM-5 catalysts prepared by ion-exchange were more active than when the Pd was introduced into the zeolite during the process of hydrothermal zeolite synthesis. Combustion efficiencies of 100 and 98.1% for propane and natural gas combustion were achieved with Pd-ZSM-5 (Pd, 0.9 wt,-%) prepared by the ion-exchange method. The light-off temperatures were found to increase as: Pd-ZSM-5 < Cu-ZSM-5 < Cu-ZSM-11 < Cu-ZSM-48. The redox capacities of the Cu-ZSM catalysts were determined by subjecting the catalysts to redox cycles in a microbalance. The TPD of oxygen, carbon monoxide and ammonia was used to interpret the catalytic activities. The catalytic activity was related to the oxygen carrier capacities, the reducibility and the acidity of the catalysts. The state of copper was found to be of great importance in determining the catalytic activities in oxidation reactions.