Combustion of dilute propane over transition metal-doped ZrO2 (cubic) catalysts

Combustion of dilute propane (0.9 mol% propane in air) over transition metal (viz. Co, Mn, Cr, Fe and Ni) doped ZrO2 (cubic) catalysts (transition metal/Zr mole ratio = 0.25) at different temperatures (200-500degreesC) and space velocities (25,000-100,000 cm(3) g(-1) h(-1)) has been investigated. The doping of transition metal in ZrO2 was confirmed by XRD and temperature-programmed reduction by H-2 Of the catalyst. The catalysts have been compared for their propane combustion activity (measured in terms of the temperature required for 50% conversion at different space velocities and also the propane combustion rate at 50% conversion at different temperatures) and also for their activation energy and frequency factor in the propane combustion. The propane combustion performance of the catalysts was in the following order: Co-doped ZrO2 > Mn-doped ZrO2 > Cr-doped ZrO2 > Fe-doped ZrO2 > Ni-doped ZrO2. Among the Co-, Mn- and Cr-doped ZrO2 catalysts. the activation energy is the lowest and the frequency factor was the highest for the Co-doped ZrO2 catalyst. The propane combustion activity of the Co-doped ZrO2 is found to be optimum for the Co/Zr ratio of about 0.25. The pulse reaction of pure propane in the absence Of O-2 Over the Co-doped ZrO2 indicated the involvement of lattice oxygen from the catalyst in the propane combustion. It has also been shown that because of the doping of cobalt in ZrO2, the lattice oxygen in the catalyst becomes mobile or the mobility of lattice oxygen is enhanced. (C) 2003 Elsevier B.V. All rights reserved.