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

Abstract

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 (200-500°C) and space velocities (25,000-100,000 cm³ g^-1 h^-1) has been investigated. The doping of transition metal in ZrO₂ was confirmed by XRD and temperature-programmed reduction by H₂ 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 O₂ 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.