Promotion effects of ZrO2 on the Pd/HZSM-5 catalyst for low-temperature catalytic combustion of methane
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Palladium catalysts supported on the carrier of HZSM-5 (Si/Al-2 = 50), without and with additives of oxides of Zr, Zn, Cu, La, Ba, Fe, Mn, Ca, Mg and Li, were prepared by the impregnation method and investigated as catalysts for low-temperature methane oxidation. The catalysts were characterized by various techniques, including XRD, N-2-BET, O-2-TPD and CH4-TPR. Among the additives investigated, ZrO2 was found to be a good promoter for the catalytic activity and stability of the palladium catalysts. The temperatures for methane ignition (T-10%) and total conversion (T-100%) of Pd-Zr/HZSM-5 were found to be 25 and 55 degreesC lower than those of Pd/HZSM-5, respectively. Besides, the O-2-TPD and CH4-TPR results indicated that the temperatures for O-2 desorption and reduction by methane of the catalysts decreased with increasing catalytic activities. Therefore, the presence of more reactive PdOx (x > 0) species on Pd-Zr/HZSM-5 is suggested as the main reason for its remarkably promoted activity. Although deactivation did occur slightly in the presence of water vapor (4 vol.%), the Pd-Zr/HZSM-5 catalyst is thought to be promising for practical applications due to its superior activity for methane total conversion and excellent thermal stability. (C) 2002 Elsevier Science B.V. All rights reserved.