Abstract: A series of Pd/Al₂O₃-based catalysts for the purification of natural gas vehicle exhaust were developed and modified, and the effects of hydrothermal treatment, calcination temperature, and rare earth metal modification on the catalytic activity and water-resistant ability in methane oxidation were investigated by means of N₂ adsorption-desorption, XRD, thermal stability test and catalyst activity evaluation. The results showed that hydrothermal treatment could generate a large number of hydroxyl groups on the surface of synthesized catalysts, which could then be separated from the catalyst to form a large number of oxygen defect sites during in the subsequent calcinations process, and promote the dispersion of metal active sites and strengthen the interaction between metal and supports. In addition, increasing calcination temperature could significantly affect the activity as well due to the enlarged pore volume and surface areas. The introduction of rare earth metal promoters did not change the pore structure of the catalyst obviously, but enhanced the hydrothermal stability of Pd/Al₂O₃ catalysts to a certain extent. The 1%Pd/HTT-2La-B-Al2O3 catalyst with the best performance was prepared by hydrothermal treatment, calcination under 650 ℃ and modification with 2% of lanthanum using butanol as solvent. The conversion rate for methane oxidation on the catalyst was 90% at 305 ℃.

Key words: natural gas vehicles, tail gas, methane catalytic oxidation, hydrothermal treatment, calcination temperature, promoter modification