A Study Of Sulfur Tolerance Of PdO/γ-Al₂O₃Catalysts For Methane Catalytic Combustion

Pd-supported catalysts have high activity for low-temperature methanecombustion, but they are easily deactivated by a slight sulphur-containingsubstance （such as H₂S） in the reaction gas. In order to enhance the sulfurresistance of Pd-supported catalysts, Pd/γ-Al₂O₃catalysts were improvedfrom the aspects of residual chlorine ions, doping modification andpresulfiding in this article, and the sulfur resistance and activity of thecatalysts were evaluated. The paper mainly studied the internal relationsbetween the property of Pd/γ-Al₂O₃catalysts and its catalytic activity aswell as sulfur tolerance.The results of XPS, CO-chemisorption, XRD and H₂-TPR showed thatresidual chlorine ions from the precursor were shown a significant negativeimpact on initial activity and sulfur resistance of Pd/γ-Al₂O₃catalysts. Thepresence of chlorine led to the formation of stable and inactive Pd_xCl_yO_zcomplex, and could favor the combination of sulfur species and the support.Catalyst pretreatment with hydrogen or water could eliminate chloride ions,and hydrogen treatment was more effective. The results from ICP, CO-chemisorption, H₂-TPR and CH₄-TPRdisplayed that Ba modified alumina was able to trap sulfur species,delaying the sulfur species overflow from support to active PdO. Theaddition of Pt effectively improved the redox properties of Pd andadsorption dissociation of methane. The proper ratio of Pd-Pt catalystsfacilitated the cracking of carbon-hydrogen bonds and the decomposition ofsulphate. So it was favorable to improve the sulfur resistance of catalysts.According to the analysis of XRD, the catalysts treated by hightemperature and high concentration H₂S had shown better sulfur resistancethan the untreated catalyst, which could be attribute to the stable crystalstructure.