MECHANISM OF SULFUR POISONING AND REGENERATION METHODS FOR SUPPORTED METAL CATALYSTS Ⅰ. MECHANISM OF SULFUR POISONING OF Pd(Pt)/Al_2O_3 CATALYSTS IN H_2-O_2 REACTION

Sulfur poisoning mechanism of Pd(Pt)/Al_2O_3 catalysts for H_2―O_2 reaction was studied by means of micro-catalytic reaction chromatograph, TPR, XPS, AES, XRD and IR. The results show that the tolerance of Pd/Al_2O_3 catalysts to surfur poisoning is significantly affected by the O_2/H_2 ratio and enhanced with the increase of the ratio. In″weak″oxidizing atmosphere, the deactivation is swift and irreversible because of the active components, particularly at the surface, being seriously sulfided by S~(-2). In ″strong″ oxidizing atmosphere, the poisoning caused by S~(-2) is reversible to great extent owing to the reaction M_s―S/Al_2O_3(O_2,H_2O)/catalyst(M_s(M_sO)/Al_2O_3-SO_3-H_2O)where M_s signifies Pd or Pt on the surface. But, when the sulfate in catalyst is accumulated in large amount, it could cover or block the active sites, which may be an important cause of the catalyst deactivation in addition to the sulfidization of metal components.