REDUCTION OF PLATINUM DISPERSED ON DEALUMINATED BETA-ZEOLITE

The Si/Al ratio of a commercial HB-25 beta zeolite sample was increase d by treatment of dealumination and silicon-insertion. Platinum ions w ere subsequently dispersed onto the starting and the treated samples t hrough impregnation of aqueous Pt(NH,),(NO,),. Chemical environments o f dispersed platinum were characterized by temperature-programmed redu ction (TPR) technique. The obtained TPR traces varied with extents of dealumination. Nevertheless, three major signals, in reduction tempera ture regions around - 50, 80 and 480 degrees C were distinguished from these TPR traces and characterized as reductions of platinum oxides d ispersed on the external surface of zeolite (pt(e)O), platinum oxides occluded in channels ((PtOx)-O-o), and Pt-(-O-Si=)(y) complexes coordi nated to external surface or defects of zeolite, respectively. From th e variation in the contribution of the 480 degrees C peak in TPR trace s, a formation of Si-OH silanol function groups on the zeolite surface during the dealumination treatment and a elimination of these groups during the silicon-insertion treatment are indicated. (C) 1998 Elsevie r Science B.V. All rights reserved.