The SirAl ratio of a commercial HB-25 beta zeolite sample was increased by treatment of dealumination and silicon-insertion. Platinum ions were subsequently dispersed onto the starting and the treated samples through impregnation Ž . Ž . of aqueous Pt NH NO . Chemical environments of dispersed platinum were characterized by temperature-programmed 3 4 3 2 Ž . reduction TPR technique. The obtained TPR traces varied with extents of dealumination. Nevertheless, three major signals, in reduction temperature regions around y50, 80 and 4808C were distinguished from these TPR traces and characterized as Ž e . reductions of platinum oxides dispersed on the external surface of zeolite Pt O , platinum oxides occluded in channels Ž o . Ž . Pt O , and Pt--O-Si[ complexes coordinated to external surface or defects of zeolite, respectively. From the variation x y
in the contribution of the 4808C peak in TPR traces, 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.