Supported Pt and Re–Pt on Alumina Prepared by Sol-Gel Synthesis within SituWater Formation: Role of Rhenium

Abstract

Sol-gel chemistry offers flexible methods for the preparation of porous metal oxides such as the transition aluminas used as catalyst supports. The physical properties of sol-gel materials depend on the nature of the reactants, the rate of mixing, and the conditions of drying. Sol-gel chemistry has also been investigated for the preparation of supported metal catalysts such as Pt on metal oxides, including Al{sub 2}O{sub 3} and SiO{sub 2}, and Sn-Pt/Al{sub 2}O{sub 3}. In the synthesis of Pt/Al{sub 2}O{sub 3}, the physical properties of the porous material were controlled by the synthesis conditions, but only little control of the Pt dispersion was achieved. The bimetallic catalysts had high surface areas and pore volumes, but a typical Pt dispersion was not high (e.g., a H/Pt ratio of 0.3 was found for a sample containing 1 wt% Pt and 0.9 st% Sn). Because the oxophilic metal Re in Re-Pt/Al{sub 2}O{sub 3} catalysts evidently helps to maintain the dispersion of Pt, the authors investigated the role of Re in influencing the dispersion of Pt in Re-Pt/Al{sub 2}O{sub 3} prepared by a sol-gel synthesis. Alumina-supported samples were prepared in the initial absence of water under conditions allowing uniform reaction of the precursors. The precursorsmore » were Al(O-s-Bu){sub 3}, Pt(acac){sub 2}, and Re{sub 2}(CO){sub 10} in s-butyl alcohol. Acetic acid was included in the reactant mixture because it catalyzes the dehydration of the alcohol, leading to in situ formation of water uniformly in the medium and thereby to control of the rates of the hydrolysis and condensation reactions that lead to formation of a gelatinous precipitate. The gelatinous precipitate was transformed into porous products by calcination in air. 10 refs., 3 figs., 1 tab.« less