Studies of high surface area Pt/MoO3 and Pt/WO3 catalysts for selective hydrogenation reactions.: II.: Reactions of acrolein and allyl alcohol

The vapor-phase hydrogenation of acrolein, as a model molecule representing the alpha,beta-unsaturated aldehydes, was studied over Pt powder and Pt dispersed on SiO2, Al2O3 and ultrafine MoO3 and WO3 particles. The hydrogenation and isomerization of allyl alcohol were also investigated to obtain additional information about the effects of the supports and the network of these reactions. In the hydrogenation of acrolein, allyl alcohol was significantly produced only over Pt/MoO3 and Pt/WO3 catalysts previously reduced in the temperature range 673-773 K. This supports the proposal that adlineation sites created at the Pt-MoO3 and Pt-WO3 interfaces following a reduction at high temperature are responsible for the activation of carbonyl bonds. Also these adlineation sites, which contain electron-deficient cations resulting from a partial reduction of the oxide support, favor the isomerization of allyl alcohol to propanal at the expense of its hydrogenation to propanol. By contrast, for prereduction temperatures below ca. 573 K, the catalytic behavior of Pt/MoO3 and Pt/WO3 in the two reaction tests was not distinctly different from that of conventional Pt catalysts, which suggests that the molybdenum and tungsten hydrogen bronze supports do not markedly influence the catalytic properties of Pt catalysts. (C) 1997 Elsevier Science B.V.