PLATINUM CATALYSTS SUPPORTED ON CARBON-BLACKS WITH DIFFERENT SURFACE CHEMICAL-PROPERTIES

Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for plati num, which has been introduced using both H2PtCl6 in acid media and [P t(NH3)(4)]Cl-2 in basic media. The catalysts have been characterized b y H-2 chemisorption at room temperature (after different pre-treatment s), temperature-programmed reduction (TPR) and temperature-programmed desorption of adsorbed hydrogen (H-2-TPD), and their catalytic behavio r in the gas-phase hydrogenation of benzene has been determined under differential conditions. TPD profiles of oxygen surface groups in fres h catalysts evidenced the support oxidation by H2PtCl6, with the occur rence of a CO evolution peak at low temperature (630 K). The presence of oxygen surface groups in the support favors the anchoring of [Pt(NH 3)(4)](2+), but does not affect the amount of platinum retained by the support when H2PtCl6 is used as metal precursor. TPR experiments have evidenced that the oxidized support hinders the reduction of the plat inum precursor. The catalytic activities in the benzene hydrogenation reaction do not show a direct correlation with dispersion values obtai ned from hydrogen chemisorption, and it has been related to storage an d mobility of hydrogen which is spilt over the support during the redu ction treatments. (C) 1998 Elsevier Science B.V. All rights reserved.