SUPERCRITICAL FLUID REACTIVE DEPOSITION FOR THE PREPARATION OF METAL CATALYSTS ON POROUS MODEL SUPPORTS

摘要

Platinum catalysts supported on micro-, meso-, and macroporous silica (silicalite-1, MCM-41, silica gel) were prepared via supercritical fluid reactive deposition (SFRD). The porous model supports were first impregnated with the complex 1,5-(cyclooctadiene)dimethylplatinum(II) dissolved in supercritical carbon dioxide (scCO_2) at 80°C and 15.5 MPa for 2h. For SFRD, the complex was reduced to platinum metal in scCO_2 by addition of hydrogen. In order to identify appropriate conditions for SFRD, the three-phase S-L-G coexistence curve was measured in the pressure range of 0.1 to 25.0 MPa for the mixtures investigated. The supported Pt(COD)Me_2 complex and the platinum composites were characterized by elemental analysis (ICP-AES), TGA, DSC, XRD, and N_2 adsorption. DSC and XRD support a homogenous distribution of the complex over the MCM-41 support. High platinum dispersions were obtained by SFRD on the macro-and mesoporous supports, but not on the microporous silicalite-1. The Pt/MCM-41 catalysts are active for the combustion of toluene in air as a test reaction for the oxidative destruction of volatile organic compounds (VOCs).