PREPARATION OF PT-RE AL2O3 CATALYSTS BY SURFACE REDOX REACTIONS .2. INFLUENCE OF THE ACID-MEDIUM ON RE DEPOSITION AND PT-RE INTERACTION/

Bimetallic Pt-Re/Al2O3 catalysts are prepared under hydrogen atmospher e by a surface redox reaction between hydrogen adsorbed on a parent pl atinum/alumina catalyst and the perrhenate ion ReO4-. This reaction, c alled catalytic reduction, occurs only in an acidic medium, a maximum rhenium deposition appearing as a function of the concentration of the acid solution. The preparation of bimetallic Pt-Re/Al2O3 catalysts by catalytic reduction of the rhenium salt on a highly dispersed platinu m catalyst leads to bimetallic particles after activation by direct re duction under hydrogen. The calcination at 450 degrees C partially des troys the interaction between the two metals, the effect being more ob vious on chloride containing samples. The activation procedure produce s the reverse effect at high rhenium loading deposited on a parent cat alyst of low dispersion.