PROMOTED PT CATALYSTS FOR AUTOMOTIVE POLLUTION-CONTROL - CHARACTERIZATION OF PT SIO2, PT/COOX/SIO2, AND PT/MNOX/SIO2 CATALYSTS/

The characterization of Pt/SiO2, Pt/CoOx/SiO2, Pt/MnOx/SiO2, CoOx/SiO2 , and MnOx/SiO2 catalysts with 5 wt% Pt, 25 wt% MnO2, 50 wt% Co3O4, an d 3 wt% Co3O4 is described. The Pt/CoOx/SiO2 catalyst is particularly active in low-temperature CO oxidation, while the Pt/MnOx/SiO2 catalys t is more active in NO reduction by CO than the unpromoted Pt catalyst . The characterization techniques used are (1) X-ray diffraction, to d etermine the average particle size and possible alloy formation; (2) C O chemisorption, to determine the specific Pt surface area; and (3) Fo urier transform infrared spectroscopy, to study the adsorption of CO a nd NO and the interaction between CO and NO. The influence of a reduct ive or oxidative pretreatment is also examined. After a reductive pret reatment the high-loaded Pt/50CoO(x)/SiO2 catalyst shows the formation of a PtCo alloy and Co-0 metal. No alloy formation was detected for t he Pt/3CoO(x)/SiO2 catalyst. Fourier transform infrared measurements s how the characteristic bands of linearly adsorbed CO on Pt at 2070 cm( -1), and linear and bent NO on cobalt oxide at 1870 and 1790 cm(-1), r espectively. For the high-loaded Pt/50CoO(x)/SiO2 a shoulder at 2023 c m(-1) is observed and ascribed to CO linearly bound to cobalt metal. A n isocyanate band at 2200 cm(-1) is found for the Pt/3CoO(x)/SiO2, Pt/ 50CoO(x)/SiO2, Pt/MnOx/SiO2, and MnOx/SiO2 catalysts on coadsorption o f CO and NO. (C) 1996 Academic Press, Inc.