EXPERIMENTAL STUDY OF CHARACTERISTICS OF Pt/TiO2 CATALYST

Chemisorption of hydrogen, carbon monoxide, and oxygen on 2 wt% Pt/TiO₂ was investigated to determine a satisfactory method for measuring the platinum dispersion on titania. The reduction of Pt/TiO₂ at high temperature results in sharp decrease in hydrogen and carbon monoxide chemisorption capacities and catalytic activity which cannot be accounted for by metal sintering. Oxidation-reduction treatments restore the usual properties of the catalyst. The TPD spectrum of hydrogen on Pt/TiO₃ shifts to higher temperature upon reduction at high temperature and shifts again to its original position upon oxidation. Shift of TPD spectrum does not appear in other catalysts. Oxygen adsorption method is inaccurate to measure crystallite diameter of platinum because oxygen uptake is enhanced not only due to reduced nonstoichiometric oxide support but also to penetration of oxygen into bulk platinum. Hydrogen chemisorption method, however, is a satisfactory technique to measure the platinum dispersion only if the strong metal-support bonding has been destroyed completely. Sintering rate in oxygen is greater than that in hydrogen regardless of the nature of the supports, and sintering resistance of Pt/TiO₂ in hydrogen is much greater than that of other supported platinum catalysts whereas stability of the platinum in oxygen is not dependent on the supports. The influence of chlorine in the presence of oxygen on the redispersion phenomena is found to be very important.