Effect of strong metal-support interaction on the rate of hydrogenation of adsorbed carbon monoxide over titania-supported noble metal catalysts as revealed by pulse surface reaction rate analysis

Abstract

On the basis of the rate constant per active site determined by pulse surface reaction rate analysis (PSRA), the effect of the strong metal-support interaction (SMSI) on the hydrogenation of adsorbed CO was studied for titania-supported noble metal catalysts. Reduction at 773 K resulted in a drastic decrease in the amount of CO adsorbed on all noble metals examined. The observed suppression of CO chemisorption resulted mainly from SMSI, because the chemisorption ability was restored considerably by heating these catalysts in an O 2 atmosphere and then reducing at 523 K. It was found that the effect of SMSI on the hydrogenation of adsorbed CO was different from one noble metal to another, although its effect on CO chemisorption was common to all titania-supported noble metals. Pt and Pd exhibited a much higher hydrogenation activity in their SMSI state than in their normal state, whereas Rh, Ru, and Ir exhibited almost the same activity in both states. By heating titania-supported Pt and Pd in O 2 and then reducing at 523 K, concomitant with destruction of the SMSI state, the high hydrogenation activity disappeared to near each original value. Subsequent reduction at 773 K again brought these catalysts to the SMSI state, accompanied by an increase in their activity. From these results, a possible cause is discussed for the high activity on Pt and Pd in the SMSI state and for its absence on Rh, Ru, and Ir in the SMSI state.