Spillover rate from Pd to AI 20 3

Abstract

To measure the rate of spillover on Pd/Al[sub 2]O[sub 3], the authors used interrupted TPR and isotope exchange before a complete TPR experiment. In this approach, [sup 12]CO was adsorbed at 300 K and the catalyst temperature was then raised in H[sub 2] flow to facilitate spillover. The heating ramp was interrupted before a significant amount of CH[sub 4] formed, and the sample was quickly cooled to 300 K. Then the catalyst was exposed to [sup 13]CO to displace any [sup 12]CO that remained on the Pd surface. At room temperature, gas phase CO readily exchanges with adsorbed CO on Pd. The authors also observed previously that gas phase CO does not exchange with CH[sub 3]O on Al[sub 2]O[sub 3] of Ni/Al[sub 2]O[sub 3]. Thus, any [sup 12]CO remaining on the catalyst after exchange was assumed to be present as [sup 12]CH[sub 3]O on the Al[sub 2]O[sub 3] surface. The amount of [sup 12]CH[sub 4] that formed during the subsequent TPR was thus a measure of how much [sup 12]CO had spilled over to the Al[sub 2]O[sub 3] since all the adsorbed [sup 12]CH[sub 3]O was hydrogenated to [sup 12]CH[sub 4]. A series of TRP experiments with different interruption temperaturesmore » yielded a TPR spectrum for spillover and an estimate of the activaiton energy for spillover.« less