Role of alkali metal and co-promoter on coke reduction on an active site of the Pt/r-Al2O3 catalyst

Abstract

Deposition of coke on metal active sites decreases the activity of catalysts. Extensive researches on the spillover phenomena been the subject of numerous reviews (18). Spillover is known to affect have catalyst performance, which may lead to modifications in the reactivity. This work investigates the effect of spillover hydrogen on coke reduction on metal active sites of bifunction catalysts Pt/Al2O3, Pt-Sn/Al2O3, Pt-K/Al2O3 and Pt-Sn-K/Al2O3. TPD of hydrogen was used to display the hydrogen spillover ability of catalysts which was formed to follow the sequence : Pt-Sn-K/Al2O3 > Pt-Sn/Al2O3, Pt-K/Al2O3 > Pt/Al2O3. It is shown that Sn and K affected the adsorption of hydrogen and the hydrogen spillover on the Pt/Al2O3 catalyst. In addition, TPR profiles supported that the doping of Sn and K increased the quantity of adsorbed hydrogen on the catalyst, and increased the spillover hydrogen. Dehydrogenation of n-hexane was reacted to identify the type ofhydrogen spillover (reversible and irreversible hydrogen spillover). It was found that the reversible spillover hydrogen on the catalysts followed the sequence: Pt-Sn-K/Al2O3 > Pt-Sn/Al2O3, Pt-K/Al2O3 > Pt/Al2O3. Thus, the promotion of Sn incorporated with K contributed reversible spillover hydrogen on the Pt/Al2O3 catalyst more than the promotion of only Sn or K. However, this study difplayed that reversible spillover hydrogen helped reduce coke on the metal active sites