Mechanistic and microkinetic study of nonoxidative coupling of methane on Pt-Cu alloy catalysts: From single-atom sites to single-cluster sites

Abstract

Desirable catalysts possessing the ability to selectively break C–H bond and controllably catalyze C–C bond formation are highly demanded for the nonoxidative coupling of methane (NOCM). Herein, a series of Pt-Cu alloy catalysts including Pt1©Cu(111), Pt2©Cu(111) and Pt3©Cu(111) are deliberately designed and systematically studied for NOCM. Density functional theory calculations reveal that the Pt1, Pt2, and Pt3 sites on Cu(111) can selectively break the C–H bond to generate CH3, CH2, and CH species, respectively. However, direct coupling of corresponding CHx (x = 3, 2, 1) to form C2H6, C2H4, and C2H2 are favorable on Pt3, Pt1, and Pt2 sites on Cu(111), respectively. The different reactivity trends of the three Pt sites mainly originate from the varying bonding abilities of CHx species at the Pt sites. Microkinetic modeling manifests that the Pt1©Cu(111) is the most active for methane dissociation (TOF = 2.98 s–1 at 1000 K) and can selectively convert methane into ethylene with the highest selectivity up to 96.2% at 750 K. Moreover, Pt1©Cu(111) also shows superb stability under reaction conditions. Overall, our studies not only provide a comprehensive understanding of the reaction mechanism of NOCM on Pt single-atom sites (SASs) and Pt single-cluster sites (SCSs) but also predict that Pt SASs are advantageous over Pt SCSs for NOCM.