Effect of Pt addition on resistance to carbon formation of Ni catalysts in methane dehydrogenation over Ni-Pt bimetallic surfaces: A density functional theory study

Abstract

Methane dehydrogenation is a well-studied reaction that is of both scientific and industrial importance. We performed systematic density functional theory computations to examine the catalytic performance of pure and Pt modified Ni(111) surfaces for carbon formation from methane dehydrogenation. To address these processes, Ni-Pt surface alloys of 6 different bimetallic compositions are applied to investigate the detailed catalytic dehydrogenation for methane, and their catalytic activities as well as resistance to carbon formation are compared with monometallic Ni(111) surface. Through the systematic examination, the results show that CH4 dissociation into CH3+H and CH decomposition into C+H are the two key steps. Moreover, it is found that CH dissociation barriers on the Ni-Pt bimetallic surfaces are evidently higher that on pure Ni(111). Especially for NiPt(111)-B1 surface, energy barrier for CH dissociation is remarkably increased by around 1.7eV compared to that on Ni(111) and the carbon adsorption energy is the lowest one among all surfaces. The enhanced barrier suppresses the CH cracking reaction and reduced carbon adsorption energy diminishes the possibility of coke formation. Additionally, carbon formation is significantly inhibited even with a small amount of Pt addition. Considering the balance between the catalytic performance and the economic cost, we proposed that NiPt(111)-B1 surface not only exhibits good resistance to carbon formation, but also has the moderate cost due to the less doped Pt atoms, although there is a slight decrease in activation for methane. Finally, BEP relationships between reaction energy and activation energy have been developed for every methane dehydrogenation step on all Ni(111) and NiPt(111) surfaces in this paper. These results could provide new mechanistic insight into the role of Pt in improving the ability to anti carbon formation of Ni catalysts, and are helpful to understand the mechanisms of methane dissociation from the atomic scale.