Mechanistic Insight into the Role of N Doping in Pt/N-Tio2 Catalyst for Improved Ch4 Selectivity in Co2 Hydrogenation

Abstract

The adsorption/desorption of the key intermediate at the molecular level in CO2 hydrogenation deserves significant attention since the intermediate stability can greatly affect the products selectivity. Herein, the Pt/N-TiO2 catalysts was reported to enhance stability of the key intermediate Pt-CO species for improving CH4 products selectivity in CO2 hydrogenation. The XPS, DFT calculations and In-situ FTIR experiments demonstrate that the πp-d molecular orbital is formed between N and Pt elements over Pt/N-TiO2, which can improve the electron density of Pt nanoparticles (NPs) as well as strengthen CO binding, and then the key intermediate Pt-CO species in CO2 hydrogenation will prefer to react with adsorbed hydrogen to form CH4 rather than desorbing to yield CO product in gas phase. As a result, the CH4 selectivity of Pt/N-TiO2 was improved by 2.4 times compared with Pt/TiO2, and the Pt/N-TiO2 started to catalyze the CO2 methanation reaction at 220 ℃ during CO2 hydrogenation reaction, which was 30 ℃ lower than that of Pt/TiO2 (250 ℃). Furthermore, the CO methanation tests revealed that CH4 selectivity over Pt/N-TiO2 was also improved by 2.8 times compared with Pt/TiO2, in accordance with the improved CH4 selectivity in CO2 hydrogenation. In contrast, the CO products selectivity was improved over several cations (Cd2+, Mn2+, Ba2+, K+ and Na+) modified Pt/TiO2 (Pt/M-TiO2), which was ascribed to the reduced electron density of Pt NPs and enhanced instability of Pt-CO species, which will contribute to CO evolution. Such a key intermediate regulating strategy will be a versatile method to obtain high effective catalysts with controlled products selectivity in CO2 hydrogenation.

Keywords: CO2 Hydrogenation, CH4 selectivity, electrons density, CO binding, Pt-CO species