Nickel phyllosilicates functionalized with graphene oxide to boost CO selectivity in CO2 hydrogenation

Abstract

Thermal reduction of CO2 by green H2 is one of the most effective strategies for CO2 utilization and preparation of value-added C1 chemicals, which is highly dependent on the catalyst compositions and structures. In this work, hollow mesoporous nickel phyllosilicate (mNiSiO3) with an average size of 250 nm was used as catalysts for CO2 hydrogenation after the partial extraction of Ni ions from nickel phyllosilicate. After the reduction treatment by H2 at 400 °C, the mNiSiO3-R400 showed CO2 conversion of 22.9% and CH4 selectivity of 80.9% (300 °C, 0.1 MPa). Interestingly, by functionalization of two-dimensional graphene oxide (GO) onto the nickel phyllosilicate to obtain mNiSiO3/GO catalyst, more CO product was obtained and the CO/CH4 ratio in the products can be easily tuned via the change of GO loading amount. It was found that the functionalization of GO nanosheets on mNiSiO3 would affect the reduction degree of nickel phyllosilicate and stabilize the structure against collapse during high-temperature reduction. In accordance, the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in different transient states suggested that the formation of bidentate carbonate species may play a vital role in the high selectivity of CO and that CH3O* was the key intermediate species over the Ni site for CH4 formation. Due to the electronic interaction between GO and Ni0, it might weaken the interaction between Ni0 and H2, which prevents the direct decomposition of CO* into C* and the further hydrogenation of C* into methane over the Ni0 sites. This work will provide new references for adjusting the CO/CH4 selectivity in CO2 hydrogenation over the Ni-based catalysts.