IRRAS evidence of reaction precursor and carboxyl intermediate for CO2 hydrogenation reduction on Ni(1 1 0)

Abstract

The CO2 reduction on Ni catalyst surfaces has been extensively reported, however, the catalytic reaction mechanisms at molecular scale are still not very clear. Firstly, the reaction precursor in CO2 reduction on Ni catalysts has not been identified by experiments. Secondly, the direct experimental evidence of the carboxyl intermediate which plays a critical role in CO2 hydrogenation reduction on Ni catalysts is still lacking. Herein, via a combination of ultra-high vacuum - infrared reflection absorption spectroscopy (UHV-IRRAS) and density functional theory (DFT) calculations, we studied CO2 reduction on Ni(110) model catalyst surfaces. The convincing evidence of reaction pathways of CO2 with and without hydrogen on Ni(110) was achieved by UHV-IRRAS experiments. The hollow up (HU)–CO2 activated state at 90 K is identified as the precursor in both direct and hydrogen-involved CO2 dissociation reactions. The carboxyl intermediate (HOCO) is evidently confirmed by IRRAS during CO2 hydrogenation. Such intermediate effectively reduces the dissociation energy of CO2 to CO. Our work not only provides the direct experimental evidence of reaction precursor and carboxyl intermediate for CO2 hydrogenation on Ni(110), but also experimentally confirms the non-formate associate pathway of RWGSR, which will shed light on understanding the CO2 hydrogenation reduction mechanisms by Ni-based catalysts.