The Effect Of ZrO₂ Phase Of Ga₂O₃/ZrO₂ Catalyst For The Performance For CO₂ Hydrogenation

As a common greenhouse gas,the high concentration of CO₂ in the atmosphere leads to global warming and a series of severe environmental problems.However,CO₂also can be used as the recyclable carbon source.It is of great economic and ecological significance to react with renewable hydrogen to produce methanol and other chemicals.The excellent stability and catalytic performance of bimetallic oxide catalysts have attracted widely attention.ZrO₂ shows great stability and catalytic performance,but the preparation of its single phase（tetragonal and monoclinic zirconia）was challenging,and the structure-activity relationship of ZrO₂-based bimetallic oxide catalysts need in-depth research.In this paper,Ga₂O₃/t-ZrO₂ and Ga₂O₃/m-ZrO₂ were prepared by solvothermic-impregnation method under similar conditions and used in CO₂ hydrogenation to prepare methanol.The structure of the catalyst was verified by X-ray diffraction,Raman spectroscopy and transmission electron microscopy.It was found that Ga₂O₃/t-ZrO₂ catalyst performed better Me OH+DME yield.Ga₂O₃/t-ZrO₂ catalyst tended to produce Me OH+DME（selectivity>70%）,while Ga₂O₃/m-ZrO₂catalyst had a higher selectivity of CO（>60%）.Further,through kinetic experiments,CO₂ temperature programmed desorption,H₂ temperature programmed desorption,H₂-D₂ exchange and electron paramagnetic resonance experiments,it is proved that the CO₂ adsorption and activation capacity on the surface of Ga₂O₃/t-ZrO₂ and Ga₂O₃/m-ZrO₂ catalysts is similar.Ga₂O₃/t-ZrO₂ catalyst has stronger H₂ activation ability,showing better catalytic performance.The hydrogenation of CO₂ to formate was revealed by solid state nuclear magnetic and CO probe molecular experiments and HCOOH temperature programmed desorption-mass spectrometry.HCOOH is more stable on the surface of Ga₂O₃/t-ZrO₂ catalyst.The signal of^*HCO was seen in the Fourier infrared spectroscopy characterization,which suggested that the existence of the hydrogenation for adsorbed CO to^*HCO on the catalyst surface.The CO hydrogenation experiment verified the above conclusion,so the CO selectivity in Ga₂O₃/t-ZrO₂ catalyst is low.Both mono-and oligomeric Ga species were found on the catalyst surface by time-of-flight secondary ion mass spectrometry,but the mono-Ga species were more likely to be the active site structure on the catalyst surface.We hope that the research of this paper can provide a new idea for the design and development of new catalysts.