Study On The Performance Of UiO-66 Derived Zirconium-based Catalyst For Catalytic CO₂ Hydrogenation To Methano

As a major component of greenhouse gases,excess CO₂ is one of the major problems that the global humans have to face and solve at present and for a long time.A great deal of efforts have been made by all countries to reduce CO₂ emissions,among which,using CO₂ to react with H₂ from clean sources to generate methanol under certain conditions is a promising method for resource utilization.In₂O₃/ZrO₂ catalysts exhibit excellent catalytic activity for CO₂ hydrogenation to methanol due to the large number of oxygen vacancies on the surface of In₂O₃,the promotion effect of ZrO₂ and the synergistic effect between In₂O₃ and ZrO₂.While conventional In₂O₃/ZrO₂catalysts have been studied for CO₂ hydrogenation to methanol,researchers prefer to define the structure at the nanoscale or atomic level to manipulate the catalyst activity.The Metal Organic Frameworks（MOFs）and their derivative catalysts offer an opportunity for this new path.In this paper,the performance of CO₂ hydrogenation to methanol over UiO-66-derived In₂O₃/ZrO₂ catalyst was investigated using UiO-66 as the support.Firstly,a series of In₂O₃/ZrO₂ catalysts with different In₂O₃ loadings were prepared to investigate the effect of In₂O₃ loading on the performance of CO₂hydrogenation to methanol.The results showed that the loading of In₂O₃ had a large effect on the catalytic performance,in which the 10%In₂O₃/ZrO₂ catalyst exhibited the highest CO₂ conversion of 7.16%and methanol selectivity of 96.58%.The CO₂adsorption and H₂ dissociation capacity of the catalyst is critical to the catalytic activity.The CO₂ adsorption capacity is not only related to the surface oxygen vacancy defects,but also closely linked to the surface basicity.The addition of moderate amount of In₂O₃ is beneficial to the increase of medium intensity basic sites and enhance the dissociation capacity of H₂.The 10%In₂O₃/ZrO₂ catalyst has more medium intensity basic sites on the surface to facilitate CO₂ adsorption activation and stabilization of the intermediate.Meanwhile,the electron-rich In₂O₃ in the 10%In₂O₃/ZrO₂ catalyst improves the H₂ dissociation capacity of the catalyst when the oxygen vacancy change is small.It is more favorable for further hydrogenation reaction to produce methanol,thus showing the best catalytic performance.Secondly,the 10%In₂O₃/ZrO₂-T（T=350℃,450℃and 600℃）catalysts were prepared by calcining the indium-loaded UiO-66 precursor at different temperatures to investigate the effect of calcination temperature on the performance of CO₂hydrogenation to methanol,under the determination of the optimal In₂O₃ loading of10%.Combined with the results of XRD,TG analysis and catalytic performance evaluation,the calcination temperature mainly affects the catalyst performance by changing the state of the support.The strong CO₂ and H₂ adsorption capacity of the catalyst after calcination at 350°C mainly originated from the physical adsorption of UiO-66,but did not contribute well to the catalytic performance improvement.While UiO-66 was transformed into ZrO₂ after calcination at 600℃,the catalyst had stronger interaction with CO₂ and thus had better catalytic performance.Finally,the In₂O₃/ZrO₂ catalysts were prepared by UiO-66 derivatization and ZrO₂-loaded indium prepared by the co-precipitation method to investigate the relationship between the structure and performance of the two catalysts.The results of catalytic activity evaluation showed that the UiO-66-derived In₂O₃/ZrO₂ catalyst had better catalytic performance（280°C:CO₂ conversion of 7.16%and methanol selectivity of 96.58%）.The XRD and Raman spectra showed that ZrO₂ was dominant in the tetragonal phase in the UiO-66-derived In₂O₃/ZrO₂ catalyst（10%In₂O₃/ZrO₂）,while ZrO₂ was dominant in the monoclinic phase in the ZrO₂-loaded indium catalyst prepared by the co-precipitation method（10%In₂O₃/ZrO₂-CP）.The XPS characterization results indicated that the UiO-66-derived In₂O₃/ZrO₂ catalyst has more oxygen vacancy defects,which dominate in methanol synthesis relative to electron transfer,and the oxygen vacancies can affect the CO₂ adsorption capacity of the catalyst as well as further hydrogenation.Meanwhile,the In₂O₃ showed higher surface dispersion on the UiO-66-derived ZrO₂ support,leading to easier reduction of In₂O₃ on the surface,which in turn enhanced the rate of H₂ dissociation and promoted CO₂ conversion,thus exhibiting high methanol selectivity and CO₂ conversion.This thesis illustrated the structure and performance interrelationships in In₂O₃/ZrO₂ catalysts of CO₂ hydrogenation,and provided new ideas for the development of highly active CO₂ hydrogenation catalysts for methanol synthesis.