The Study Of Catalysts For The Reaction Of CO₂ Hydrogenation To CH₄/CH₃OH

The excessive emission of CO₂ caused by the consumption of fossil fuels has led to a series of environmental problems.Carbon capture,utilization,and storage（CCUS）has become a promising research area as China has formulated the‘Carbon Peaking and Carbon Neutrality Goals’strategy.The utilization of CO₂ can not only alleviate the problem of excessive CO₂ emissions but also promote the realization of CO₂resourcing and carbon cycle economy.At present,the performance of CO₂ hydrogenation catalysts still needs to be improved.This paper focuses on the efficient catalysts for CO₂ methanation and the CO₂hydrogenation to methanol.Additionally,we explore the impact of catalyst structure and the interface on the performance of active sites,elucidating the reaction mechanism of CO₂ hydrogenation.It provides new theoretical basis and research ideas for subsequent research on CO₂ hydrogenation catalysts.The main works are as follows:1.We used conventional Ni/Si O₂ as a unique silicon source to synthesize the Ni@Beta（Si/Al=40）catalyst with a specific encapsulated structure by a simple hydrothermal synthesis.The Ni@Beta simultaneously exhibited high CO₂conversion（74.2%）and methane selectivity（93.5%）,with good stability during the methanation reaction.All obtained catalysts were characterized by BET,ICP-OES,XRD,SEM-EDS,HRTEM,H₂-TPR,CO₂-TPD,In situ XPS,In situ DRIFTS,and NAP-XPS.Compared with the Ni@Silicalite-1（Al-free zeolite）,the aluminum-containing zeolite frameworks of the Ni@Beta got more electrons from the nickel active phases,so the metal-support interaction on the Ni@Beta was stronger,which was favorable for the stability of the Ni⁰phase.Furthermore,the Al-containing zeolite frameworks of the Ni@Beta inhibited the formation of volatile metal molecular intermediates（gaseous Ni（CO）_x）,thereby suppressing the sintering and loss of active Ni species.The In situ DRIFTS and NAP-XPS results not only successfully unveiled that the main reaction pathway was a formate route,but also showed that the Ni@Beta had the strongest capacity to adsorb and convert CO₂,so it had the highest methanation activity.2.We used conventional Pd-Zn/Si O₂ as a unique silicon source to synthesize the Pd-Zn@Silicalite-1 catalyst with a specific encapsulated structure by a simple hydrothermal synthesis.The interaction between Pd and Zn O of the Pd-Zn@Silicalite-1 was stronger than that of the Pd-Zn/Silicalite-1,and thus the Pd-Zn@Silicalite-1 had higher catalytic activity for methanol synthesis from CO₂.The 1Pd5Zn@Silicalite-1 exhibited a high methanol selectivity（95.2%）.The results of characterization demonstrated the existence of the embedment structure in the 1Pd5Zn@Silicalite-1,and the special structure modulated the Pd-Zn O interactions leading to the retention of more Pd²⁺species after reduction,which facilitated the adsorption and conversion of CO₂,resulting in the highest CO₂ conversion of the 1Pd5Zn@Silicalite-1.The In situ DRIFTS results successfully unveiled that the main reaction pathway was a formate route during the CO₂ hydrogenation to methanol.Furthermore,the 1Pd5Zn@Silicalite-1 generated more HCO₃*species after the adsorption of CO₂,and the intermediate conversion on this catalyst is the fastest.Therefore,the 1Pd5Zn@Silicalite-1 exhibited the highest methanol selectivity.3.In order to investigate the effect of different promoters on the performance of the Pd active phase for CO₂ hydrogenation to methanol,Zn O,In₂O₃,and Ce O₂ metal oxide promoters were loaded on Pd/Zr O₂,respectively.The reaction results showed that,the Zn O-Pd/Zr O₂ catalyst exhibited the highest CO₂ conversion（12.0%）,methanol selectivity（95.6%）,and STY of methanol(472 g _{Me OH}kg_cat^-1h^-1),with excellent stability.The results of HRTEM,H₂-TPR,in situ XPS,and XAFS showed that the Zn O-Pd/Zr O₂ had the typical Pd-Zn O interface with Pd²⁺species after the H₂ reduction,which could enhance the adsorption and activation of CO₂.In addition,the In situ DRIFTS and NAP-XPS results implied that the Pd-Zn O interface significantly improved the formation of formate and methoxy species,which were considered to be the key intermediates of methanol generation.Therefore,the Zn O-Pd/Zr O₂ showed the highest methanol selectivity and STY _methanol.