Synthesis Of Hafnium-based High Efficiency Catalysts And Their Application On Carbon Dioxide/Epoxide Cycloaddition Reactions Under Mild Conditions

With the burning of fossil fuels,a large amount of greenhouse gases are emitted into the atmosphere,which makes global warming produce greenhouse effect.In order to achieve the goal of carbon peaking and carbon neutrality,China is actively promoting the technology of capturing and converting CO₂ into high value-added chemical products.CO₂,as an abundant,non-toxic,cheap and renewable C₁ resource,its conversion and utilization have also received widespread attention in academia.The reaction of CO₂ with epoxide cycloaddition to form cyclic carbonate is in line with the atomic and environmental friendly concept because of its high atomic utilization rate of 100%.The concept of economy and environmental friendliness is considered as an efficient and economical as well as environmentally friendly method of fixing CO₂.However,the high stability of CO₂ limits the conversion of CO₂ as a carbon source into high value-added industrial products.Currently,the catalysts used in the industrial catalytic cycloaddition of CO₂ are mainly quaternary ammonium salts and metal halides,but they suffer from low catalytic activity,harsh reaction conditions requiring high temperature or high pressure,and difficulties in recycling,limiting their wide application.Therefore,developing multi-phase catalysts with high stability,mild reaction conditions,easy recycling and reuse,and good cyclic performance is an important research objective for CO₂ cycloaddition.Based on the mechanism of CO₂ activation,hafnium-based heterogeneous catalysts have a high stable physical and chemical properties,which can provide rich unsaturated metals sites as Lewis acid sites.They could be ideal candidates for CO₂ cycloaddition reactions.The purpose of this paper is to synthesize high efficient,inherent stability hafnium-based heterogeneous catalysts through magnesium thermal.1.Hafnium carbide nanoparticles were synthesized by magnesium thermal reaction using commercial conductive carbon powder as carbon source at 1000℃,which reduced the energy consumption beyond traditional methods.The nanoparticles cooperated with tetrabutylammonium bromide as a co-catalyst,and had an efficient catalytic effect on the epoxidation of different epoxides with carbon dioxide to form cyclic carbonates at the pressure of carbon dioxide of 0.8 MPa and100℃.The catalyst possesses high stability,high catalytic efficiency that can maintain after many experiments,and the synthesis conditions of the catalyst are lower than those of traditional methods,and the scale-up synthesis is easy,so it is a potential and efficient catalyst for epoxidation and addition of carbon dioxide.2.Low cost,accessible and environmentally friendly biomass,bamboo,was hydrothermal treated with alkali.Then the cellulosic was carbonization to cellulosic carbon（CC）,which would be the carbon sources for our reaction.The two-dimensional HfC/CC with regular morphology was generated via the Magnesiothermic reaction at 1000°C using Cellulosic carbon as a template for the reaction with hafnium metal Two-dimensional HfC/CC was used as a catalyst with a co-catalyst（TBAB）synergistically catalyzed the reaction of catalytic addition of carbon dioxide with different epoxides to form cyclic carbonates under room temperature and pressure and light induction.The experimental results showed that the reaction of epichlorohydrin attained 100%conversion after 12hours of reaction,and the catalyst demonstrated high stability and excellent cycling performance after 15 cycles of testing,which is a green,environmentally friendly,and economical catalyst.3.Different nitrogen-containing compounds were introduced as nitrogen sources,and low-energy consumption reactions were used to synthesize different phases and morphologies of nitrogen-doped hafnium oxides through magnesiothermic and Maillard reactions at a relatively low reaction temperature（800℃）.This method enriches the synthesis approach for nitrogen-doped hafnium oxides and is conducive to large-scale synthesis.Under the conditions of a temperature of85℃,CO₂ pressure of 0.8 MPa,and nitrogen-doped hafnium oxide as the catalyst in conjunction with a co-catalyst（TBAB）,cycloaddition reactions between CO₂ and epoxides were catalyzed to generate cyclic carbonates.The experimental results showed that 100%conversion was achieved after 6 hours of reaction,demonstrating the efficient catalytic performance of nitrogen-doped hafnium oxide.The synthesis conditions of nitrogen-doped hafnium oxide are simple,and the reaction raw materials are cheap and easily obtainable.Therefore,it is easy to scale up the synthesis,making it a potentially viable commercial catalyst for catalyzing the cycloaddition of CO₂ and epoxides.