Design Of In-Zr/Cu-SSZ-13 Bifunctional Catalyst And Its Performance For CO₂ Hydrogenation To LPG

The combustion of fossil fuels generates a large amount of greenhouse gases such as CO₂,which aggravates global warming and other environmental problems.Hydrogenation of CO₂ into high valueadded chemicals and fuels is one of the effective ways to solve this problem.Currently,CO₂ hydrogenation to hydrocarbons can convert CO₂ into methane,methanol,light olefin and LPG（Liquefied Petroleum Gas）.CO₂ hydrogenation to LPG is a process in which green hydrogen produced by renewable resources such as solar energy and wind energy reacts with excess CO₂ emissions to produce hydrocarbons through methanol intermediates.In this reaction,the first stage is the hydrogenation of CO₂ on the alcohol-forming catalyst to produce methanol,and the second stage is the methanol on the acidic zeolite to produce hydrocarbons.Due to the thermodynamic mismatch between the hydrogenation of CO₂ to methanol and the dehydration reaction of methanol,the Reverse Water Gas Shift（RWGS）side reactions are prone to occur at higher temperatures,resulting in high selectivity of CO byproducts,generally more than 60%.In order to solve the above problems,an In-Zr/Cu-SSZ-13 bifunctional catalyst was designed and synthesized.By coupling CO₂ hydrogenation to methanol and the conversion of methanol to hydrocarbons,which realized the high selectivity of CO₂ hydrogenation to LPG and effectively reduced the selectivity of the byproduct CO.Combined with XRD,N2-BET,SEM-EDS mapping,TEM,CO₂-TPD,NH3-TPD,Py-IR,ICP-OES,XPS,and other characterization methods,The CO₂ hydrogenation performance of catalyst and the effect of zeolite modification on the reaction were studied.The specific research contents and results are as follows.（1）In this paper,metal oxide catalysts with different In-Zr molar ratios were prepared by precipitation deposition method,and Cu-SSZ-13 zeolite catalysts were prepared by ion exchange method,and the two catalysts were connected in series.The effects of different In-Zr ratios,combinations of active components,temperatures and space velocities on the reaction performance were investigated.Experiments show that the In-Zr ratio of 1:4 metal oxide catalyst and Cu-SSZ-13 zeolite mixed by particles can show the best reaction performance,at the reaction conditions of 350℃,4500 mL·g·-1 h-1,3 MPa,metal oxides and zeolite’s mass ratio of 1:1,The catalyst can achieve 85%selectivity of LPG,the CO₂ conversion is above 35%,and the CO selectivity can be reduced to 25%.（2）SSZ-13 zeolite was modified by impregnating Ni,Cu and Ce elements,and the effect of modified zeolite on the reaction performance of CO₂ hydrogenation to LPG was investigated.The experimental results show that the modified Cu element can achieve the best reaction performance.The SSZ-13 zeolite was treated with different concentrations of NaOH solution,and the effect of alkali treatment on the reaction performance of the zeolite was investigated.The results showed that the pore structure could be effectively improved by using 0.05 mol/L NaOH solution.The conversion of CO₂ increased from unmodified 25%to 32%and the selectivity of CO decreased from unmodified 29%to 23%.With the further increase of NaOH solution concentration,the selectivity of low carbon olefin increased from 2%to 37%after 0.2 mol/L NaOH solution treatment.However,too high alkali concentration will lead to the reduction of acid content and strength of zeolite,and the methanol intermediates cannot be rapidly consumed,which inhibits the forward movement of the reaction and leads to the reduction of CO₂ conversion.