Co₂ Hydrogenation To Lower Hydrocarbons On Supported Catalysts With The Synergy Of Non-Thermal Plasma

It is difficult to activate CO₂ molecules under mild conditions,but high temperature is not conducive to the hydrogenation,so it is very challenging to achieve CO₂ directional conversion under mild conditions.Dielectric barrier discharge plasma has the characteristics of every high energy but low temperature,which can be used to activate some reactions hard to happen under mild conditions.This paper makes full use of the advantage of dielectric barrier discharge plasma,to boost the growth of carbon chain with the synergy of corresponding catalysts,completing CO₂ hydrogenation to lower hydrocarbons reactions under mild conditions.The specific work was as follows:A series of supported metal catalysts,including Fe/ZSM-5,Co/ZSM-5,Ni/ZSM-5,Cu/ZSM-5,Zn/ZSM-5,Cr/ZSM-5,Cd/ZSM-5 and Mo/ZSM-5,were synthesized by incipient-wetness impregnation method,and evaluated in the catalytic CO₂ hydrogenation to lower hydrocarbons with the synergy of plasma in a dielectric-barrier discharges?DBD?reactor.Among various metal catalysts,Ni/ZSM-5 catalyst possessed the highest CH₄ selectivity and Co/ZSM-5 catalyst exhibited the highest C₂-C₄ selectivity.The active phase of the cobalt catalyst and the synergy between plasma and catalysis were tentatively studied,and the reaction network of CO₂ hydrogenation in a DBD reactor was proposed.In a DBD reactor,a significant synergetic effect was observed between the non-thermal plasma and cobalt catalysts for CO₂ hydrogenation to lower hydrocarbons.It was exhibited that Co⁰ was the active phase of Co/ZSM-5 catalyst for CO₂ hydrogenation.C₂-C₄ in the products were mainly produced by chain growth reactions from active C₁ monomer generated by CH₄,and CH₄ might be produced by the pathway through CO as an intermediate.Cobalt-based catalysts were selected as catalyst for CO₂ hydrogenation to lower hydrocarbons,optimizing the preparation and reaction conditions.As for the preparation conditions,carriers and metal loading were considered.Among various carriers?ZSM-5,SAPO-34,SiO₂,ZrO₂,?-Al₂O₃?,ZSM-5 exhibited the best catalyst performance.And among various cobalt metal mass fractions?5%,10%,15%,20%,25%?,15%was a best choice.As for the reaction conditions,the mole ratio of H₂/CO₂ in the feed gas,gas hourly space velocity?GHSV?and the input power were studied.It was found that when 15%Co/ZSM-5 was taken as the catalyst,the CO₂ conversion,C₂-C₄ selectivity and mole ratio of alkene/alkane were45%,13.7%and 0.26,respectively at the following reaction conditions:input power=14 W;mole ratio of H₂/CO₂=3;GHSV=4800 h^-1.In order to further improve the catalyst performance of Co/ZSM-5 catalyst,a series of promoters?Fe,Ni,Mo,Cd,Cr?were added to modify it.It was found that the addition of Ni as a promoter led to marked improvement in the catalytic performance of Co/ZSM-5 catalyst for CO₂ hydrogenation to lower hydrocarbons.At the optimal mass ratio of Co to Ni?4.0?,CO₂conversion was increased to 52.3%,and the selectivity of C2-C4 hydrocarbons was 17.9%.