Plasma Catalytic Reduction Of CO₂ By Hydrogen And Methane

CO₂ reduction is an effective way for CO₂ utilization.Various approaches for CO₂ reduction have been explored,including photo-catalytic approach,electrochemical method,conventional catalytic?CC?process and plasma catalytic?PC?route.Among these,photocatalytic and electrochemical method are still under basic research.Conventional catalytic method reduces CO₂ to syngas,and then through Fischer-Tropsch synthesis process to obtain high value-added chemicals and fuels.Although conventional catalytic method has been close to industrialization,but this method exists disadvantages of high energy cost and low energy efficiency due to limitation of thermodynamic equilibrium and properties of catalysts.Plasma catalytic method which combines plasma with catalysts could be expected to achieve efficient CO₂ reduction due to advantages of quick start and high energy efficiency.This work aimed at CO₂ reduction investigated the application of non-thermal plasma into reverse water gas shift?RWGS?and dry reforming of methane?DRM?.Three major aspects of research were included,which are investigation into enhancement effect of cold plasma produced by dielectric barrier discharge?DBD?in plasma catalytic RWGS reaction over Au/CeO₂,research on RWGS reaction promoted by gliding arc plasma only and research on gliding arc plasma-assisted DRM reaction.Main results are summarized as below.In plasma?DBD?catalytic RWGS reaction,CO₂ conversion is higher than that in conventional catalytic RWGS reaction,and even exceeds thermodynamic equilibrium conversion.Enhancement factor was introduced to quantify the enhancement effect.The influences of reactor temperature,weight hourly space velocity?WHSV?and molar ratio of H2/CO₂ on enhancement factor were investigated.Under the conditions of 300 oC,Ft=200 SCCM,WHSV=12000 mL·g-1cat·h-1,the enhancement factor could be up to 1.76,which means great enhancement effect.By in-situ temperature programed decomposition characterization,enhancement effect was thought to be derived from acceleration of surface intermediate's formation and decomposition.In the study of RWGS reaction promoted by gliding arc plasma only,higher CO₂ conversion and lower energy cost than those by DBD were achieved.Influences of specific energy input?SEI?,molar ratio of H2/CO₂?R?and total gas flow rate?Ft?on RWGS reaction performance were investigated.Modification of reaction conditions has a certain effect on promoting RWGS reaction,but the effect is very limited.DBD and gliding arc plasma applied into RWGS could achieve CO₂ conversion at 25% and 59%,which means still low in conversion.RWGS reaction is ineffective for CO₂ reduction in conversion.As can be seen from the thermodynamic equilibrium calculation,DRM reaction at the temperature greater than 600 oC is more thermodynamically favorable than RWGS reaction.In the study of gliding arc plasma-assisted DRM reaction,influences of SEI,R for CH₄/CO₂ and Ft were firstly investigated in one-stage reactor for DRM reaction by gliding arc plasma only.Due to carbon deposition under high CH₄ concentration,one-stage reactor couldn't ensure the stability of reaction,which could lead to low CO₂ conversion?only 33%?and low H2 selectivity?66%?.Therefore,study of two-stage gliding arc plasma catalytic DRM reaction was carried out to achieve higher CO₂ conversion and better selectivity.With increasing of temperature and decreasing of gas hourly space velocity?GHSV?,conversion and selectivity increase a lot.Under the conditions of 850 oC,CH₄/CO₂=1,GHSV=3185 h-1,SEI=85 kJ/mol,conversion of CO₂ and CH₄ exceeds 90%,selectivity of product approaches to 100%.In addition,energy cost of syngas is only 1.9 kWh/Nm3.Compared to reported research?CO₂ conversion is 70%,H2 selectivity is less than 70%,syngas energy cost is higher than 4 kWh/Nm3?,DRM reaction was greatly promoted by two-stage gliding arc plasma catalytic method.