DBD Plasma Combined With Hydrotalcite-like Catalysts For Reduction Of CO₂

With the increasingly serious global greenhouse effect,the rational utilization of greenhouse gases-carbon dioxide and methane has become an urgent task for human.Therefore,developing and researching the technology of less energy consumption for carbon dioxide reduction is the key now.The high specific surface area and high alkalinity of hydrotalcite-like?LDHs?catalysts,and high energy electrons produced by DBD plasma discharge under mild reaction conditions,which were the important reasons for promoting the conversion of raw gas with stable structure.Catalysts with good catalytic activity at low temperature were prepared,and TiO₂was also added into catalysts,and dielectric barrier discharge?DBD?combined with the catalysts catalytic for reduction of CO₂ with CH₄.First,Ni-Mg-Al-Ce catalysts were prepared by co-precipitation method for the CH₄-CO₂ reforming reaction.The optimum proportion of component and the optimum calcination temperature of the catalysts were determined,and the catalyst performance were studied by fixed bed reactor at 500-750?.The catalysts were characterized by XRD,CO₂-TPD,XPS,BET.In addition,Ni-Mg-Al-Ce/TiO₂ catalysts were also prepared besides Ni-Mg-Al-Ce catalysts in the plasma-catalytic synergistic system.The influence of Reactor parameters?reactor discharge gap and materials height?and preparation condition of catalysts?the radio and components of catalysts,calcination temperature,TiO₂contents?were investigated.When the molar ratio of M²⁺/M³⁺was 3,Al/Ce was 9,Mg/Ni was 6,and 450?calcination temperature,catalysts revealed better low temperature catalytic activity.Under the conditions of 650?and 200 mL·g^-1·min^-1of space velocity,the conversions of CH₄ and CO₂ were 91.7%and 85.3%,respectively,and the selectivity of CO and H₂were 94.6%and 96.2%,respectively.When the reaction temperature was 750?,conversion of methane and carbon dioxide were up to 98.06%and 91.94%,respectively.,and selectivity for both carbon monoxide and hydrogen exceeds 98%.There were very few by-products in this condition.The dielectric barrier discharge plasma was introduced into the catalytic system and combined with catalysts were used for the reduction of CO₂ with CH₄.When the discharge voltage kept unanimous,the optimum discharge gap and the best height of the filling medium were 2mm and 8cm,respectively.The conversion rates of CO₂ and CH₄ increased by 8%and 10%,respectively,compared to that of empty discharge with a discharge gap of 2mm.The optimal Mg/Ni mole ratio was 6 and the optimum calcination temperature was 450?.The conversion rate of feedstock gas was greatly affected by the content of Ce.The conversion rates of CO₂ and CH₄ were respectively22.5%and 36.1%when Al/Ce was 0.035/0.015.When the mass fraction of TiO₂ was33.3%,CO₂ and CH₄ were 6.8%and 5.1%higher than that of Ni-Mg-Al-Ce catalyst at the same ratio.Combined with characterization results and experimental data,it was found that the alkali strength of the catalyst and the interaction force of metal elements were main influence for the performance of the catalyst in thermal catalytic reactions.Catalysts revealed better performance,strong alkaline living-sites and interaction force when Mg/Ni was 6 and Al/Ce was 9.Meanwhile,the surface oxygen vacancies were also formed,which were beneficial for elimination of carbon deposition and improvement of the catalytic performance.DBD plasma and Ni-Mg-Al-Ce/TiO₂ catalysts showed good synergistic effect in the reduction of CO₂.The specific surface area of catalysts and filling materials were main influence for the conversion of raw gas,which would change the discharge state of plasma and the residence time of raw gas in the reactor.