Study On Metal Organic Framework Materials For CO₂ Methanation

The burning of fossil fuels has brought unprecedented development to human society but correspondingly results in excessive emissions of carbon dioxide.CO₂methanation,as one of the efficient methods to convert CO₂,can not only achieve the recycle of CO₂ but also contribute to produce CH₄.In this work,the nickel and cobalt based catalysts derived from MOFs are prepared and their CO₂ methanation performances are investigated.Nickel-based catalysts are prepared by directly carbonizing or loading nickel salts with MOFs as precursor and support respectively.The Ni-MOF-74 metal organic framework material containing metal Ni in the skeleton is directly carbonized as a precursor to investigate the carbonization temperature.It is found that the Ni/C catalyst carbonized at 450 ^oC presents the best activity,while that carbonized at 600 ^oC shows decreased CH₄ selectivity and increased CO selectivity,indicating the reverse water-gas-shift reaction activity increases with temperature rises.However,the synthesis of supported Ni/ZIF catalyst by exploiting ZIF-67 or ZIF-8 as support and hydrazine hydrate as reducing agent is failed due to the weak interaction between Ni and the support.The ZIF-67 containing metal Co is successfully synthesized and used as the precursor to prepare Co-based catalyst.The effect of carbonization temperature on the catalyst performance is studied and the results indicate that the catalyst carbonized at500 ^oC shows the best activity.At this temperature,the effect of carbonization atmosphere is investigated and the results demenstrate that H₂ promotes the formation of carbon nanotubes and oxygen vacancies which consequently enhancs the thermal stability of the catalyst and the electron transfer between Co and carbon matrix.Among them,the catalyst carbonized in 5%H₂/Ar mixed gas has the highest graphite N content and CO₂conversion.The effects of reaction conditions including space velocity and whether or not through H₂ reduction are investigated.The results show that the influence of space velocity on catalyst activity is little,while the catalyst after further H₂ reduction is slightly more active than that without H₂ reduction.With the increase of reaction temperature,the effect further H₂ reduction becomes not obvious.The effect of dielectric barrier discharge plasma（DBD）on the Co/C catalyst is studied.The results show that compared with ZIF-67 without DBD treatment,the Co particle size after DBD treatment increases after carbonization and CO₂ conversion increases.Among them,the catalyst obtained by pre-treatment of ZIF-67 at 30W shows the highest catalytic activity.