Synthesis Of Porous CoCe Composite Catalyst And Study For CO₂ Hydrogenation Technology

With the rapid increasing of world population,declining of forest area and using great mount of fossil flues,it caused CO₂ emission increasing by years.Excessive CO₂content in the air will not only endanger people’s health and life,but also lead to severe environmental problems,such as intensified greenhouse effect,global warming and frequent occurrence of extreme weather.Therefore,it should be paid much attention on comprehensive-utilization of CO₂,realizing the purpose that reducing the CO₂ contents and changing inorganic carbon into organic carbon while CO₂ converts to added-value industrial raw materials.Traditional physical and simple chemical utilization have low efficiency（<1.0%）but high energy consumption.Therefore,the CO₂ hydrogenation technology has taken more attention from researchers.And the catalyst,as the core of the CO₂ hydrogenation technology,catches researchers’fancy.In this paper,it was investigated that the relationship between physical-chemical properties and CO₂ hydrogenation performance of prepared porous CoCe catalyst.X-ray diffraction（XRD）,N₂ adsorption-desorption（BET）,Inductively coupled plasma（ICP）,Scanning electron microscope（SEM）,Transmission electron microscope（TEM）,In-situ X-ray photoelectron spectroscope（In-situ XPS）,H₂-temperature programmed reduction（H₂-TPR）,H₂-temperature programmed desorption（H₂-TPD）and CO₂-temperature programmed desorption（CO₂-TPD）has been used to study the physical-chemical properties of porous CoCe catalysts.Meanwhile,the structure,Co loading and Zr addition on the activity and selectivity of CO₂ hydrogenation were investigated.The main conclusions were drawn as follows:1.CoCe-CA,CoCe-CP,CoCe-HY and CoCe-HT catalysts have different phase and morphology structure which prepared by complex method,co-precipitation method,hydrothermal method and hard-template method,respectively.The CO₂conversion of studied catalysts follows the order:CoCe-HT>CoCe-CP>CoCe-CA>CoCe-HY.Although CoCe-CA catalyst has a large specific surface area,its stability was poor due to its fragile pore structure which was easy to collapse.CoCe-HY and CoCe-CP catalysts,with high crystallinity and compact structure,are not conducive to the exposure of active sites and exhibit poor H₂ molecule adsorption-activation ability,so the catalytic activity of CoCe-HY and CoCe-CP catalysts was poor.CoCe-HT precursors have high reducibility with large specific surface area and ordered mesoporous structure,and then it can form abundant Co⁰species with high dispersed-degree.As the interaction between Co and Ce species was strong,it can inhibit species gathered and sintering on catalyst surface,forming Co-O-Ce solid solution and oxygen vacancy,which conducive to the adsorption-activation of H₂ and CO₂ molecules.CO₂ hydrogenation activity of CoCe-HT catalyst was 53.9%.2.Using mesoporous CeO₂ as support prepared by hard template,mesoporous Co/CeO_2-δcatalysts were prepared by impregnation method.Relative toCo₃O₄ and CeO_2-δsamples,Co₃O₄/CeO_2-δprecursor has a higher reducibility.It is conducive toCo species dissoluting intoCeO₂ lattice and formating Co-Ce-O solid solution as the interaction between Co and CeO_2-δ.And the large specific surface area and ordered mesoporous structure are beneficial to inhibiting the aggregation and sintering of Co species,so that Co species are highly dispersed on the catalyst surface,which can form abundant active centers.With the increasing Co loading,interaction between Co and CeO₂,the number of Co⁰ species and Co-Ce-O solid solution was increased,hence the number of active centers and the activation ability of CO₂ and H₂ were enhanced,resulting in the improvement of catalyst catalytic activity.At atmospheric pressure and400℃,the CO₂ conversion and CH₄ selectivity of the catalyst with 15% Co loading are 59.7% and 93.8%,and maintain well stability in nine reaction cycles.3.The Ce_xZr_1-xO₂ support,with different Ce/Zr molar ratios,had large specific surface area and ordered mesoporous structure which was prepared by hard-template method.Evidently,the ordered mesoporous structure of support was unbroken after loading Co species.With the adding Zr species,the specific surface area and pore volume of Co/Ca_xZr_1-xO_2-δcatalyst gradually increased,while the order of mesoporous structure gradually decreased.The cubic phase converted to tetragonal phase of catalysts,too.After introducting appropriate Zr species,metal-support interaction,formation of Co-Ce-O-Zr solid solution,reductability of Co₃O₄/Co_xZr_1-xO₂ precursor,Co species dispersed degree and oxygen vacancy of the Co/Co_xZr_1-xO_2-δcatalysts were significantly improved,which is beneficial to formating active sites,thus promoting CO₂ hydrogenation reaction.CoCe_0.99Zr_0.01 catalyst shows a well CO₂ hydrogenation activity,and it exhibits excellent stability during 850 min of CO₂ hydrogenation reaction.