Study On Preparation And Higher Alcohol Synthesis Performance Over Supported Co-Ni Bi-Metallic Catalysts

Higher alcohols obtained by the syngas conversion can be used as energy additives or directly as energy sources,and also can be used as raw materials for many chemical products.However,the process has not yet achieved industrialization,mainly because the selectivity and stability of the catalyst can’t meet the requirements of industrialization.In this thesis,a series of Co-Ni alloy nanoparticles（NPs）catalysts were prepared by using perovskite,hydrotalcite and spinel as precursors.The structure evolution of the catalyst and the relationship between the structure and performance of the catalyst were investigated,and the catalytic mechanism for higher alcohols synthesis over the Co-Ni alloy catalysts was studied,and the stability and regenerability of the catalysts have also been investigated to a certain extent.Using La Co_1-xNi_xO₃/Si O₂perovskite as the precursor,the La₂O₃-Si O₂supported Co-Ni alloy NPs catalyst was obtained after reduction.The formation of Co-Ni alloy improves the ability to activate H₂and CO and adjusts the amount of the dissociatively and associatively adsorbed CO,and the mutual dilution of nickel and cobalt in Ni-Co alloy NPs effectively reduces the isolated Co or Ni-clusters,thus promoting the formation of higher alcohols.During the reaction process,the surface enrichment of Co inhibited the loss of Ni element.In addition,a small amount of poorly alloyed Co-clusters would be covered by the generated coke with the reaction going on,improving the selectivity of alcohols.Using Co_10-xNi_xMg₇₇Al_43.5hydrotalcite as the precursor,the Mg-Al-O supported and confined Co^δ+-Co₂C decorated-Co-Ni alloy NPs catalyst was fabricated via an in-situ reduction and topochemical carbonization strategy.The formation of Co-Ni alloy promotes the electron-transfer from Co to Ni.During the reaction process,some Co would migrate onto the surface of the metallic NPs and be partially carbonized into Co₂C,further adjusting the valence state of Co,and a Ni-Co alloy@Co-Co₂C core-shell structure with Ni-Co alloy as the core and Co-Co₂C as the shell was formed.The Co^δ+-Co₂C sites in the metallic NPs adjust the ratio of the dissociatively and associatively adsorbed CO,thus the catalyst exhibits excellent selectivity towards higher alcohols,and a CO conversion rate of 12.8%,a total alcohol selectivity of43.0%with 68.6 wt.%of higher alcohol in the total alcohol can be achieved over the optimal catalyst.Using Co_1-xNi_xAl₂O₄/Si O₂spinel as the precursor,the Si O₂supported Co-Ni alloy NPs confined by Al₂O₃catalyst with good stability and regenerability was obtained after reduction.By adjusting the ratio of Co/Ni,the both amount of dissociatively adsorbed CO on the metallic Co/Ni and associatively adsorbed CO on Co^δ+-Co₂C have been effectively adjusted,and the better coordination of the two forms of adsorbed CO species is conducive to the production of higher alcohols.Co-Ni alloy NPs are firmly confined in the small area of Al₂O₃,thus the catalyst maintained stable in the 400-hour stability test.The spinel structure can be destroyed and reconstructed in multiple reduction-oxidation cycles,providing a basis for the regeneration of the catalyst,thus the catalyst showed excellent regenerability.In addition,based on the comparative analysis of the above three parts of works,it is found that the degree of Co surface enrichment and the strength of associatively and dissociatively adsorbed CO significantly affect the selectivity towards alcohols,which appropriate Co surface enrichment and close strength of associatively and dissociatively adsorbed CO are beneficial to the formation of alcohols.And the size of the metal NPs has a greater impact on the carbon deposition of the catalyst.