Preparation And Properties Of Molybdenum Oxide Based Catalyst For Synthesis Of Higher Alcohol From Syngas

China is rich in coal resources,and the implementation of"coal instead of oil"strategy can replace and supplement oil and gas resources,which is also related to China’s economic and energy security and stability.The synthesis of higher alcohols from syngas is an important technical method for the production of clean fuels,petroleum additives and basic chemical raw materials by non-oil pathway,and it is also an important part of carbon-chemical research.Among them,MoO_x-based catalysts show high selectivity for total and higher alcohols(C₂₊alcohols)under mild reaction conditions（240℃,5 MPa）and have good prospects for future industrial applications.The design and preparation of catalysts with high activity and selectivity at low temperatures is the focus of research on the reaction of higher alcohols in syngas.MoO_x-based catalysts for higher alcohol synthesis are usually modified with alkali and transition metals as additives,which help to improve the selectivity of higher alcohols.In this paper,the effect of different alkali additives as well as the amount and the way of introduction of additives on the performance of Ni-Mo-based catalysts for the reaction is investigated.The relationship between the physical structure,chemical properties and catalytic performance of the synthesized catalysts was also explored.The main contents and conclusions are as follows:（1）The effects of different alkali promoters（K and Na）on the performance of Ni-Mo-based catalysts for the synthesis of higher alcohols from syngas were investigated.Ni-Mo/Na SiZr,Ni-Mo/KSiZr and Ni-Mo/SiZr catalysts were prepared by ammonia evaporation combined with physical grinding and mixing,and applied to the synthesis of higher alcohols from syngas.By comparing and analyzing the catalytic performance of the synthesized catalysts,it was found that the Ni-Mo/KSiZr catalyst exhibited higher total alcohol and lower hydrocarbon selectivity under the reaction conditions of 250℃ and 5 MPa.The selectivity of total alcohol reached 65.6%,the selectivity of C₂₊alcohol was 72%,and the spatiotemporal yield of total alcohol was 85 mg·g^-1·h^-1.Combined with the CO₂-TPD characterization results and evaluation data of the catalyst,it can be concluded that Ni-Mo/KSiZr with medium and strong alkaline is conducive to improving the selectivity of total alcohols and C₂₊alcohols,and inhibiting the production of methanol and hydrocarbons.（2）The effect of different alkali metal additives on the performance of Ni-Mo-based catalysts in the synthesis of syngas to higher alcohols was investigated.The precursor of Ni-Mo-based catalysts was synthesized by hydrothermal method,and then a series of K-Ni-Mo-based catalysts with close contact between Ni and K₂MoO₄ were obtained by in-situ treatment with different contents of K.The synthesized catalysts were characterized by XRD,N₂ physical adsorption and desorption,H₂-TPR,HR-TEM,SEM-EDS,XPS,H₂-TPD,CO-TPD and CO₂-TPD.The results showed that the introduction of K into the Ni-Mo-based catalyst could produce K₂MoO₄ phase.At the same time,with the decrease of Ni MoO₄ phase content,the non-dissociative adsorption and activation ability of CO on the K-Ni-Mo-based catalyst was significantly improved,thereby promoting the formation of alcohols.Increasing the surface alkalinity of the catalyst can increase the number of basic hydroxyl groups on the catalyst and effectively reduce the generation of hydrocarbon compounds.Among them,K_0.4-Ni-Mo catalyst has the best catalytic performance.Under the reaction conditions of 5MPa,240 ^oC and 5000 h^-1,the CO conversion is 19.6%,the total alcohol selectivity is 57.8%,and the C₂₊alcohol selectivity is 66.5%,and the spatiotemporal yield of total alcohol was 71mg·g^-1·h^-1.（3）The effects of different introduction methods of promoter K on the performance of Ni-Mo-based catalysts were studied.D-K-Ni-Mo,G-K-Ni-Mo and I-K-Ni-Mo catalysts were prepared by direct,impregnation and grinding.Through CO₂-TPD characterization combined with catalytic performance,it can be seen that the introduction of additive K by grinding method can make the catalyst have appropriate medium/strong basic position,thus promoting the formation of alcohol products and inhibiting the selectivity of hydrocarbons.