Study On Complete Liquid Phase-Pyrolysis CuZnAl Catalyst For CO Hydrogenation To Higher Alcohols On Fixed Bed Reactor

China has vast land and abundant resources,and its energy storage volume ranks first in the world.Due to the unique geographical conditions,coal is as the main energy consumption in China.With the rapid development of economic construction,our country's demand for primary energy is increasing.Converting coal into liquid fuel and basic chemical raw materials is one of the important measures to ensure China's economic development.It is also of great significance to China's future energy structure optimization and adjustment.The process of selective hydrogenation of carbon monoxide as a raw material for the preparation of higher alcohols has been one of the research hotspots since the oil crisis in the 1970s.The used catalysts mainly include noble metal Rh-based catalysts,F-T component elements or alkali-modified Cu-based catalysts and K-Mo-based catalysts.In our previous studies,it was unexpectedly found that the CuZnAl catalyst prepared by the complete liquid phase method without F-T elements or alkali metals had better synthesis ability of ethanol and higher alcohols in slurry bed reactor.Subsequent studies had demonstrated that complete liquid phase preparation techniques imparted some unique properties to the catalyst distinguishing from catalysts prepared by conventional methods.In order to further expand the application of complete liquid phase preparation technology,and to examine whether these unique properties can be reflected in other bed reactor types,we applied the complete liquid phase catalyst on the fixed bed after solid-liquid separation.It was found that the direct use of the catalyst has low activity because the surface of the catalyst obtained after solid-liquid separation had a carbon film covering the active site,but if the catalyst was calcinated in air to eliminate carbon,the performance of the catalyst was same with the conventional method catalyst.Based on the above facts,the active sites was exposed by pyrolysis of the catalyst precursor prepared by the complete liquid phase method in an inert atmosphere,and the activity of the catalyst on the fixed bed was significantly improved,and showed excellent stability.In this paper,the complete liquid phase catalyst was subjected to pyrolysis after solid-liquid separation to finally obtained the CuZnAl catalyst.The effects of pyrolysis temperature,pyrolysis time,addition and amount of different alkali additives on the performance of the catalyst for the synthesis of higher alcohols in a fixed bed reactor were investigated.The following conclusions were obtained by characterization of the catalyst by XRD,H₂-TPR,NH₃-TPD-MS,BET,TG-MS,XPS and the activity evaluation of the catalyst:1.The CuZnAl catalyst prepared by the complete liquid phase technique combined with the pyrolysis method could retain the special properties of the catalyst by the complete liquid phase technology.The catalyst has good stability and higher alcohol selectivity in the reaction of CO hydrogenation to higher alcohol,indicating that the complete liquid phase-pyrolysis method can be developed into a complete liquid phase technology to expand the preparation method of fixed bed catalyst.2.When the pyrolysis temperature was 800°C,the activity of the catalyst and the selectivity of C₂₊OH were both highest.The presence of a certain amount of reducible Cu species,stable pore structure,and suitable amount of weak acid sites in the catalyst facilitated the formation of higher alcohols.3.Excessive or too low pyrolysis temperatures were detrimental to the increase in catalyst activity and could also result in the formation of a large amount of by-products.When the pyrolysis temperature was low,the catalyst was not sufficiently pyrolyzed,and the carbon species on the surface were less decomposed,which blocked the mass transfer of the reactants and products;The higher the pyrolysis temperature,the more fully the carbon species decomposed,but the excessive temperature would destroy the stability of pore structure.4.The introduction of an inorganic alkali metal promoter can increase the selectivity of C₂₊OH,but was mainly not isobutanol,which was different from the catalyst prepared by the conventional methods.The organic base additive was polarized due to the presence of complexation and the change of the amount of acid,which as a promoting effect and an obstructive effect.5.The addition of alkali metal promoter can facilitate the dispersion of Cu.In addition,it also was able to promote the reduction of CuO to Cu and neutralize the acidity.The addition of Cs was advantageous for the formation of higher alcohols,and the optimum addition amount was 1.64 mol%.However,it inhibited the reduction of Cu and caused a decrease in catalyst activity.