Preparation Of Gd-modified ZrO₂ Catalysts For Catalyzing CO Hydrogenation To Olefins

Light olefins are utilized widely in industrial manufacturing as vital raw materials for basic chemicals.The byproducts of petroleum cracking are the main focus of the conventional production method.Fischer-Tropsch synthesis(FTS)and the methanol to olefin methods are the two main reaction pathways that are used in the direct synthesis of light olefins in CO hydrogenation,which has become a significant non-petroleum approach in recent years.Due to the complicated CO hydrogenation reaction pathway,tendency to secondary reactions,and restrictions of the Anderson-Schulz-Flory(ASF)distribution,it is challenging to increase the selectivity of light olefins via FTS.The C-O activation and C-C coupling are controlled at various sites in metal oxide-molecular sieve(OX-ZEO)catalysts employed in methanol to olefin pathway,leading to high selectivity to light olefins.However,the CO hydrogenation activity is low and CO2 selectivity is high.The design of new catalysts is crucial.ZrO2 catalyst is widely used in CO hydrogenation to produce light olefins and isomerization synthesis due to its unique physicochemical properties such as acid-base sites,oxygen vacancies,and redox properties.Especially,its catalytic performance for CO hydrogenation can selectively produce isobutylene.However,traditional water solvent prepared ZrO2catalyst exhibits lower catalytic activity and poor reproducibility in CO hydrogenation.Based on the above issues,this study designed and prepared monoclinic ZrO2 and GdxZryOz catalysts through solvent modification and additive modification.These catalysts were used for CO hydrogenation to olefins,which significantly improved CO hydrogenation activity and light olefin selectivity.The surface properties and phase structure of the catalysts were systematically characterized by XRD,BET,TEM,NH3-TPD,CO2-TPD,XPS,and ESR methods.The catalyst activity and product distribution were extensively studied.The main progresses were as follows:(1)ZrO2 catalysts with different phases were prepared with solvothermal method using methanol,ethanol,ethylene glycol,and water as solvents.The performance of ZrO2 catalysts prepared with different solvents for CO hydrogenation to olefins was studied.The results showed that ZrO2 prepared in different solvents had significant effects on CO hydrogenation activity and product selectivity.The activity of CH3OH-ZrO2 and H2O-ZrO2 is relatively low,maintaining around 10%;The catalytic activity of C2H5OH-ZrO2 and(CH2OH)2-ZrO2 catalysts was significantly improved,and the CO conversion rate increased from the initial 5%to 23%;In the product distribution,C2=-C4= can reach 76.8%,methane selectivity is 9.0%,and the O/P value reaches 10.9 on C2H5OH-ZrO2 catalyst.BET characterization results showed that C2H5OH-ZrO2 catalyst had the largest specific surface area and pore size,which were 59.030 m2/g and 22.132 nm,respectively.NH3-TPD and CO2-TPD showed the largest acid-base sites,which reached 1010 μmol/g and 650 μmol/g,respectively.The number of oxygen vacancies in XPS characterization accounted for 23.2%,and the number of oxygen vacancies was relatively large.The characterization results indicate that the C2H5OH-ZrO2 catalyst promoting CO adsorption,significantly improving CO conversion rate and light olefin selectivity.The use of alcohol solvents has good reproducibility in CO hydrogenation.(2)On the basis of C2H5OH-ZrO2,Gd agent was doped for modification.Impregnation method was used to evaluate the process of GdxZryO2 catalyst with different loads.The distribution law of CO hydrogenation products of GdxZryOz catalyst with different loads was compared and studied.NH3-TPD and CO2-TPD showed that the acid site decreased and the basic site remained unchanged,the base/acid increased,So the selectivity of isomerization reaction to isobutene was improved.XPS showed that the oxygen vacancy number of Gd.ZryOz catalyst modified by Gd increased to about 42%,and the oxygen defect of GdiZr100Oz catalyst was the most by ESR.The results showed that the CO conversion rate of GdiZr100O2 and GdiZr200Oz catalysts increased from 14%to 23%,and the low carbon olefin selectivity reached 80.3%.The content of isobutene in C4=was 96.3%.The addition of rare earth element Gd increased the oxygen vacancy of the catalyst,and activated CO to increase the conversion rate of the reaction,thus improving the selectivity of isobutene.