Study On The Performance Of ZrO₂ Supported Cobalt-molybdenum Catalyst For 4-Methylphenol Hydroconversion

Coal tar contains a large number of phenolic compounds.Alkylphenols occupies a large proportion of the phenolic compounds in coal tar.The conversion of alkylphenols into high-value aromatic hydrocarbons through catalytic hydrogenation was one of the important directions for the high-value utilization of coal tar.There were many catalysts for the hydroconversion of phenol,the active components mainly include Co,Mo,Pt,Ru,Pd,Ru,Ni and other elements,and the carrier components mainly include Si O₂,Ti O₂,Ce O₂,Al₂O₃,ZrO₂,etc.Our previous studies had shown that the Co Mo S/ZrO₂ catalyst has high activity for 4-methylphenol hydrodeoxygenation（HDO）.The carrier component in the HDO reaction of phenolic compounds was mainly responsible for storing and transferring oxygen,and the hydrogenation reaction of phenols will generate water,so the catalyst was required to have a certain degree of water resistance.ZrO₂ has oxygen-philic sites that could store and transfer oxygen,and it has a certain degree of water resistance.Therefore,the HDO reaction of phenolic compounds could be promoted.However,the research on the effect of ZrO₂ properties on the catalyst performance was not in-depth.In this paper,a series of Co Mo S/ZrO₂ catalysts were prepared,by changed the preparation method of ZrO₂ and adjusted the preparation conditions of ZrO₂.Futhermore,the effect of the properties of ZrO₂ on the performance of the catalysts for the HDO of 4-methylphenol was investigated.（1）The preparation method has a great influence on the performance of ZrO₂,and the catalyst performance of different preparation methods for the HDO of 4-methylphenol was quite different.The catalyst prepared by UIO-66 pyrolysis method and NH₄F-assisted hydrothermal method has uniform structure,regular morphology,and good performance.The conversion of 4-methylphenol was close to 100%,and the selectivity of toluene which was the product retaintng the aromatic ring was 81.89%and 92.38%,respectively.However,the catalysts prepared by sol-gel method,precipitation method and hydrothermal method presented more agglomeration,uneven structure and poor performance.（2）The effect of different pyrolysis temperature and pyrolysis time of UIO-66 on the HDO performance of catalyst was investigated.The ZrO₂ crystal phases of UIO-66 products at different pyrolysis temperatures were different.When the pyrolysis temperature was lower,it was a tetragonal phase,and when the pyrolysis temperature was higher,it was a mixed crystal phase of tetragonal and monoclinic phases.With the increase of pyrolysis temperature,the structure of UIO-66 changed from incomplete pyrolysis to collapse and aggregation.When the pyrolysis time of UIO-66 was short,the structure pyrolysis is incomplete and the catalyst performance was poor.When the pyrolysis time of UIO-66 was too long,the structure started to accumulate and the performance of the catalyst weakened.When the pyrolysis temperature of UIO-66 was 500℃and the pyrolysis time was 4h,the prepared catalyst had higher performance,The conversion of 4-methylphenol was 99.89%,and the selectivity of toluene was 81.89%.（3）The influence of F-molar concentration on the performance of the catalyst in the NH₄F-assisted hydrothermal method was investigated.The F^-molar concentration could lead to changes in the morphology of the catalyst.Changing the F^-mole concentration had a certain impact on the HDO performance of the catalyst.When the molar ratio of F^-to Zr⁴⁺was 1.3,the prepared catalyst had the best performance.The conversion of 4-methylphenol was 99.73%,and the selectivity of toluene was 92.38%.（4）The HDO activity of the catalyst was related to the structure and properties of the carrier.The catalyst with uniform structure,regular morphology,and smaller agglomeration had stronger performance.The preparation method and preparation conditions had different effects on the HDO performance of the catalyst,and the catalyst prepared under suitable preparation conditions had better performance.