The Investigation On Hydrogenation Characteristic Of Tetramethylcyclobutanedione Over Ruthenium-based Catalysts

Hydrogenation is an important organic chemical reactions,and the hydrogenation products of ketones are often used as chemical intermediates or active ingredients in industrial flavor.2,2,4,4-Tetramethyl-1,3-cyclobutanediol（TMCD）is an important intermediate for the production of various polyester materials with superior properties.At present,TMCD is mainly obtained by hydrogenation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione（TMCB）,the development of high-performance catalysts is one of the research priorities in this field..In this thesis,the hydrogenation catalysts of TMCB have been thoroughly studied.Usingγ-alumina as the carrier,the ruthenium as the main active metal,ruthenium-based monometallic catalysts and ruthenium-tin bimetallic catalysts were prepared by equal volume impregnation-chemical reduction method.The effects of catalyst preparation technology and reaction conditions on the conversion of TMCB and selectivity of TMCD were mainly discussed,and the mechanism of reaction and deactivation of the catalysts was further analyzed.The following results are obtained:（1）A series of ruthenium-based monometallic catalysts were synthesized,and the effects of Ru loading,reaction temperature,reaction time,pressure and solvent type on the hydrogenation activity of the catalyst were investigated.Under the optimal conditions,the conversion of raw material TMCB reached about 100%,the selectivity of TMCD reached 70.4%,and the cis-trans ratio was 1.03.Through the characterization and analysis of the catalyst,it was found that ruthenium on the catalyst existed in the form of Ru⁰,and then plays an important catalytic role in the hydrogenation of ketones.（2）Secondly,using the above-mentioned optimal catalyst as the basic catalysts,four different kinds of metal promoters were mixed into it,and different ruthenium-based bimetallic catalysts were synthesized.It was found that the ruthenium-tin bimetallic catalysts exhibited the best catalytic performance for the selective hydrogenation of TMCB.Then the influence of relevant conditions on the hydrogenation effect of the catalyst was investigated.Under the optimal operation condition,the conversion of ketone reached 100%,the selectivity of TMCD reached73.5%,and the cis-trans ratio was 1.11.The characterization results indicated that the interaction between tin element and the supported alumina possessed a certain influence on the activity of the catalyst.And tin existed in the form of oxide on the catalysts,which would increase the adsorption of the reaction substrate on the catalyst,and consequently improve the catalytic activity.The Ru⁰ was more uniformly dispersed onto the catalysts.It shows that the introduction of tin element could increase the rate of the hydrogenation to a certain extent,and improve the yield of the target product cis.（3）The service life of the bimetallic catalysts,the deactivation mechanism of the catalysts and the hydrogenation mechanism of TMCB on the catalysts were investigated.The results showed that the activity of the catalyst began to decline significantly after 12 cycles of reaction,which indicated the stable catalytic performance.The deactivation mechanism of the catalyst was explored by means of XRD,SEM,TG and XPS methods.It was found that the main reason for the deactivation of the catalyst was that Ru⁰ was oxidized to Ru^δ+during the reaction process,and the deactivation of the catalysts could be recovered by reduction again.For the hydrogenation process of TMCB,firstly,the hydrogen molecule is activated at the active site on the catalyst surface and hetero-cracked into H^δ+-H^δ-,and the reaction substrate is adsorbed onto the catalyst surface so that the carbonyl group of the substrate is activated,and the carbon-oxygen double bond polarization occurs,then it combines with the hetero-fission hydrogen species to form the intermediate 3-hydroxy-2,2,4,4-tetramethylcyclobutanone,which is then adsorbed on the catalyst surface again,and the second carbonyl group is activated and combined with the hetero-cleaving hydrogen species,a two-step hydrogenation completed.and the product desorbs from the catalyst surface to form the final product TMCD.