Vapor Phase Selective Hydrogenation Of Crotonaldehyde Over Supported Ir Catalysts

α,β-unsaturated alcohols are widely used in fine chemicals such as coatings,pharmaceuticals and plastics.Catalytic hydrogenation ofα,β-unsaturated aldehydes is an atomically economic reaction for the syntheses of unsaturated alcohols.However,the conjugated C=C bond in the aldehyde molecule is more easily to be activated and hydrogenated,which makes the selectively hydrogenation of C=O bond very challenging.Various investigations have revealed that metal-support or metal-additive interface in the catalyst can significantly alter the adsorption and activation process of the aldehyde,by which the catalytic activity and selectivity of the catalyst could be effectively tuned.In this work,a series of FeO_x-promoted Ir catalysts were prepared and tested for gas phase selective hydrogenation of crotonaldehyde.The roles of Ir-FeO_x interface in the reaction has been thoroughly investigated based on detailed characterization results and reactivity evaluation.By adjusting the properties of such interfae,the effects of the morphologies and electronic structure of the interface on the catalytic behaviors were discussed,and the findings provide important insights for the understanding of“interface-induced adsorption/activation process”and the establishment of a reliable structure-performance relationship of the catalyst system.The main contents of this thesis are as follows:1.Selective hydrogenation of crotonaldehyde over Ir/FeO_x-SiO₂ catalyst.A series of FeO_x-SiO₂ supports were prepared by a sol-gel method and Ir/FeO_x-SiO₂catalysts were prepared by a deposition precipitation method.The catalysts were tested for gas phase selective hydrogenation of crotonaldehyde.It is found that the catalytic behaviors are gonverned by the catalyst structure and the properties of the Ir-FeOx interface.For example,7Ir/0.5Fe-SiO₂ catalyst increases the activity by 35%（from 30%to 65%）and remains the selectivity of 89%under conditions of pH is 8,aging temperature and reaction temperature are 60 ^oC and 80 ^oC respectively.The adjustment of experimental parameters such as pH,the content of additives and precipitation temperature exerts remarkable influences on the morphologies of the Ir species,the surface acidity of the catalyst and Ir-FeO_x interaction,which in turn affects the observed catalytic behaviors.2.Kinetic study of selective hydrogenation of crotonaldehyde over Fe-promoted Ir/BN catalysts.The Ir/BN and Ir-Fe/BN catalysts were prepared by an impregnation method and tested for gas phase selective hydrogenation of crotonaldehyde.It is found that the addition of FeO_x greatly improves the catalytic performance,and the best results is obtained on a catalyst with the Fe content was 0.05 wt.%,with a crotonaldehyde conversion of 55.6%and a crotyl alcohol selectivity of 84.4%at reaction temperature of 80 ^oC.In addition,the addition of FeO_x brings the formation of Ir-FeO_x interface and the interaction results in the charge transfer from Ir species to Fe species,which alther the electronic properties of the catalyst.The roles of the Ir-FeO_x interface in the adsorption/activation of crotonaldehyde were further clarified by detailed kinetic investigations on the 3Ir/BN and 3Ir-0.05Fe/BN catalysts.It is found that the addition of FeO_x enhances the adsorption of crotonaldehyde while inhibits the adsorption of H₂;the apparent activation energy of crotyl alcohol formation is significantly decreased,which implies the generation of new active sites and thus new reaction pathway.Moreover,the addition of FeO_x increases the rate constant of crotyl alcohol formation by a factor of 10,indicating that the activity of the Ir-FeO_x active site is much higher than that of the Ir⁰-Ir^δ+active site,which explains the enhancement of the activity over 3Ir-0.05Fe/BN catalyst.Based on the kinetic results,the elementary steps of the catalytic reactionon are derived over 3Ir/BN and 3Ir-0.05Fe/BN catalysts.