The Interfacial Effect On The Selective Hydrogenation Of Crotonaldehyde Over Ir-Mo Catalysts

?,?-unsaturated alcohols are important intermediates in the synthesis of fine chemicals such as perfumery and medicine.The selective hydrogenation of?,?-unsaturated aldehydes to?,?-unsaturated alcohols is an atomic economic reaction,and thus it has received much attention from the industry.However,the hydrogenation ability of C=C bond is thermodynamically and kinetically easier than that of the C=O bond,which results in low selectivity to desired unsaturated alcohols.Therefore,the development of highly selective catalyst has been the goal of the current research.Many researches revealed that the addition of promoters in noble metal catalysts could remarkabley improve the selectivity to the unsaturated alcohol,which is attributed to metal-promoter interface generated via thier interaction.However,the lack of deep understanding of the nature of such interface results in difficulty in the design of highly efficient catalysts.Therefore,in this thesis,we have conducted selective hydrogenation over Ir-Mo catalysts to investigate the effect of Ir-Mo interface on the catalytic behaviors of the catalysts.The main contents of this research are as follows:1.The effects of MoOx decoration on the selective hydrogenation of crotonaldehyde over MoOx-promoted Ir/TUD-1 catalysts.A series of MoO_x-promoted Ir/TUD-1 catalysts were tested for liquid phase selective hydrogenation of crotonaldehyde.The promoted catalysts showed higher activity and selectivity than the unpromoted one,with the best performance being obtained on an Ir-0.1Mo/TUD-1?with a crotyl alcohol yield of 86.7%and a turnover number of 325.7 h-1?.The large pore sizes of the TUD-1 is beneficial to the diffusion of the reactant and thus the supported catalyst is more active than that supported on the commercial SiO2.The characterization results revealed decoration of Ir particles by MoOx,which altered the morphologies and electronic properties of the catalysts.Such decoration resulted in the generation of Ir-MoO_x interfacial sites,which altered the adsorption and activation of crotonaldehyde molecule and brought up enhanced activity and selectivity.However,at high MoOx content,the Ir surface was fully covered by MoOx,which results in strong adsorption of crotonaldehyde and fewer surface Ir atoms for H₂ dissociation and thus declined activity.2.The effect of impregnation sequence on the selective hydrogenation performance of crotonaldehyde in Ir/Mo/BN system.The effect of impregnation sequence on the catalyst behaviors of the Ir/Mo/BN catalysts was investigated.In the gas-phase hydrogenation reaction of crotonaldehyde,the addition of MoO_x could significantly improve the reactivity,while the impregnation sequence exerted remarkable influences.The impregnation of Ir then MoOx results in obvious catalyst deactivation?with a decline of crotonaldehyde conversion from 100 to 80%,80 ^oC,3 h?,while the impregnation of MoO_x then Ir results in stable activity?maintained at about 98%?.Beside,the content of MoO_x in the catalyst has influence on the performance,and the best result was obtianed on the3Ir-0.5Mo/BN catalyst.A crontonaldehyde conversion of 87%and a crotyl alcohol selectvity of 85%were obtained on this catalyst for liquid phase hydrogenation.The characterizations revealed that the improved performane might be related to the modification of the electronic properties of Ir and Mo species by their interaction.