Metal-Support Interactions Of Iridium Catalysts And Application In The Chemoselective Hydrogenation Of α,β-Unsaturated Aldehydes

α,β-unsaturated alcohols are important intermediates in the production of perfumes, pharmaceuticals and fine chemicals. The unsaturated alcohols are commercially achieved by using Na BH₄ or Al Li H4 as reductant, but this proeess involves a lot of pollutants. Heterogeneous catalysis via direct hydrogenation of α,β-unsaturated aldehydes are able to reduce the conjugated C=O double bond in the presence of molecular H₂. This process provides a clean and economic approach to produce α,β-unsaturated alcohols. However, the the selective hydrogenation to-unsaturated alcohols is of considerable challenge, as it is thermodynamically favored to produce saturated aldehyde. Therefore, development of the alternative green processes for the synthesis of α,β-unsaturated alcohols has an important economic benefit and academic value.It have been documented that lots of metal-based catalyst is prone to hydrogenate C=C bond instead of C=O. In recent years, Metal-support interactions（MSI） play essential roles in the catalytic applications of supported nanocatalysts, which affect the size, morphology and valence state of active species via mass transport and interfacial charge redistribution. The combined effect of above factors would facilitate the achievement of high catalytic conversion and selectivity. In this dissertation, the Ir catalysts have been investigated systematically for the hydrogenation of α,β-unsaturated aldehydes. The influence of the MSI between Ir and support of Mo₂ C and H-Mo O_x were studied, focusing on the structure, electronic properties, the size of active species in experimental and theoritical investigations.The theoretical calculations show that the surface on negatively-charged Ir（Irδ-） was in favor of C=O hydrogenation. The hydrogenation reaction paths of crotonaldehyde（CRAL） on neutral Ir0（111） and negative Ir δ-（111） were calculated by density functional theory（DFT）. The results showed that the energy barrier of +12 hydrogenation path was significantly decreased on Ir δ-（111）, which benefited the hydrogenation of C=O and the formation of unsaturated alcohols. Obviou sly, improving the electron density of Ir catalytic center is the key to optimize the selectivity of C=O hydrogenation, which can be achieved through MSI.We develop Ir/Mo₂ C catalyst for crotonaldehyde hydrogenation with the high selectivity of crotyl alcohol（CROL）. Mo₂ C possesses the similar electronic properties with noble metalsstrong, presenting the obvious MSI with Ir. Owing to the lower work function of Mo₂C（5.00 e V） than that of Ir（5.22 e V）, the transfer of electrons through the interface was ptromoted. The formation of Irδ- on Mo₂ C favored the hydrogenation of C=O and the formation of CROL. At the reaction time of 150 min, when the maximum yield of CROL is achieved, 3.7%Ir/Mo₂ C shows CROL selectivity as high as 80% with an almost complete CRAL conversion. Our Ir/Mo₂ C can be considered in a sense as a universal catalyst for the selective hydrogenation of α,β-unsaturated aldehydes, and show the satisfied cycleability. The strong MSI are also observed in the Mo₂ C supported Pt and Au, confirming the MSI be feasible to change the electronic properties of the metal surface and thus improve the selective hydrogenation efficiency.Ir/H-Mo O_x catalyst was prepared by H₂ spill-over for the selective hydrogenation of cinnamaldehyde（CAL） to cinnamalcohol（COL）. Due to the rich d orbitals near the Fermi level, H-Mo O_x is able to show interactions with the Ir to form Irδ-. An increasing electronic density around Ir will enhance the repulsive force with C=C, and also promote the electron feedback to π* in polar C=O. At the reaction time of 120 min, when the maximum yield of COL is achieved, Ir/H-Mo O_x shows a COL selectivity as high as 93% with an almost complete CAL conversion, and show the satisfied cycleability.We have prepared Mo₂C/CNT catalysts for cinnamaldehyde hydrogenation. Through characterization techniques, Mo₂C/CNT is comparable to the traditional load metal catalyst, showing the potential as a promising substitute for high-cost noble metals.This work proved MSI in loaded iridium on different supports（Mo₂C and H-Mo O_x）, in which Irδ- active species resulting from electron transfer on interfaces contributes to the selective route towards unsaturated alcohol. It opens up new opportunities for the design of efficient and selective catalysts through interface engineering.