Highly Dispersed Pt Catalysts Based On Layered Double Hydroxides For Selective Hydrogention/dehydrogention

Selective hydrogenation/dehydrogenation is one of the most important processes in petrochemical,coal chemical industry and biomass conversion and utilization.As the supported Pt catalysts have the excellent activity for hydro genati on/dehydrogenation,they are widely used in various hydrogenation/dehydrogenation processes,such as catalytic reforming,selective hydrogenation/dehydrogenation of hydrocarbons,selective hydrogenation/dehydrogenation or hydrogenation/deoxygenation of biomass platform molecules and et al.In the hydrogenation/dehydrogenation process,the side reactions,such as hydrogenolysis,deep hydrogenation and carbon deposition.which are caused by poor Pt dispersion and would lead to selectivity decreasing,should be avoided..Moreover,for some hydrogenation/dehydrogenation processes under high temperature,the rapid and irreversible deactivation as a result of Pt sintering is still a chanllenge.In this dissertation,based on the properties of the anion-type layered hydrotalcites(LDHs),the Pt site dispersed at atom level could be achieved by the interaction between Pt and the induced promoter or secondary active component that can be inserted into the lattices of brucite-like layers of LDHs.The designed Pt catalysts exhibit excellent catalytic performances for the catalytic reforming,dehydrogenation of propane and furfural hydrogenation,highly dispersed Pt exhibited excellent catalytic performances,respectively.The main innovative research findings and conclusions are as follows:1.The catalytic reforming suffers low selectivity due to the hydrogenolysis reaction,which are the result from the poor dispersion of Pt sites.Highly dispersed Pt has been prepared by the induction of Sn? confined in the lattices of brucite-like layers of layered double hydroxides.The Pt dispersion(0.3 wt%Pt loading)reaches 96%,and single Pt atoms and the small Pt cluster(consisting of less than 10 Pt atoms)account for 91%.In the n-heptane reforming reaction,the methane selectivity could be controlled below 2%and high activity is achieved(TOF reaches 1.5 s-1).2.For catalytic dehydrogenation of light alkanes to olefins under high temperature,it has been a great challenge to stabilize the highly dispersed Pt to suppress the sintering of Pt centers,coking and hydrogenolysis which account for the irreversible deactivation and low propene selectivity.Also by the induction effect of the confined Sn? in lattice of LDHs on the Pt,two-dimensional raft-like Pt clusters are prepared,which could be stable even at high temperature.The Pt centers are electron-rich result from the strong interacion with the confined Sn sites.For the dehydrogenation of propane to propene,up to 30%propane conversion and>99%propene selectivity are achieved at 550?.The reaction runs stably for 10 days without significant inactivation.Even at 600?,propene selectivity and propane conversion still reach>98%and 48%.The studies have further shown that the fast desorption of propene on highly dispersed Pt centers with strong Pt-Sn interactions is essential for the high propene selectivity.After the reaction,no visible Pt sintering is observed.The limited migration of Sn?/? in the Mg(Al)O lattice at high temperature is the key factor for the stability of Pt sites in atomic scale.3.The hydrogenation of furfural to cyclopentanone suffers poor selectivity of the target product(cyclopentanone)due to the untimely conversion of the reaction intermediate product and the excessive hydrogenation.To solve this problem,Cu-containing hydrotalcite was used as the precursor to obtain supported Cu nanoparticles with high concentration of surface defects through topological transformation,and then Pt was induced to be highly dispersed on the Cu surface.A Pt/Cu catalyst with Pt dispersed in atomic level was obtained.For the hydrogenation of furfural to cyclopentanone,the Pt/Cu catalyst exhibits excellent hydrogenation performance.The reaction pressure was set at 0.1 MPa instead of the conventional 2-8 MPa.After reaction at 160? for 10 h,furfural almost completely converted and the selectivity of cyclopentanone reaches 99.1%.