The Lattice Confinement Of Perovskite And The Dehydrogenation Performance Of Isobutane

With the development and utilization of downstream products of isobutene,the demand for isobutene in the world continues to rise.Isobutane direct dehydrogenation to isobutene has been regarded as one of the most promising routes for isobutene production.However,the problems of carbon deposition and Pt sintering for the industrial Pt-based catalysts have to be settled urgently.The perovskite has a lattice confinement on the lattice ions and can achieve uniform dispersion of various metal elements.In this paper,a series of supported perovskite precursors,in which the active component Pt and transition metal promoter together with La and Fe elements were introduced into the perovskite structure,were obtained by citrate complexation method on the surface of supports,especially in the mesopores of supports:（1）LaFe0.577Ni0.417Pt0.006O3 supported on different supports and LaFe1-x（M,Pt）xO3/SiO2（M=Ni,Co,Cu）with different additives;（2）Pt/LaFe_0.7Cu_0.3O₂/SiO₂、LaFe0.68Cu0.3Pt0.02O3/SiO2 by different preparation methods;（3）LaFe1-x（Ni,Pt）xO3.Then the supported Pt-based bimetallic catalysts were obtained by lattice ionic-confined reduction of perovskite precursors.First,the influences of supports and transition metal additives on the isobutane dehydrogenation performance were investigated.The influence of supports（SiO2,Al2O3,TiO2）on the isobutane dehydrogenation performance was investigated using LaFe0.577Ni0.417Pt0.006O3 as the perovskite precursor.As a result,it was found that the catalyst with SiO2 as support has a better dehydrogenation performance than Al2O3 and TiO2.At the same time,the dehydrogenation performance of LaFe1-x（M,Pt）xO3/SiO2（M=Ni,Co,Cu）with different additives were investigated.As a result,it was found that when Ni was used as an additive,the dehydrogenation performance was better than Cu and Co additives.Second,the preparation of Pt-Cu bimetallic catalysts and their isobutane dehydrogenation properties were studied.The structure and performance differences of the catalysts obtained by conventional impregnation method and the catalysts obtained by lattice ionic-confined reduction of perovskite precursors were compared.It was found that the Pt-Cu catalysts prepared by the lattice confinement reduction method had better isobutane conversion,isobutene yield and carbon deposition per unit conversion than the Pt-Cu catalyst obtained by traditional impregnation method.Finally,the preparation of Pt-Ni bimetallic catalysts and its isobutane dehydrogenation performance were studied.A series of novel Pt-Ni bimetallic catalysts supported on LaFeO3/SiO2 with different amount of Ni were prepared by lattice ionic-confined reduction of LaFe1-x（Ni,Pt）xO3/SiO2 perovskite precursors and applied in isobutane dehydrogenation to isobutene reaction.The catalysts were characterized by XRD,H2-TPR,BET,TEM,EDX,CO chemisorption,XPS and TGA techniques.The as-synthesized Pt-Ni bimetallic catalysts possess the smaller most probable particle size with tunable Pt-Ni interaction depending on the varied Ni content.The catalyst with Ni content of 3.0 wt.%shows excellent activity and stability（the isobutane conversion and isobutene selectivity still stay at about 38%and 92%after 310 min,respectively）for the isobutane dehydrogenation reaction.And it provides approximately six times turnover frequency compared with the catalyst without Ni.The excellent activity and stability of 3.0 wt.%Ni-containing catalyst can be attributed to the small metal nanoparticles with high dispersion and suitable interaction between Pt and Ni.Moreover,the Pt（Ni）-LaFeO3/SiO2 catalyst with Ni content of 3.0 wt.%has been run more than 35 h without obvious loss of activity due to the long-term stability.And the decrease of Pt-Ni interaction accompanying the formation of FeNi alloy phase is thought to be responsible for the slightly decreased activity.