Preparation And Characterization Of Kaolin-supported Metal Oxide Catalysts And Their Catalytic Performances For Oxidative Dehydrogenation Of Propane

With the rapid development of science and technology,the investigation and utilization of natural clay resources has become an advanced subject in the field of scientific research and application at home and abroad.Its application and research level has become an important aspect influencing the development of the science and technology of a country.Kaolin is an important nonmetallic mineral,whose main component is kaolinite,composed of Si-O tetrahedron and Al-O octahedral layered structure,and is a pure texture of fine clay,with good plasticity,adsorption capacity,decentrality,high whiteness and excellent electrical insulation,which is currently widely used in chemical,environmental protection,agriculture,construction and other fields.Kaolin in Inner Mongolia Autonomous Region is rich in resources,cheap and easy to obtain.Kaolin can be modified with a certain pore structure and high specific surface area of the material for the new heterogeneous catalytic field,which is a very good catalyst or support.The comprehensive utilization of kaolin resources is of great significance.Propylene is one of the basic raw materials for petrochemical industry.With the rapid increase in demand for propylene downstream products such as acrylonitrile,acrolein and acrylic acid,the demand for propylene is growing rapidly.The traditional propylene preparation method is difficult to meet the demand.The oxidative dehydrogenation of propane to propylene has a huge economic prospect,and has become a hot research field of catalysis.But propylene is easy to deep oxidation under the aerobic conditions,propylene selectivity is not ideal.Therefor,it is the key that the preparation of the catalysts with stability and high propylene selectivity at low temperature.In this study,the kaolin-supported metal oxide catalysts were prepared by using the mesopore modification-impregnation and coprecipitationroasting method,which were characterized by XRD,N₂ adsorption-desorption,H₂-TPR,NH₃-TPD,XPS and conductivity.Their catalytic performances of propane oxidative dehydrogenation were optimized and the influence factors on catalytic performance were studied.1.The kaolin through 200-mesh sieve was acidified with sulfuric acid,and then modified with P123 and roasted at 550 ?.The as-prepared modified kaolin has a uniform pore structure.The specific surface area was 389.4 m²/g.2.V₂O₅/modified kaolin catalysts were prepared by the impregnation method.The surface of the series of catalysts is weakly acidic;the modified kaolin is p-type semiconductor and the supported V₂O₅ catalysts are the n-type semiconductor.The catalyst with loading of 5% V₂O₅ has more V⁵⁺ on the surface.The increase of the lattice oxygen content,the increase of propylene selectivity.The highest catalytic performance was obtained at 600 ?: the conversion of propane is 28.11%;the selectivity to propylene is 62.38%.3.NiO/modified kaolin catalysts were prepared by the impregnation method.With the increase of nickel loading,the conductivity type of the catalysts remained the p-type semiconductor.The catalyst with 7.5% NiO loading is the best: the conversion of propane is 18.20% and the selectivity to propylene is 49.80% at 450 ?.4.The supported Ni-Al-O/kaolin and Ni-Cr-O/kaolin composite oxide catalysts were prepared by the coprecipitation-roasting method.The conversion of propane is 19.88% and the propylene selectivity is 47.71% at a 525 ?over 10% Ni-Al-O/kaolin composite oxide catalyst.The conversion of propane is 22.98% and the selectivity to propylene is 44.50% at 450 ? over 10% Ni-Cr-O/kaolin composite oxide catalyst.