Synthesis And Characterization Of Co-based Layered Catalysts For Oxidative Dehydrogenation Of Propane

The oxidative dehydrogenation of propane to prepene is a potential route to fulfill the increasing demand of propene.But it is challenging because the desired product propene is rather more active than the reactant propane,and more easily oxidized into COx.Therefore,it becomes the main pursued goal to obtain a catalyst with high selectivity and high activity.Due to characteristics of large surface,more exposed surface atoms and easier modification of the surface,layered materials are regarded as efficient component as support or catalyst and has gained widespread concern.In this dissertion,a series of layerd materials containing highly-dispersed CoOx species were synthesized and characterized.The emphasis was placed on determining the correlation between the interaction of the active phase/site and the support with properties of the catalyst and ODHP performance.In summary,we obtained the following results:1.Layered double hydroxide with different components were synthesized by hydrothermal method.And related LDO catalyst were obtained and its ODHP performance were tested.Among these catalyst,Co-Al LDO pillared by different anions were characterized and studied,focusing on the host-guest interaction.As the results showed,the ODHP performance at low temperature was related to the Co3+ of the CoOx in the LDO.The sulfate and phosphate more evidently modified the reducibility and distribution of oxygen species of CA-S and CA-P LDO.The sulfate around cobalt made the reduction of Co(III)to Co(II)be more difficult relatively,and then the mobility of oxygen(lattice)in LDO was reduced;the phosphate around cobalt provided the significant amount of oxygen vacancy,and enhanced the mobility of oxygen(surface adsorbed oxygen species).As both CA-S and CA-P exhibited good catalytic performances in ODHP than the other LDO samples,the mechanisms of propaneactivation over CA-S and CAP were different.The mechanism over CA-S depended on the mobility oflattice oxygen,and that over CA-P was related to the participation of the surface adsorbed/lattice oxygenin ODHP.2.The catalysts were prepared by using PVP-assisted impregnation method using nano-magnesia,alumina,titanium oxide and zirconium oxide as support.The interaction between the support and the cobalt species was investigated on different supports with different modifiers.The results showed that different cobalt species was formed due to the different interaction on different support.On the surface of Al2O3,TiO2 and MgO,the cobalt species tend to present as Co2+ species,while it showed mainly as Co3O4 on ZrO2.The interaction between the ZrO2 and cobalt is moderate and better ODHP performance can be obtained.The modification of phosphate enhances the interaction between the support and cobalt species,e.g ZrP2O7 formed on the surface of ZrO2 and evidently improved the selectivity of the catalyst,but excessive phosphate would lead to increased crystalline size of ZrP2O7,therefore appropriate dose of phosphate(3%-5mol%)is required for best ODHP performance.3.The zirconium phosphate supported CoOx catalyst was prepared by PVP assisted impregnation method and electrostatic adsorption method using a-zirconium phosphate as support.The interaction between the CoOx and a-ZrP was studied.The results show that a-ZrP is conducive to prepare highly dispersed catalyst with smaller CoOx particles than the amorphous zirconium phosphate,and the stronger interaction allows the cobalt on the layered zirconium phosphate present predominantly in the form of cobalt phosphate,and showed best propene selectivity.When the Co3O4 nanoparticles are directly supported on the a-ZrP,the weaker interaction result in higher catalytic performance at the lower temperature and lower selectivity to propene,while after exfoliation,the interaction between zirconium phosphate and nanoparticles was enhanced,and the catalyst showed good catalytic performance at low temperature and better propylene selectivity.