Synthesis Of Ordered Mesoporous Phosphate By Ternary Co-assembly Method And Its Catalytic Properties

Mesoporous materials possess regular pore structure,larger pore size and specific surface area,which is favorable for the adsorption,separation,activation and shape-selective catalysis of macromolecules.The amorphous pore wall structure makes it easy to introduce other active components and the modification of surface acidity and alkalinity.Based on the above advantages,the mesoporous material becomes the most popular catalyst carrier for the oxidative dehydrogenation of propane but there are few reports on mesoporous phosphate as catalyst carrier for propane oxidation and dehydrogenation.Propane oxidative dehydrogenation is gas phase reaction with high temperature but the thermal stability of multi-metal mesoporous phosphate molecular sieves are very poor by traditional hydrothermal synthesis and the order of the channel is not high.Evaportion-induced self-assembly?EISA?is a non-aqueous synthesis technology with simple synthetic process and the mesoporous phosphate molecular sieves generally have high thermal stability and highly ordered mesoporous structure.In this paper,ordered mesoporous CaZrPO,MgZrPO and AlZrPO were synthesized by EISA method using triblock copolymer F127 as template and ethanol as solvent.The mesoporous structure,surface acidity,phase structure,Composition,coordination structure and valence state,the thermal stability of materials and other properties are characterized and analyzed in detail.A series of vanadium-based catalysts were prepared by using ordered mesoporous phosphates as carrier.The catalytic performance of the catalysts was studied in the oxidative dehydrogenation of propane.The results showed that:?1?The ordered mesoporous CaZrPO,MgZrPO and AlZrPO synthesized by EISA method had regular 2D-hexagonal pore phase mesoporous structure and p6mm space group.The pore wall structure was amorphous,the average pore size is more than 7nm,the specific surface area was up to 258m2/g and the thermal stability of the material was good.After calcination with high temperature,the amorphous pore structure changes to the crystalline state and the phase transition was the main reason leading to the collapse of the mesoporous structure.?2?Due to the different components,the thermal stability of the mesoporous materials was somewhat different.Under the premise that the mesoporous structure was not destroyed,CaZrPO and MgZrPO can withstand the maximum calcination temperature 700?,while the maximum calcination temperature of AlZrPO was 800 ?.The difference of coordination ability of metal ions in mesoporous materials might be the main reason for difference of thermal stability.?3?The catalytic activity of the catalyst was studied by using ordered mesoporous CaZrPO and AIZrPO as the catalyst carrier and supporting the active constituent vanadium.N2 adsorption-desorption curve and pore size distribution curve showed that the loading of vanadia species will plug the mesoporous channels and with the increase of the loading,the specific surface area would continue to decrease and the pore size distribution curve became broader.Raman spectroscopy showed that the vanadium oxide species supported by the impregnation method were dispersed on the surface of the carrier unevenly.With the increase of the loading,the isolated,polymerized and crystalline V2O5 vanadia species may commonly exist on the surface of the carrier.?4?Propane conversion and propene selectivity increased with increasing reaction temperature,so propene yield would continue to increase.By comparing different vanadium-based catalysts V/CaZrPO and V/AIZrPO in the oxidative dehydrogenation of propane at different reaction temperatures and the change of propane conversion and propylene selectivity with different vanadium oxide species loading.at different temperatures.It found that propane oxidative dehydrogenation reaction showed different characteristics in the low temperature range?500?-550??and the high temperature range?570?-600??,which indicated that oxidative dehydrogenation of propane experience different reaction paths and the reaction type at high temperature were more complicated.?5?The influence of surface acid properties and the redox properties of vanadia species on the catalytic performance of propane oxidative dehydrogenation were elucidated by the characterization of pyridine-IR,NH₃-TPD and H₂-TPR.