Study On Preparation And Propane Dehydrogenation Performance Of Non-precious Metal Catalysts

Propylene,a key industrial feedstock for the production of polymers,oxygenates,and other compounds,is mainly produced from thermal or catalytic cracking of crude oil-derived naphtha.In recent years,the gap of propylene market is gradually increasing.Propane dehydrogenation is another important industrial route for on-purpose producing propylene,effectively relieving the overdependence of propylene raw material on limited oil reserves.Recent boom in shale gas production has once again promoted the development of propane dehydrogenation process based on metallic platinum and chromium oxide catalysts.However,the platinum resources are very rare in nature and chromium is high toxic in environment,thus looking for a new catalyst system with both resource and environmental advantages always is a research hotspot in this filed.Cobalt-based catalyst has attracted extensive attentions because of its proper ability to activate C–H bonds and suitable dehydrogenation energy barrier,but the activity,selectivity,and stability of cobalt-based catalysts need to be further improved.The supported CoFe/Al₂O₃catalyst was prepared,with the doping of iron,promoted both activity and selectivity of cobalt catalyst in propane dehydrogenation.Meanwhile,we revealed the modification effect of the promoter Fe:Compared to 5wt%Co/Al₂O₃ catalysts with propane conversion of 15.8%and propylene selectivity of 97%,a higher propane conversion（22.5%）presented at a cobalt loading of 5wt%and iron loading of 1.6wt%,respectively,with the desired propylene（97.2%）.There was no obvious deactivation of catalyst for 10 hours under the dehydrogenation reaction.Spectroscopic analysis for local coordination of active species revealed that an iron doping promoted the generation of active tetrahedral Co²⁺sites.The H₂-TPR analysis disclosed that the doping of iron efficiently prohibited the reduction of cobalt species,and correspondingly improved the durability of cobalt catalyst in propane dehydrogenation.Lastly,the synergistic promotion of active Co²⁺sites and surface Al_cus sites of?-Al₂O₃ nanosheet for the catalytic performance of propane dehydrogenation were found.Metal nitrides have the characteristics of precious metals,which has attracted wide attention in the field of hydrocarbon hydrogenation,and is also a potential alternative system of precious metal dehydrogenation catalysts.Based on the the strategy of entropy stabilized oxides,high entropy metal nitrides were successfully prepared by mixed ball milling of various metal chloride precursor salts and urea,and applied to the dehydrogenation of propane to propylene.The M_xC_yN catalyst prepared by pyrolysis at 700°C has the best propane dehydrogenation performance;under the reaction conditions of atmospheric pressure,590°C,4.7 g_C3H8·gcat^-1·h^-1 and N₂ dilution,the conversion of propane can reach 12.6%,the selectivity of propylene can reach 96.8%,and there is no obvious deactivation after 6 hours of reaction;H₂ as carrier gas can improve the stability of the reaction,however,the hydrogenation ability of the catalyst promotes the occurrence of hydrogenolysis side reaction and loses the selectivity of the product.The kinetics shows that the reaction order and activation energy of propane on the high entropy metal nitride catalyst are similar to those of the platinum catalyst,and its catalytic activity is derived from the noble metal-like properties of the metal nitride catalyst.The characterization of the structure of the catalyst before and after the reaction showed that no obvious structural change was observed during the high temperature propane dehydrogenation process,with the cubic molybdenum nitride structure,which was stable in the industrial propane dehydrogenation process.