Preparation Of Metal Borate Catalyst And Its Oxidative Dehydrogenation Performance Of Propane

Propene serves as an important industrial raw material;the current production capacity cannot fill the gap of the propene market.The increase of oil-based propene production process is not in line with China’s high dependence on foreign oil imports and is not conducive to energy security.China is relatively rich in natural gas and other gas resources,the development and utilization of propane from natural gas into propene can not only improve the production of propene,but also relieve the pressure of oil resources,which is of great practical significance to the healthy development of energy in China.In particular,the oxidative dehydrogenation of propane（ODHP）process is thermodynamically exothermic which can significantly reduce the energy consumption during propene production.However,the propene tends to undergo excessive oxidation in the ODHP reaction,releasing a large amount of carbon oxides leading to lower propene yields.Therefore,the development of catalysts with high propene selectivity is crucial for ODHP technology.Non-metallic boron-based catalysts exhibit excellent olefin selectivity in ODHP reactions,but usually require high temperatures to be catalytically active.Since the boron oxide layer on the surface of boron-based catalysts is easily liquefied and leached from the catalyst surface during the reaction,it can lead to the loss of active phase and affect the stability of the catalyst.Therefore,in this work,a borate catalyst with high thermal stability was designed and prepared by combining metal ions with borate ions to address the above problem,and the intrinsic correlation between catalyst composition and ODHP reaction performance was investigated through a series of characterizations.The main work is as follows:（1）Nickel borate（Ni₃B₂O₆）and cobalt borate（Co B₄O₇）catalysts were prepared by co-precipitation combined with high-temperature calcination using nickel nitrate and cobalt nitrate as metal ion sources and ammonium borate as boron source.Both prepared metal borates can effectively catalyze the dehydrogenation of propane at 450～540℃with high selectivity and stability.In particular,the Co B₄O₇catalyst could reach 17.6%propane conversion and maintain 91.4%light olefin selectivity after 38 h activation at 490℃.The morphology and crystal structure of the catalysts did not change significantly after 10 h of ODHP reaction,showing good structural stability.The characterization analysis showed that the content of M-B-O（M=Co,Ni）and B-OH species on the catalyst surface was related to its ODHP reaction activity,and this component gradually increased and stabilized during the induction period of the catalyst,thus obtaining a high catalytic activity and light olefin selectivity.（2）A series of cobalt borate catalysts（Co B₄O₇-x）with different cobalt contents were prepared and reacted with ODHP by introducing cobalt into its precursor in a grinding process to study the effects of cobalt content on the morphology,crystal structure and surface properties of cobalt borate catalysts and their performance in ODHP reaction.The results showed that the activity of the catalysts varied with the amount of cobalt.The results showed that the activity of the catalyst increased with the increase of cobalt content and then decreased,and the best low-temperature activity was achieved at 30 wt%loading,with 20.1%propane conversion and 86.7%light olefin selectivity at 480℃.Structural characterization showed that the introduction of moderate amount of cobalt to the Co B₄O₇precursor could increase the surface area of the catalyst and increase the electron concentration on the catalyst surface,which is beneficial to expose more active sites and enhance the adsorption activation of the catalyst for oxygen.In contrast,the increase of BO₄and M-O on the surface after excessive addition of cobalt inhibits the reactivity,which can lead to the cleavage of propane and reduce the olefin selectivity.