Study On Non-Precious Metal Ni-based Ordered Alloy Catalysts Induced By Alumina Coordination Structure And Mechanism Of Selective Hydrogenation

Ethylene is one of the important petrochemical products,and its production capacity is often used as a standard to measure a country’s petrochemical level.At present,the main way to prepare ethylene is from naphtha steam cracking.However,a small amount of acetylene impurities will be produced in this process,which will lead to catalyst poisoning in the downstream polymerization process,resulting in irreversible deactivation.Therefore,it is of great significance to remove the trace acetylene in ethylene.The most commonly used method is the selective hydrogenation of acetylene to ethylene using catalytic hydrogenation.Precious metal Pd is widely used as a selective hydrogenation catalyst for industrial acetylene due to its excellent hydrogenation capability.However,in recent years,precious metal resources have become increasingly scarce,leading to the gap between total demand and aggregate supply widening year by year,resulting in rising production costs.Therefore,it is very urgent to develop inexpensive and abundant non precious metal catalysts to replace precious metal catalysts.Non precious metal Ni exhibits a certain ability to activate hydrogen due to its unfilled d electron orbitals,which has aroused great interest among researchers.However,acetylene is prone to overhydrogenation to form ethane or polymerization to form green oil at continuous Ni sites.In order to improve catalytic performance,a strategy of constructing isolated Ni sites is usually adopted to promote efficient directional conversion of acetylene to ethylene.The introduction of second metal alloying is beneficial for the isolation of continuous Ni sites.However,due to the different chemical properties and reduction potentials of different types of metals,it is difficult to control the nucleation and growth processes simultaneously,making it difficult for bimetallic atoms in catalysts prepared by traditional impregnation methods to be arranged in an orderly manner.Therefore,exploring a simple and green new method to construct bimetallic ordered alloy catalysts is of great significance.Based on this,this paper focuses on the problem of difficulty in improving both activity and selectivity during the selective hydrogenation of acetylene.A study was conducted on the influence of support coordination structure induced construction of a supported bimetallic Ni based catalyst with ordered atomic arrangement.The effect of the isolation degree of active metal Ni sites and electronic states on the adsorption and desorption behavior of acetylene molecules and reaction intermediates was explored,The mechanism of Ni centers with electron enrichment and highly isolated sites in improving the hydrogenation performance of acetylene has been revealed.The specific research results are as follows:（1）The r-Al₂O₃ with high content of unsaturated penta coordination was prepared by hydrothermal method,and the Ni-Cu/r-Al₂O₃ alloy catalyst with orderly arrangement of Ni and Cu atoms was prepared based on the coordination structure inductive effect.The effect of isolation degree of active Ni sites and electronic state of Ni-Cu/r-Al₂O₃ catalyst on acetylene hydrogenation performance was investigated by comparing sh-Al₂O₃ with sp-Al₂O₃ supported Ni-Cu catalyst with low content of unsaturated penta coordination.The results showed that the Ni-Cu/r-Al₂O₃catalyst,which achieved complete isolation of the Ni site,achieved complete conversion of acetylene at 130℃,with an ethylene selectivity of86%,much higher than Ni-Cu/sh-Al₂O₃ and Ni-Cu/sp Al₂O₃.This is due to the formation of electron enriched and highly isolated Ni active centers on Ni-Cu/r-Al₂O₃ catalysts,which contribute to the activation and dissociation of hydrogen,improve reaction activity,and promote C₂H₄*to be more easily desorbed at the catalytic siteσConfiguration adsorption significantly improves ethylene selectivity.（2）In view of the problem that tin aluminate complex is easy to form between Sn and alumina support in the process of traditional impregnation strategy,and the structure of M-Sn alloy is easy to segregate in the reaction process,the number of unsaturated Al³⁺coordination is adjusted by adjusting the preferred exposed crystal plane of Al₂O₃,and a stable Ni-Sn/r-Al₂O₃ alloy catalyst is constructed by using the inductive effect of coordination structure,explored the influence of unsaturated five coordination content on the interaction strength between Sn and alumina support,the degree of Ni Sn alloying,and its catalytic performance in acetylene hydrogenation reaction.The results indicate that the Ni-Sn catalyst supported on r-Al₂O₃ forms a uniform and structurally stable alloy structure.At 225℃,acetylene is 100%converted,and ethylene selectivity is as high as 95%.After 24 hours of continuous reaction,the alloy structure remains stable without significant segregation.At an 80%acetylene conversion rate,ethylene selectivity remains at 95%.