MoO_(3)纳米带修饰MCM-22催化甲烷无氧芳构化反应

MoO_(3) nanobelts modified MCM-22 catalyze methane non-oxidative aromatization

利用天然气生产芳烃是一个有吸引力的课题,这个过程需要具有高性能活性位点的催化剂,以活化稳定的碳氢键.在甲烷直接转化方法中,将甲烷无氧脱氢芳构化(MDA)转化为高附加值芳烃(如苯、甲苯和萘)是甲烷增值的有效途径.本研究采用MoO_(3)纳米带作为Mo源,微孔分子筛MCM-22作为载体制备双功能Mo基催化剂,结果表明MoO_(3)纳米带高度分散在分子筛内部,与分子筛中Bronsted酸中心结合形成有效活性中心,改善了甲烷无氧脱氢芳构化反应的催化活性,提高了催化剂的稳定性.在甲烷无氧脱氢芳构化反应测试中,当MoO_(3)纳米带的负载量质量分数为6%时,N-Mo-HMCM-22催化剂催化的甲烷转化率达到14.1%,苯产率可达8.2%.本研究为合成高性能、稳定的MDA催化剂提供了一种更为简易的策略.

The production of natural gas has been greatly improved with the development of shale gas mining technology.It is of great significance to transform natural gas into high value-added chemicals efficiently and economically.Methane dehydro-aromatization(MDA)is widely concerned because of its high atom utilization rate and good aromatics selectivity.This process requires catalysts with high performance active site to activate stable C—H bonds.Mo based zeolite is a good catalyst for methane dehydro-aromatization.However,it requires a higher reaction temperature because MDA reaction is a thermodynamic limiting process,therefore carbon deposition is easy to generate in the zeolite and leads to poor stability in the reaction.So far,many strategies have been applied to improve the dispersion of Mo species in zeolite carriers in order to enhance the catalytic activity and stability in MDA reaction.In this study,we use MoO_(3) nanoribbons as the Mo source and microporous zeolite MCM-22 as the carrier to prepare bifunctional Mo based catalysts.The structure and acidity of the catalysts are studied using characterization techniques such as XRD,FT-IR,SEM,BET,NH_3-TPD and TG.The test results show that the morphology and structure of MCM-22 will not change after introducing MoO_(3) nanobelts in MCM-22zeolite.The thermogravimetric analysis results indicate that MoO_(3) nanoribbons are more prone to sublimation compared to commercial MoO_(3) and thus promote the high dispersion of Mo species in the channel of HMCM-22 zeolite,leading to a decrease in the specific surface area and pore volume of the catalyst.At the same time,the acidic sites of the zeolite have been regulated in an orderly manner,inducing better anchoring positions of Mo metal components in the catalyst surface/channel and binding with Bronsted acid centers in the HMCM-22zeolite to form effective active centers.In hence,the catalytic activity in MDA reaction has been improved.The reaction performance test shows that the catalyst HMCM-22loaded with 6%MoO_(3) nanoribbons(N-Mo-HMCM-22)has higher methane conversion rate(14.1%)and benzene yield(8.2%)under the reaction conditions of 700℃ at an air flow rate of 1500 mL·g^(-1)·h^(-1).The thermogravimetric analysis results of post-reaction catalyst perform that the weight loss rate of MoO_(3) nanoribbon modified zeolite is lower,indicating that it has stronger resistance to carbon deposition,thus improving the stability of the catalyst.This study provides a simpler strategy for synthesizing high-performance and stable MDA catalysts.