高效钼基催化剂上正丁烯自歧化生成乙烯和己烯（英文）

烯烃歧化反应(又称烯烃复分解反应)是两分子烯烃通过碳-碳键断裂重排生成新烯烃分子的反应,自1964年Phillips公司的Banks等发现以来,引起了研究者的广泛关注,且在均相催化体系的发展尤为迅速;与此同时,多相烯烃歧化催化剂因其在分离简单、可循环再生利用方面的优势而在工业界崭露锋芒.多相烯烃歧化催化剂通常由活性金属组分(Re,Mo,W)分散到大比表面积的多孔载体制备而成.多相催化剂上烯烃歧化反应主要集中在乙烯和2-丁烯反歧化制丙烯反应,其中WO_3/SiO_2催化剂先后应用于Phillips公司的Triolefin Process和ABB Lummus公司的OCT工艺,低温Re系催化剂被法国石油研究院应用到Meta-4歧化工艺.同时丙烯歧化也是研究最多的反应,多数情况下被用作探针反应来研究催化剂的性能.烯烃歧化反应可以根据市场需求灵活调变产物分布,为碳四烃类的高效转化利用提供很好的途径.受国内拉动内需的政策及下游应用行业强劲需求的影响,中国液化石油气的产量逐年递增.2014年我国液化气产量约为2550万吨,其中仅有39%左右用于碳四深加工,大部分当做燃料直接烧掉.从组成来看,液化气中烯烃含量在40%-50%,可以转化为高附加值的乙烯和丙烯进一步利用.本文重点开发了一条从1-丁烯出发生产乙烯/己烯的反应路线及对应的催化剂.首先从热力学角度分析了碳四歧化反应网络中各反应路径发生的难易程度.在此基础上,以Mo/Al_2O_3为催化剂考察了Mo负载量和反应条件对产物分布的影响-.在优化的6Mo/Al_2O_3催化剂上,80°C,1.0 MPa和丁烯空速3 h1的条件下,产物中乙烯和己烯的摩尔选择性超过85%,并且在48 h内保持良好的反应稳定性.为了进一步探究催化剂结构与反应性能的关系,系统考察了催化剂载体差异对Mo物种状态和反应性能的影响.借助N2吸附,NH_3-TPD,Py-IR,H_2-TPR,UV-Vis和HRTEM等表征手段,发现催化剂反应活性与其酸密度直接相关.催化剂酸量越大,丁烯转化率越高,但副反应越多;载体适宜的酸量和较大的比表面积更有利于钼物种的分散和四配位钼物种的形成,促进目标1-丁烯自歧化制乙烯/己烯反应的发生.

Self-metathesis of 1-butene to ethene and hexene over molybdenum-based heterogeneous catalysts

A novel route involving self-metathesis of 1-butene under mild conditions that gave high yields of ethene and hexene was proposed. The results of thermodynamic analysis revealed that the Gibbs energy of the target Metathesis I reaction (1-butene → ethene + 3-hexene) was much higher than that of the main side Metathesis II (1-butene + 2-butene → propene + 2-pentene). Suppression of 1-butene double-bond isomerization was the key step to increase the selectivity for the target olefin in the reaction network. The relationship between the catalytic performance and support nature was investigated in detail. On basis of H₂-TPR, UV-Vis spectra and HRTEM results, an alumina (Al₂O₃) support with large surface area was beneficial for the dispersion of molybdenum (Mo) species. Both suitable acidity and sufficient Mo dispersion were important to selectively promote the self-metathesis reaction of 1-butene. On the optimal 6Mo/Al₂O₃ catalyst, 1-butene conversion reached 47% and ethene selectivity was as high as 42% on the premise of good catalytic stability (80 °C, 1.0 MPa, 3 h^?1).