摘要
Due to the shortage supply of propylene and the development of shale gas,there is increased interest in on-purpose propane dehydrogenation(PDH)technology for propylene production.Ga-based catalysts have great potential in PDH,due to the high activity,low carbon deposit and deactivation.Ga-hydrides formed during PDH reduce the rate,selectivity and yield of propylene.In this contribution,CO_(2)is introduced into PDH as a soft oxidant to eliminate the unfavorable intermediate species Ga^(δ+)-Hx re-generating Ga^(3+)-O pairs,and also minimize coke deposition thereby improving the catalytic performance.In situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy experiments show that CO_(2)can effectively eliminate Ga^(δ+)-Hx.At different temperatures,co-feeding CO_(2)during PDH over Ga_(2)O_(3)/SiO_(2)catalysts with different loadings significantly improves the stability of the conversion and selectivity,especially the latter,and provide a new dimension for improving the performance of PDH process.
丙烯是一种基础石油化工原料,在全球石油化工生产中占有重要地位.以丙烯为原料可生产许多石油化学品,如丙烯腈、环氧丙烷和聚丙烯等.经济快速发展带动了丙烯下游衍生物产业的发展,进而增加了对丙烯的需求量,因此尽管近年来丙烯产能逐年上升,丙烯产量与需求量之间仍存在较大缺口.传统的丙烯生产路径主要是石脑油蒸汽裂解和重质油催化裂化.然而,随着石油资源的短缺和页岩气的发展,丙烷脱氢作为一种直接生产丙烯的技术,成为丙烯生产领域的研究热点.近年来,镓基催化剂由于其较少的积碳和较高的催化活性受到了越来越多的关注.镓基催化剂在丙烷脱氢反应中的活性位点也得到了更多研究.在镓基催化剂中,镓氧化物具有丙烷脱氢活性,而丙烷脱氢反应过程中产生的镓氢(Ga^(δ+)-Hx)物种不稳定,且会造成丙烯选择性降低,导致丙烯产率降低.因此,反应过程中原位消除镓氢物种对于提高丙烷脱氢反应性能具有非常重要的意义.本文将CO_(2)作为温和氧化剂引入Ga_(2)O_(3)/SiO_(2)催化的丙烷脱氢反应中,促进不利的中间产物Ga^(δ+)-Hx的转化,再生丙烷脱氢的活性位点Ga^(3+)-O,从而提高催化性能.原位红外光谱实验结果表明,CO_(2)可有效消除Ga^(δ+)-Hx.在不同反应温度下,引入CO_(2)可显著提高Ga_(2)O_(3)/SiO_(2)催化丙烷脱氢的转化率,特别是选择性.反应4.5 h时,3Ga_(2)O_(3)/SiO_(2)催化丙烷脱氢的选择性从93%降低到89%;引入CO_(2)后,丙烯选择性可提高到并维持在93%.Ga_(2)O_(3)负载量由3 wt%提高到10 wt%时,引入CO_(2)仍可促进反应性能.当CO_(2):C3H8由0.5增加到3时,引入CO_(2)带来的反应性能提升基本相同.同时,引入CO_(2)大大减少反应过程中产生的积碳.本文对镓基催化剂丙烷脱氢活性中心的认识和提高丙烷脱氢反应性能提供了新方向.
基金
国家自然科学基金(21902019)
国家重点研发计划(2016YFB0600902-4)
中央高校基本科研业务费(DUT20RC(5)002)
辽宁省兴辽英才计划项目.
