乙炔氢氯化失活Au/C催化剂的再生性能及其机理研究

Vinyl chloride is a monomer for industrially important polymeric material polyvinyl chloride. Commercial catalyst HgCl2 supported on carbon is highly toxic and shortly lived due to loss of mercuric chloride. It was recently found chloro Au(III) complexes supported on carbon demonstrated high activity, selectivity and not suffering from loss. However, the durability of gold catalyst is relative short and irreversible deactivation. Various deactivation mechanisms have been proposed including the important fact of gold sintering due to the reduction of Au3+ to Au0. And methods to control the dispersion of gold in supported heterogeneous catalysis are very valuable due to the strong size effect on their activity and selectivity. Our preliminary work indicated the use of iodohydrocarbons, such as triiodomethane, was able to regenerate/redisperse inert gold particles from about 30 nm downsizing to below 1 nm. And the redispersed gold catalysts displayed better performance than that of the as-prepared, which demonstrated the gold catalysts were regenerated. Nevertheless, more efforts to investigate the methods of preparation, mechanism of deactivation and regeneration are necessary. The overall aim was to explore milder, safer treatments for this process could be obtained compared with the previous process methods. The support from NSFC will promote to perform all the works.

氯乙烯是生产工业聚氯乙烯的重要单体。乙炔氢氯化工业用催化剂HgCl2是一种环境非友好型催化剂。非汞催化剂中，AuCl3催化剂展现出高的催化性能和不易流失等特点。但活性物种Au3+在反应体系中易被乙炔还原为Au0，进而团聚形成较大尺寸的Au粒子，导致其不可逆失活。本课题前期工作发现，失活Au粒子经三碘甲烷（CHI3）等卤代烃再生处理后，Au纳米尺寸从~30 nm分散为小于1 nm，且分散后的Au催化剂具有更好的催化性能，表明失活的Au催化剂经重新分散而再生。以此为基础，本项目将围绕负载型Au催化剂的制备、失活和再生研究这一任务，在卤代烃种类、碳链长度、制备方法的优化、失活和再生机理等展开理论研究。通过本研究项目的实施，在乙炔氢氯化负载型Au催化剂的失活再生过程及其机理研究中开发出一类反应温和且安全的再生方法，为乙炔氢氯化Au催化剂的关键制备技术奠定科学基础。

负载型Au基催化剂在工业过程中具有非常广泛的潜在应用，如催化加氢/脱氢过程、精细化学品合成、能源催化转化及环境保护等过程，表现出很高的催化活性和选择性Au基催化剂活性物种或活性中心基本由纳米粒子或化合物构成，但在应用过程中因Ostwald熟化效应或粒子迁移作用，尤其是高温高压等苛刻反应条件下，均随应用时间延长从小尺寸粒子逐渐长为大粒子，造成活性降低或完全失活，这也是负载型催化剂失活的最主要原因之一。其中因成本、稀缺等特性，负载型Au催化剂的烧结问题是影响和制约其应用的主要因素.除可通过载体改性、助剂和官能团配位稳定等方法来延缓其失活过程外，对已烧结催化剂的高效、快捷和绿色的再分散/再生过程也具有基础和应用研究的重要意义。本项目采用系列卤代烃（碘代烃、溴代烃和氯代烃）对烧结的Au/AC进行再分散/再生研究.结果表明，在室温常压条件下CHI3可以快捷高效地对烧结Au/AC催化剂进行再分散/再生，具有最优的再分散性能；通过对系列碘代烃C-I键的解离能分析，发现C-I解离能越低越有利于大粒子Au的再分散。同时，溴代烃和氯代烃对烧结的Au/AC催化剂也具有再分散能力，但比碘代烃的再分散效率低。C-X键的解离能与再分散效率有高相关性，即C-X键的解离能越低越有利于Au的再分散.总体上，三类卤代烃再分散效率高低顺序为C-I > C-Br > C-Cl.进而，通过不同分散过程中Au粒子分散状态推测了卤代烃对Au粒子的再分散机理，即卤代烃先在Au粒子表面化学吸附，然后C-X键解离，形成Au-X物种，小粒子Au在AC表面聚集并稳定，最后形成高分散Au粒子（粒径<1 nm）催化剂。以乙炔氢氯化反应考察了再生Au/AC催化剂性能，结果表明，该催化剂上乙炔转化率可达79.4%，基本恢复至初始水平，且该方法可对失活催化剂进行多次高效再生。同时，对于形成高稳态Au基催化剂用于乙炔氢氯化催化过程，我们研发了三类高稳定性催化体系，即重稀土元素促进型Au基催化剂；非金属元素官能团稳定高价态Au催化剂；以及金属载体强相互作用自动再生Au基催化剂体系。所研发催化剂表现出巨大的应用价值。