乙苯脱氢制苯乙烯氧化铁系催化剂的研究——晶格氧的作用

本文探讨了乙苯催化脱氢制苯乙烯工业氧化铁系催化剂晶格氧与水蒸汽氧的交换以及晶格氧参与反应的微观机理.实验结果表明:催化剂晶格氧参与反应,与水蒸汽氧有交换,反应途径以直接脱氢为主,并发生氧转移脱氢.讨论了两种脱氢反应途径中,晶格氧参与反应的微观过程.强调指出,晶格电子传递和邻近活性位氧化还原周期协同进行是氧转移脱氢机理的必要条件.

Mechanistic Studies on Catalytic Dehydrogenation of Ethylbenzene Over Iron-Oxide-Based Catalyst Systems --Role of Lattice Oxygen

The role of lattice oxygen in catalytic dehydrogcnation of ethylbenzene over industrial iron-oxide-based catalysts, 11^# (Cr-consaining) and 210^#(Cr-free), has been investigated by means of the following experiments: (1) Determination of amounts of H₂Oproduced due to removal of lattice oxygen by reaction with ethyl-benzene used as the feed without addition of steam, and observation of gradual decay of catalytic activities, and changes in the X-ray powder-diffraction patterns of the used catalysts; (2) with elhylbcnzcne plus D_{2Oas the feed, determination of the change in D2/H2 ratio in the exit gas for very high and very low space velocities; and (3) vvith ethylbenzene plus D2¹⁸Oas the feed, observation of isotopic exchange of lattice ¹⁶Owith steam ¹⁸Ofrom the red shifts in the IRspectra of the used catalyst. The results indicate that direct heterolytic dehydrogenalion of ethylbenzene appcared to be the major rcction pathway, but a minor reaction pathway of cthyl-benzcne dehydiogenation by oxygen-transfer mechanism also appeared to make an appreciable contribution (about 20%) to the overall conversion. Mechanisms of these two reaction pathways are discussed. For the oxygen-transfer dehydrogenation mechanism, the importance of electron transport between neighboring active-sites operating cooperatively in opposite phases of their redox cycles is pointed out.}