The Role of Lattice Oxygen and Potassium in Iron-Oxide-Based Catalyst For Dehydrogenation of Ethylbenzene

采用程序升温还原反应（TPr）、XPS、高温真空Xrd及活性和比表面测定等方法对单组分fE_2O_3、双组分fE_2O_3-k_2O催化剂及工业用XH-03催化剂研究晶格氧的性质和钾的助催作用；结果表明，纯fE_2O_3催化剂表面氧种的还原程度差别较大，反应时晶格氧易于失去，造成缺氧而迅速失活，钾的加入使催化剂生成新的k_2f_E2O_4相，其表面氧种的还原性趋向一定的温度范围，晶格氧数量增加，且其稳定性也增加，从而同时促进了氧转移脱氢和直接脱氢反应的活性，因此认为k_2fE_2O_4可能是活性相，脱氢反应的活性中心应由fE--（2＋）、fE--（3＋）、还原程度一定的晶格氧和k--＋组成。The role of lattice oxygen and potassium in iron-oxide-based catalysts (Fe_2O_3, Fe_2O)3-K)2O and commercial XH-0 3 ) has been investigated by using TPR(temperature programmed reduction), XPS, high temperature XRD and determination of activity and speciFic surFace area, The high temperature XRD study of the K-promoted iron-oxide catalyst has been shown to have the Formation of new crystalline phase of K_2Fe_2O_4, which promoted the reaction activity. The reduction levels of lattice oxygen are considerably diFFerent at the surFace of Fe_2O_3 catalyst beFore and aFter the reaction.The lattice oxygen was Found to lose easily and resulted in deFiciency of oxygen, which brought about the deactivation of the catalyst on the unpromoted Fe_2O_3 catalyst.At the surFace of K-promoted catalyst, it has an increase in quantity and stability of lattice oxygen and , consequently , increases the activity of the direct heterolytic dehydrogenation and oxygen-transFer dehydrogenation of ethylbenzene.The role of K is to stabilize the interconversion between Fe￣(2+) and Fe￣(3+) and to improve the electron transport between the neighboring active-sites, subseqently promoted the dehydrogenation and the selFregeneration.In this paper, the active phase of the catalyst is suggested to be K_2Fe2O_4 and the active center ofdehydrogenation to be consisted of Fe￣(2+), Fe￣(3+), lattice oxygen at certain reduction level and K￣+

铈助催铁系乙苯脱氢催化剂的XPS、TPR研究

通过XPS、TPr-gC和Xrd发现，铁系乙苯脱氢催化剂中的CEO＿2在反应条件下会被部分还原，而且，氧化钵和氧化铁之间有一定程度的相互作用，其结果是使负电荷由铁向铈迁移并增加了氧化铁的抗还原能力。基于上述事实，讨论了铈助催化作用的本质。中国石油化工总公司资助项

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

[中文文摘]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.[英文文摘]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 H2O produced 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 ethylbenzene plus D2O as the feed,determination of the change in D2/H2 ratio in the exit gas for very high and very low space velocities;and(3)with ethylbenzene plus D218O as the feed,observation of isotopic exchange of lattice 16O with steam 18O from the red shifts in the IR spectra of the used catalyst.The results indicate that direct heterolytic dehdrogenation of ethylbenzene appcared to be the major rection pathway,but a minor reaction pathway of ethylbenzene dehydiogenation by oxygen-transfer mechanism also appcared to make an apprceiable 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 phascs of their redox cycles is pointed out