共查询到20条相似文献,搜索用时 93 毫秒
1.
本文用“原位”FT-IR光谱研究乙苯在氧化铁系催化剂上的吸附物种,结合动力学同位素效应对反应速率控制步骤的考察,讨论了该反应的微观机理。 相似文献
2.
3.
4.
采用共沉淀法在多种条件下分别制备氧化铁及其负载金催化剂,测定其水煤气变换反应活性.通过BET-PS,XRD,H2-TPR和CO-TPD等表征手段,研究负载纳米金对氧化铁载体结构、结晶行为、还原性能以及CO吸脱附性质的影响,探讨氧化铁负载金催化剂的活性相.结果表明:(1)负载纳米金能抑制氧化铁载体在焙烧时的结晶过程,提高其还原性能以及增加表面CO吸附中心.但这种抑制作用与催化剂的制备条件(如沉淀剂种类、沉淀方式和焙烧温度等)密切相关.(2)氧化铁负载金催化剂的低温高活性(<300℃)可能是纳米金粒子与Fe3O4相协同作用的结果,在高温区(>300℃)仍是Fe3O4相起主要催化作用. 相似文献
5.
6.
乙苯脱氢制苯乙烯氧化铁系催化剂的研究——晶格氧的作用 总被引:1,自引:0,他引:1
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. 相似文献
7.
8.
9.
苯乙烯是一种重要的化工原料 ,是合成聚苯乙烯等高分子材料的单体 .目前 ,工业上苯乙烯的生产采用两步法工艺 ,即苯和乙烯在 Al Cl3或 HZSM- 5催化剂上烷基化合成乙苯 ,然后乙苯再在含有助催化剂的氧化铁系催化剂上脱氢得到苯乙烯 .在另一部分工作中 ,我们采用金属负载 HZSM- 5分子筛催化剂研究了苯和乙烯一步合成苯乙烯反应 ,结果表明 ,Co/HZSM- 5是较好的催化剂[1] ,并提出了反应是经过中间物乙苯脱氢生成苯乙烯的机理 [2 ] .实验还发现 ,催化剂的焙烧和还原温度对苯乙烯的收率有很大影响 .本工作结合 XRD,TPR和 DRS等方法对 Co… 相似文献
10.
由于传统化石燃料的不可再生性和使用过程中对环境的污染,近年通过太阳光驱动催化水分解制备氢气或CO_2还原制备甲醇等高能化学燃料是人工光合作用制备太阳能燃料领域的研究重点.水的氧化反应是制备太阳能燃料的重要半反应,为质子或CO_2的还原提供必需的质子和电子,开发基于非贵金属氧化物的高效水氧化催化剂是人工光合作用制备太阳能燃料的重要挑战之一.最近我们课题组的研究发现,无定形氧化钴作为水氧化催化剂时,其本征活性比结晶态的高出一个数量级.与氧化钴催化剂相比,铁基氧化物作为水氧化催化剂具有许多优点,比如成本低、环境友好、对动植物不产生生理毒性.基于此,本文探索了开发制备具有高催化活性的铁基氧化物作为水氧化催化剂.结果发现,氧化铁水氧化催化剂活性不但受其结晶度影响,还与其水合状态密切相关.水合氧化铁在进行室温真空干燥脱水处理后,在Ru(bpy)3~(2+)-Na_2S_2O_8光催化水氧化体系中,其催化水氧化活性降低了一个数量级.热重分析、XRD和拉曼测试等结果表明,室温下进行脱水处理后,氧化铁基本不含有水分子的信号,其体相结构没有发生显著的变化. XRD和拉曼结果表明,催化水氧化测试后回收的氧化铁催化剂结构没有发生改变,表明该水合状态的氧化铁是水氧化过程中真实的催化剂成分,并不是充当前驱体的角色.基于此,我们进一步制备了尺寸较小且为水合状态的无定形氧化铁纳米粒子,后者在Ru(bpy)_3~(2+)-Na_2S_2O_8光催化水氧化体系中显示出极高的催化活性, TOF值高达9.3 s~(-1),基于产生的氧气分子计算的光催化量子效率达到67%.该尺寸较小的水合状态氧化铁纳米粒子还可以有效地负载在SiO_2表面进行催化水氧化反应,循环测试结果表明,负载的水合状态氧化铁纳米粒子连续进行三个催化水氧化循环测试,其活性未明显衰减,显示了较高的稳定性.该结果表明,未来设计铁基氧化物作为高活性的水氧化催化剂时,需要特别考虑其水合状态. 相似文献
11.
V. R. Choudhary V. H. Rane S. T. Chaudhari 《Reaction Kinetics and Catalysis Letters》1998,63(2):371-377
Pulse reaction of methane in the presence and absence of free (or gaseous) oxygen and that of ethane and ethylene in the absence
of free oxygen over Li−MgO, La−MgO and Sm−MgO (Li or La or Sm/Mg ratio=0.1) have been investigated for elucidating the role
of lattice and free oxygen in oxidative coupling of methane (OCM) over these catalysts. No significant role is played by the
lattice oxygen from these catalysts in the OCM process. The presence of free oxygen is essential for all these catalysts to
be active and selective in OCM process. However, lattice oxygen plays some role in ethane conversion but a very significant
role in ethylene conversion over these catalysts. 相似文献
12.
Abdelhakim Kaddouri 《Reaction Kinetics and Catalysis Letters》2004,82(2):401-409
The reaction of C2H6with lattice oxygen, O2- (in the absence of gaseous oxygen), or “adsorbedℍ oxygen (in the presence of gaseous oxygen) over NiMoO4 catalysts has been performed and compared to C3H8 activation. The results obtained indicate that adsorbed oxygen exhibits a higher reactivity to C2H6, while lattice oxygen is more reactive relative to C3H8. Kinetic studies of these two reactions in presence of molecular oxygen have indeed shown that the ethane oxidative dehydrogenation
(ODH) is dependent on the oxygen partial pressure, whilst on the contrary propane ODH is not. In order to confirm the presence
of “adsorbed” oxygen for ethane activation, ODH tests have been performed with N2O. On increasing temperature, the O- adsorbed species enhances the mild oxidation of ethane. The activation energy of ethane consumption EC2H6, relative to propane (EC3H8 = 133 kJ/mol) is 145 kJ/mol. A possible mechanism is proposed for the oxidative dehydrogenation of ethane.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
Experimental data are presented for comparison of the determination of oxygen by the16O(3He, p)18F,16O(3He, α)15O and18O(p, α)15N prompt nuclear reactions, and of their use in the lattice location, by the ion-channelling technique, of oxygen atoms in
single crystal targets of elements such as niobium, where oxygen contents of ≈0.1 atomic % or more can be obtained. Both reaction
cross-sections and lattice-defect production rates are considered in the comparison. Details are given of an arrangement for
automatic crystallographic angular scanning of nuclear reaction and backscattering yields in channelling/lattice location
measurements. 相似文献
14.
SrxBi1-xFeO3-δ (SBF) series mixed conductors were synthesized using standard ceramic method. The properties of such materials were characterized
by XRD, O2-TPD techniques. Abnormal crystal phenomena were found and explained and correlated with the oxygen permeation results. By
analysis of the critical radius (rc), the degree of openness of the lattice (Fv) and the average metal-oxygen bonding energy of the perovskite lattice (ABE), it was proposed that the oxygen permeation
flux is determined mainly by the oxygen diffusion rate in bulk when 1-x⩽0.5, and by the concentration of oxygen vacancy when 1-x ⩾ 0.5. The stability of Sr0.5Bi0.5FeO3-δ was also investigated, and the high stability of it was attributed to the stable BO6 octahedra. 相似文献
15.
L. A. Isupova I. S. Yakovleva G. M. Alikina V. A. Rogov V. A. Sadykov 《Kinetics and Catalysis》2005,46(5):729-735
Oxygen species and their reactivity in La1 − x
Sr
x
FeO3 − y
perovskites prepared using mechanochemical activation were studied by temperature-programmed reduction (TPR) with hydrogen
and methane. The experimental data were compared with data on the catalytic activity in oxidation reactions. It was found
that the rates of CO and methane oxidation on the perovskites in the presence of gas-phase oxygen correlated (k = 0.8) with the amount of reactive surface oxygen species that were removed by TPR with hydrogen up to 250°C. Maximum amounts
of this oxygen species were released from two-phase samples (x = 0.3, 0.4, and 0.8), which exhibited an enhanced activity in the reaction of CO oxidation. In the absence of oxygen in the
gas phase, methane is oxidized by lattice oxygen. In this case, the process activity and selectivity depend on the mobility
of lattice oxygen, which is determined by the temperature, the degree of substitution, the degree of reduction, and the microstructure
of the oxide. Thus, the high mobility of oxygen, which is reached at high concentrations of point defects or interphase/domain
boundaries, is of importance for the process of deep oxidation. However, the process of partial oxidation occurs in single-phase
samples at low degrees of substitution (x = 0.1–0.2).
__________
Translated from Kinetika i Kataliz, Vol. 46, No. 5, 2005, pp. 773–779.
Original Russian Text Copyright ? 2005 by Isupova, Yakovleva, Alikina, Rogov, Sadykov. 相似文献
16.
17.
Evaluating the Effect of Radiation Damage on the Photocatalytic Performance of H2+‐implanted Hematite Electrodes
下载免费PDF全文
![点击此处可从《中国化学会会志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kun Qin Chien‐Hsu Chen Jianrong Li Yi‐Kong Hsieh TsingHai Wang Chu‐Fang Wang 《中国化学会会志》2016,63(8):725-733
The content of oxygen vacancy in hematite is known to play an important role in photocurrent enhancement. We found that implanting high energy H2+ to hematite photoelectrodes indeed injected additional oxygen vacancy and thus the conductivity of hematite was increased. However, inevitable radiation damage on the other hand distorted hematite lattice structure. Although post annealing will relax the lattice distortion to a certain degree, most implanted and post annealed hematite photoelectrodes exhibited deteriorated photocatalytic activities than the one without implantation. It seems that structure engineering is more effective in photocurrent enhancement than the injection of additional oxygen vacancy. 相似文献
18.
Catalytic reactions with oxygen are divided into two groups: electrophilic oxidation proceeding through activation of oxygen, and nucleophilic oxidation in which insertion of nucleophilic oxygen species into previously activated organic molecule occurs. The role of different types of lattice oxygen in the nucleophilic oxygen addition as well as catalyst properties determining the electrophilic pathway are discussed. 相似文献
19.
Elena L. Gubanova Vladislav A. Sadykov Andre C. van Veen Claude Mirodatos 《Reaction Kinetics and Catalysis Letters》2009,97(2):349-354
The temporal analysis of products (TAP) technique coupled with the oxygen TPD was used to elucidate the effects of the Pt-supported
fluorite-like doped ceria–zirconia oxide chemical composition and the type of pretreatment on their oxygen bonding strength,
mobility, and reactivity as related to catalytic properties in the partial oxidation of methane into synthesis gas. A rapid
evolution of hydrogen under CH4 pulse observed for oxidized catalysts agrees with the direct route of the methane selective oxidation into syngas. This route
is favored by the Pt-support interaction and a moderate bonding strength of surface oxygen species along with a high lattice
oxygen mobility. 相似文献
20.
Enyue Zhao Qinghao Li Fanqi Meng Jue Liu Junyang Wang Lunhua He Zheng Jiang Qinghua Zhang Xiqian Yu Lin Gu Wanli Yang Hong Li Fangwei Wang Xuejie Huang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4367-4371
Lattice‐oxygen redox (l‐OR) has become an essential companion to the traditional transition‐metal (TM) redox charge compensation to achieve high capacity in Li‐rich cathode oxides. However, the understanding of l‐OR chemistry remains elusive, and a critical question is the structural effect on the stability of l‐OR reactions. Herein, the coupling between l‐OR and structure dimensionality is studied. We reveal that the evolution of the oxygen‐lattice structure upon l‐OR in Li‐rich TM oxides which have a three‐dimensional (3D)‐disordered cation framework is relatively stable, which is in direct contrast to the clearly distorted oxygen‐lattice framework in Li‐rich oxides which have a two‐dimensional (2D)/3D‐ordered cation structure. Our results highlight the role of structure dimensionality in stabilizing the oxygen lattice in reversible l‐OR, which broadens the horizon for designing high‐energy‐density Li‐rich cathode oxides with stable l‐OR chemistry. 相似文献