Cr/NaZSM-5催化剂上CO2氧化丙烷脱氢反应

以亚微米级NaZSM-5为载体合成了一系列负载型Cr催化剂, 采用氮气吸附、 XRD、 UV-Vis和H2-TPR对Cr/NaZSM-5催化剂的结构和织构性质进行了表征, 并评价了催化剂在CO2气氛下的丙烷脱氢性能. 硅铝摩尔比为60, Cr质量分数为3%的催化剂具有最高的反应活性, 于550 ℃反应10 min和8 h后的丙烷转化率分别为48.3%和30.1%, 丙烯选择性则分别为86.0%和91.8%. 催化剂中的Cr6+含量和反应初活性具有良好的对应关系, 表明高Cr6+含量对催化剂表现出高的丙烷脱氢活性是至关重要的. CO2气氛下的丙烯产率明显比氮气气氛下的高, 这是由于CO2气氛下催化剂表面有较多量的Cr6+, 并且CO2可通过逆水煤气变换反应除去脱氢反应生成的氢.     

钴基催化剂上乙烷氧化脱氢的催化作用

比较了氧化钴、氧化镍分别对乙烯、乙烷氧化的催化性能,结果发现：乙烯在氧化钴较氧化镍上更易进一步深度氧化生成CO2．通过对新制担载型Co-基催化剂随反应温度反复升、降温的乙烷氧化脱氢(ODHE)性能研究,展现了氧化钴活性相与SiO2载体相互作用对催化性能的影响．Weiss原位磁研究结果表明：SiO2担载的氧化钴催化剂较难还原,即使在反应气中氧被完全耗完时,钴仍停留在Co^2 的价态上．通过对数十个担载和未担载、不同载体、不同担载量的Co-基催化剂的ODHE性能考察表明：在Co-基催化剂上ODHE反应机理一般遵从Hetero-homogeneous机理．     

Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane

Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B₂O₃ due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B₂O₃ from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h⁻¹ g⁻¹, which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN.     

Radical Chemistry and Reaction Mechanisms of Propane Oxidative Dehydrogenation over Hexagonal Boron Nitride Catalysts

Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas‐phase methyl radicals (CH₃^.) in the ODHP reaction over boron‐based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C?H activation of propane, while C₂ and C₁ products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts.     

异丁烷在Cr2（MOO4）3,Fe2（MoO4）3催化剂上的无氧脱氢与氧化脱氢

研究了Ｃｒ２（ＭｏＯ４）３、Ｆｅ２（ｍＯ４）３、对异丁烷无氧脱氢与氧化氢的催化性能，在无氧脱氧反应中，催化剂的表面酸性既有利于异丁烷活性生成异丁烯，又易引起裂和异构化等副反应，在氧化脱氢反应中，异丁烯选择性较低，催化剂的表面酸中心对反应中间体的吸附将导致深度氧化。     

Influence of the Time Scale on the Reaction Mechanism of CO Oxidation over a Au/TiO2 Catalyst

Knowledge of the reaction mechanism is key for rational catalyst improvement. Traditionally mechanistic studies focus on structure and the reaction conditions like temperature, pH, pressure, etc., whereas the time dimension is often overlooked. Here, we demonstrate the influence of time on the mechanism of a catalytic reaction. A dual catalytic mechanism was identified for the CO oxidation over Au/TiO₂ by time-resolved infrared spectroscopy coupled with modulation excitation spectroscopy. During the first seconds, CO on the gold particles is the only reactive species. As the reaction proceeds, the redox properties of TiO₂ dominate the catalytic activity through electronic metal-support interaction (EMSI). CO induces the reduction and reconstruction of TiO₂ whereas oxygen leads to its oxidation. The activity of the catalyst follows the spectroscopic signature of the EMSI. These findings demonstrate the power of studying short-time kinetics for mechanistic studies.     

稀土氟氧化物在丙烷,异丁烷氧化脱氢中的催化作用

稀土氟氧化物在丙烷、异丁烷氧化脱氢中的催化作用张伟德＊洪碧凤古萍英万惠霖蔡启瑞（厦门大学化学系，固体表面物理化学国家重点实验室，物理化学研究所厦门３６１００５）关键词丙烷，异丁烷，催化氧化脱氢，稀土氟氧化物１９９７－１０－０６收稿，１９９８－０１－０...     

环氧丙烷的合成及反应机理

综述了环氧丙烷的合成方法,包括氯醇法、间接氧化法(Halcon法)、丙烯的H_2O_2氧化法及生物催化氧化法,探讨了Halcon过程的反应机理。概述了环氧丙烷的主要用途。参考文献26篇。     

溶胶-凝胶和浸渍法制备的铜催化剂在仲丁醇脱氢反应中的研究

采用溶胶-凝胶和浸渍法制备Cu/SiO2催化剂, 研究了不同制备方法对催化剂表面Cu物种的存在状态和其催化性能的影响. 采用BET, XRD, EPR和TPR等手段对催化剂进行了表征, 结果表明, 溶胶-凝胶法可制备高分散铜催化剂, 该催化剂中存在孤立的不可还原的Cu2+和可还原的Cu2+簇两种物种. 浸渍法制备的催化剂中含有可还原的Cu2+簇物种. 反应活性测试结果表明, 不可还原的孤立Cu2+呈高分散状态, 但其对仲丁醇脱氢反应没有活性; 可还原的Cu2+在反应过程中被还原成Cu0, Cu0是反应稳定脱氢的活性中心.     

MOPO/SiO2催化剂上丙烷选择氧化制丙烯醛反应机理

 考察了丙烷以及丙烷选择氧化反应的有关中间体或其探针分子(如丙烯、烯丙醇、异丙醇和正丙醇)和产物(如丙烯醛、丙酮和丙醛)在MoPO/SiO2催化剂上的反应行为,用以探明该催化剂上丙烷选择氧化制丙烯醛反应的可能路径. 结果表明,异丙氧基是MoPO/SiO2催化剂上丙烷选择氧化制丙烯醛反应的主要中间体,异丙氧基脱β-H生成丙烯或脱α-H生成丙酮,而丙烯则经σ-氧烯丙基转化为丙烯醛.     

开环茂金属成环及氢分子消除反应机理的理论研究

采用密度泛函方法(DFT)在M06-2X/def2-TZVPP//B3LYP/def2-TZVPP+ZPE水平下, 对以开环的(η⁵-C₅H₇)₂Ru为前驱体生成闭环(η⁵-C₅H₅)₂Ru的各种可能的反应路径进行了详细的研究. 最终确定其反应机理为: (η⁵-C₅H₇)₂Ru的一个η⁵-C₅H₇发生端碳成键的成环反应形成(η³-C₅H₇)Ru(η⁵-C₅H₇), 经过两步氢原子迁移到Ru原子上, 之后脱掉一个氢气分子形成(η⁵-C₅H₅)Ru(η⁵-C₅H₇), 而后另一个η⁵-C₅H₇再重复成环并进行两步氢迁移以及氢气分子消除而得到最终的产物(η⁵-C₅H₅)₂Ru.     

乙烷氧化脱氢制乙烯反应中制备方法及助剂对镍基催化剂性能的影响

采用不同方法制备了镍基催化剂,并考察了乙烷氧化脱氢制乙烯(ODE)的反应活性,结果表明,在3种不同制备方法的催化剂上,ODE反应的活性及产物选择性存在明显差异,浸渍法制备的催化剂性能最佳.在相同的条件下,以共浸渍法引入CeO2助剂后,N iO/-γA l2O3催化剂上的低温选择氧化活性显著提高,而目的产物C2H4的选择性变化不大.XRD,还原TG和XPS对催化剂进行表征的结果显示:反应的活性物相可能是易于还原的高度分散于催化剂表面的微晶N iO和表面尖晶石N iA l2O4物相;高分散的微晶N iO,类似于纯N iO,有利于ODE反应低温选择氧化生成目的产物C2H4,而易还原的表面尖晶石N iA l2O4物相的存在则可能是在高温下获得高选择氧化活性和选择性的主要原因之一.     

激光促进钼、钒氧化物表面乙烷氧化脱氢反应规律的研究

制备了Ｖ２Ｏ５、ＭoＯ３和Ｖ２Ｏ５．ＭoＯ３复合氧化物催化剂,并进行了ＩＲ表征;对催化剂表面乙烷的吸附性能进行了ＩＲ和ＴＰＤ表征。用激光促进表面反应（ＬＳＳＲ）技术,考察了乙烷氧化脱氢生乙烷的反应规律。结果表明,氧化物表面的Ｖ＝Ｏ和Ｍo＝Ｏ键的吸附能力,在不同的激光激发频率下,ＬＳＳＲ反遵循吸附态激发机理或固体表面键激发机理。温度对ＬＳＳＲ反应有一定的辅助作用。     

Oxidative Dehydrogenation of Propane over a VO2‐Exchanged MCM‐22 Zeolite: A DFT Study

The adsorption and the mechanism of the oxidative dehydrogenation (ODH) of propane over VO₂‐exchanged MCM‐22 are investigated by DFT calculations using the M06‐L functional, which takes into account dispersion contributions to the energy. The adsorption energies of propane are in good agreement with those from computationally much more demanding MP2 calculations and with experimental results. In contrast, B3LYP binding energies are too small. The reaction begins with the movement of a methylene hydrogen atom to the oxygen atom of the VO₂ group, which leads to an isopropyl radical bound to a HO? V? O intermediate. This step is rate determining with the apparent activation energy of 30.9 kcal mol^?1, a value within the range of experimental results for ODH over other silica supports. In the propene formation step, the hydroxyl group is the more reactive group requiring an apparent activation energy of 27.7 kcal mol^?1 compared to that of the oxy group of 40.8 kcal mol^?1. To take the effect of the extended framework into account, single‐point calculations on 120T structures at the same level of theory are performed. The apparent activation energy is reduced to 28.5 kcal mol^?1 by a stabilizing effect caused by the framework. Reoxidation of the catalyst is found to be important for the product release at the end of the reaction.     

Reaction Mechanism and Product Branching Ratios of OH+C2H3F Reaction: A Theoretical Study

Ab initio CCSD(T)/CBS//B3LYP/6-311G(d, p) calculations of the potential energy surface for possible dissociation channels of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F, as well as Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of rate constants, were carried out, in order to predict statistical product branching ratios in dissociation of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F at various internal energies. The most favorable reaction pathway leading to the major CH\begin{document}$_2$\end{document}CHO+HF products is as the following: OH+C\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F\begin{document}$\rightarrow$\end{document}i2\begin{document}$\rightarrow$\end{document}TS14\begin{document}$\rightarrow$\end{document}i6\begin{document}$\rightarrow$\end{document}TS9\begin{document}$\rightarrow$\end{document}i3\begin{document}$\rightarrow$\end{document}TS3\begin{document}$\rightarrow$\end{document}CH\begin{document}$_2$\end{document}CHO+HF, where the rate-determining step is HF elimination from the CO bridging position via TS11, lying above the reactants by 3.8 kcal/mol. The CH\begin{document}$_2$\end{document}O+CH\begin{document}$_2$\end{document}F products can be formed by F atom migration from C\begin{document}$_\beta$\end{document} to C\begin{document}$_\alpha$\end{document} position via TS14, then H migration from O to C\begin{document}$_\alpha$\end{document} position via TS16, and C-C breaking to form the products via TS5, which is 1.8 kcal/mol lower in energy than the reactants, and 4.0 kcal/mol lower than TS11.     

Theoretical Study on Mechanism and Kinetics of Reaction of O(3P) with Propane

The reaction of C₃H₈+O(³P)→C₃H₇+OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Møller-Plesset perturbation method and the single-point energy is computed using the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C₃H₈+O(³P)→i-C₃H₇+OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogen-abstraction from propane involving reaction channel competitions is helpful for the under-standing of propane combustion.     

Selective Cascade Reaction of Bisallenes via Palladium‐Catalyzed Aerobic Oxidative Carbocyclization–Borylation and Aldehyde Trapping

A cascade reaction, consisting of a palladium‐catalyzed regioselective aerobic oxidative carbocyclization–borylation of bisallenes and a final aldehyde trapping, afforded triene alcohols with high diastereoselectivity. The cascade reaction occurs under mild reaction conditions and proceeds via an allylboron intermediate that is trapped by the aldehyde in a stereoselective manner.