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1.
通过仿生催化,将苯乙烯、氧气(O2)和二氧化碳(CO2)直接合成环状碳酸酯在现代化学中极具学术研究意义和工业应用价值。采用钴卟啉-四丁基溴化铵为双组分催化剂,以2-氧代环戊烷羧酸甲酯为助剂,在O2和CO2条件下,直接将苯乙烯转化为碳酸苯乙烯酯。系统考察了催化剂用量等因素对催化性能的影响。在最佳反应条件下,苯乙烯的转化率高达99%,环状碳酸酯的收率可达35%。利用在线紫外与在线红外探讨了该串联反应可能的机理。结果表明,钴中心与2-氧代环戊烷羧酸甲酯的环内氧原子配位后活化氧气形成过氧活性物种,进而形成高价钴-氧中间体,其通过传递氧原子给苯乙烯而生成环氧苯乙烷。而后,环氧苯乙烷在四丁基溴化铵的催化作用下开环,并通过CO2插入反应和分子内闭环反应最终生成环状碳酸酯。 相似文献
2.
Carbon dioxide (CO2) utilization and fixation have become one of the most important research areas nowadays due to the increase of global greenhouse effect. Cyclic carbonate, which is widely used in various fields, can be synthesized by fixation of CO2 with epoxide in industry. Moreover, the synthesis of cyclic carbonate is a 100% atom economical reaction, which makes it eco-friendly and promising. To enhance the reaction efficiency and safety, a microreaction system was used as the platform for cycloaddition reaction. In this work, tetrabutylammonium bromide (TBAB) was chosen as catalyst, and propylene oxide (PO) as a mode substrate. Interestingly, the addition of water can increase the propylene carbonate (PC) yield and decrease the activation energy considerably, proving water as catalyst promoter for PC synthesis. PC yield and selectivity could reach 91.6% and 99.8%, respectively. The Influence factors and kinetic equation for CO2 cycloaddition were obtained as well. 相似文献
3.
Zhen Lu Jie He Bogeng Guo Yulai Zhao Jingyu Cai Longqiang Xiao Linxi Hou 《中国化学工程学报》2022,43(3):110-115
The cycloaddition between CO2 and epoxides to produce cyclic carbonate is an attractive and efficiency pathway for the utilization of CO2 as C1 source. The development of catalyst to mediate cycloaddition between CO2 and epoxides at low temperature and pressure is still a challenge. Herein, a series of polypyrazoles with glass transition temperature (Tg) in the range of 42.3–52.5 ℃ were synthesized and served as catalyst to mediate the cycloaddition of CO2 and epoxides by the assistant of tetrabutylammonium bromide. The catalytic behaviors of polypyrazole on the model cycloaddition of CO2 to epichlorohydrin, including the reaction parameters optimization and versatility were investigated in detail, and excellent yield (99.9%) and selectivity (99%) were obtained under the optimized reaction conditions of 70 ℃ and 1.0 MPa for 6.0 h. Noteworthily, the polypyrazole acts as homogeneous catalyst during reaction (higher than Tg). And under room temperature, polypyrazoles can be easily separated and recovered, which is a promising feature of a heterogeneous catalyst. Furthermore, the reaction mechanism was proposed. The DFT calculation suggested that the formation of hydrogen bond between pyrazole and epoxide greatly reduced the energy barrier, which play an important role in promoting CO2 cycloaddition. 相似文献
4.
A study is reported of the CO2 dissociation pressures for molten carbonates using an emf technique. In the gas concentration cell Au/O2(CO2)diss/CO32−/CO2, O2/Pt, the conditions are adjusted so that the CO2 in the Au compartment is due to the carbonate dissociation. It is shown that EoAu(CO2/O2) = EoPt(CO2/O2) and it follows that this technique may thus be used to monitor the CO2 dissociation pressures of the electrolyte in a continuous manner, with minimum disturbances. The method appears particularly suited for very low dissociation pressure measurements. 相似文献
5.
流化床富氧燃烧湿烟气循环兼具经济与环保优势。湿烟气循环(O2/CO2/H2O)条件下煤焦与O2、CO2及H2O的反应同时发生。为探究O2/CO2/H2O气氛下煤焦-O2、煤焦-CO2、煤焦-H2O反应间的相互作用机制,在自制高精度热重实验装置上系统考察了O2、CO2、H2O及其混合气氛下,典型烟煤焦在900℃的反应特性。基于吸附和脱附原理的Langmuir-Hinshelwood(L-H)机理性模型分别计算了烟煤焦与O2、CO2和H2O反应的动力学参数。通过采用单独活性位点与竞争活性位点两种假设分析了O2/CO2、O2/H2O和CO2/H2O气氛下烟煤焦-O2、烟煤焦-CO2和烟煤焦-H2O两两反应间的作用机制,揭示了H2O分子优先吸附于烟煤焦表面活性位点,O2分子次之,而CO2分子相对滞后。O2/CO2/H2O气氛下烟煤焦-O2、烟煤焦-CO2、烟煤焦-H2O反应表现出部分竞争反应活性位点,传统的单独活性位点与竞争活性位点假设均无法准确描述其反应速率特性。基于H2O分子优先,O2分子次优先吸附的原理,建立了O2、CO2、H2O混合气氛下煤焦反应速率L-H动力学方程,方程计算结果与实验值良好吻合。研究结果为深入分析煤焦颗粒流化床富氧燃烧特性及构建可靠、准确的燃烧反应模型提供了理论支撑。 相似文献
6.
富氧燃烧是最具工业化前景的燃烧中碳捕集技术之一,为更深入掌握煤粉富氧燃烧的着火模式和污染物生成特性,本文构建了热重-质谱联用实验系统,以烟煤和无烟煤标准煤样为对象,针对3个不同的氧气体积分数:21%、30%和50%,研究了O2/Ar和O2/CO2气氛下煤粉的富氧燃烧特性。结果表明,O2/CO2气氛下煤粉着火温度和燃尽温度均降低,燃烧速率提高,燃烧时间缩短;两种煤粉在O2/Ar气氛下的燃烧都属于非均相着火,而富氧燃烧都属于均相着火模式;氧气体积分数在30%以上时,无烟煤O2/CO2燃烧的表观活化能明显低于O2/Ar气氛,在相同工况下烟煤的表观活化能均低于无烟煤;O2/CO2气氛促进了CO和挥发分NO的逸出,生成温度均低于O2/Ar气氛,CO会对NO起到还原作用。 相似文献
7.
S. J. Korf J. A. Roos J. A. Vreeman J. W. H. C. Derksen J. G. van Ommen J. R. H. Ross 《Catalysis Today》1990,6(4):417-426
The rate of reaction of methane with oxygen in the presence of a Li/Sn/MgO catalyst has been studied as a function of the partial pressures of CH4, O2 and CO2 using a well-mixed reaction system which is practically gradientless with respect to gas-phase concentrations. It is concluded that the rate-determining step involves reaction of a molecule of CH4 adsorbed on the catalyst surface with an adsorbed di-atomic oxygen species. The kinetics are consistent with a Langmuir-Hinshelwood type mechanism involving competitive adsorption of CH4, O2 and CO2 on a single site. A comparison is made with previously published results for the Li/MgO material. 相似文献
8.
本研究主要在光照条件下,利用Na2CO3/H2O2反应体系降解偶氮染料酸性橙8(AO 8),考察了光照条件对AO 8降解的影响,探究了不同活性基团对AO 8降解的贡献。结果表明,在光照条件下Na2CO3和H2O2可以产生协同效应,与单独加入Na2CO3或H2O2相比,能够有效促进偶氮染料AO 8的降解。在优化条件下,该体系中AO 8的降解率达到73.83%。同时研究分析了不同活性基团在AO 8降解过程中的作用,其中贡献率表现依次为CO3·->HO·>O2·->1O2。本研究结果可为偶氮染料废水的处理提供了一条新的途径。 相似文献
9.
Soot formation was investigated numerically with CO2 addition in a jet-stirred/plug-flow reactor (JSR/PFR) C2H4/OJN2 reactor (C/O ratio of 2.2) at atmospheric pressure. An updated Kazakov mechanism empha- sizes the effect of the O2/CO2 atmosphere instead of an O2/N2 one in the premixed flame. The soot formation was taken into account in the JSR/PFR for C2H4/O2/N2. The effects of CO2 addition on soot formation in different C2H4/O2/CO2/N2 atmospheres were studied, with special emphasis on the chemical effect. The simulation shows that the endothermic reaction CO2 + H - CO + OH is responsible of the reduction of hydrocarbon intermediates in the CO2 added combustion through the supplementary formation of hydroxyl radicals. The competition of CO2 for H radical through the above forward reaction with the single most important chain branching reaction H + O2, ' O + OH reduces significantly the fuel burning rate. The chemical effects of CO2 cause a significant increase in residence time and mole fractions of CO and OH, significant decreases in some intermediates (H, C2H2), polycyclic aromatic hydrocarbons (PAHs, C6H6 and CI6H10, etc.) and soot volume fraction. The CO2 addition will leads to a decrease by only about 5% to 20% of the maximum mole fractions of some C3 to Clo hydrocarbon intermediates. The sensitivity analysis and reaction-path analysis results show that C2H4 reaction path and products are altered due to the CO2 addition. 相似文献
10.
DECOMPOSITION BEHAVIOR AND MECHANISM OF CALCIUM SULFATE UNDER THE CONDITION OF O2/CO2 PULVERIZED COAL COMBUSTION 总被引:3,自引:0,他引:3
The decomposition behavior and mechanism of calcium sulfate in O2/CO2 pulverized coal combustion were studied in an entrained flow reactor. A reaction rate expression correlating the influence of various factors was proposed for CaS04 decomposition and it is able to predict CaS04 decomposition satisfactorily. Under the conditions investigated, the decomposition of CaS04 was found to be a regime of chemically controlled shrinking core reaction. A CO2-rich atmosphere enhances CaSO4 decomposition in absence of oxygen. CaSO4 particles have catalytic effect on formation of CO from CO2. A high SO2 concentration inhibits CaSO4 decomposition. The kinetics of CaSO4decomposition has obvious dependence on experimental facilities and conditions, whereas the activation energy has much lower dependence. The kinetics derived in this work is more appropriate for investigating desulfurization in O2/CO2 pulverized coal combustion because an entrained flow reactor has a much closer condition to that in O2/CO2 pulverized coal combustion than a TGA. 相似文献
11.
Angela Dibenedetto Michele Aresta Francesco Nocito Carlo Pastore Anna M. Venezia Ekaterina Chirykalova Vladimir I. Kononenko Vladimir G. Shevchenko Irina A. Chupova 《Catalysis Today》2006,115(1-4):117-123
Reticular oxygen of Al2O3 or CeOx supported on Al2O3 was used for the epoxidation of propene without any double bond cleavage. In batch reaction, Al2O3 alone was able to convert propene into propene oxide (PO) with 100% selectivity and 2% conversion of propene with a close to 3:1 ratio with respect to the number of Al(III) reduced to elemental Al. When Ce2O3/Al2O3 or CeO2/Al2O3 was used, Al remained in its +3 oxidation state, while the Ce oxide was the oxidant as demonstrated by XPS analyses. CeOx/Al2O3 was more active (propene conversion yield of 4–5%) but the selectivity was lower (70%) as PO was isomerized into acetone and propionaldehyde.
Interestingly the use of reticular oxygen very much improves the selectivity with respect to the use of pure O2. In fact, while propene was more efficiently oxidized (10%) with O2 in presence of Al2O3 or CeOx/Al2O3, the selectivity was as low as 40% because C1 and C2 products were formed. However, the use of reticular oxygen represents a selective two-step technique for the use of molecular oxygen as oxidant of propene. The used oxides can be re-oxidized and the whole process can be further improved towards higher yields.
PO is quantitatively converted into propene carbonate by reaction with CO2 in presence of Nb2O5. 相似文献
12.
传统随机孔模型基于简单一步反应建立,不适用于处理O2/CO2气氛下焦炭颗粒复杂气固反应。针对此问题,基于焦炭本身具有多种碳基的特点,以及焦炭颗粒在O2/CO2气氛下燃烧的特性,建立复杂气固反应下的多种碳基随机孔模型和孔隙结构模型。模拟直径为100 μm的焦炭颗粒在O2/CO2气氛下燃烧的过程,使用FORTRAN语言自主编程计算并分析结果。研究表明,燃烧初期颗粒呈现竞争效应,孔隙内部气体浓度产生剧烈波动。波动的生成原因是化学反应与物理扩散之间的竞争,可以通过增加环境氧浓度和减小焦炭颗粒粒径来改善。所提出的多种碳基随机孔模型对于表征O2/CO2气氛下焦炭颗粒的燃烧特性有着良好的适应性。 相似文献
13.
Aiyu Yan Vasiliki Maragou Antonino Arico Mojie Cheng Panagiotis Tsiakaras 《Applied catalysis. B, Environmental》2007,76(3-4):320-327
The effect of carbon dioxide on the chemical stability of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode in the real reaction environment at 450 °C was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), temperature programmed desorption (TPD), X-ray diffraction (XRD) and electrochemical impedance spectra (EIS) techniques. It was found that the presence even of very small quantities of CO2 seriously deteriorates the fuel cell performance at 450 °C. XPS, TPD and XRD results strongly evidenced the formation of carbonates involving strontium and possibly barium after the BSCF cathode was operated in 1% CO2/O2 gas mixture at 450 °C for 24 h. SEM-EDX analysis of the BSCF cathode surface, after treatment in CO2/O2 environment at 450 °C, showed small particles on the surface probably associated with a carbonate phase and a segregated phase of the perovskite. The corresponding EDX spectra confirmed the presence of a carbonate layer and also revealed the surface enrichment of strontium and barium elements. EIS results indicated that both ohmic and polarization resistances increased gradually with the introduction of carbon dioxide in the oxidant stream, which could be interpreted by the decreased oxygen reduction kinetics and the formation of carbonate insulating layer. 相似文献
14.
CO2气体水合物形成热力学性质是实施海水淡化、沼气纯化、碳捕集和封存、能源利用、天然气储存等技术的关键。采用恒容温度搜索法,在温度272.75~294.35 K,压力0.35~4.50 MPa的范围内,探究了四种季铵盐促进剂对CO2气体水合物相平衡的影响。结果表明,相同条件下,季铵盐作用下CO2水合物的相平衡温度由高到低分别为:四丁基氟化铵(TBAF)>四丁基溴化铵(TBAB)>四丁基氯化铵(TBAC)>苄基三乙基氯化铵(TEBAC)。基于Clausius-Clapeyron方程,计算了不同体系的相变潜热,探讨了其对水合物稳定性的影响。可以看出,水合物的相平衡压力对数与温度倒数呈线性关系,其中,TBAF、TBAB作用下的CO2水合物相变潜热相接近且明显高于其他季铵盐,说明其促进效果最好,所对应的水合物生成条件也最为温和。利用Chen-Guo模型,结合PR状态方程和改进Joshi经验活度模型,分别计算了TBAF、TBAB、TBAC和TEBAC作用下CO2水合物热力学相平衡数据,计算结果与实验数据吻合良好,最大平均相对误差为7.50%。 相似文献
15.
The purpose of this study is to investigate the characteristics of soot particles in C2H4/CO2/O2/N2 combustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO2/O2/N2 mixture, the key species C2H2, C3H3 responsible for formation of first aromatic ring, the typical aromatics and 4-ring aromatics total production rate all decrease greatly. In addition, with CO2 mole fraction from 0.2 to 0.5 in the mixture, the soot particle number density, volume fraction, surface area density, which are three most important parameters to soot particle property, are suppressed obviously. Furthermore, the increasing content of CO2 in the oxidizer influences mostly H, OH radical concentrations by two reactions: CO+OH=CO2 H and H+O2=O+OH, and the production rate of H, OH from the two reactions declined, which revealed that CO2 in mixture has an inhibiting effect on soot particle generation. 相似文献
16.
Guoxing Chen Marc Widenmeyer Binjie Tang Louise Kaeswurm Ling Wang Armin Feldhoff Anke Weidenkaff 《Frontiers of Chemical Science and Engineering》2020,14(3):405
A series of novel dense mixed conducting ceramic membranes based on K2NiF4-type (La1–xCax)2 (Ni0.75Cu0.25)O4+δ was successfully prepared through a sol-gel route. Their chemical compatibility, oxygen permeability, CO and CO2 tolerance, and long-term CO2 resistance regarding phase composition and crystal structure at different atmospheres were studied. The results show that higher Ca contents in the material lead to the formation of CaCO3. A constant oxygen permeation flux of about 0.63 mL·min−1·cm−2 at 1173 K through a 0.65 mm thick membrane was measured for (La0.9Ca0.1)2 (Ni0.75Cu0.25)O4+δ, using either helium or pure CO2 as sweep gas. Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO2 concentration. The membrane showed excellent chemical stability towards CO2 for more than 1360 h and phase stability in presence of CO for 4 h at high temperature. In addition, this membrane did not deteriorate in a high-energy CO2 plasma. The present work demonstrates that this (La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δ membrane is a promising chemically robust candidate for oxygen separation applications. 相似文献
17.
综述了近年来离子液体介质中CO2电活化合成有机碳酸酯的研究进展, 着重概述了电催化合成碳酸二甲酯(DMC)和环状碳酸酯的研究现状, 并简述了CO2间接电活化和直接电活化技术, 以及反应介质、电极材料等因素对反应产物的影响, 对电催化还原CO2的关键技术和今后研究重点进行了探讨。离子液体具有不易挥发、可循环使用、导电性好、对CO2有较高溶解度等优点, 在CO2固定和有机资源化研究中日益受到重视。电化学作为一种环境友好的绿色合成新技术, 在CO2有机资源化方面有很好的应用前景, 对缓解日益严峻的温室效应、实现CO2的资源化利用具有十分重要的现实意义。 相似文献
18.
The kinetics of CO and H2 oxidation over a CuO-CeO2 catalyst were simultaneously investigated under reaction conditions of preferential CO oxidation (PROX) in hydrogen-rich mixtures with CO2 and H2O. An integral packed-bed tubular reactor was used to produce kinetic data for power-law kinetics for both CO and H2 oxidations. The experimental results showed that the CO oxidation rate was essentially independent of H2 and O2 concentrations, while the H2 oxidation rate was practically independent of CO and O2 concentrations. In the CO oxidation, the reaction orders were 0.91, −0.37 and −0.62 with respect to the partial pressure of CO, CO2 and H2O, respectively. In the H2 oxidation, the orders were 1.0, −0.48 and −0.69 with respect to the partial pressure of H2, CO2 and H2O, respectively. The activation energies of the CO oxidation and the H2 oxidation were 94.4 and 142 kJ/mol, respectively. The rate expressions of both oxidations were able to predict the performance of the PROX reactor with accuracy. The independence between the CO and the H2 oxidation suggested different sites for CO and H2 adsorption on the CuO-CeO2 catalyst. Based on the results, we proposed a new reaction model for the preferential CO oxidation. The model assumes that CO adsorbs selectively on the Cu+ sites; H2 dissociates and adsorbs on the Cu0 sites; the adsorbed species migrates to the interface between the copper components and the ceria support, and reacts there with the oxygen supplied by the ceria support; and the oxygen deficiency on the support is replenished by the oxygen in the reaction mixture. 相似文献
19.
为了揭示电场对火焰效应与火焰传播速率的关系,在定容燃烧弹上研究了常温常压下、负直流电场(U=0、-5、-10 kV)对当量燃空比f为1.0的C3H8/O2/Ar/CO2预混火焰影响规律随混合气中CO2掺混浓度(混合气中CO2体积分数分别为0、10%、15%、20%)的变化关系。实验结果表明:给定加载电压,随着CO2掺混浓度的增大,C3H8/O2/Ar/CO2预混火焰传播速率降低,规范化火焰变形率与平均火焰传播速率变化率均增大。当U=-10 kV时,CO2掺混浓度为0、10%、15%、20%时对应的平均火焰变形率分别为1.01、1.31、1.80、3.12,平均火焰传播速度变化率分别为10.87%、17.87%、19.16%和34.63%。研究结果表明负直流电场对C3H8/O2/Ar/CO2火焰传播的促进效应随着火焰传播速率的降低而显著增强。 相似文献
20.
Catalytic combustion of diesel soot on Co, K supported catalysts 总被引:8,自引:0,他引:8
Catalysts containing 12% Co and 4.5% K, supported on MgO and CeO2 have been studied for diesel soot catalytic combustion. It has been found that this reaction occurs by a redox mechanism when Co and K are deposited on any of the above-mentioned supports. On MgO-supported catalysts, CoOx species are responsible for the supply of oxygen by a redox reaction. In this catalyst, K plays different roles, one of them being the stabilization of the CoOx particles. On CeO2-supported catalysts, Co does not significantly improve the activity of the K/CeO2 catalyst, since in this case the support itself displays redox properties. XPS analyses indicate that the oxygen availability on the surface is much higher on CeO2 than on MgO. On both CeO2 and MgO-supported catalysts, K might provide a route for CO2 release through a carbonate intermediate species. The presence of NO in the gas phase improves the catalytic activity for soot elimination. NO is oxidized to NO2 on the Co, K/CeO2 catalyst, and NO2 is a stronger oxidizing agent than O2, therefore decreasing the temperature needed to burn the soot. 相似文献