Carbonate-catalyzed chemiluminescence decomposition of peroxynitrite via (CO2)2 intermediate

Peroxynitrous acid (ONOOH) was formed by the on-line rapid reaction of acidified hydrogen peroxide with nitrite in a simple flow system. A weak chemiluminescent (CL) signal was observed due to the production of singlet oxygen (¹O₂) when ONOOH reacted with NaOH, whereas the replacement of NaOH by Na₂CO₃ markedly enhanced the CL intensity. The predominant CL-enhanced pathway was achieved by the carbonate-catalyzed decomposition of peroxynitrite (ONOO⁻). Carbonate species was regenerated in the process, that is, carbonate acts as a catalyst. Based on the studies of CL and fluorescence spectra, a possible CL mechanism from the reaction of carbonate with ONOOH was proposed. In brief, ONOOH was an unstable compound in acidic solution and could be quenched into ONOO⁻ in basic media. It was suggested that ONOO⁻ reaction with excess HCO₃⁻ proceeded via one-electron transfer to yield bicarbonate ion radicals (HCO₃√). The recombination of HCO₃√ may directly generate excited triplet dimers of two CO₂ molecules [(CO₂)₂^*]. With the decomposition of this unstable intermediate to CO₂, the energy was released by CL emission. The addition of uranine into carbonate solution caused enhancement of the CL signal, which was due to a part of excited triplet dimers of two CO₂ molecules energy to transfer to uranine, resulting in two CL peaks.     

浅析CO_2汽提法尿素装置合成系统的NH_3/CO_2

介绍CO2汽提法尿素装置合成系统的NH3/CO2的控制方法,合成系统NH3/CO2异常的症状,判断方法,偏离正常时的处理和防范措施。     

Stainless steel membrane distributor-type dielectric barrier discharge plasma reactor for co-conversion of CH4/CO2

Flow arrangement in a dielectric barrier discharge (DBD) plasma reactor is key to affecting multi-component gas reactions. Herein, a stainless-steel membrane distributor-type DBD reactor was developed to allow the change of gas flow arrangements freely to understand their effect on plasma-assisted CH₄/CO₂ co-conversion to syngas. Variation of gas flow arrangements in the DBD reactor could regulate the reaction performance. Also, the inclusion of quartz wool in the DBD reactor could enhance the effect of gas flow arrangement compared to the plasma-alone DBD. Especially, the DBD reactor with CO₂ feed in the quartz wool-packed discharge zone and CH₄ distributed via the membrane exhibited good stability over 600 min on stream, with rather stable CO₂/CH₄ conversions of ~25%/20%, H₂/CO selectivities of ~50%/32%, H₂/CO molar ratio of 0.9–1.1, and energy efficiency of ~0.20 mmol·kJ⁻¹ based on the conversion of feed gases.     

H2 production by ethanol decomposition with a gliding arc discharge plasma reactor

A gliding arc discharge (GRD) reactor was used to decompose ethanol into primarily H₂ and CO with small amounts of CH₄, C₂H₂, C₂H₄, and C₂H₆. The ethanol concentration, electrode gap, input voltage and Ar flow rate all affected the conversion of ethanol with results ranging from 40.7% to 58.0%. Interestingly, for all experimental conditions the S_H2/S_CO selectivity ratio was quite stable at around 1.03. The mechanism for the decomposition of ethanol is also described.     

Experimental study on CO2 capture conditions of a fluidized bed limestone decomposition reactor

In this study, the decomposition conditions of limestone particles (0.25-0.50 mm) for CO₂ capture in a steam dilution atmosphere (20-100% steam in CO₂) were investigated by using a continuously operating fluidized bed reactor. The results show that the decomposition conversion of limestone increased with the steam dilution percentage in the CO₂ supply gas. At a bed temperature of 920 °C, the conversions were 72% without steam dilution and 98% with 60% steam dilution. The conversion was 99% with 100% steam dilution at 850 °C of the bed temperature. Steam dilution can decrease not only the decomposition temperature of limestone, but also the residence time required for nearly complete decomposition of CaCO₃. The hydration and carbonation reactivities of the CaO produced were also tested and the results show that both the reactivities increased with the steam dilution percentage for decomposing limestone.     

Simulation and thermodynamic analysis of an integrated process with H2 membrane CPO reactor for pure H2 production

A one-dimensional steady-state heterogeneous model has been used to simulate the H₂ membrane reactor. The simulation work is the basis for the thermodynamic analysis of the integrated pure H₂ production process. The simulation and analysis also provide a quantitative tool for insight into and understanding the process.The simulation and thermodynamic analysis results indicate that increasing the inlet ratio H₂O/CH₄ cannot enhance the pure H₂ production rate. With increasing the inlet ratio H₂O/CH₄, the overall exergy efficiency of the process decreases, because a large amount of energy is required to obtain the steam.When the geometric parameters of membrane reactor and inlet temperature are given, there is a maximum feeding rate of methane for the integrated process. The pure hydrogen production rate increases with the inlet methane rate increasing, while the overall exergy efficiency decreases as inlet methane rate increases.For the same inlet rate of methane, operating the process at higher inlet temperature increases hydrogen production rate. Whereas, the overall exergy efficiency is lowered.Three suggestions are discussed to improve the overall exergy efficiency. All of them require more equipment investment. There will be an optimal point to balance equipment investment, pure hydrogen production rate and overall exergy efficiency. To find the optimum, thermo-economic analysis will be helpful.     

Kinetics of CO and H2 oxidation over CuO-CeO2 catalyst in H2 mixtures with CO2 and H2O

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.     

Modeling and simulation of non-isothermal catalytic packed bed membrane reactor for H2S decomposition

The recovery of H₂ from H₂S is an economical alternative to the Claus process in petroleum and minerals processing industries. Previous studies [React. Kinet. Catal. Lett. 62 (1997) 55; Catal. Lett. 37 (1996) 167] have demonstrated that catalytic decomposition of H₂S over bimetallic sulfide can proceed at relatively higher rates than over mono-metallic systems due to chemical synergism although conversions are still thermodynamically limited. In the present study, the performance of a catalytic membrane reactor containing a packed bed of Ru–Mo sulfide catalyst has been investigated with a view to improving H₂ yield beyond the equilibrium ceiling. A system of differential equations describing the non-isothermal reactor model has been solved to examine the effect of important hydrodynamic and transport properties on conversion. The results were obtained using a Pt-coated Nb membrane tube as the catalytic reactor enclosed in a quartz shell cylinder. Reynolds number for shell and tube side (Re^s and Re^t) as well as the modified wall Peclet number, Pe_m, dramatically affect H₂S conversions. Membrane reactor conversion rose monotonically with axial distance exceeding the equilibrium conversion by as much as eight times under some conditions.     

纳米颗粒及分散剂对TETA溶液吸收CO2的影响

为探究纳米颗粒对TETA溶液吸收CO₂的影响及分散剂对纳米流体吸收CO₂的促进效果,采用两步法配制了不同纳米颗粒种类及粒径、不同震荡时间、不同TETA浓度、不同纳米颗粒固含量和不同分散剂固含量及种类的纳米流体,搭建TETA溶液鼓泡吸收CO₂试验台,分别测试了不同工况下制备的纳米流体对CO₂的吸收情况,并与空白TETA溶液进行对比。结果表明,纳米流体的脱除率增强系数随着纳米颗粒质量分数的增加而先提升后降低,粒径较大的纳米颗粒具有较好的传质性能,大尺寸可以减少相对表面积和能量,使得纳米颗粒的表面和量子尺度效应减弱;CO₂吸收速率在初始阶段随着超声破碎时间的增加而提升,但超声破碎时间超过1 h,吸收速率减缓;TETA浓度及纳米颗粒固含量影响试验中,随着浓度及固含量上升,脱除率增强系数均呈现先升高后降低的趋势,存在最佳值。综上,在浓度1 mol/L的TETA中添加固含量0.1%、粒径60 nm的TiO₂,经超声震荡1 h后对CO₂的吸收效果最好,脱除率增强系数最高可达1.9。以TiO₂-TETA-H₂O纳米流体为基液在其中添加C-Na、SDBS、X-100等分散剂时,由于TiO₂颗粒表面带正电荷,分散剂类型对TiO₂-TETA-H₂O纳米流体稳定性的影响大致呈现以下趋势:阴离子型>非离子型>阳离子型,且以双电子层理论为依据,添加阴离子型分散剂C-Na的质量分数为0.1%时对阳离子型纳米流体TiO₂-TETA-H₂O的稳定效果最好。     

二氧化碳液化与输送技术

CO2过度排放导致的环境问题使世界各国都在想方设法将其回收后埋存或利用。但是,CO2的资源地离利用地一般较远,而且CO2在常温常压下为气态,如何将CO2安全经济地运输到目的地成为二氧化碳捕集技术大规模利用的技术关键。研究表明,采用液体输送方式可以降低系统能耗和成本。文章分析对比了不同二氧化碳液化方法的优劣性,并探讨了管线输送中需要注意的问题。     

Characterization and catalytic activity of soft-templated NiO-CeO2 mixed oxides for CO and CO2 co-methanation

Nanosized NiO,CeO₂ and NiO-CeO₂ mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method.All the samples were characterized by different techniques as to their chemical composition,structure,morphology and texture.On the catalysts submitted to the same reduction pretreatment adopted for the activity tests the surface basic properties and specific metal surface area were also determined.NiO and CeO₂ nanocrystals of about 4 nm in size were obtained,regardless of the Ni/Ce molar ratio.The Raman and X-ray photoelectron spectroscopy results proved the formation of defective sites at the NiO-CeO₂ interface,where Ni species are in strong interaction with the support.The microcalorimetric and Fourier transform infrared analyses of the reduced samples highlighted that,unlike metallic nickel,CeO₂ is able to effectively adsorb CO₂,forming carbonates and hydrogen carbonates.After reduction in H2 at 400°C for 1 h,the catalytic performance was studied in the CO and CO₂ co-methanation reaction.Catalytic tests were performed at atmospheric pressure and 300°C,using CO/CO₂/H₂ molar compositions of 1/1/7 or 1/1/5,and space velocities equal to 72000 or 450000 cm³?h^-1?gcat^-1.Whereas CO was almost completely hydrogenated in any investigated experimental conditions,CO₂ conversion was strongly affected by both the CO/CO₂/H₂ ratio and the space velocity.The faster and definitely preferred CO hydrogenation was explained in the light of the different mechanisms of CO and CO₂ methanation.On a selected sample,the influence of the reaction temperature and of a higher number of space velocity values,as well as the stability,were also studied.Provided that the Ni content is optimized,the NiCe system investigated was very promising,being highly active for the CO_x co-methanation reaction in a wide range of operating conditions and stable(up to 50 h)also when submitted to thermal stress.     

A CO and CO2 tolerating (La0.9Ca0.1)2(Ni0.75Cu0.25)O4+d Ruddlesden-Popper membrane for oxygen separation

A series of novel dense mixed conducting ceramic membranes based on K₂NiF₄-type (La_1–xCa_x)₂ (Ni_0.75Cu_0.25)O_4+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 (La_0.9Ca_0.1)₂ (Ni_0.75Cu_0.25)O_4+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 (La_0.9Ca_0.1)₂(Ni_0.75Cu_0.25)O_4+δ membrane is a promising chemically robust candidate for oxygen separation applications.     

Preparation of Cu/ZrO2 catalysts for methanol synthesis from CO2/H2

Cu/ZrO₂ catalysts for methanol synthesis from CO₂/H₂ were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO₂ and selectivity of methanol are higher for DP catalysts than for SP catalysts.     

Selective oxidehydrogenation of ethane with CO2 over CeO2-based catalysts

Ceria catalysts were found active and selective to the oxidehydrogenation of ethane (ODE) with CO₂ and the actual contribution for C₂H₄ formation from heterogeneous catalysis was 75–55% in the range 953–993 K. The presence of calcium ions in solid solution in the ceria crystalline network increased significatively the selectivity to ethene and the efficiency of CO₂ as oxidant in the heterogeneous reaction.     

The maximum capture efficiency of CO2 using a carbonation/calcination cycle of CaO/CaCO3

The use of natural calcium carbonates as regenerable CO₂ sorbents in industrial processes is limited by the rapid decay of the carbonation conversion with the number of cycles carbonation/calcination. However, new processes are emerging to capture CO₂ using these cycles, that can take advantage of the intrinsic benefits of high temperature separations in energy systems. This work presents an analysis of a general carbonation/calcination cycle to capture CO₂, incorporating a fresh feed of sorbent to compensate for the decay in activity during sorbent re-cycling. A general design equation for the maximum CO₂ capture efficiency is obtained by incorporating to the cycle mass balances a simple but realistic equation to estimate the decay in sorbent activity with the number of cycles.     

Calcium oxides for CO2 capture obtained from the thermal decomposition of CaCO3 particles coprecipitated with Al ions

Calcium-carbonate powders were coprecipitated with Al³⁺ and then decomposed in air and/or under a CO₂ flux between 590 °C and 1150 °C. The data were analysed using a consecutive-decomposition-dilatometer method and the kinetic results were discussed according to the microstructure analysis done by N₂ adsorption isotherms (78 K), SEM and FT-IR measurements. Below 1000 °C, CaCO₃ particle thermal-decomposition was pseudomorphic, resulting in the formation of a CaO grain porous network. When the CaO grains were formed, the Al³⁺ diffused among them, producing AlO₄ groups that promoted the CaO grain coarsening and reduced O²⁻ surface sites available to CO₂ adsorbed molecules to form CO₃²⁻. In pure CaO, CO₃²⁻ diffused through the grain boundary, enhancing Ca²⁺ and O²⁻ mobility; AlO₄ groups reduced CO₃²⁻ penetration and CaO sintering rate. Above 1000 °C, the sintering rate of the doped samples exceeded that of the undoped, likely because of Al³⁺ diffusion in CaO and viscous flow.     

Nickel(II) ion-intercalated MXene membranes for enhanced H2/CO2 separation

Hydrogen fuel has been embraced as a potential long-term solution to the growing demand for clean energy. A membrane-assisted separation is promising in producing high-purity H₂. Molecular sieving membranes (MSMs) are endowed with high gas selectivity and permeability because their well-defined micropores can facilitate molecular exclusion, diffusion, and adsorption. In this work, MXene nanosheets intercalated with Ni²⁺ were assembled to form an MSM supported on Al₂O₃ hollow fiber via a vacuum-assisted filtration and drying process. The prepared membranes showed excellent H₂/CO₂ mixture separation performance at room temperature. Separation factor reached 615 with a hydrogen permeance of 8.35 × 10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹. Compared with the original Ti₃C₂T_x/Al₂O₃ hollow fiber membranes, the permeation of hydrogen through the Ni²⁺-Ti₃C₂T_x/Al₂O₃ membrane was considerably increased, stemming from the strong interaction between the negatively charged MXene nanosheets and Ni²⁺. The interlayer spacing of MSMs was tuned by Ni²⁺. During 200-hour testing, the resultant membrane maintained an excellent gas separation without any substantial performance decline. Our results indicate that the Ni²⁺ tailored Ti₃C₂T_x/Al₂O₃ hollow fiber membranes can inspire promising industrial applications.     

TiO2基催化剂还原CO2研究进展

能源危机和环境污染是当今世界发展面临的两大挑战,如何有效缓解煤、石油等不可再生化石资源过度消耗所引发的能源危机,以及由此造成CO₂过量排放引起的温室效应问题,是当前人类发展亟待解决的重大科学问题之一。基于此,本文综述了近年来以TiO₂为光催化剂,以绿色、清洁的太阳光能催化还原CO₂成低价态含碳燃料(如CH₄、CH₃OH、HCHO、HCOOH、C₂H₅OH等)研究进展。在TiO₂光还原CO₂机理基础上,对元素掺杂、半导体复合与染料敏化、高活性晶面调控、低维纳米结构设计、助催化剂、Z型结构设计和单原子催化等方法来提高光还原CO₂反应效率和选择性进行分析,并指出目前研究存在的关键问题和未来CO₂光还原的发展方向。     

NO decomposition and reduction by CH4 over Sr/La2O3

Both NO decomposition and NO reduction by CH₄ over 4%Sr/La₂O₃ in the absence and presence of O₂ were examined between 773 and 973 K, and N₂O decomposition was also studied. The presence of CH₄ greatly increased the conversion of NO to N₂ and this activity was further enhanced by co-fed O₂. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH₄ in the absence of O₂, and reduction with 1% O₂ in the feed were 8.3·10⁻⁴, 4.6·10⁻³, and 1.3·10⁻² μmol N₂/s m², respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N₂ formation by decomposition was inhibited by O₂ in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH₄ continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O₂ with equal activation energies of 26 kcal/mol. The addition of O₂ increased the reaction order in CH₄ at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O₂ was 0.26 up to 0.5% O₂ during which time the CH₄ concentration was not decreased significantly. N₂O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10⁻⁴ μmol N₂/s m² at 623 K and 1220 ppm N₂O and an activation energy of 24 kcal/mol. The addition of CH₄ inhibits this decomposition reaction. Finally, the use of either CO or H₂ as the reductant (no O₂) produced specific activities at 773 K that were almost 5 times greater than that with CH₄ and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H₂ to reduce NO to N₂ over these REO catalysts.     

Catalytic conversion of methane and CO2 to synthesis gas over a La2O3-modified SiO2 supported Ni catalyst in fluidized-bed reactor

In this contribution, a commercial spherical SiO₂ was modified with different amounts of La₂O₃, and used as the support of Ni catalysts for autothermal reforming of methane in a fluidized-bed reactor. Nitrogen adsorption, XRD and H₂-TPR analysis indicated that La₂O₃-modified SiO₂ had higher surface area, strengthened interaction between Ni and support, and improved dispersion of Ni. CO₂-TPD found that La₂O₃ increased the alkalescence of SiO₂ and improved the activation of CO₂. Coking reaction (via both temperature-programmed surface reaction of CH₄ (CH₄-TPSR) and pulse decomposition of CH₄) disclosed that La₂O₃ reduced the dehydrogenation ability of Ni. CO₂-TPO, O₂-TPO (followed after CH₄-TPSR) confirmed that only part amount of carbon species derived from methane decomposition could be removed by CO₂, and O₂ in feed played a crucial role for the gasification of the inactive surface carbons. Ni/xLa₂O₃-SiO₂ (x = 10, 15, 30) possessed high activity and excellent stability for autothermal reforming of methane in a fluidized-bed reactor.