Low-temperature synthesis of DME from CO2/H2 over Pd-modified CuO–ZnO–Al2O3–ZrO2/HZSM-5 catalysts

Three series of Pd-modified CuO–ZnO–Al₂O₃–ZrO₂/HZSM-5 catalysts were prepared and characterized by BET, XRD and TPR analysis. The catalytic system was evaluated in the development of direct synthesis of dimethyl ether (DME) from carbon dioxide hydrogenation at low temperature (T=200 °C, P=3.0 MPa). The results indicated that the addition of palladium markedly enhanced the DME synthesis and retarded the CO formation. An explanation of this promoting effect of Pd on the DME synthesis could be attributed to the spillover of hydrogen from Pd⁰ to the neighboring phase.     

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La₂NiO₄ catalyst active in CH₄/CO₂ reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH₄ and CO₂ in CH₄/CO₂ reforming over this catalyst are significantly higher than those over a Ni/La₂O₃ catalyst prepared by wet impregnation and those over a La₂NiO₄/-Al₂O₃ catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La₂NiO₄ catalyst.     

Mechanistic studies of CO2/CH4 reforming over Ni–La2O2/5A

The mechanism of CO₂/CH₄ reforming over Ni–La₂O₃/5A has been studied. The results of the CO₂‐pulsing experiments indicated that the amount of CO₂ converted was roughly proportional to the amount of H present on the catalyst, implying that CO₂ activation could be H‐assisted. Pulsing CH₄ onto a H₂‐reduced sample and a similar sample pretreated with CO₂, we found that CH₄ conversion was higher in the latter case. Hence, the idea of oxygen‐assisted CH₄ dissociation is plausible. The fact that the amount of CO produced in 10 pulses of CO₂/CH₄ was larger than that produced in 5 pulses of CO₂ followed by 5 pulses of CH₄, indicated that CO₂ and CH₄ could activate each other synergistically. In the chemical trapping experiments, following the introduction of CD₃I onto a Ni–La₂O₃/5A sample pretreated with CH₄/CO₂, we observed CD₃COOH, CD₃CHO, and CD₃OCD₃. In the in situ DRIFT experiments, IR bands attributable to formate and formyl were observed under working conditions. These results indicate that formate and formyl are intermediates for syngas generation in CO₂/CH₄ reforming, and active O is generated in the breaking of a C–O bond. Based on these results, we suggest that during CO₂/CH₄ reforming, CO₂ activation is H‐promoted and surface O species generated in CO₂ dissociation reacts with CH_x to give CO. A reaction scheme has been proposed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Corrosion protection of steel in molten Li2CO3–K2CO3 and Na2CO3–K2CO3 mixtures in a hydrogen-containing atmosphere

The electrochemical behaviour of TiN-, TiN–AlN-, Cr- and CrN-coated 316L stainless steel in molten Li₂CO₃–K₂CO₃ and Na₂CO₃–K₂CO₃ melts in a reducing gaseous atmosphere (10% H₂–90% N₂) was studied using voltammetry and scanning electron microscopy combined with energy-dispersed X-ray analysis in the temperature range of 600–730 C. To facilitate the identification of the electrochemical reactions the voltammetric behaviour of stainless steel, titanium, nickel and gold was also investigated. Voltammetric characteristics obtained at AlN–TiN coated electrodes showed no anodic reactions at potentials more negative than that of CO^2– ₃ oxidation. Cr- and CrN-coated electrodes demonstrated a suppressed anodic dissolution after the first steady state voltammetric cycle. The voltammograms obtained for the other electrodes studied displayed the corresponding anodic metal-dissolution waves. TiN, AlN, Cr and CrN coatings seem to be the most promising as corrosion-resistant materials for the anodic compartments of molten carbonate fuel cells.     

K2CO3/金属氧化物吸附CO2的研究

研究了K_2CO_3/MgO和K_2CO_3/Al_2O_3吸附CO_2的性能。研究表明:K_2CO_3/MgO和K_2CO_3/Al_2O_3对CO_2吸附的容量分别为105.8 mg/g和66 mg/g。吸附剂载体是钾基吸附剂吸附CO_2性能差异的原因之一,MgO载体的CO_2吸附容量(42.3 mg/g)大于Al_2O_3(20 mg/g)。钾在不同载体中的物相差异是造成CO_2吸附性能差别的另一原因。在K_2CO_3/MgO吸附剂中,钾仅以K_2CO_3形式存在,在吸附CO_2过程中,CO_2与K_2CO_3以及MgO共同作用生成了K_2Mg(CO_3)_2。而在K_2CO_3/Al_2O_3吸附剂中,不仅有K_2CO_3物相,还检测出KAl(CO_3)_2(OH)_2物相,在吸附CO_2过程中,K_2CO_3转化成KHCO_3,而KAl(CO_3)_2(OH)_2未参与CO_2的吸附。     

Oxidative Dehydrogenation of Ethylbenzene to Styrene with CO2 Over V2O5–Sb2O5–CeO2/TiO2–ZrO2 Catalysts

Utilization of CO₂ as a soft oxidant in the oxidative dehydrogenation of ethylbenzene to styrene, a remarkable V₂O₅–Sb₂O₅–CeO₂/TiO₂–ZrO₂ catalyst has been accomplished. Preparation of TiO₂–ZrO₂ support by co-precipitation followed by a single step deposition of V and Ce and Sb as stabilizers yielded a highly active and selective catalyst. Acid–base and redox properties including sustained stability of active species (V⁵⁺) are responsible for high activity of V₂O₅–Sb₂O₅–CeO₂/TiO₂–ZrO₂ catalyst. The redox cycle is related to the dispersed V⁵⁺ and lattice reduced vanadium site in the VSbO₄ phase. The antimony oxide inhibits the easy redox cycle between different vanadia species.     

Performance of yttria-stabilized zirconia fuel cell using H2–CO2 gas system and CO–O2 gas system

This paper reports the performance of an yttria-stabilized zirconia fuel cell (YSZ) using five kinds of gas systems. The final target of this research is to establish the combined fuel cell systems which can produce a H₂ fuel and circulate CO₂ gas in the production process of electric power. A large electric power was measured in the H₂–O₂ gas system and the CO–O₂ gas system at 1073 K. The formation process of O²⁻ ions in the endothermic cathodic reaction (1/2O₂+2e⁻→O²⁻) controlled the cell performance in both the gas systems. The electric power of the H₂–CO₂ gas system, which allowed to change CO₂ gas into a CO fuel (H₂+CO₂→H₂O+CO) in the cathode, was 1/31–1/11 of the maximum electric power for the H₂–O₂ gas system. This result is related to the larger endothermic energy for the formation of O²⁻ ions from CO₂ molecules at the cathode (CO₂+2e⁻→CO+O²⁻) than from O₂ molecules. The CO–H₂O gas system and the H₂–H₂O gas system was expected to produce a H₂ fuel in the cathode (CO+H₂O→H₂+CO₂, H₂+H₂O→H₂+H₂O). Although relatively high OCV values (open circuit voltage) were measured in these gas systems, no electric power was measured. At this moment, it was difficult to apply H₂O vapor as an oxidant to the cathodic reaction in a YSZ fuel cell.     

O2/N2、O2/CO2和O2/CO2/NO气氛下煤粉燃烧NOx排放特性

利用滴管炉研究了O₂/N₂、O₂/CO₂和O₂/CO₂/NO气氛下煤燃烧过程中NO_x的排放特性。实验结果表明,在O₂/N₂和O₂/CO₂气氛下,高温或高O₂浓度均使NO排放量增加。O₂/CO₂气氛下NO排放量比O₂/N₂气氛下NO排放量低大约30%～40%。在O₂/CO₂/NO气氛下,温度不同时,O₂浓度变化对NO排放量的影响规律不同,对循环NO降解的影响规律也不同。高温不利于循环NO降解。随停留时间的延长NO排放量出现两个峰值。     

CO/CO2加氢制芳烃的研究进展

将CO/CO₂直接转化为芳烃是一种极具挑战性的非石油路线合成途径。本文主要对CO/CO₂通过不同反应途径制取芳烃过程中复合催化剂的开发和反应机理的研究进展进行了综述。阐述了利用反应耦合思想,构筑的复合催化剂在CO/CO₂的高效转化和产物调控等方面取得了突破性的进展。重点介绍了复合催化剂用于CO加氢制芳烃主要的两种反应途径,活性金属的类别、分子筛的结构与酸性和活性组分的组装方式与接触度对CO₂加氢制芳烃催化性能的影响。指出协同加氢与芳构化反应活性的匹配是影响催化剂性能的关键。提出开发高效稳定的催化剂用于提高CO/CO₂的转化率和芳烃产物的产率以及反应机理的探索仍然是未来研究的重点。     

CO2 absorption into K2CO3/KHCO3 solution enhanced by organic phase in a rotor–stator reactor

ABSTRACT

This work studied the gas–liquid–liquid (G–L–L) reaction system of CO₂ absorption into K₂CO₃/KHCO₃ buffer solution enhanced by organic phase in a rotor–stator reactor (RSR). The effects of volume fraction of organic phase, type of organic phase, rotational speed of RSR, gas and liquid volumetric flow rate, and temperature on CO₂ absorption percentage were investigated. Results indicate that the addition of the organic phase with a volume fraction of 1.3–1.6% had significant promoting effect on CO₂ absorption. CO₂ absorption percentage increased with increase in the rotational speed of the RSR but decreased with rise in liquid temperature and gas–liquid ratio. This work demonstrates that RSR can significantly enhance liquid–liquid mixing and gas–liquid mass transfer processes in the G–L–L system.     

一种具有高CO吸附容量和高CO/N2及CO/CO2分离选择性的CuCl@β吸附剂

研制了一种新型的CuCl@β分子筛吸附剂材料,它不仅对CO有着高吸附容量,而且对CO/N₂和CO/CO₂的二元混合气有着高吸附选择性。利用自发单层分散的原理制备了一系列的CuCl@β分子筛材料,分别应用氮气吸附以及XRD进行表征。CO在CuCl@β分子筛上吸附等温线和动态透过曲线分别通过静态吸附和固定床实验获得。依据IAST理论模型计算了CuCl@β分子筛对CO/N₂二元混合物和CO/CO₂二元混合物的吸附选择性。研究结果表明:(1)氯化亚铜的负载增强了一氧化碳在CuCl@β分子筛上的吸附容量,其最佳负载量为0.4 g·g^-1。(2)CuCl@β分子筛吸附剂在增强CO的吸附量的同时,还降低了对二氧化碳和氮气的吸附。由于Cu⁺-CO π位络合键的存在,提高了CuCl@β分子筛对二元混合物CO/N₂和CO/CO₂的吸附选择性。(3)在低压下(0～10 kPa)下0.4CuCl@β分子筛对CO/N₂和CO/CO₂的吸附选择性分别高达1600～5200和120～370,远大于原始的β分子筛。CuCl@β分子筛对CO有着超高吸附容量以及吸附选择性,将会是一种很有潜力的CO分离提纯材料。     

The refined e-NRTL model applied to CO2–H2O–alkanolamine systems

The electrolyte NRTL (e-NRTL) model by Chen (1982) and Chen and Evans (1986) is perhaps the most commonly used activity coefficient based thermodynamic model for industrial systems. It has been shown by Bollas et al. (2008) that the original e-NRTL model is inconsistent for systems with multiple cations and/or anions, in the same work the model equations for the so-called refined e-NRTL model were given. In this work the refined e-NRTL model is applied to CO₂–H₂O–alkanolamine systems. The interaction parameters of the refined e-NRTL model are regressed to partial pressure of CO₂, binary vapour–liquid-equilibrium, freezing point depression data and excess enthalpy data. The model is in the end used to predict partial pressures and speciation for the CO₂–H₂O–MEA and CO₂–H₂O–MDEA systems.     

H2 and H2/CO oxidation mechanism on Pt/C, Ru/C and Pt–Ru/C electrocatalysts

The oxidation kinetics of H₂ and H₂ + 100 ppm CO were investigated on Pt, Ru and Pt–Ru electrocatalysts supported on a high-surface area carbon powder. The atomic ratios of Pt to Ru were 3, 1 and 0.33. XRD, TEM, EDS and XPS were used to characterize the electrocatalysts. When alloyed with ruthenium, a decrease in mean particle size and a modification of the platinum electronic structure were identified. Impedance measurements in H₂SO₄, at open circuit potential, indicated different mechanisms for hydrogen oxidation on Pt/C (Tafel–Volmer path) and Pt–Ru/C (Heyrowsky–Volmer path). These mechanisms also occur in the presence of CO. Best performances, both in H₂ and H₂ + CO, were achieved by the catalyst with the ratio Pt/Ru = 1. This is due to a compromise between the number of free sites and the presence of adsorbed water on the catalyst. For CO tolerance, an intrinsic mechanism not involving CO electroxidation was proposed. This mechanism derives from changes in the electronic structure of platinum when alloyed with ruthenium.     

Low-temperature methanol synthesis catalyzed over Cu/γ-Al2O3–TiO2 for CO2 hydrogenation

A titanium-modified -alumina-supported CuO catalyst has been prepared and used for methanol synthesis from CO₂ hydrogenation. XRD and TPR were used to characterize the phase, reduction property and particle size of the reduced catalyst. The addition of Ti to the CuO/-Al₂O₃ catalyst made the copper in the catalyst exist in much smaller crystallites and exhibit an amorphous-like structure. The adding of Ti made the reduction peak shift toward lower temperature in comparison with the CuO/-Al₂O₃ catalyst. The effect of the addition of Ti and the reaction conditions on the activity and selectivity to methanol from CO₂ hydrogenation were investigated. The activity was found to increase with increasing surface area of metallic copper, but it is not a linear relationship. This indicated that the catalytic activity of the catalysts depends on both the metallic copper area and the synergy between the copper and titanium dioxide. The effect of contact time on the relative selectivity (=SCH₃0H /S_CO) and selectivity of methanol were also investigated. The results indicated that methanol was formed directly from the hydrogenation of CO₂.     

Freeze-drying optimized Ce–P/γ-Al2O3 coating on ceramic-supported Pd catalysts for CO2 methanation and CO oxidation

Ce–P/γ-Al₂O₃ coatings applied with the freeze-drying technique were deposited on foam ceramics before being further prepared as Pd catalysts. According to the research, phosphoric acid replaced the hydroxyl on the surface of γ-Al₂O₃ to produce polyhydroxy P-containing sites that readily attracted cerium oxide. The palladium oxide was then embedded into the cerium oxide vacancy. The impacts of the drying technique on the catalysts were investigated, and the results indicated that freeze drying created a special coating with a large specific surface area and uniform mesoporous structure by inhibiting nanoparticle agglomeration. H₃PO₄'s altering action was augmented to boost the number of active sites and the percentage of weakly acidic sites. Due to better P–Ce interactions, more Ce³⁺ was added into CeO₂, which created numerous oxygen vacancies. By adjusting the P-containing sites, the dispersion of cerium oxide and the active phase could be controlled, which aided the activation and spillover of hydrogen. Furthermore, the capacity for oxygen adsorption and desorption was enhanced, and the amount of adsorbed oxygen species increased. As a result, the freeze-drying technique improved the advantages of the Ce–P/γ-Al₂O₃ coating, increasing the conversion and selectivity of CO₂ methanation to 81% and 94%, respectively, and lowering the complete conversion temperature of CO oxidation to 116 °C. This research has a guiding influence on the development of foam ceramic-loaded palladium catalysts in the fields of energy and the environment.