二氧化碳加氢合成甲醇铜基催化剂研究进展

二氧化碳加氢合成甲醇研究的催化剂体系有多种,包括铜基催化剂、贵金属为主要活性组分的负载型催化剂以及其他类型催化剂。其中,对铜基催化剂的研究较多,其催化性能也较好。目前选用的铜基催化剂以Cu—Zn系催化剂为主,综述了包括CuO—ZnO—Al2O3、CuO—ZnO—ZrO2、CuO—ZnO—SiO2等典型的催化剂。     

CO/FTIR Spectroscopic Characterization of Pd/ZnO/Al2O3 Catalysts for Methanol Steam Reforming

An as-synthesized 8.8wt% Pd/ZnO/Al₂O₃ catalyst was either pretreated under O₂ at 773 K followed by H₂ at 293 K or under H₂ at 773 K to obtain, respectively, a supported metallic Pd° catalyst (Pd°/ZnO/Al₂O₃) or a supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃). Both catalysts were studied by CO adsorption using FTIR spectroscopy. For the supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃), exposure to a mixture of methanol and steam, simulating methanol steam reforming reaction conditions, does not change the catalyst surface composition. This implies that the active sites are PdZn alloy like structures. The exposure of the catalyst to an oxidizing environment (O₂ at 623 K) results in the break up of PdZn alloy, forming a readily reducible PdO with its metallic form being known as much less active and selective for methanol steam reforming. However, for the metallic Pd°/ZnO/Al₂O₃ catalyst, FTIR results indicate that metallic Pd° can transform to PdZn alloy under methanol steam reforming conditions. These results suggest that PdZn alloy, even after an accidental exposure to oxygen, can self repair to form the active PdZn alloy phase under methanol steam reforming conditions. Catalytic behavior of the PdZn/ZnO/Al₂O₃ catalyst also correlates well with the surface composition characterizations by FTIR/CO spectroscopy.     

Heterogeneously Catalyzed Hydrogenation of Supercritical CO2 to Methanol

Interest in energy storage technologies is still increasing in times of excess of electricity generated by wind farms or solar plants. A key part of the energy storage technologies plays the efficient conversion of H₂ and CO₂ from renewable resources. Here, the process conditions for continuous catalytic hydrogenation of CO₂ to CH₃OH under supercritical conditions over lab‐synthesized Cu/ZnO/Al₂O₃ catalysts were investigated. A possible in situ phase separation of reaction products within the reactor due to the higher densities of the reaction mixture by the higher pressure could affect the kinetics and simplify downstream processing. The combination of thermodynamic studies and catalytic performance tests for CO₂ hydrogenation under supercritical conditions is discussed and a process concept is presented.     

Supported Vanadia Catalysts for Dehydrogenation of Ethylbenzene with CO2

Alumina supported vanadia catalysts (V/Al) for selective oxidehydrogenation of ethylbenzene with CO₂ were prepared by impregnation method. During preparation the effect of promoters and calcined temperature was investigated, it was found these two items had a strong influence on the activity of V/Al catalysts. Dehydrogenation reaction with CO₂ was happened in the fixed-bed reactor at 450 °C. Results showed that 15.2% ethylbenzene conversion and 99.2% styrene selectivity were acquired when V₂K/Al catalyst was used.     

Effect of Pd on Cu-Zn Catalysts for the Hydrogenation of CO2 to Methanol: Stabilization of Cu Metal Against CO2 Oxidation

A palladium–copper–zinc catalyst (PdO:CuO:ZnO=2:28:70), prepared by sequential precipitation of the respective cations, was tested in the hydrogenation of CO₂ at high pressure (conditions: 60 bar, CO₂:H₂=1:3 (molar), W/F=0.0675 kg h/m³, 453-513 K). The methanol yield was improved on using this Pd-containing catalyst at all temperatures with respect to the reference copper–zinc catalyst (CuO:ZnO=30:70). This improvement was not due to an additional effect in which palladium was acting as an independent catalytic site but was caused by a synergetic effect of Pd on the active Cu sites. This effect was explained in terms of hydrogen spillover and an increased stability against CO₂ oxidation of the surface copper. Therefore, the present contribution not only supports previous literature findings concerning the hydrogen spillover mechanism but also resulted in a complementary view regarding the role of palladium in Pd-modified CuO-ZnO-based catalysts.     

二氧化碳加氢制甲醇研究进展

从反应机理、催化剂和国内外研究进展等方面,全面介绍CO2加氢制甲醇技术,并对该项目存在的问题进行归纳,对其发展方向提出建议。     

CO2加氢合成二甲醚催化剂的研究进展

介绍了二甲醚的性质及主要用途,对CO2加氢合成二甲醚过程的甲醇合成催化剂、甲醇脱水催化剂及复合型催化剂进行了综述,重点分析了复合型催化剂的优势及发展前景。     

CH4重整CO2化学储能固定床反应器研究进展

CH4重整CO2化学储能对于充分利用太阳能,实施节能减排有非常重要的意义.文章从节约能源这个主题出发,概括了热化学储能技术、反应器研究及催化剂堆积研究进展,最后对CH4重整CO2化学储能的发展现状及前景作出了总结及展望.     

Steam Reforming of Methanol on Copper Catalysts Supported on Large-Surface-Area ZnAl2O3

Steam reforming of methanol on various supported Cu catalysts was examined. Supports strongly affected catalyst activity and, among the catalysts tested, Cu catalyst supported on large-surface-area ZnAl₂O₄ showed the highest activity, which, to the best of our knowledge, was higher than those for the supported catalysts reported so far. For supported Cu catalysts, two species were observed. One was a dispersed Cu species having strong interaction between Cu and support, and the other was an isolated Cu species. The activity of the former species strongly depended on supports.     

Investigation of the Phase Equilibria of CO2/CH3OH/H2O and CO2/CH3OH/H2O/H2 Mixtures

The storage of excess electricity from renewable energy sources is nowadays a crucial topic. One promising technology is the methanol (CH₃OH) synthesis from H₂/CO₂ mixtures. The achievable one‐pass conversion is limited within this exothermic equilibrium reaction. A possibility to overcome this limitation would be withdrawing CH₃OH and H₂O from the gas phase through in situ condensation under reaction conditions. In this work, the phase equilibrium for mixtures representative for different degrees of conversion was studied. A view cell was employed to determine systematically the single‐ and two‐phase regimes and obtain phase envelopes for mixtures of H₂, CO₂, CH₃OH, and H₂O from 66 to 305 °C and 61 to 233 bar. Furthermore, the densities in the single‐phase area were determined and quantified by an empirical model.     

Structure and Catalytic Performance of Mg‐SBA‐15‐Supported Nickel Catalysts for CO2 Reforming of Methane to Syngas

A series of Mg‐modified SBA‐15 mesoporous silicas with different MgO contents were successfully synthesized by a simple one‐pot synthesis method and further impregnated with Ni. The Mg‐modified SBA‐15 materials and supported Ni catalysts were characterized by N₂ physisorption (BET), X‐ray diffraction (XRD), temperature‐programmed desorption of CO₂ (CO₂‐TPD), temperature‐programmed H₂ reduction (H₂‐TPR), and temperature‐programmed hydrogenation (TPH) techniques and used for methane dry reforming with CO₂. CO₂‐TPD results proved that the addition of Mg increased the total amount of basic sites which was responsible for the enhanced catalytic activity over the Mg‐modified Ni catalyst. The excellent catalytic stability of Ni/8Mg‐SBA‐15 was ascribed to less coking and higher stability of the Ni particle size due to the introduction of Mg.     

Catalytic Oxidation of Methanol by Aqueous POM on Al2O3 Supported Catalysts and Electrochemical Performance of POM

Phosphomolybdic acid (H₃PMo₁₂O₄₀, POM) was attempted to be used as the energy‐storage agent in this paper to avoid some problems of the direct methanol fuel cell (DMFC), such as catalyst poisoning and methanol permeation. Catalytic oxidation of methanol by aqueous POM on Al₂O₃ supported catalysts with Pt and Ru active metal was evaluated in the presence of liquid water. The process takes advantage of the high catalytic activities of platinum for methanol oxidation. The effects of temperature, reaction time, and methanol concentration on activity were observed. The catalytic activity of Pt/Al₂O₃ is better than that of Ru/Al₂O₃ for the oxidation of methanol by POM. The methanol conversion rate reached 93.55% on the Pt/Al₂O₃ at 80 °C after reaction for 1 h. The electrochemical experiments indicate that POM shows a larger current density in redox processes on an Au electrode than methanol. The redox process of reduced POM is a reversible multi‐electron transfer process.     

Highly dispersed nickel boosts catalysis by Cu/SiO2 in the hydrogenation of CO2-derived ethylene carbonate to methanol and ethylene glycol

The efficient hydrogenation of CO₂-derived ethylene carbonate (EC) to yield methanol (MeOH) and ethylene glycol (EG) is a key process for indirect conversion of CO₂ to MeOH. However, a high H₂/EC molar ratio during the hydrogenation process (usually as 180–300) is generally required to achieve good catalytic performance, resulting in high cost and energy consumption for H₂ circulation in the promising industrial application. Here, we prepared a series of Ni-modified Cu/SiO₂ catalysts and explored the effects of synthesis methods and Ni contents on catalytic performance under different H₂/EC molar ratios. The Cu/SiO₂ catalyst with 0.2% (mass) Ni loading prepared by co-ammonia evaporation method exhibited above 99% conversion of EC, 91% and 98% selectivity to MeOH and EG respectively at H₂/EC ratio of 60. And no significant deactivation was observed within 140 h at a lower H₂/EC of 40. It is demonstrated that a few of Ni addition could not only promote Cu dispersion and increase surface Cu⁺ species due to the strong interaction between Cu and Ni species, but also form uniformly-dispersed CuNi alloy species and thus enhance the adsorption and dissociation of H₂. But the excess Ni species would aggregate and segregate to cover partial surface of Cu nanoparticles, leading to a significantly drop of catalytic performance in EC hydrogenation. These insights may provide guidance for further design of catalysts for the ester hydrogenation reactions.     

La2O3掺杂SiO2-B2O3-Nb2O5复相微晶玻璃相界及储能性能研究

采用可控析晶法制备了La₂O₃掺杂的SiO₂-B₂O₃-Nb₂O₅ (SBN)复相微晶玻璃,利用DSC、Raman、XRD、SEM、铁电和介电性能测试等分析表征了La₂O₃掺杂对SBN复相微晶玻璃结构与储能性能的影响。结果表明:La₂O₃掺杂能够有效提高复相微晶玻璃的热稳定性,随着La₂O₃含量增加,系统析晶势垒增大,热膨胀系数先降低后升高,价键振动加剧,介电常数先增大后减小,介电损耗先减小后增大;掺杂1.00%(摩尔分数)La₂O₃时,复相微晶玻璃在40 kV/cm电场下的储能密度和储能效率最大,分别为0.031 J·cm^-3和77.6%;储能性能主要通过介电常数和击穿场强的协同作用来评价,La₂O₃能通过提高结构热稳定性和降低介电损耗来提高介电常数,当其引入体系后处于玻璃网络的空隙中,可有效增强材料耐击穿性能;复相微晶玻璃结构可以增加结构无序度,从而降低弛豫损耗,有效提高材料的储能性能。     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Effects of Na2CO3/K2CO3 on Chemical Looping Combustion Using Fe2O3/Al2O3 as Oxygen Carrier

The performance of the Fe₂O₃/Al₂O₃ oxygen carrier modified by the alkali metals, Na and K, was studied by thermogravimetric analysis and in a laboratory-scale fluidized-bed reactor. Different factors, such as the alkali metal content, the alkali metal type, and the interaction between Na and K, were taken into account. Both Na and K had strong catalytic effects on the conversion of Fe₂O₃. A high K content caused serious agglomeration. Increasing the Na content led to slagging because of the low-melting point solid solution. The possibility of agglomeration and slagging was reduced when Na and K were added together. The oxygen carrier with 1.5 wt % Na and 1.5 wt % K had better combustion efficiency and optimal thermal stability. Na and K could enhance the attrition resistance and prolong the lifetime of the oxygen carriers.     

CO2 Hydrogenation to Methanol Over Cu/ZnO/Al2O3 Catalysts Prepared by a Novel Gel-Network-Coprecipitation Method

A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from CO₂ hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al₂O₃ catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al₂O₃ catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO₂ hydrogenation to methanol.     

Chemical Fixation of Carbon Dioxide to Propylene Carbonate Using Smectite Catalysts with High Activity and Selectivity

The reaction of propylene oxide and carbon dioxide to propylene carbonate was carried out using Mg-, Ni- and Mg-Ni-containing smectite catalysts which contain different amounts of alkali atoms such as sodium, potassium and lithium. These catalysts are highly active and selective for this reaction. The catalytic activity strongly depends on the elemental composition of the catalyst used. Particularly the amount of alkali atoms incorporated in the catalyst is the most important factor governing the catalytic performance. The most active catalyst among those prepared in the present study shows a turnover number of 105 mmol/g for the propylene carbonate formation, which is the highest turnover number compared with those reported so far (10 mmol/g) for the title reaction.     

Low Temperature Growth of In2O3 and InN Nanocrystals on Si(111) via Chemical Vapour Deposition Based on the Sublimation of NH4Cl in In

Indium oxide (In₂O₃) nanocrystals (NCs) have been obtained via atmospheric pressure, chemical vapour deposition (APCVD) on Si(111) via the direct oxidation of In with Ar:10% O₂ at 1000 °C but also at temperatures as low as 500 °C by the sublimation of ammonium chloride (NH₄Cl) which is incorporated into the In under a gas flow of nitrogen (N₂). Similarly InN NCs have also been obtained using sublimation of NH₄Cl in a gas flow of NH₃. During oxidation of In under a flow of O₂ the transfer of In into the gas stream is inhibited by the formation of In₂O₃ around the In powder which breaks up only at high temperatures, i.e. T > 900 °C, thereby releasing In into the gas stream which can then react with O₂ leading to a high yield formation of isolated 500 nm In₂O₃ octahedrons but also chains of these nanostructures. No such NCs were obtained by direct oxidation for T _G < 900 °C. The incorporation of NH₄Cl in the In leads to the sublimation of NH₄Cl into NH₃ and HCl at around 338 °C which in turn produces an efficient dispersion and transfer of the whole In into the gas stream of N₂ where it reacts with HCl forming primarily InCl. The latter adsorbs onto the Si(111) where it reacts with H₂O and O₂ leading to the formation of In₂O₃ nanopyramids on Si(111). The rest of the InCl is carried downstream, where it solidifies at lower temperatures, and rapidly breaks down into metallic In upon exposure to H₂O in the air. Upon carrying out the reaction of In with NH₄Cl at 600 °C under NH₃ as opposed to N₂, we obtain InN nanoparticles on Si(111) with an average diameter of 300 nm.     

The Effect of Preparation Variables on the CO Hydrogenation Activity of Coprecipitated Co/Al2O3 Catalysts

Studies have been conducted on the effect of preparation variables on the activity of coprecipitated cobalt–alumina catalysts to be used for the production of C₁–C₄ hydrocarbons by CO hydrogenation. The preparation parameters considered were the precipitation pH, the precipitation agent, the metal loading, the reduction temperature and the reduction period. It was found that changing pH precipitation with a constant final pH between 11·0 and 12·5 and the use of NaOH together with nitrates as precursors yielded better catalysts with maximal metal surface area. The optimum cobalt loading for the selective production of C₁–C₄ hydrocarbons is around 35 wt%. Optimum activity and selectivity are obtained by applying an 8-h reduction scheme at 648 K under 100 cm³ min⁻¹ hydrogen. Calcination prior to reduction has a detrimental effect on metal surface area and hence on catalytic activity. © 1997 SCI.