Methanol decomposition to synthesis gas over supported Pd catalysts prepared from synthetic anionic clays

Supported Pd or Rh catalysts were prepared by the solid-phase crystallization method starting from hydrotalcite anionic clay minerals based on [Mg₆Al₂(OH)₁₆CO ₂ ²⁻ ]·4H₂O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd²⁺ and various trivalent metal ions which can replace each site of Mg²⁺ and Al³⁺ in the hydrotalcite. Rh³⁺ was also used for preparing the catalyst as comparison. The precursors were then thermally decomposed and reduced to form supported Pd or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of Mg–Cr hydrotalcite containing Pd²⁺ resulted in the formation of efficient Pd supported catalysts for the production of synthesis gas by selective decomposition of methanol at low temperature. Although Pd²⁺ cannot well replace the Mg²⁺ site in the hydrotalcite, the Pd supported catalyst (Pd/Mg–Cr) prepared by the solid-phase crystallization method formed highly dispersed Pd metal particles and showed much higher activity than that prepared by the conventional impregnation method. When the precursor was prepared under mild conditions, more fine particles of Pd metal were formed over the catalyst, resulting in high activity. It is likely that the high activity may be due to the highly dispersed and stable Pd metal particles assisted by the role of Cr as the co-catalyst. This revised version was published online in November 2006 with corrections to the Cover Date.     

Methanol Decomposition and Synthesis Over Palladium Catalysts

Palladium is generally active in the catalytic decomposition and synthesis of methanol. The activity of palladium is largely affected by its support. Cerium oxide is an effective support especially when the catalyst is prepared by the coprecipitation or depositionprecipitation method which leads to a strong interaction between palladium and the support. Cationic palladium species formed in the catalyst are probably active species for both decomposition and synthesis while formation of Pd-O-Ce bonding is rather important in the synthesis reaction.     

Deactivation of Copper Metal Catalysts for Methanol Decomposition, Methanol Steam Reforming and Methanol Synthesis

Laboratory and industrial results are reviewed to elucidate the general features of the deactivation of supported copper metal catalysts in various reactions involving methanol as reactant or product. Most catalyst types are based on Cu/ZnO formulations that contain stabilisers and promoters such as alumina, alkaline earth oxides and other oxides. These additional materials have several roles, including the inhibition of sintering and absorption of catalyst poisons. All copper catalysts are susceptible to thermal sintering via a surface migration process, and this is markedly accelerated by the presence of even traces of chloride. Care must be taken, therefore, to eliminate halides from copper catalysts during manufacture, and from reactants during use. Operating temperatures must be restricted, usually to below 300°C.In methanol synthesis involving modern promoted Cu/ZnO/Al₂ O₃ catalysts neither poisoning nor coking is normally a significant source of deactivation; thermal sintering is the main cause of deactivation. In contrast, catalyst poisoning and coking have been observed in methanol decomposition and methanol steam reforming reactions.     

Promotional SMSI Effect on Supported Palladium Catalysts for Methanol Synthesis

High-temperature reduction (HTR) of palladium catalysts supported on some reducible oxides, such as Pd/CeO₂, and Pd/TiO₂ catalysts, led to a strong metal-support interaction (SMSI), which was found to be the main reason for their high and stable activity for methanol synthesis from hydrogenation of carbon dioxide. But low-temperature-reduced (LTR) catalysts exhibited high methane selectivity and were oxidized to PdO quickly in the same reaction. Besides palladium, platinum exhibited similar behavior for this reaction when supported on these reducible oxides. Mechanistic studies of the Pd/CeO₂ catalyst clarified the promotional role of the SMSI effect, and the spillover effect on the HTR Pd/CeO₂ catalyst. Carbon dioxide was decomposed on Ce₂O₃, which was attached to Pd, to form CO and surface oxygen species. The carbon monoxide formed was hydrogenated to methanol successively on the palladium surface while the surface oxygen species was hydrogenated to water by spillover hydrogen from the gas phase. A reaction model for the hydrogenation of carbon dioxide was suggested for both HTR and LTR Pd/CeO₂ catalysts. Methanol synthesis from syngas on the LTR or HTR Pd/CeO₂ catalysts was also conducted. Both alcohol and hydrocarbons were formed significantly on the HTR catalyst from syngas while methanol formed predominantly on the LTR catalyst. Characterization of these two catalysts elucidated the reaction performances.     

非贵金属在甲醇裂解中的应用研究进展

甲醇裂解以生成氢气和一氧化碳,是提高甲醇能源利用效率的一个重要途径。而选择合适的催化剂,是裂解反应的关键。综述了应用于甲醇裂解反应的非贵金属催化剂,如Cu、Ni等,包括它们的催化活性、选择性、稳定性,并对部分催化剂的制备方法、产物分析、反应动力学以及催化机理进行了概述。     

New Supported Pd and Pt Alloy Catalysts for Steam Reforming and Dehydrogenation of Methanol

The catalytic performances of supported Group 810 metal (Co, Ni, Ru, Pd, Ir and Pt) catalysts for steam reforming of methanol, CH₃OH + H₂O CO₂ + 3H₂, and dehydrogenation of methanol to methyl formate, 2CH₃ OH HCOOCH₃ + 2H₂, are markedly affected by the kinds of supports as well as the metals used. The selectivity for steam reforming and the formation of methyl formate was markedly improved when Pd or Pt were supported on ZnO, In₂O₃ and Ga₂O₃. The combined results of temperature-programmed reduction, XRD, XPS and AES revealed that Pd-Zn, Pd-In, Pd-Ga, Pt-Zn, Pt-In and Pt-Ga alloys were formed upon reduction. Over the catalysts having an alloy phase, the reactions proceeded selectively, whereas over the catalysts having a metallic phase, methanol was decomposed to carbon monoxide and hydrogen predominantly. It was shown that the reactivity of formaldehyde intermediate over the Pd and Pt alloys was markedly different from that over metallic Pd and Pt. Over Pd and Pt alloys, aldehyde species were stabilized and transformed into carbon dioxide and hydrogen or methyl formate by nucleophilic addition of water or methanol, respectively. By contrast, over metallic Pd and Pt, aldehyde species were rapidly decarbonylated to carbon monoxide and hydrogen.     

Cu-Zn-Al-Li催化生物质合成气合成甲醇

在模拟生物质合成气气氛(CO/H2/CO2/N2=22/47/27/4, 体积比)下对Cu-Zn催化生物质合成气合成甲醇进行活性评价,发现Cu-Zn催化剂合成甲醇活性随反应时间单调下降,40 h后Cu-Zn催化剂活性比初始活性下降15%,添加Al能提高Cu-Zn催化剂的稳定性,添加Al后的Cu-Zn-Al及Cu-Zn-Al-Li催化剂40 h内合成甲醇的活性均未见明显下降. SEM和XRD表征研究发现,添加Li助剂有助于分散Cu活性组分,从而提高催化剂活性. 不同压力、空速及气体成分下,CO转化率均远高于CO2转化率,CO是生物质合成气合成甲醇的主要C来源.     

铜基甲醇合成催化剂前驱体对催化剂性能影响的研究

采用并流共沉淀法制备铜基甲醇合成催化剂,研究了不同前驱体作原料对所制备的Cu／ZnO／Al2O3甲醇合成催化剂活性的影响。结果表明,铜和锌都以醋酸盐代替硝酸盐制备的催化剂活性得到提高,单独以醋酸盐代替硝酸盐制备催化剂活性还不如全部以硝酸盐制备催化剂活性高。催化剂TPR研究表明,不同前驱体的催化剂的还原存在一定差异。XRD结果表明铜和锌都以醋酸盐代替硝酸盐制备的催化剂中CuO和ZnO的分散．铜锌间作用增强。     

Catalytic Methanol Decomposition Over Palladium Deposited on Mesoporous Cerium Oxide

Ultrafine palladium particles can be deposited on mesoporous cerium oxide by a deposition–precipitation method. After reduction with hydrogen at 300 °C, palladium on the mesoporous compound is cationic with a valence close to +1 whereas the particles have a metallic structure. The catalytic activity in selective methanol decomposition to hydrogen and carbon monoxide at 180 °C is significantly higher than that of palladium supported on non-porous cerium oxide, suggesting that the mesoporous structure is advantageous to the reaction. When the palladium content is high, part of mesopores are probably choked with large palladium particles, which will cause saturation of the activity.     

秸秆气合成燃料甲醇

秸秆是可再生能源,来源丰富。以秸秆气为原料,在国产C301铜基催化剂上进行了合成燃料甲醇的试验研究,结果表明:在压力5.0 MPa、温度237℃和空速8 500 L/〔kg(cat).h〕的试验条件下,甲醇最大时空收率为0.23 kg/〔kg(cat).h〕。并对催化剂的失活原因进行了初步探讨。     

低压合成甲醇CuO-ZnO-ZrO_2催化剂的活性测定和红外光谱研究

以硝酸铜、硝酸锌、氯氧化锆为原料,碳酸钠为沉淀剂,通过共沉淀、洗涤、干燥和３００°Ｃ下焙烧制备了一系列含锆合成甲醇催化剂。活性测定结果表明：在２１０～２７０°Ｃ、４．０ＭＰａ下单组分ＣｕＯ、ＺｎＯ及双组分ＣｕＯ－ＺｒＯ２没有活性,双组分ＣｕＯ－ＺｎＯ具有一定活性,再添加ＺｒＯ２则能显著增加这种催化活性。红外光谱考察表明：ＣｕＯ、ＺｎＯ组分间具有较强的相互作用,添加锆组分能增强这种相互作用。分析认为,这种相互作用正是该种催化剂合成甲醇的活性来源。     

合成气直接制取低碳烯烃的铁基负载型催化剂的制备与性能

采用浸渍法制备了合成气直接制取低碳烯烃的铁基负载型催化剂,在固定床反应器中考察了载体、助剂、焙烧温度及反应温度与压力、原料气空速对催化性能的影响,并对其进行了表征. 结果表明,焙烧温度对催化剂活性有重要影响,FeK/ZSM-5催化剂经500℃焙烧3 h后具有最佳的催化活性,提高反应压力可明显提高活性,而增加原料气空速活性明显降低;添加助剂K和Mn明显提高了催化剂的低碳烯烃选择性,在H2/CO=2(j)、反应温度380℃、压力1.0 MPa、原料气空速4400 h-1条件下,FeMnK/ZSM-5可将CO转化率从Fe/ZSM-5催化剂的18.7%升至63.8%, C2=~C3=选择性从4.8%升至14.1%.     

甲醇合成气温度超标的解决方法

分析了甲醇合成气温度超标的原因,介绍了相应的解决方法:将水冷器重新设计换型、加强循环水管理、除蜡或减少蜡的生成等,改造后,解决了甲醇合成气温度超标的问题,产生了较好的经济效益。     

C207和C301甲醇催化剂精制气高氢还原浅析

介绍C207和C301甲醇催化剂的还原经验和使用情况。应用精制气高氢还原,催化剂具有起始还原温度低、出水集中在低温段、还原时间短、易操作等特点。还原后的催化剂活性好,使用寿命长,1炉催化剂可使用3年左右。     

Deactivation of Supported Copper Catalysts for Methanol Synthesis

Binary Cu/ZnO and Cu/Al₂O₃ as well as ternary Cu/ZnO/Al₂O₃ catalysts were investigated with respect to their catalytic activity and stability in methanol synthesis. In a rapid aging test, activity measurements were carried out in combination with the determination of the specific Cu surface area. A close correlation between the loss of catalytic activity and the decrease in specific Cu surface area was found due to sintering of the Cu particles. Differences in the deactivation behavior and the area-activity relationship of each catalyst system imply that the catalysts should be grouped in different classes.     

合成甲醇催化剂的研究进展

介绍了国内外合成甲醇催化剂的研究情况;从性能参数、测定数据、制备方法等方面阐述了锌铬催化剂、铜基催化剂、合金催化剂等国外新型金属催化剂的研究进展。     

Methanol Synthesis from CO2 Under Atmospheric Pressure over Supported Pd Catalysts

Pd/ZnO catalyst exhibits high activity and selectivity for methanol synthesis in the hydrogenation of CO₂ under atmospheric pressure. PdZn alloys are formed upon reduction of the Pd/ZnO catalyst at high temperatures. The catalytic activity and selectivity are greatly enhanced upon the formation of such PdZn alloys. The turnover frequency and selectivity of methanol formation are markedly larger than those of a Cu/ZnO type control catalyst.     

直接甲醇燃料电池钯基催化剂研究进展

直接甲醇燃料电池(DMFC)阳极催化剂是直接甲醇燃料电池的关键材料之一。由于钯的价格便宜、储量丰富、在碱性条件下活性较高,成为取代铂作为DMFC的潜在的阳极催化剂。着重介绍了近年来钯基阳极催化剂在碱性条件下对甲醇的电氧化的研究进展,展望了其发展前景。     

Methanol to Long-chain Oxygenates Over Mg/Al Mixed Oxides Supported Cu Catalysts

The concept of a hydrocarbon reformer trap is proposed as a novel technology for cleaning up automobile emissions. Zeolite beta with/without metal species such as iron, manganese, or cobalt is synthesized through a solid phase transformation of mesoporous (metallo)aluminosilicate MCM-41 along with tetraethylammonium cations for structure direction to zeolite beta. The microporosity of zeolite functions as a hydrocarbon trap, and the metal species inside the pores provide a reforming site.