High-Performance Bimetallic Catalysts for Low-Temperature Carbon Dioxide Reforming of Methane

Catalytic dry reforming of methane (DRM) is a promising way for renewable syngas production due to the utilization of both CO₂ and CH₄ greenhouse gases. Current approaches were made to improve the catalytic activity and coke resistance by introducing a second metal into the Ni-based catalytic system. This bimetallic catalytic system showed a significant improvement in coke resistance due to the synergistic effect of both metals towards the reaction. This review summarizes recent developments in bimetallic catalysts in DRM which focused on the evaluation of catalysts, deactivation studies, and reaction mechanisms of developed bimetallic catalysts.     

CO2 Methanation on Fe Catalysts Using Different Structural Concepts

The hydrogenation of carbon dioxide towards methane and water is evaluated on different types of iron catalysts. The catalysts refer to different structural concepts implying a bare iron oxide, a silica-supported and a core-shell system. Highest CO₂ conversion of about 20 % is achieved with the bulk catalysts and the supported material. However, although revealing reduced CH₄ formation rate, the core-shell catalyst exhibits pronounced resistance against coke formation as well as thermal sintering and particle attrition upon syngas reaction.     

Ultra-rapid synthesis of syngas by the catalytic reforming of methane enhanced byin-situ heat supply through combustion

Development in highly active catalysts for the reforming of methane with CO₂ and partial oxidation of methane was conducted to produce hydrogen and carbon monoxide with high reaction rates. An Ni-based four-components catalyst, Ni-Ce₂O₃-Pt-Rh, supported on an alumina wash-coated ceramic fiber in a plate shape was suitable for the objective reaction. By combining the catalytic combustion of ethane or propane, methane conversion was markedly enhanced, and a high space-time yield of syngas, 25,000 mol/l·h was obtained at a catalyst temperature of 700 ‡C or furnace temperature of 500 ‡C. The extraordinary high space-time yield of syngas was also confirmed even under the very rapid flow rate conditions as a contact time of 3 m-sec by using a monolithic shape of catalyst bed without back pressure.     

Simultaneous oxidative conversion and CO2 reforming of methane to syngas over Ni/vermiculite catalysts

Modified-vermiculite supported Ni catalysts were prepared and characterized by XRD, BET, TGA, TPR and TEM. The catalytic activity of these catalysts for simultaneous oxidative conversion and CO₂ reforming of methane to syngas was evaluated. The results indicated that vermiculite has a great potential as a support of Ni component due to its excellent thermal stability. Among these catalysts, the expanded-vermiculite supported Ni catalyst exhibited the highest catalytic activity and stability. It was found that Ni oxides supported on vermiculite was reduced more easily and also Ni-based vermiculite catalysts suppressed coke depositing in the reaction, in comparison with alumina-supported Ni catalyst.     

Increasing carbon utilization in Fischer-Tropsch synthesis using H2-deficient or CO2-rich syngas feeds

Fischer-Tropsch technology has become a topical issue in the energy industry in recent times. The synthesis of linear hydrocarbon that has high cetane number diesel fuel through the Fischer-Tropsch reaction requires syngas with high H₂/CO ratio. Nevertheless, the production of syngas from biomass and coal, which have low H₂/CO ratios or are CO₂ rich may be desirable for environmental and socio-political reasons. Efficient carbon utilization in such H₂-deficient and CO₂-rich syngas feeds has not been given the required attention. It is desirable to improve carbon utilization using such syngas feeds in the Fischer-Tropsch synthesis not only for process economy but also for sustainable development. Previous catalyst and process development efforts were directed toward maximising C₅₊ selectivity; they are not for achieving high carbon utilization with H₂-deficient and CO₂-rich syngas feeds. However, current trends in FTS catalyst design hold the potential of achieving high carbon utilization with wide option of selectivities. Highlights of the current trends in FTS catalyst design are presented and their prospect for achieving high carbon utilization in FTS using H₂-deficient and CO₂-rich syngas feeds is discussed.     

Electrodeposited Re-promoted Ni foams as a catalyst for the dry reforming of methane

The dry reforming of methane (DRM) utilizes carbon dioxide (CO₂) as the oxidizing agent in order to produce synthesis gas. Catalyst deactivation via coking, oxidation, and sintering has stymied the industrialization of catalysts for the DRM. Here, we utilized electrodeposition followed by de-alloying in order to synthesize metal alloy foams (5 m²/g). Through this process we have created the first electrodeposited DRM catalyst capable of converting more than 10,000 mL/g 1 h at near-equilibrium conversion. Rhenium promotion was observed over the entire temperature range studied (700–800 °C), with the most dramatic enhancement at 700 °C. After 50 h of reaction, no significant accumulation of carbonaceous deposits were detected, making electrodeposited structures a viable candidate for stable methane conversion catalysts.     

CO2 reforming of methane to syngas: I: evaluation of hydrotalcite clay-derived catalysts

Several important chemicals can potentially be manufactured from natural gas (mostly methane) by first converting it to syngas (CO+H₂). The high cost of converting methane to syngas currently limits the large scale commercial use of syngas to produce methanol. This study focuses on the CO₂/steam reforming of methane to produce inexpensive syngas using nickel and magnesium containing hydrotalcite clay-derived catalysts. Several of these catalysts were prepared and evaluated. The results are compared with commercial Ni/Al₂O₃ or Ni/MgAl₂O₄ catalysts. At 815°C and 300 psi pressure, the fresh clay-derived catalysts showed identical performance as the commercial catalysts. However, under more severe operating conditions, the clay-derived catalysts exhibited superior activity and stability. Aging studies clearly showed that the clay-derived catalysts are more stable and coke resistant than commercial catalysts.     

Catalytic dry-reforming on Ni-zeolite supported catalyst

In the present work, the catalytic behaviour in the dry reforming of methane on Ni-based Silicalite-1 type catalyst was studied. The Silicalite-1 support has been synthesized in order to check the role of the silanol groups on the overall catalyst performance: methane and carbon dioxide conversion, hydrogen/carbon monoxide ratio and coke deposition. The population of defect groups on the Silicalite-1 surface was modified by aging of the gel, thermal treatment, ionic exchange and silylation procedure. Among these treatments, the silylation of the support surface leads to the formation of smaller and more reducible Ni-oxide species that not only improve the CH₄ and CO₂ conversion but also reduce the deactivation of the catalyst due to coke deposition and the obtained H₂/CO value is 1.04.     

Steam reforming of n-hexadecane over noble metal-modified Ni-based catalysts

Steam reforming of n-hexadecane, a main constituent of diesel, over noble metal-modified Ni-based hydrotalcite catalyst was carried out in a temperature range of 700–950 °C, at an atmospheric pressure with space velocity of 10,000–100,000 h⁻¹ and feed molar ratio of H₂O/C = 3.0. The catalysts were prepared by a co-precipitation and dipping methods. The noble metal-modified Ni-based hydrotalcite catalyst displayed higher resistance for the sintering of active metal than the Ni-based hydrotalcite catalyst prepared by the conventional method. It was found that the Rh-modified Ni-based catalysts showed high resistance to the formation of carbon compared to Ni-based catalysts. The results suggest that Rh-modified Ni-based catalyst can be applied for the steam reforming (SR) reaction of diesel.     

Experimental study on catalytic steam gasification of natural coke in a fluidized bed

The gasification characteristics of natural coke from Peicheng mine with steam were investigated in a fluidized bed reactor. The effects of catalyst type, composition and dosage of catalyst on the yield, components and heating value of product gas, and carbon conversion rate were examined. The results show that fluidized bed gasification technology is an effective way to gasify natural coke. Also the results indicate that individual addition of K-, Ca-, Fe-, Ni-based catalyst effectively increases the gasification reaction rate of the natural coke samples. With the increase in catalyst dosage, the yield and heating value of product gas per hour increase obviously, and carbon conversion rate is improved substantially. Each of aforementioned catalysts has similar catalytic effect and trend, among which the effect of Ca-based catalyst is a little weaker. The optimum metal atom ratio of mixed catalyst is Fe/Ni/others = 35/55/10, and the mixed catalyst displays maximum catalytic performance when the catalyst dosage in the natural coke is about 4%. The experimental findings provide an interesting reference for large-scale development and utilization of natural coke.     

二氧化碳转化为合成气及高附加值产品的研究进展

由于二氧化碳（CO₂）过度排放导致全球变暖日益严峻,发展零碳技术已成为人类社会面向可持续发展的战略选择。将CO₂捕集并转化为高附加值化学和能源产品,可以优化化石能源为主体的能源结构、有效缓解环境问题,并实现碳资源的充分利用,是一项可以大规模实现低碳减排的技术。本文重点介绍了CO₂高效利用新途径,通过二氧化碳-合成气-高附加值化学品的产品工艺路线,实现CO₂的资源化利用。对比综述了热催化法、电催化法和光催化法高效转化合成气的最新进展,总结了热、电、光催化制备合成气过程中催化剂的设计原理和方法以及目前工业化应用前景;简单概述了合成气作为重要平台分子,进一步通过费托合成路线或接力催化路线转化为低碳烯烃和液态燃料或芳烃等化学品过程中催化剂设计研究进展。最后,总结了大规模工业化CO₂转化为合成气及高附加值产品过程催化剂设计和反应器优化的技术难题,并对未来CO₂高效转化利用方向进行了展望。同时指出目前各技术还普遍存在反应机理不清晰、催化剂成本高以及缺乏大规模合成等问题,未来开发出高效、高活性、低成本且稳定的催化剂是各技术推广应用的关键。     

Low-temperature catalytic conversion of lignite: 3. Tar reforming using the supported potassium carbonate

Alumina-supported K₂CO₃–LaMn_0.8Cu_0.2O₃ was investigated for the catalytic conversion of tar, produced from lignite, into syngas under inert and steam-reforming conditions. A double-bubble fluidized bed reactor system, equipped with a micro gas chromatograph and a collecting system to analyze permanent gases and condensable species, was developed to screen the catalytic conversion of tar components below 700 °C. The redox properties of catalysts, estimated by hydrogen temperature programmed reduction analyses, were correlated with their catalytic performance in tar conversion. The synthesized catalyst effectively converted tars into hydrogen-rich syngas and also improved tar reforming by inhibiting coke deposition.     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

The effects of bimetallic interactions for CO2-assisted oxidative dehydrogenation and dry reforming of propane

The catalytic reduction of CO₂ by propane may occur via dry reforming to produce syngas (CO + H₂) or oxidative dehydrogenation to yield propylene. Utilizing propane and CO₂ as coreactants presents several advantages over conventional methane dry reforming or direct propane dehydrogenation, including lower operating temperatures and less coke formation. Thus, it is of great interest to identify catalytic systems that can either effectively break the C C bond to generate syngas or selectively break C H bonds to produce propylene. In this study, several precious and nonprecious bimetallic catalysts supported on reducible CeO₂ were investigated using flow reactor studies at 823 K to identify selective catalysts for CO₂-assisted reforming and dehydrogenation of propane.     

煤制天然气甲烷化催化剂及机理的研究进展

煤制天然气技术是将高碳能源转化为富氢、低碳能源的有效途径,发展以煤为原料、将合成气通过甲烷化反应制备天然气是今后煤清洁利用的重要途径。介绍了国内外煤制天然气的研究现状和甲烷化反应在煤制天然气中的应用。阐述了近年来CO、CO₂甲烷化催化剂中几种常见的氧化物负载型Ni基催化剂载体(Al₂O₃、ZrO₂、SiO₂、TiO₂)和催化剂助剂的制备方法以及化学结构特点,分析了一些新型催化剂载体（MWCNT、SiC、LaFeO₃）、贵金属催化剂、非晶态合金催化剂、钙钛矿催化剂的研究现状和制备方法对催化剂催化性能的影响。分别对因高温烧结、催化剂中毒和催化剂积炭在工业上引起的甲烷化催化剂失活进行分析,并提出催化剂的改进方法。阐述CO甲烷化反应的次甲基机理、表面碳机理和变换-甲院化反应机理;近年来CO₂甲烷化反应机理尽管一直存在分歧,但在催化过程中生成含碳中间物种的理论已被认同。今后甲烷化催化剂的研究方向包括开发新型甲烷化催化剂（低温催化剂、催化剂掺杂改性）、新型复合载体、抗硫催化剂（钼、钨催化剂）以及开发甲烷化新工艺和进一步深入探索甲烷化反应机理。     

Enhanced stability of a direct-methane and carbon dioxide protonic ceramic fuel cell with a PrCrO3 based reforming layer

Dry reforming of methane (CH₄ + CO₂ = 2CO + 2H₂) is a very interesting approach both to reduce the overall carbon footprint of the increasing worldwide fossil-based methane consumption as well as to cut emission greenhouse gas of CO₂. Utilizing the produced syngas as fuel directly in protonic ceramic fuel cell can further kill two birds with one stone: obtain power output and high purity CO. However, the drawback of the coking deposition limits the process of the above strategy. Here, we synthesis a Ni-based catalyst with high conversion rates (∼88% for CO₂ and ∼89% for CH₄) and excellent stability (>160 h at 700 °C) proceeded by Ce doping, and further employ it as reforming layer on solid oxide fuel cell. The results demonstrate that the Ce substitution plays an important role for homogenous Ni nanoparticles exsolution, benefiting for the coking resistance of the catalyst then the stability of the cell using CH₄ and CO₂ as fuel directly.     

Decomposition of ammonia with iron and calcium catalysts supported on coal chars

Decomposition of NH₃ to N₂ with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH₃ diluted with He at 750 °C and at a space velocity of 45,000 l/h, 2-6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20-50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH₃. The co-feeding of H₂ with 2000 ppm NH₃ improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H₂=2) deactivates it remarkably, whereas the addition of CO₂ to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH₃ decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N₂.     

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.     

炭基材料低温SCR烟气脱硝催化剂的研究进展

燃煤电站机组低温SCR技术研究是近年来烟气脱硝技术研究的主要方向,低温SCR催化剂是该技术的核心,炭基材料因其比表面积大和孔隙结构发达在低温SCR催化剂研发中占重要地位。综述炭基材料包括活性炭、碳纳米管、活性炭纤维、碳包覆材料和活性焦在低温SCR催化剂的研究进展,对多种炭基材料的催化反应机理进行阐述,总结水和二氧化硫对炭基材料催化剂性能的影响,为炭基材料在低温SCR催化剂进一步研究提供参考。     

Synthesis gas production by steam reforming of ethanol

A two-layer fixed-bed catalytic reactor for syngas production by steam reforming of ethanol has been proposed. In the reactor, ethanol is first converted to a mixture of methane, carbon oxides and hydrogen over a Pd-based catalyst and then this mixture is converted to syngas over a Ni-based catalyst for methane steam reforming. It has been shown that the use of the two-layer fixed-bed reactor prevents coke formation and provides the syngas yield closed to equilibrium.