Graph-theoretic and energetic exploration of catalytic pathways of the water-gas shift reaction

The catalytic mechanisms or pathways of water-gas shift (WGS) reaction have been the focus of intense research interest because of its immense importance in hydrogen production. At the outset, 116 stoichiometrically feasible independent pathways (IP_i's) have been exhaustively generated within 2 s on a PC through a novel graph-theoretic method based on P-graphs (process graphs) from a set of 17 plausible elementary reactions. This is followed by the determination of IP₁₈ among these 116 stoichiometrically feasible IP_i's as the plausibly dominant pathway via energetic analysis.     

Thermodynamic analysis of glycerol dry reforming for hydrogen and synthesis gas production

A thermodynamic analysis of glycerol dry reforming has been performed by the Gibbs free energy minimization method as a function of CO₂ to glycerol ratio, temperature, and pressure. Hydrogen and synthesis gas can be produced by the glycerol dry reforming. The carbon neutral glycerol reforming with greenhouse gas CO₂ could convert CO₂ into synthesis gas or high value-added inner carbon. Atmospheric pressure is preferable for this system and glycerol conversion keeps 100%. Various of H₂/CO ratios can be generated from a flexible operational range. Optimized conditions for hydrogen production are temperatures over 975 K and CO₂ to glycerol ratios of 0-1. With a temperature of 1000 K and CO₂ to glycerol ratio of 1, the production of synthesis gas reaches a maximum, e.g., 6.4 mol of synthesis gas (H₂/CO = 1:1) can be produced per mole of glycerol with CO₂ conversion of 33%.     

Thermodynamic analysis of glycerol partial oxidation for hydrogen production

Thermodynamics of glycerol partial oxidation for hydrogen production has been studied by Gibbs free energy minimization method. The optimum conditions for hydrogen production are identified: reaction temperatures between 1000 and 1100 K and oxygen-to-glycerol molar ratios of 0.4-0.6 at 1 atm. Under the optimal conditions, complete conversion of glycerol, 78.93%-87.31% yield of hydrogen and 75.12%-87.97% yield of carbon monoxide could be achieved in the absence of carbon formation. The glycerol partial oxidation with O₂ is suitable for providing hydrogen-rich fuels for Molten Carbonate Fuel Cell and Solid Oxide Fuel Cell. The carbon-formed and carbon-free regions are found, which are useful in guiding the search for suitable catalysts for the reaction. Inert gases have a positive effect on the hydrogen and carbon monoxide yields.     

Negative apparent kinetic order in steady-state kinetics of the water-gas shift reaction over a Pt–CeO2 catalyst

The kinetics of the water-gas shift reaction were studied on a 0.2% Pt/CeO₂ catalyst between 177 and 300 °C over a range of CO and steam pressures. A rate decrease with increasing partial pressure of CO was experimentally observed over this sample, confirming that a negative order in CO can occur under certain conditions at low temperatures. The apparent reaction order of CO measured at 197 °C was about −0.27. This value is significantly larger than that (i.e. −0.03) reported by Ribeiro and co-workers [A.A. Phatak, N. Koryabkina, S. Rai, J.L. Ratts, W. Ruettinger, R.J. Farrauto, G.E. Blau, W.N. Delgass, F.H. Ribeiro, Catal. Today 123 (2007) 224] at a similar temperature. A kinetic peculiarity was also evidenced, i.e. a maximum of the reaction rate as a function of the CO concentration or possibly a kinetic break, which is sometimes observed in the oxidation of simple molecules. These observations support the idea that competitive adsorption of CO and H₂O play an essential role in the reaction mechanism.     

Enhanced CeO2-supported Pt catalyst for water-gas shift reaction

Sodium-promoted, CeO₂-supported, Pt catalyst were synthesized and investigated for water-gas shift (WGS) reaction. The ceria supports were synthesized by conventional precipitation method. The effect of the basic aqueous solutions used in the preparation procedure on the nature of Pt/CeO₂ catalyst was examined by physical and chemical characterization analyses. The catalytic activity for the WGS reaction was observed. In the Pt/CeO₂ catalyst prepared by NaOH, the presence of sodium (1.64 wt.%) on the support modified the base and electronic properties and consequently enhanced the catalytic activity of Pt/CeO₂. Based on temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFTS) analyses, we concluded that sodium introduced through the ceria preparation procedure played an important role in the WGS reaction as a promoter to induce the fast build-up of surface intermediates of the WGS reaction and also as an electron donor to modify the adsorption strength between CO and Pt.     

Hydrogen production by aqueous-phase reforming of glycerol over nickel catalysts supported on CeO2

Nickel catalysts supported on CeO₂ were prepared and evaluated in aqueous-phase reforming of glycerol. Three different methodologies of synthesis were used: wet impregnation, co-precipitation and combustion, and the catalysts were characterized by chemical composition, textural analysis, crystalline structure and reducibility. The reaction was carried out in a batch reactor with solution of 1 and 10 wt.% glycerol, at 523 and 543 K. A maximum glycerol conversion of 30% was achieved by the catalyst prepared by combustion at 543 K using solution 1% glycerol. In the gas phase, the molar fraction of H₂ was always higher than 70% and formation of CH₄ was very low (< 1%). The increase in glycerol concentration decreases the conversion and H₂ formation.     

Co/Al2O3 catalysts promoted with noble metals for production of hydrogen by methane steam reforming

The effect of noble metal addition on the catalytic properties of Co/Al₂O₃ was evaluated for the steam reforming of methane. Co/Al₂O₃ catalysts were prepared with addition of different noble metals (Pt, Pd, Ru and Ir 0.3 wt.%) by a wetness impregnation method and characterized by UV–vis spectroscopy, temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) of the reduced catalysts. The UV–vis spectra of the samples indicate that, most likely, large amounts of the supported cobalt form Co species in which cobalt is in octahedral and tetrahedral symmetries. No peaks assigned to cobalt species from aluminate were found for the promoted and unpromoted cobalt catalysts. TPO analyses showed that the addition of the noble metals on the Co/Al₂O₃ catalyst leads to a more stable metallic state and less susceptible to the deactivation process during the reforming reaction. The Co/Al₂O₃ promoted with Pt showed higher stability and selectivity for H₂production during the methane steam reforming.     

Gold supported on mesoporous titania thin films for application in microstructured reactors in low-temperature water-gas shift reaction

Au (1 wt.%)/TiO₂ catalytic thin films were prepared on a surface-modified titanium substrate for application in a water-gas shift (WGS) microstructured reactor. Au-containing mesoporous titania films were synthesized using Pluronic 127 surfactant as a structure directing agent and titanium tetrabutoxide as titania source. Colloidal gold nanoparticles of 4 nm diameter were added to the synthesis sol prior to spin-coating. The resulting thin films were characterized by X-ray diffraction, transmission electron microscopy, ethanol adsorption–desorption isotherms and spectroscopic ellipsometry. Catalytic activity and selectivity were measured for the WGS reaction at temperatures between 220 and 290 °C. The reaction rate measured at CO conversions of below 10% was similar to that reported for gold supported on mesoporous titania and on ceria modified mesoporous titania pelletized catalysts prepared via deposition–precipitation.     

汽油氧化重整制氢反应催化剂失活因素研究

对汽油氧化重整制氢反应催化剂失活因素进行了理论分析与实验研究 ,研究结果表明 :在进行反应中 ,催化剂表面积碳是造成催化剂失活的原因 ,为避免催化剂表面积碳 ,反应的最小水碳比应大于理论计算的最小水碳比。计算了在不同反应温度条件下的最小理论水碳比     

Hydrogen production by glycerol steam reforming with/without calcium oxide sorbent: A comparative study of thermodynamic and experimental work

Thermodynamic analysis and experimental tests of glycerol steam reforming with/without calcium oxide (CaO) as a carbon dioxide (CO₂) sorbent have been performed and compared in this work. Methanol, ethanol, acetaldehyde, acetone and ethylene do not exist in equilibrium conditions according to the equilibrium calculations. Without CaO present, thermodynamic predictions show that a maximum hydrogen concentration of 67% can be obtained at 925 K, with a water to glycerol ratio (WGR) of 9. In the experiments, the Ni/ZrO₂ catalyst fails to catalyze the reactions to thermodynamic equilibrium under the selected conditions as the highest hydrogen concentration obtained is 64%. With the presence of CaO, thermodynamic analysis implies hydrogen purity exceeding 95% can be achieved below 925 K at WGRs of 6 and 9. However, CaCO₃ does not exist at temperatures greater than 1025 K. In the experiments, a hydrogen purity of 95% with only 5% CH₄ as impurity can be reached at 850 K with a WGR of 9. The Ni/ZrO₂ catalyst is not active enough to convert excess CH₄ to hydrogen in glycerol steam reforming as CH₄ concentrations are usually higher than the equilibrium values. The addition of CaO to this system greatly enhances the hydrogen production while reducing the CO concentration.     

Effect of support on hydrogen production by auto-thermal reforming of ethanol over supported nickel catalysts

Nickel catalysts supported on various supports such as ZnO, MgO, ZrO₂, TiO₂, and Al₂O₃ were prepared by an impregnation method to investigate the effect of support on catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Among the supported catalysts, the Ni/ZrO₂ and Ni/TiO₂ catalysts showed better catalytic performance than the other catalysts. The electronic structure of nickel species supported on ZrO₂ and TiO₂ was favorably modified for the reaction, and thus, the reducibility of nickel species supported on ZrO₂ and TiO₂ was increased due to the weak interaction between nickel and support. On the other hand, the Ni/MgO and Ni/ZnO catalysts exhibited poor catalytic performance in the auto-thermal reforming of ethanol due to the formation of a solid solution phase.     

Mesoporous and nanostructured CeO2 as supports of nano-sized gold catalysts for low-temperature water-gas shift reaction

Mesoporous particles and 1D nanorods of cerium oxides have been prepared by modifying the hydrothermal route of a surfactant-assisted controllable synthesis. Mesoporous cerias were obtained in a sealed glass vessel under continuous stirring, while ceria nanorods were obtained in a Teflon-lined autoclave without stirring. The mesoporous cerias did not show long-range mesoscopic organization, exhibiting a broad mesopore size distribution in the region 8–15 nm. A BET surface area of 100 m²/g with a total pore volume of 0.33 cm³/g is obtained for as-synthesized mesoporous ceria. The ceria nanorods exhibit a cubic crystalline structure after calcination, having the lengths in the range of 150–300 nm and diameters in the range of 10–25 nm. The growth direction of ceria nanorods is along [1 1 0]. A surface area of above 50 m²/g is obtained in the calcined nanorods. These synthesized ceria materials were used as supports of nano-sized gold catalysts, prepared by deposition–precipitation method. Their catalytic activity was evaluated by the low-temperature water-gas shift reaction. The gold/mesoporous ceria catalytic system exhibited higher catalytic activity than gold/ceria nanorods. It is revealed that the mesoporous and nanostructured cerias are of much interest as potential supports for gold-based catalysts that are effective for low-temperature water-gas shift reaction.     

以丙三醇和氯化氢为原料制备环氧氯丙烷的工艺研究

介绍了以丙三醇和氯化氢为原料制备环氧氯丙烷的工艺,以己二酸为催化剂进行丙三醇的氯化反应,生成的二氯丙醇再和碱反应生成环氧氯丙烷。对影响反应的因素进行了研究,得出了最佳工艺条件：氯化反应温度120℃,氯化氢的通气量326．4mL／min,反应时间20h,催化剂物质的量为丙三醇的16％,环化反应采用1．9mol／L的氢氧化钠在30℃下进行较为合适。在此条件下得到的环氧氯丙烷收率为91．79％。     

甘油水相重整制氢研究进展

甘油作为生物柴油的副产物,当前的产能严重过剩。甘油制氢,尤其是通过水相重整（APR）制取可以供燃料电池直接使用的高品质氢气,是提高甘油附加值、降低生物柴油成本的重要途径和手段。本文简述了当前生物柴油及其副产物甘油的生产,阐述了甘油的水相重整制氢反应,详细介绍了甘油水相重整制氢反应的热力学和动力学影响因素。分别从催化剂的贵金属活性组分、非贵金属活性组分和载体等三方面对甘油水相重整制氢反应进行了详细的综述,最后提出了双金属催化剂可能具有优异的催化甘油水相重整制氢性能。     

Gold nanoparticles supported on ceria-modified mesoporous titania as highly active catalysts for low-temperature water-gas shift reaction

New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C₁₃(EO)₆–Ti(OC₃H₇)₄] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H₂O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO₂ and mesoporous TiO₂, as well as gold/ceria-modified titania and reference catalyst Au/TiO₂ type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR.     

甘油催化重整制氢/合成气的研究进展

随着生物柴油的大规模化发展,副产物甘油的合理利用成为生物柴油产业发展的关键问题之一。对甘油蒸汽重整、水相重整和超临界重整制氢气和合成气的研究进行了综述和评价,对未来甘油重整制氢气/合成气的研究提出了不足和展望。     

Chloride poisoning of water-gas shift activity in nickel catalysts during steam reforming

This Letter reports preliminary findings on the role of chloride poisoning during steam reforming of chlorocarbons over nickel catalysts. When conversions of chlorocarbon are very high and thermal pyrolysis absent, the principal effect of chloride is to decrease water-gas shift and CH₄-steam reforming activity. Product carbon dioxide/carbon monoxide ratios are then far from equilibrium and methane remains unconverted when introduced into the feed. These results are linked to previously published surface science studies.     

Iron-ruthenium catalyst for the water-gas shift reaction

Iron-ruthenium catalysts prepared by impregnation of calcination products of -, , -and -iron oxide-hydroxides with either ruthenium chloride or ruthenium red were tested for the activity for the water-gas shift reaction. The effect of support, ruthenium containing impregnation agent and thermal treatment on catalyst performance was discussed.     

Hydrogen production from fluidized bed steam reforming of hydrocarbons

Steam reforming of methane, kerosene and heavy oil over a nickel/alumina commercial catalyst and other materials such as limestone, dolomite and iron ore, was studied using a 5 cm i.d. fluidized bed reactor. The effects of operating parameters on conversion, hydrogen yield, product gas composition and elutriation of fine catalysts were investigated. It was found that a fluidized bed is flexible enough to handle various feedstocks, including hydrocarbons heavier than naphtha, because it permits the addition of catalyst to, or withdrawals of, coked catalyst from the bed. The yield of hydrogen obtained from fluidized bed steam reforming of heavy oil at 800‡C over limestone was similar to that obtained over commercial nickel-based catalyst. This indicates that limestone could be a promising catalyst for the production of hydrogen from heavy oil. However, hydrogen yield decreased with reaction time in the experiments using the limestone catalyst. The main cause of the decrease in hydrogen yield was elutriation of fine catalysts from the bed during the reaction.     

Sustainable hydrogen production via reforming of ethylene glycol using a novel spouted bed reactor

Hydrogen produced from renewable energy sources is of great interest as an alternative to fossil fuels and as a means for clean power generation via fuel cells. The aqueous fraction of bio-oil can be effectively reformed to hydrogen rich streams in the presence of active catalytic materials. In this paper we present the experimental work carried out in a novel spouted bed reactor for the reforming of bio-oil. The use of a specially designed injection nozzle in combination with the particular hydrodynamic characteristics of the spouted bed resulted in efficient processing of the organic feed. The known problem of coking was notably avoided regardless of the loading material of the reactor. The effect of reaction temperature and steam to carbon ratio in the feed was investigated in the presence of various catalytic and non-catalytic particles. Runs were conducted with ethylene glycol as a representative model compound of the aqueous phase of bio-oil. Olivine, when associated with nickel, proved to be a very suitable catalytic material for the process combining high activity in reforming, anti-coking characteristics combined with exceptional mechanical strength.