Selective CO oxidation in presence of H2 over Cu/Cr/Ba catalysts

Cu/Cr/Ba based catalysts were found to be nonprecious metal catalysts that can selectively oxidize CO in a H₂-containing stream. The CO concentration in the methanol reformer effluent can be reduced from 1–2 mol% to about 0.3 mol% with only a very small extent of H₂ oxidation.     

Effects of Activation Atmospheres on Structure and Activity of Mo-based Catalyst for Synthesis of Higher Alcohols

Activated carbon supported Mo-based catalysts were prepared and reduced under different activation atmospheres, including pure H₂, syngas (H₂/CO=2/1), and pure CO. The catalysts structures were characterized by X-ray diffraction, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic performance for the higher alcohol synthesis from syngas was tested. The pure H₂ treatment showed a high reduction capacity. The presence of a large amount of metallic Co⁰. and low valence state Mo^φ+ (0<φ<2) on the surface suggested a super activity for the CO dissociation and hydrogenation, which promoted hydrocarbons formation and reduced the alcohol selectivity. In contrast, the pure CO-reduced catalyst had a low reduction degree. The Mo and Co species at the catalyst mainly existed in the form of Mo⁴⁺ and Co²⁺. The syngas-reduced catalyst showed the highest activity and selectivity for the higher alcohols synthesis. We suggest that the syngas treatment had an appropriate reduction capacity that is between those of pure H₂ and pure CO and led to the coexistence of multivalent Co species as well as the enrichment of Mo^δ+ on the catalyst's surface. The synergistic effects between these active species provided a better cooperativity and equilibrium between the CO dissociation, hydrogenation and CO insertion and thus contributed beneficially to the formation of higher alcohols.     

A study on methanol steam reforming to CO2 and H2 over the La2CuO4 nanofiber catalyst

The La₂CuO₄ crystal nanofibers were prepared by using single-walled carbon nanotubes as templates under mild hydrothermal conditions. The steam reforming of methanol (SRM) to CO₂ and H₂ over such nanofiber catalysts was studied. At the low temperature of 150 °C and steam/methanol=1.3, methanol was completely (100%, 13.8 g/h g catalyst) converted to hydrogen and CO₂ without the generation of CO. Within the 60 h catalyst lifespan test, methanol conversion was maintained at 98.6% (13.6 g/h g catalyst) and with 100% CO₂ selectivity. In the meantime, for distinguishing the advantage of nanoscale catalyst, the La₂CuO₄ bulk powder was prepared and tested for the SRM reaction for comparison. Compared with the La₂CuO₄ nanofiber, the bulk powder La₂CuO₄ showed worse catalytic activity for the SRM reaction. The 100% conversion of methanol was achieved at the temperature of 400 °C, with the products being H₂ and CO₂ together with CO. The catalytic activity in terms of methanol conversion dropped to 88.7% (12.2 g/h g catalyst) in 60 h. The reduction temperature for nanofiber La₂CuO₄ was much lower than that for the La₂CuO₄ bulk powder. The nanofibers were of higher specific surface area (105.0 m²/g), metal copper area and copper dispersion. The in situ FTIR and EPR experiments were employed to study the catalysts and catalytic process. In the nanofiber catalyst, there were oxygen vacancies. H₂-reduction resulted in the generation of trapped electrons [e] on the vacancy sites. Over the nanofiber catalyst, the intermediate H₂CO/HCO was stable and was reformed to CO₂ and H₂ by steam rather than being decomposed directly to CO and H₂. Over the bulk counterpart, apart from the direct decomposition of H₂CO/HCO to CO and H₂, the intermediate H₂COO might go through two decomposition ways: H₂COO=CO+H₂O and H₂COO=CO₂+H₂.     

Development of high performance Cu/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction

Our groups studies on Cu/ZnO-based catalysts for methanol synthesis via hydrogenation of CO₂ and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al₂O₃, ZrO₂ or SiO₂ improved its specific activity for methanol synthesis and the reverse water-gas shift reaction, but did not improve its specific activity for methanol steam reforming and the water-gas shift reaction. Methanol synthesis from CO₂ and H₂ over Cu/ZnO-based catalysts was extensively studied under a joint research project between National Institute for Resources and Environment (NIRE; one of the former research institutes reorganized to AIST) and Research Institute of Innovative Technology for the Earth (RITE). It was suggested that methanol should be produced via the hydrogenation of CO₂, but not via the hydrogenation of CO, and that H₂O produced along with methanol should greatly suppress methanol synthesis. The Cu/ZnO-based multicomponent catalysts such as Cu/ZnO/ZrO₂/Al₂O₃ and Cu/ZnO/ZrO₂/Al₂O₃/Ga₂O₃ were highly active for methanol synthesis from CO₂ and H₂. The addition of a small amount of colloidal silica to the multicomponent catalysts greatly improved their long-term stability during methanol synthesis from CO₂ and H₂. The purity of the crude methanol produced in a bench plant was 99.9 wt% and higher than that of the crude methanol from a commercial methanol synthesis from syngas. The water-gas shift reaction over Cu/ZnO-based catalysts was also studied. The activity of Cu/ZnO/ZrO₂/Al₂O₃ catalyst for the water-gas shift reaction at 523 K was less affected by the pre-treatments such as calcination and treatment in H₂ at high temperatures than that of the Cu/ZnO/Al₂O₃ catalyst. Accordingly, the Cu/ZnO/ZrO₂/Al₂O₃ catalyst was considered to be more suitable for practical use for the water-gas shift reaction. The Cu/ZnO/ZrO₂/Al₂O₃ catalyst was also highly active for the water-gas shift reaction at 673 K. Furthermore, a two-stage reaction system composed of the first reaction zone for the water-gas shift reaction at 673 K and the second reaction zone for the reaction at 523 K was found to be more efficient than a one-stage reaction system. The addition of a small amount of colloidal silica to a Cu/ZnO-based catalyst greatly improved its long-term stability in the water-gas shift reaction in a similar manner as in methanol synthesis from CO₂ and H₂.     

Production of Mixed Alcohols from Bio-syngas over Mo-based Catalyst

A series of Mo-based catalysts prepared by sol-gel method using citric acid as complexant were successfully applied in the high effcient production of mixed alcohols from bio-syngas, derived from the biomass gasification. The Cu₁Co₁Fe₁Mo₁Zn_0.5-6%K catalyst exhibited a higher activity on the space-time yield of mixed alcohols, compared with the other Mo-based catalysts. The carbon conversion significantly increases with rising temperature below 340 oC, but the alcohol selectivity has an opposite trend. The maximum mixed alcohols yield derived from biomass gasification is 494.8 g/(kg_catal·h) with the C2⁺ (C2-C6 higher alcohols) alcohols of 80.4% under the tested conditions. The alcohol distributions are con-sistent with the Schulz-Flory plots, except methanol. In the alcohols products, the C2⁺ alcohols (higher alcohols) dominate with a weight ratio of 70%-85%. The Mo-based cata-lysts have been characterized by X-ray diffraction and N2 adsorption/desorption. The clean bio-fules of mixed alcohols derived from bio-syngas with higher octane values could be used as transportation fuels or petrol additives.     

H2 Production via the Steam Reforming of Methanol Over NiAl-layered Double Hydroxide Derived Catalysts

This article reviews our recent results on the steam reforming of methanol over a series of NiAl-layered double hydroxide catalysts prepared by the co-precipitation method. The influence of calcination temperature, reaction temperature, pretreatment temperature and atmospheres, inorganic salt ions and steam to methanol ratio on the catalytic performance was studied. The major products for many of the catalysts were H₂, CO, CO₂ and CH₄. However, the product composition varies significantly with the experimental parameters and high selectivity for CO₂ and H₂ was observed under various conditions, showing the potential of Ni based catalysts for the production of highly pure hydrogen.     

A Molecular Cobalt Hydrogen Evolution Catalyst Showing High Activity and Outstanding Tolerance to CO and O2

There is a demand to develop molecular catalysts promoting the hydrogen evolution reaction (HER) with a high catalytic rate and a high tolerance to various inhibitors, such as CO and O₂. Herein we report a cobalt catalyst with a penta‐dentate macrocyclic ligand ( 1‐Co ), which exhibits a fast catalytic rate (TOF=2210 s^?1) in aqueous pH 7.0 phosphate buffer solution, in which proton transfer from a dihydrogen phosphate anion (H₂PO₄^?) plays a key role in catalytic enhancement. The electrocatalyst exhibits a high tolerance to inhibitors, displaying over 90 % retention of its activity under either CO or air atmosphere. Its high tolerance to CO is concluded to arise from the kinetically labile character of undesirable CO‐bound species due to the geometrical frustration posed by the ligand, which prevents an ideal trigonal bipyramid being established.     

Size-Dependent Nickel-Based Electrocatalysts for Selective CO2 Reduction

Closing the anthropogenic carbon cycle by converting CO₂ into reusable chemicals is an attractive solution to mitigate rising concentrations of CO₂ in the atmosphere. Herein, we prepared Ni metal catalysts ranging in size from single atoms to over 100 nm and distributed them across N-doped carbon substrates which were obtained from converted zeolitic imidazolate frameworks (ZIF). The results show variance in CO₂ reduction performance with variance in Ni metal size. Ni single atoms demonstrate a superior Faradaic efficiency (FE) for CO selectivity (ca. 97 % at −0.8 V vs. RHE), while results for 4.1 nm Ni nanoparticles are slightly lower (ca. 93 %). Further increase the Ni particle size to 37.2 nm allows the H₂ evolution reaction (HER) to compete with the CO₂ reduction reaction (CO₂RR). The FE towards CO production decreases to under 30 % and HER efficiency increase to over 70 %. These results show a size-dependent CO₂ reduction for various sizes of Ni metal catalysts.     

Influence of copper precursors in the steam reforming of methanol over Cu/SnO2/SiO2 catalysts

Cu/SnO₂/SiO₂ catalysts, prepared with three different copper precursors (copper nitrate, sulfate and chloride), were characterized and investigated for the steam reforming of methanol. Cu/SnO₂/SiO₂ catalyst, prepared with copper nitrate, showed the highest activity among the tested catalysts. The highest activity of the catalyst prepared with copper nitrate was ascribed to the highly dispersed Cu particles from CO adsorption experiment. The selectivity of methanol to H₂ decreased with an increase in the amount of acid on the surface of Cu/SnO₂/SiO₂ catalysts from FT-IR experiments.This revised version was published online in December 2005 with corrections to the Cover Date.     

Pt的氧化状态对甲醇氧化活性的影响

采用NaBH4还原法制备了XC-72碳黑负载的Pt电催化剂,并在化学还原后用H2O2处理部分催化剂以改变Pt的氧化状态,以期改善Pt活性中心上水的离解而提高催化活性.X射线光电子能谱结果表明,经H2O2处理的催化剂含有较多的氧化态Pt.通过循环伏安法和记时电流法考察了经处理和未经处理的催化剂在酸性条件下的甲醇氧化的催化...     

Methanol Synthesis at a Wide Range of H2/CO2 Ratios over a Rh-In Bimetallic Catalyst

There is increasing interest in capturing H₂ generated from renewables with CO₂ to produce methanol. However, renewable hydrogen production is expensive and in limited quantity compared to CO₂. Excess CO₂ and limited H₂ in the feedstock gas is not favorable for CO₂ hydrogenation to methanol, causing low activity and poor methanol selectivity. Now, a class of Rh-In catalysts with optimal adsorption properties to the intermediates of methanol production is presented. The Rh-In catalyst can effectively catalyze methanol synthesis but inhibit the reverse water-gas shift reaction under H₂-deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with reported values. This work demonstrates a strong potential of Rh-In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (such as H₂/CO₂ from biomass derivatives) with lower energy cost can be established.     

Antimony Complexes for Electrocatalysis: Activity of a Main-Group Element in Proton Reduction

Main-group complexes are shown to be viable electrocatalysts for the H₂-evolution reaction (HER) from acid. A series of antimony porphyrins with varying axial ligands were synthesized for electrocatalysis applications. The proton-reduction catalytic properties of TPSb(OH)₂ (TP=5,10,15,20-tetra(p-tolyl)porphyrin) with two axial hydroxy ligands were studied in detail, demonstrating catalytic H₂ production. Experiments, in conjunction with quantum chemistry calculations, show that the catalytic cycle is driven via the redox activity of both the porphyrin ligand and the Sb center. This study brings insight into main group catalysis and the role of redox-active ligands during catalysis.     

Polymerization of 1-ethynylcyclohexene by tungsten and molybdenum-based catalysts

1-Ethynylcyclohexene, an acetylene derivative having cyclohexenyl substituent, was polymerized by various W- and Mo-based catalysts. WCl₆-EtAlCl₂ catalyst system was found to be very effective for this polymerization. The effects of the monomer-to-catalyst mol ratio, the initial monomer concentration, the temperature, and the cocatalysts for the polymerization of 1-ethynylcyclohexene by WCl₆ were investigated. The catalytic activity of Mo-based catalysts was found to be similar to that of W-based catalysts. The polymer structure was identified to have a conjugated polymer backbone carrying a cyclohexenyl substituent. The resulting polymers were light-brown powder and completely soluble in aromatic and halogenated hydrocarbon solvents such as chlorobenzene, benzene, chloroform, carbon tetrachloride, etc. Studies of the thermal properties and morphology of poly(1-ethynylcyclohexene) were also carried out. © 1995 John Wiley & Sons, Inc.     

Decomposition of methanol vapour over solid catalyst,measured by DSC

The activity of copper containing catalysts for the formation of methanol from CO and H₂ is investigated by DSC measurement of the methanol decomposition. Calibration of the DSC signal can be performed by melting experiments with tin under reaction conditions. Comparison of catalysts is well possible by measurement of the standard activity at 240°, the apparent activation energy for the methanol decomposition reaction and the aging of the catalyst samples.

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Zusammenfassung In DSC-Messungen an der Zersetzung von Methanol wurde die Aktivität von kupferhaltigen Katalysatoren für die Bildung von Methanol aus CO und H₂ untersucht. Das DSC-Signal kann mittels Zinn-Schmelzexperimenten unter Reaktionsbedingungen kalibriert werden. Ein Vergleich der Katalysatoren ist ohne weiteres durch die Messung der Standardaktivität bei 240°C, der scheinbaren Aktivierungsenergie der Methanol-Zersetzungsreaktion und des Alterns der Katalysatorproben möglich.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

Methanol Synthesis at a Wide Range of H2/CO2 Ratios over a Rh‐In Bimetallic Catalyst

There is increasing interest in capturing H₂ generated from renewables with CO₂ to produce methanol. However, renewable hydrogen production is expensive and in limited quantity compared to CO₂. Excess CO₂ and limited H₂ in the feedstock gas is not favorable for CO₂ hydrogenation to methanol, causing low activity and poor methanol selectivity. Now, a class of Rh‐In catalysts with optimal adsorption properties to the intermediates of methanol production is presented. The Rh‐In catalyst can effectively catalyze methanol synthesis but inhibit the reverse water‐gas shift reaction under H₂‐deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with reported values. This work demonstrates a strong potential of Rh‐In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (such as H₂/CO₂ from biomass derivatives) with lower energy cost can be established.     

On the hydrogenation of CO and CO2 over copper/zirconia and palladium/zirconia catalysts

Summary Zirconia-supported hydrogenation catalysts were obtained by activation of the amorphous precursors Cu₇₀Zr₃₀ and Pd₂₅Zr₇₅ under CO₂ hydrogenation conditions. Catalysts of comparable compositions prepared by co-precipitation and wet impregnation of zirconia with copper- and palladium salts, respectively, served as reference materials. The catalyst surfaces under reaction conditions were investigated by diffuse reflectance FTIR spectroscopy. Carbonates, formate, formaldehyde, methylate and methanol were identified as the pivotal surface species. The appearance and surface concentrations of these species were correlated with the presence of CO₂ and CO as reactant gases, and with the formation of either methane or methanol as reaction products. Two major pathways have been identified from the experimental results. i) The reaction of CO₂/H₂-mixtures on Cu/zirconia and Pd/zirconia primarily yields surface formate, which is hydrogenated to methane without further observable intermediates. ii) The catalytic reaction between CO and hydrogen yields -bonded formaldehyde, which is subsequently reduced to methylate and methanol. Interestingly, there is no observable correlation between absorbed formaldehyde or methylate on the one hand, and gas phase methane on the other hand. The reactants, CO₂ and CO, can be interconverted catalytically by the water gas shift reaction. The influence of the metals on this system of coupled reactions gives rise to different product selectivities in CO₂ hydrogenation reactions. On zirconia-supported palladium catalysts, surface formate is efficiently reduced to methane, which consequently appears to be the principal CO₂ hydrogenation product. In contrast, there is a favorable reaction pathway on copper in which CO is reduced to methanol without C-O bond cleavage; surface formate does not participate significantly in this reaction. In CO₂ hydrogenations on copper/zirconia, methanol can be obtained as the main product, from a sequence of the reverse water gas shift reaction followed by CO reduction.     

Electrochemical Conversion of CO2 to Syngas with Controllable CO/H2 Ratios over Co and Ni Single‐Atom Catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) to yield synthesis gas (syngas, CO and H₂) has been considered as a promising method to realize the net reduction in CO₂ emission. However, it is challenging to balance the CO₂RR activity and the CO/H₂ ratio. To address this issue, nitrogen‐doped carbon supported single‐atom catalysts are designed as electrocatalysts to produce syngas from CO₂RR. While Co and Ni single‐atom catalysts are selective in producing H₂ and CO, respectively, electrocatalysts containing both Co and Ni show a high syngas evolution (total current >74 mA cm^?2) with CO/H₂ ratios (0.23–2.26) that are suitable for typical downstream thermochemical reactions. Density functional theory calculations provide insights into the key intermediates on Co and Ni single‐atom configurations for the H₂ and CO evolution. The results present a useful case on how non‐precious transition metal species can maintain high CO₂RR activity with tunable CO/H₂ ratios.     

Electrochemical Conversion of CO2 to Syngas with Controllable CO/H2 Ratios over Co and Ni Single-Atom Catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) to yield synthesis gas (syngas, CO and H₂) has been considered as a promising method to realize the net reduction in CO₂ emission. However, it is challenging to balance the CO₂RR activity and the CO/H₂ ratio. To address this issue, nitrogen-doped carbon supported single-atom catalysts are designed as electrocatalysts to produce syngas from CO₂RR. While Co and Ni single-atom catalysts are selective in producing H₂ and CO, respectively, electrocatalysts containing both Co and Ni show a high syngas evolution (total current >74 mA cm⁻²) with CO/H₂ ratios (0.23–2.26) that are suitable for typical downstream thermochemical reactions. Density functional theory calculations provide insights into the key intermediates on Co and Ni single-atom configurations for the H₂ and CO evolution. The results present a useful case on how non-precious transition metal species can maintain high CO₂RR activity with tunable CO/H₂ ratios.     

Ni nanoparticles as electron-transfer mediators and NiSx as interfacial active sites for coordinative enhancement of H2-evolution performance of TiO2

The development of efficient photocatalytic H₂-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H₂ production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron-transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H₂-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H₂ by Ni-modified TiO₂, the formation of NiS_x as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO₂/Ni-NiS_x photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO₂ surface and the subsequent formation of NiS_x on the Ni surface by a hydrothermal reaction method. It was found that the TiO₂/Ni-NiS_x photocatalysts exhibited enhanced photocatalytic H₂-evolution activity. In particular, TiO₂/Ni-NiS_x(30%) showed the highest photocatalytic rate (223.74 μmol h^?1), which was greater than those of TiO₂, TiO₂/Ni, and TiO₂/NiS_x by factors of 22.2, 8.0, and 2.2, respectively. The improved H₂-evolution performance of TiO₂/Ni-NiS_x could be attributed to the excellent synergistic effect of Ni and NiS_x, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO₂ surface and NiS_x serves as interfacial active sites to capture H⁺ ions from solution and promote the interfacial H₂-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.     

甲醇-H2能源体系的催化研究:进展与挑战

甲醇是优异的储氢化合物,质量储氢密度高达12.5%。甲醇-氢能源体系着力于解决氢能应用中储存和输送的瓶颈问题,助力氢能的推广和应用。甲醇高效高选择性原位产氢是甲醇-氢能源体系中的重要环节。基于此,本文介绍了甲醇制氢催化研究的最新进展和面临的挑战。从甲醇储氢的优势、经济合理性出发,结合笔者自身研究情况,对甲醇储氢-原位制氢的方式、应用形式及重整产氢催化剂的结构和催化机理研究进行了梳理、总结。期望为甲醇-氢能源体系的催化研究提供参考,促进氢能走向实用。