Hydrogen production via methanol steam reforming over Au/CuO,Au/CeO2, and Au/CuO–CeO2 catalysts prepared by deposition–precipitation

The production of hydrogen (H₂) with a low concentration of carbon monoxide (CO) via steam reforming of methanol (SRM) over Au/CuO, Au/CeO₂, (50:50)CuO–CeO₂, Au/(50:50)CuO–CeO₂, and commercial MegaMax 700 catalysts were investigated over reaction temperatures between 200 °C and 300 °C at atmospheric pressure. Au loading in the catalysts was maintained at 5 wt%. Supports were prepared by co-precipitation (CP) whilst all prepared catalysts were synthesized by deposition–precipitation (DP). The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and scanning electron microscopy (SEM). Au/(50:50)CuO–CeO₂ catalysts expressed a higher methanol conversion with negligible amount of CO than the others due to the integration of CuO particles into the CeO₂ lattice, as evidenced by XRD, and a interaction of Au and CuO species, as evidenced by TPR. A 50:50 Cu:Ce atomic ratio was optimal for Au supported on CuO–CeO₂ catalysts which can then promote SRM. Increasing the reaction time, by reducing the liquid feed rate from 3 to 1.5 cm³ h^?1, resulted in a catalytic activity with complete (100%) methanol conversion, and a H₂ and CO selectivity of ～82% and ～1.3%, respectively. From stability testing, Au/(50:50)CuO–CeO₂ catalysts were still active for 540 min use even though the CuO was reduced to metallic Cu, as evidenced by XRD. Therefore, it can be concluded that metallic Cu is one of active components of the catalysts for SRM.     

Production of hydrogen by steam reforming of methanol over Cu/CeO2 catalysts derived from Ce1−xCuxO2−x precursors

The Ce_1−xCu_xO_2−x mixed oxides were synthesized using the coprecipitation method, and were reduced to form the Cu/CeO₂ (cop) catalysts for the steam reforming of methanol. All the Cu-containing catalysts tested in this study showed high selectivities to CO₂ (over 97%) and H₂. A 3.9 wt% Cu/CeO₂ (cop) catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513 K, which was higher than those over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/Al₂O₃ (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the 3.9 wt% Cu/CeO₂ (cop) catalyst was due to the highly dispersed Cu metal particles and the Cu⁺ species stabilized by the CeO₂ support.     

Steam reforming of methanol over copper–manganese spinel oxide catalysts

The steam reforming of methanol was studied over a series of copper–manganese spinel oxide catalysts prepared with the urea–nitrate combustion method. All catalysts showed high activity towards H₂ production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/(Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu_xMn_3 − xO₄ phase in the oxidized catalysts is responsible for the high activity. Cu–Mn catalysts were found to be superior to CuO–CeO₂ catalysts prepared with the same technique.     

Effect of steam content and O2 pretreatment on the catalytic activities of Au/CeO2–Fe2O3 catalysts for steam reforming of methanol

The Au/CeO₂–Fe₂O₃ prepared by deposition–precipitation were studied by steam reforming of methanol at a reaction temperature range of 200–400 °C. Complete methanol conversion was obtained at the optimal steam/methanol ratio of 2 at 400 °C. A high steam content strongly depressed both methanol conversion and hydrogen concentration since this led to a complex mechanism and the formation of carbonate and formate species. After pretreating with oxygen, the catalytic activity dramatically decreased with the presence of an inhomogeneous Ce_xFe_1−xO₂ solid solution phase; the covering Au sites by the free α-Fe₂O₃ particles; and an agglomeration of both free α-Fe₂O₃ and Au particles.     

Formation of anisaldehyde via hydroxymethylation of anisole over SnO2–CeO2 catalysts

Hydroxymethylation of anisole has been carried out over SnO₂–CeO₂ catalysts in the temperature range 623–723 K. Methoxybenzaldehyde (anisaldehyde) and condensation products were formed along with minor quantities of methoxybenzyl alcohol, o‐cresol, phenol and 2,6‐xylenol. A maximum anisaldehyde selectivity of 64% was obtained at 623 K at an anisole conversion of 46% under optimized conditions. Catalytic activity of these systems in the formation of aldehyde is ascribed to the presence of weak acid sites and redox metal sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen production from glycerol steam reforming over molybdena–alumina catalysts

The glycerol steam reforming was investigated on alumina supported molybdena catalysts (with 2, 5 and 12 wt.%) prepared by the sol–gel method and gel combustion. The catalysts were characterized by XRD, BET, UV–VIS, DRIFT, SEM and TEM. The catalytic performances were studied at 400–500 °C, steam to glycerol molar ratio between 9:1 and 20:1 and feed flow rate 0.04–0.08 ml/min. The conversion is directly proportional to molybdena loading, while the hydrogen selectivity has reached greater value on catalyst with 2% MoO₃. The optimum ratio steam to glycerol for reforming is 15:1 and for decomposition in syngas 9:1 and the ratio 20:1 favors water gas shift reaction.     

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al₂O₃ nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N₂ as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N₂ during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.     

Hydrogen production by ethanol reforming over Rh/CeO2–ZrO2 catalysts

Reforming of ethanol in excess of water (1–8 molar ratio) has been investigated on Rh/CeO₂, Rh/ZrO₂ and Rh/CeO₂–ZrO₂ (Ce/Zr=4, 2 and 1). Catalysts characterization was conducted by X-ray diffraction, BET surface area measurements, CO₂ adsorption, and temperature programmed reduction (TPR). At 400–500 °C all catalysts showed high activity and selectivity towards hydrogen production (between 5 and 5.7 mol of H₂ per mol of ethanol inlet) despite the considerable textural differences of the oxides (fluorite, monoclinic and tetragonal). The large variations of Rh dispersion (as monitored by TPR) between all catalysts had a small effect on H₂ production. Although it appears that the reaction is not sensitive to either the oxide or the metal structure Rh/CeO₂ (the most basic catalyst investigated) was the least reactive.     

Highly dispersed sol–gel synthesized Cu–ZrO2 materials as catalysts for oxidative steam reforming of methanol

New nanodispersed Cu–ZrO₂ systems (containing 0 and 8.3 mol% Cu) were synthesized by sol–gel method. Homogeneous gels were prepared starting from Zr propoxide and Cu(NO₃)₂·2.5H₂O. The materials were characterized by XRD, TG/DTA, N₂ adsorption, TPR techniques and N₂O surface oxidation. In the Cu-containing material part of Cu²⁺ ions were incorporated into the zirconia lattice and strongly influenced the crystallisation behaviour of zirconia matrix. After treatment at 450–600 °C, the materials contained ZrO₂ nanocrystals of the tetragonal polymorph. The samples heat treated up to 450 °C showed high surface areas in the range 140–180 m²/g. Copper oxide species with different reducibility were detected by TPR measurements. The H₂ reduction treatments gave rise to metallic copper with very high dispersion. The catalysts showed high activity for the oxidative steam reforming of methanol. A noticeable activity was observed also with the not pre-reduced catalyst, although a previous reduction in H₂ led to a higher selectivity and H₂ production.     

Nickel–magnesia catalysts for the steam reforming of light hydrocarbons

The advantages of using magnesia prepared using two techniques as a support for nickel catalysts for the steam reforming of light hydrocarbons has been examined. The initial specific activities of nickel supported on alumina or magnesia were similar, but deactivation as a result of coke formation was significantly greater on alumina-supported nickel. The steam reforming of ethane and propane over nickel/magnesia catalysts was much less affected by coke formation over longer times-on-line. The effects of variation in the preparation of magnesia were small, differences only appearing in rates of coking of higher hydrocarbons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Parallel screening of Cu/CeO2/γ-Al2O3 catalysts for steam reforming of methanol in a 10-channel micro-structured reactor

Steam reforming of methanol (SRM) was investigated over Cu/CeO₂/γ-Al₂O₃ catalysts with different compositions in a parallelized 10-channel micro-structured reactor. The catalytic activity was found to be strongly dependent on the copper loading. The parallel screening result was tentatively discussed with surface analysis characterization results and previous proposals. A reaction mechanism is proposed to rationalize the catalytic activity data and characteristics of the catalysts, which supposes that the copper/ceria interfacial area (partially oxidized copper nanoparticle and defective ceria) is the active site for SRM. The oxygen reverse spillover from ceria to copper is suggested to be involved in the catalysis cycle.     

CuO–CeO2 mixed oxide catalysts for the selective oxidation of carbon monoxide in excess hydrogen

A series of mixed oxide CuO–CeO₂ catalysts were prepared by coprecipitation and tested for the selective oxidation of carbon monoxide in the presence of excess hydrogen. These catalysts were found to be very active and exceptionally selective for this reaction and exhibited a good resistance towards CO₂ and H₂O. The catalytic performance of these non-noble metal containing catalysts is compared with that of other selective CO oxidation catalysts reported in literature.     

Synergetic effect of combined use of Cu–ZnO–Al2O3 and Pt–Al2O3 for the steam reforming of methanol

Commercial Cu–ZnO–Al₂O₃ catalysts are used widely for steam reforming of methanol. However, the reforming reactions should be modified to avoid fuel cell catalyst poisoning originated from carbon monoxide. The modification was implemented by mixing the Cu–ZnO–Al₂O₃ catalyst with Pt–Al₂O₃ catalyst. The Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture created a synergetic effect because the methanol decomposition and the water–gas shift reactions occurred simultaneously over nearby Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalysts in the mixture. A methanol conversion of 96.4% was obtained and carbon monoxide was not detected from the reforming reaction when the Pt–Al₂O₃ and Cu–ZnO–Al₂O₃ catalyst mixture was used.     

Important properties associated with catalytic performance over three-dimensionally ordered macroporous CeO2–CuO catalysts

Three-dimensionally ordered macroporous CeO₂–CuO catalysts were prepared by the template and sol–gel method. The catalysts were characterized via SEM, TEM, XRD, H₂-TPR, XPS, CO₂-TPD and N₂ adsorption–desorption techniques. It is found that the CeO₂–CuO catalysts present the well-defined interconnected macroporous structure in three dimensions, and the skeleton of macroporous structure is composed of the CuO and CeO₂ particles. Catalytic performance for preferential CO oxidation is determined by various properties including composition, structural and textural properties as well as reduction and desorption behavior. The 3DOM CeO₂–CuO structure improves the interaction between CuO and CeO₂, the structural and textural properties, the reduction of oxides and desorption of the adsorbed molecules on the active sites.     

Correlation of activity and stability of CuO/ZnO/Al2O3 methanol steam reforming catalysts with Cu/Zn composition obtained by SEM–EDAX analysis

A series of CuO/ZnO/Al₂O₃ catalysts were prepared and characterized by TPR, surface area, metal area, XRD and SEM–EDAX analysis. These systems were evaluated in the development of a methanol steam reforming catalyst (MSR). A correlation of activity and stability of MSR catalysts with the Cu/Zn ratio derived by SEM–EDAX analysis is observed. The stable activity of these catalysts is also supported by the method of preparation, low temperature reducibility and the presence of reversibly oxidizable Cu species observed by TPR of fresh and used catalysts.     

Intramolecular selective hydrogenation of cinnamaldehyde over CeO2–ZrO2-supported Pt catalysts

Selective liquid phase hydrogenation of cinnamaldehyde is reported, for the first time, over CeO₂, ZrO₂, and CeO₂–ZrO₂-supported Pt catalysts. Cinnamyl alcohol is the selective product. These catalysts are highly active and selective even at 25 °C and found to be superior to most of the hitherto known supported Pt catalysts. Alkali addition (NaOH) has enhanced the performance of these catalysts. At an optimized reaction condition, 95.8% conversion of cinnamaldehyde and 93.4% selectivity of cinnamyl alcohol have been obtained. Acidity of the support (due to the presence of ZrO₂ component) and higher electron density at Pt (due to CeO₂ component) are attributed to be responsible for the superior catalytic activity of Pt supported on CeO₂–ZrO₂ composite material.     

Highly efficient ruthenium and ruthenium–platinum cluster-derived nanocatalysts for hydrogen production via ethanol steam reforming

Alumina-supported Ru and Ru–Pt nanoparticles, obtained by the decarbonylation of organometallic cluster precursors, were found to be highly active and selective catalysts for ethanol steam reforming. These catalysts outperformed a commercial Ru/Al₂O₃ catalyst, as well as catalysts that had been prepared from inorganic salts using the conventional impregnation method. The highly dispersed nanoparticles derived from cluster precursors were much smaller than the salt-derived nanoparticles, as evidenced by TEM and powder XRD studies; this might account for the improved catalytic performance of the cluster-derived catalysts. Finally, EDX studies suggest that Pt played a role in resisting coke formation in both cluster- and salt-derived catalysts.     

Hydrogenation of CO<Subscript>2</Subscript> to methanol over Au–CuO/SBA-15 catalysts

A series of Au–CuO/SBA-15 catalysts with 1–3 wt% Au and 30 wt% CuO were successfully prepared for CO₂ hydrogenation to methanol by chemical reduction and the following impregnation. The influence of Au content on the physicochemical properties of Au–CuO/SBA-15 catalysts was investigated in terms of ICP-AES, N₂ physisorption, XRD, TEM, N₂O titration, XPS and H₂–TPR technique. The results showed that the as-prepared Au–CuO/SBA-15 catalysts exhibited higher catalytic activity than CuO/SBA-15 catalyst. 2 % Au–CuO/SBA-15 catalyst showed the best catalytic activity with 13.5 % methanol selectivity and 24.2 % CO₂ conversion for CO₂ hydrogenation to methanol. The addition of Au NPs played an important role in improving the catalytic activity for CO₂ hydrogenation to methanol, which may be attributed to the interaction between Au and CuO.     

Glycerol steam reforming over Ni/γ-Al2O3 catalysts modified by metal oxides

The metal oxides modified Ni/γ-Al₂O₃ catalysts for glycerol steam reforming were prepared by impregnation. Characterization results of fresh catalysts indicated that the molybdates modification abated the acidity and the stronger metal-support interaction of Ni/γ-Al₂O₃ catalysts, leading to a stable catalytic activity. Especially, NiMoLa-CaMg/γ-Al₂O₃ (NiMoLa/CMA) catalyst exhibited no deactivation along with glycerol complete conversion to stable gaseous products containing 69% H₂, 20% CO and 10% CO₂ during time-on-stream of 42 h. TPO of spent Ni/γ-Al₂O₃ catalysts modified by different components showed that the carbon deposit on acidic sites and NiAl₂O₄ species led to catalysts deactivation. A lower reforming temperature and a higher LHSV and glycerol content were helpful to the production of syngas from GSR over NiMoLa/CMA; the reverse conditions would improve the formation of H₂.     

Bio-ethanol steam reforming and autothermal reforming in 3-μm channels coated with RhPd/CeO2 for hydrogen generation

A silicon micromonolith of 7 mm diameter and 0.2 mm length containing 1.5 million regular channels with a diameter of 3.3 μm was used for obtaining hydrogen through ethanol or bio-ethanol steam reforming (ESR) and oxidative steam reforming (OSR). The microchannels were coated with RhPd/CeO₂ catalyst by a two-step method. First a CeO₂ layer of ca. 100 nm thickness was deposited from cerium methoxyethoxide over a SiO₂ layer, which was previously grown over the silicon microchannels by oxidation. Then, noble metals were grafted over the CeO₂ support from chloride precursors. The unit was successfully tested for hydrogen production, achieving hydrogen rates of $180{\text{L}}_{{\text{H}}_2}\text{c}{{\text{m}}_{\text{R}}}^{-3}$ for the steam reforming of bio-ethanol at 873 K, S/C = 2 and 0.009 s contact time. Reaction yields of 3.8 and 3.7 mol hydrogen generated per mol ethanol in feed were measured for ESR and OSR, respectively. A performance comparison was performed with a conventional cordierite monolith with the same catalyst formulation. Results show for the silicon microreactor an outstanding improvement of the specific hydrogen production rate, operating at considerably reduced residence times, due to the increase in contact area per unit volume.