Oxidative steam reforming of methanol over CuO/ZnO/CeO2/ZrO2/Al2O3 catalysts

The composition (CuO/ZnO/Al₂O₃ = 30/60/10) of a commercial catalyst G66B was used as a reference for designing CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts for the oxidative (or combined) steam reforming of methanol (OSRM). The effects of Al₂O₃, CeO₂ and ZrO₂ on the OSRM reaction were clearly identified. CeO₂, ZrO₂ and Al₂O₃ all promoted the dispersions of CuO and ZnO in CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts. Aluminum oxide lowered the reducibility of the catalyst, and weakened the OSRM reaction. Cerium oxide increased the reducibility of the catalyst, but weakened the reaction. Zirconium oxide improved the reducibility of the catalyst, and promoted the reaction. A lower CuO/ZnO ratio of the catalyst was associated with greater promotion of ZrO₂. The critical CuO/ZnO ratio for the promotion of ZrO₂ was approximately 0.75–0.8. Introducing of ZrO₂ into CuO/ZnO/Al₂O₃ also improved the stability of the catalyst. Although Al₂O₃ inhibited the OSRM reaction, a certain amount of it was required to ensure the stability and the mechanical strength of the catalysts.     

Steam reforming and oxidative steam reforming of methanol over CuO–CeO2 catalysts

Steam reforming (SRM) and oxidative steam reforming of methanol (OSRM) were carried out over a series of coprecipitated CuO–CeO₂ catalysts with varying copper content in the range of 30–80 at.% Cu (= 100 × Cu/(Cu + Ce)). The effects of copper content, reaction temperature and O₂ concentration on catalytic activity were investigated. The activity of CuO–CeO₂ catalysts for SRM and OSRM increased with the copper content and 70 at.% CuO–CeO₂ catalyst showed the highest activity in the temperature range of 160–300 °C for both SRM and OSRM. After SRM or OSRM, the copper species in the catalysts observed by XRD were mainly metallic copper with small amount of CuO and Cu₂O, an indication that metallic copper is an active species in the catalysis of both SRM and OSRM. It was observed that the methanol conversion increased considerably with the addition of O₂ into the feed stream, indicating that the partial oxidation of methanol (POM) is much faster than SRM. The optimum 70 at.% CuO–CeO₂ catalyst showed stable activities for both SRM and OSRM reactions at 300 °C.     

Hydrogen production from ethanol steam reforming over Ir/CeO2 catalysts: Enhanced stability by PrOx promotion

We studied ethanol steam reforming over Ir/Ce_0.9Pr_0.1O₂ and Ir/CeO₂ catalysts comparatively with respect to activity and stability. We found that PrO_x-doping have significantly promoted the oxygen storage capacity and thermal stability of the catalysts by incorporation into the ceria lattice. Ethanol was readily converted to hydrogen, methane and carbon oxides at 773 K over the Ir/Ce_0.9Pr_0.1O₂ catalyst, and this is 100 K lower than that found for the Ir/CeO₂ catalyst. Moreover, the PrO_x-doped catalyst was stable toward ethanol steam reforming at 923 K for 300 h without an apparent variation in ethanol conversion and product distribution. However, the severe aggregation of ceria particles and heavy coke deposition were observed on the Ir/CeO₂ catalyst, resulting in remarkable deactivation under the same reaction conditions.     

Nickel catalysts supported on ZrO2, Y2O3-stabilized ZrO2 and CaO-stabilized ZrO2 for the steam reforming of ethanol: Effect of the support and nickel load

Catalysts with various nickel loads were prepared on supports of ZrO₂, ZrO₂–Y₂O₃ and ZrO₂–CaO, characterized by XRD and TPR and tested for activity in ethanol steam reforming. XRD of the supports identified the monoclinic crystalline phase in the ZrO₂ and cubic phases in the ZrO₂–Y₂O₃ and ZrO₂–CaO supports. In the catalysts, the nickel impregnated on the supports was identified as the NiO phase. In the TPR analysis, peaks were observed showing the NiO phase having different interactions with the supports. In the catalytic tests, practically all the catalysts achieved 100% ethanol conversion, H₂ yield was near 70% and the gaseous concentrations of the other co-products varied in accordance with the equilibrium among them, affected principally by the supports. It was observed that when the ZrO₂ was modified with Y₂O₃ and CaO, there were big changes in the CO and CO₂ concentrations, which were attributed to the rise in the number of oxygen vacancies, permitting high-oxygen mobility and affecting the gaseous equilibrium. The liquid products analysis showed a low selectivity to liquid co-products during the reforming reactions.     

Hydrogen production by auto-thermal reforming of ethanol over Ni catalysts supported on ZrO2: Effect of preparation method of ZrO2 support

Zirconia supports were prepared by a sol–gel method (S-ZrO₂) and by a templating sol–gel method (M-ZrO₂). Nickel catalysts supported on zirconia were then prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. For comparison, a commercial zirconia (C-ZrO₂) was also employed as a support for nickel catalyst. The effect of preparation method of zirconia on the catalytic property and catalytic performance of supported nickel catalysts (Ni/C-ZrO₂, Ni/S-ZrO₂, and Ni/M-ZrO₂) was investigated. The crystalline and physical property of zirconia supports and the catalytic performance of supported nickel catalysts were strongly affected by the preparation method of zirconia. BET surface area and pore volume were decreased in the order of M-ZrO₂ > S-ZrO₂ > C-ZrO₂. Both M-ZrO₂ and S-ZrO₂ supports showed only tetragonal phase of ZrO₂, while C-ZrO₂ support exhibited tetragonal and monoclinic phases of ZrO₂. Crystalline size of nickel species in the Ni/ZrO₂ catalysts decreased with increasing surface area and pore volume of ZrO₂ supports. All the Ni/ZrO₂ catalysts exhibited 100% conversion of ethanol at 500 °C, while product distributions over the Ni/ZrO₂ catalysts were different depending on the preparation method of zirconia. Among the catalysts tested, the Ni/M-ZrO₂ catalyst showed the best catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Well developed mesopore, high surface area, and pure tetragonal phase of ZrO₂ were responsible for fine nickel dispersion and high catalytic performance of Ni/M-ZrO₂. C–C bond cleavage reaction and methane steam reforming reaction were also accelerated over the Ni/M-ZrO₂ catalyst.     

Hydrogen production from oxidative steam reforming of methanol: Effect of the Cu and Ni impregnation on ZrO2 and their molecular simulation studies

Cu and Ni were supported on ZrO₂ by co-impregnation and sequential impregnation methods, and tested in the oxidative steam reforming of methanol (OSRM) reaction for H₂ production as a function of temperature. Surface area of the catalysts showed differences as a function of the order in which the metals were added to zirconia. Among them, the Cu/ZrO₂ catalyst had the lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu–Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the monometallic samples. The reactivity of the catalysts in the range of 250–350 °C showed that the bimetallic samples prepared by successive impregnation had highest catalytic activity among all the catalysts studied. These results were also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic structures obtained by molecular simulation followed the next order: Ni_shellCu_core/ZrO₂ ≅ Cu_shellNi_core/ZrO₂ > Ni/Cu/ZrO₂ > Cu/Ni/ZrO₂ > Cu–Ni/ZrO₂ > Cu/ZrO₂ > Ni/ZrO₂. These findings agree with the experimental results, indicating that the bimetallic catalysts prepared by successive impregnation show a higher reactivity than the Cu–Ni system obtained by co-impregnation. In addition, the selectivity for H₂ production was higher on these catalysts. This result could be associated also to the presence of the bimetallic Cu–Ni and core–shell Ni/Cu nanoparticles on the catalysts, as was evidenced by TEM–EDX analysis, suggesting that the OSRM reaction may be a structure–sensitive reaction.     

Hydrogen production by oxidative steam reforming of methanol over anodic aluminum oxide-supported Cu-Zn catalyst

Oxidative steam reforming of methanol (OSRM), which is a convenient reaction for producing hydrogen, suffers from the hot spot formation problem when conventional particle catalysts are used. Recently, an anodic aluminum oxide (AAO)-supported Cu-Zn catalyst was proposed as an OSRM catalyst for its high thermal conductivity through the aluminum metal body. In this study, OSRM was conducted in a prototype reactor packed with the AAO plate catalyst strips. It was verified that the high thermal conductivity of the catalyst effectively suppresses the hot spot formation and makes the temperature profile smooth along the reactor. The start-up time of the reactor depended on the preheating temperature and was very short (less than 2 min) for preheating over 503 K. The methanol conversion and reactor temperature increased with increasing O₂/CH₃OH mole ratio, indicating that the mole ratio can be used as a control variable to operate the reactor at desired conditions. Further, a reactor model was developed and verified, and the simulation showed that for a given total reactor volume, an optimal reactor configuration could be achieved by shortening the reactor length while widening the cross-sectional area.     

Hydrogen production by steam reforming of model bio-oil using structured Ni/Al2O3 catalysts

This study focuses on hydrogen production from the steam reforming of model bio-oil over Ni/Al₂O₃ catalysts prepared in two different geometries (monolith and pellet) using the dip-coating and wet impregnation methods and characterized using Powder X-Ray diffraction, Temperature Programmed Reduction, Scanning Electron Microscopy (SEM) and BET Surface area analysis. The effects of the catalyst geometry and reforming temperatures were studied by carrying out experiments at the optimal conditions of T = (823, 923, 1023) K and S/C ratio = 13 determined from the thermodynamic analysis of the process prior to the experiments using the process simulator PRO-II. The experimental results showed high steady state H₂ yield corresponding to 2.58 and 1.73 mol (out of 5.13 mol) using monolithic and the pelletized catalysts respectively. The product distribution achieved with the monolithic catalyst was closer to the thermodynamic results suggesting a higher selectivity to hydrogen production.     

Hydrogen production by steam reforming of ethanol over an Ir/CeO2 catalyst: Reaction mechanism and stability of the catalyst

Steam reforming of ethanol over an Ir/CeO₂ catalyst has been studied with regard to the reaction mechanism and the stability of the catalyst. It was found that ethanol dehydrogenation to acetaldehyde was the primary reaction, and acetaldehyde was then decomposed to methane and CO and/or converted to acetone at low temperatures. Methane was further reformed to H₂ and CO, and acetone was directly converted into H₂ and CO₂. Addition of CO, CO₂, and CH₄ to the water/ethanol mixture proved that steam reforming of methane and the water gas shift were the major reactions at high temperatures. The Ir/CeO₂ catalyst displayed rather stable performance in the steam reforming of ethanol at 650 °C even with a stoichiometric feed composition of water/ethanol, and the effluent gas composition remained constant for 300 h on-stream. The CeO₂ in the catalyst prevented the highly dispersed Ir particles from sintering and facilitated coke gasification through strong Ir–CeO₂ interaction.     

Effect of noble metal on oxidative steam reforming of methanol over CuO/ZnO/Al2O3 catalysts

Noble metals of Pd, Pt, Ru and Rh were introduced into the CuO/ZnO/Al₂O₃(30/60/10) catalyst via incipient impregnation and co-precipitation methods to examine their effects on the oxidative steam reforming of methanol (OSRM). No obvious effect of Pd and even a negative effect of Pt were observed by incipient impregnation method. With co-precipitation, noble metals were homogeneously dispersed in CuO/ZnO/Al₂O₃(30/60/10) and interacted with CuO and ZnO. They improved the reducibility of the catalysts and enhanced the dissociative adsorption of methanol. Introducing Pd, Rh or Ru promoted the conversion of methanol, but enhanced the formation of CO. Depositing platinum exhibited a high conversion of methanol and a low selectivity of CO in the OSRM reaction. The promoting effect of noble metals involved facilitating the split and adsorption of H atoms during the dehydrogenation of the intermediates in OSRM.     

Preferential oxidation of CO in H2 stream on Au/CeO2–TiO2 catalysts

A series of Au catalysts supported on CeO₂–TiO₂ with various CeO₂ contents were prepared. CeO₂–TiO₂ was prepared by incipient-wetness impregnation with aqueous solution of Ce(NO₃)₃ on TiO₂. Gold catalysts were prepared by deposition–precipitation method at pH 7 and 65 °C. The catalysts were characterized by XRD, TEM and XPS. The preferential oxidation of CO in hydrogen stream was carried out in a fixed bed reactor. The catalyst mainly had metallic gold species and small amount of oxidic Au species. The average gold particle size was 2.5 nm. Adding suitable amount of CeO₂ on Au/TiO₂ catalyst could enhance CO oxidation and suppress H₂ oxidation at high reaction temperature (>50 °C). Additives such as La₂O₃, Co₃O₄ and CuO were added to Au/CeO₂–TiO₂ catalyst and tested for the preferential oxidation of CO in hydrogen stream. The addition of CuO on Au/CeO₂–TiO₂ catalyst increased the CO conversion and CO selectivity effectively. Au/CuO–CeO₂–TiO₂ with molar ratio of Cu:Ce:Ti = 0.5:1:9 demonstrated very high CO conversion when the temperature was higher than 65 °C and the CO selectivity also improved substantially. Thus the additive CuO along with the promoter and amorphous oxide ceria and titania not only enhances the electronic interaction, but also stabilizes the nanosize gold particles and thereby enhancing the catalytic activity for PROX reaction to a greater extent.     

Hydrogen production from acetic acid steam reforming over Ti-modified Ni/Attapulgite catalysts

Steam reforming of bio-oil derived oxygenates is a green and sustainable method for hydrogen production. In this work, hydrogen production from steam reforming of acetic acid (SRAA) was investigated over Ti-modified Ni/Attapulgite (ATP) catalysts that prepared via sequential precipitation technique. The effects of Ti additive, precipitation sequence and Ti-salt precursors (TiCl₄, TiOSO₄) on the structural and physicochemical properties of catalysts were characterized by N₂ adsorption-desorption, XRD, FT-IR, HRTEM, XPS, H₂-TPR and NH₃-TPD. These results indicated that the interaction among Ti species, Ni active metal and ATP enhanced the reduction performance as well as weakened surface acidity of the Ni/ATP catalyst, and also promoted the electron transfer to form Ni^δ? species. Obviously, compared with Ti precursor salts, the precipitation sequences played a key role in determining the surface properties of Ti-modified catalysts. Among them, the Ni–Ti_S/ATP catalyst synthesized by co-precipitation method exhibited better reducibility and lower surface acidity, as well as produced more Ni^δ? species and Ni^δ?-O_v-Ti³⁺ interface sites. Then the synergistic effects among the above-mentioned characters made the Ni–Ti_S/ATP catalyst present highest carbon conversion (93.4%) and H₂ yield (77.6%) during SRAA reactions. The analyses of XRD, HRTEM and TG were implemented on used catalysts and discovered Ni–Ti_S/ATP catalysts shown promising metal sintering and coke resistance, which mainly caused by the presence of flat Ni–Ti@ATP structures. The possible conversion mechanism of acetic acid in the flat Ni–Ti@ATP structure of co-precipitation Ti-modified catalyst was also elucidated.     

From mechanistic to kinetic analyses of ethanol steam reforming over Ir/CeO2 catalyst

This work presents a kinetic analysis of ethanol steam reforming (ESR) over a performing Ir/CeO₂ catalyst based on a bi-functional mechanism. A first conventional power-law based kinetic study was carried out by varying the main operating parameters (temperature, steam/ethanol molar ratio and partial pressure of products). A limited fit was achieved between the experimental data and the data calculated from this model based on a single type of site, demonstrating the need of a kinetic analysis integrating more closely the demonstrated bi-functional mechanism of the reaction. A kinetic model considering two distinct adsorption sites, on ceria support and on iridium particles, was then considered and only reactions involving the two types of sites, i.e. occurring at the ceria/metal interface, were used to build that model. A good agreement between the experimental data and the model was obtained, without systematic deviations. The central role of the metal-support interface was also consistent with the deactivation of this catalyst upon sintering, related to both changes in metal and support dispersion with time on stream.     

Steam reforming of methanol over Cu/ZnO/ZrO2/Al2O3 catalyst

Steam reforming of methanol was investigated over Cu–ZnO–ZrO₂–Al₂O₃ catalysts at 473 and 573 K. The Cu:Zn:(Al + Zr) molar ratio was 3:3:4; however, the Zr:Al molar ratio was varied and the catalysts were pretreated at different calcination and reduction temperatures. The synthesized catalysts were characterized by N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), X-ray diffraction, oxidized surface TPR, and infrared spectroscopy after carbon monoxide chemisorption. The crystalline size of Cu decreased on increasing the calcination temperatures from 573 to 623 K and increased on increasing the reduction temperatures from 523 to 573 K. Among the tested catalysts, the Cu–ZnO–ZrO₂ catalyst exhibited the highest and lowest hydrogen-formation rates at 473 and 573 K, respectively. After the reaction at 573 K, all the tested catalysts exhibited an increase in the Cu crystalline size, causing the catalyst deactivation. Among the tested catalysts, the Cu–ZnO–ZrO₂–Al₂O₃ catalyst, where the Cu:Zn:Al:Zr molar ratio was 3:3:2:2, showed the highest and most stable catalytic activity at 573 K. Cu dispersion and catalyst composition affected the catalytic performance for steam reforming of methanol.     

Catalytic decomposition of hydrogen iodide over pre-treated Ni/CeO2 catalysts for hydrogen production in the sulfur–iodine cycle

The Ni/CeO₂ catalysts with successive oxidization, reduction and re-oxidization have been tested for hydrogen production in sulfur–iodine (SI or IS) cycle. The samples were characterized by BET, XRD, TEM, TPR and XPS. The oxidative/reductive atmosphere affected the structure and performance of the catalysts. It was suggested that a migration of Ce⁴⁺ from the bulk to the surface occurred during the reductive treatment. The diffusion process was reversed when the atmosphere was changed to an oxidative one. The reduced and re-oxidized samples seemed to be similar all the time and showed better catalytic activity in comparison with the as-received and oxidized samples. For the re-oxidized sample, the strongest interaction compared with other samples occurred between Ni and CeO₂ and oxygen vacancies transferred from bulk to surface, which led to form more surface sites and oxygen vacancies. The metal Ni was found only on the surface of the reduced sample. The active site of metal Ni besides the surface site and oxygen vacancy were assumed to play an important role for hydrogen production.     

Hydrogen production by ethanol steam reforming: Effect of the synthesis parameters on the activity of Ni/TiO2 catalysts

Ethanol steam reforming is an attracting process to produce hydrogen in a sustainable way. In this work the performance of Ni/TiO₂ catalysts in ethanol steam reforming was studied. In particular, the effect of the synthesis procedure on the properties of the catalysts and on their activity was deeply investigated. On the basis of the experimental results, it was evidenced that TiO₂-supported Ni systems are very sensitive to the synthesis parameters. We found that a proper thermal activation by calcination at 800 °C allows to obtain stable catalysts by means of strong interactions between the active phase and the support, preserving the catalyst from sintering phenomena. Nevertheless, the synthesis conditions must be properly tuned in order to prevent Ni incorporation in scarcely reducible structures which would depress catalytic activity.     

H2 production from stable ethanol steam reforming over catalyst of NiO based on flowerlike CeO2 microspheres

Catalyst of nickle oxide based on flowerlike cerium microspheres with high dispersion was made to achieve simultaneous dehydrogenation of ethanol and water molecules on multi-active sites. XRD, 77 K N₂ adsorption and FESEM were applied to analyse and observe the catalyst's structure, porosity and morphology. This special morphology catalyst represented novel stability more than 600 h for hydrogen production at low temperature ethanol steam reforming. Ethanol-water mixtures could be converted into H₂ with average selectivity value of 61.5 mol.% and average ethanol conversion 95.0 mol.% at 350 °C, with GHSV∼1.0 × 10⁵ h⁻¹, low CO selectivity about average value of 2.1 mol.%, during 550 h reforming stability test. Catalytic parameters with respect to yield of H₂, activity, selectivity towards hydrogen production and stability with time on stream were determined.     

Electrochromic properties of heat-treated thin films of CeO2–TiO2–ZrO2 prepared by sol–gel route

CeO₂–TiO₂–ZrO₂ thin films were prepared using the sol–gel process and deposited on glass and ITO-coated glass substrates via dip-coating technique. The samples were heat treated between 100 and 500 °C. The heat treatment effects on the electrochromic performances of the films were determined by means of cyclic voltammetry measurements. The structural behavior of the film was characterized by atomic force microscopy and X-ray diffraction. Refractive index, extinction coefficient, and thickness of the films were determined in the 350–1000 nm wavelength, using nkd spectrophotometry analysis.Heat treatment temperature affects the electrochromic, optical, and structural properties of the film. The charge density of the samples increased from 8.8 to 14.8 mC/cm², with increasing heat-treatment temperatures from 100 to 500 °C. It was determined that the highest ratio between anodic and cathodic charge takes place with increase of temperature up to 500 °C.     

Steam reforming of ethanol over Ni/ZrO2 catalysts: Effect of support on product distribution

Ni catalysts supported on ZrO₂ with different crystalline phases and particle sizes were prepared to study the role of zirconia support in ethanol steam reforming for hydrogen production. Catalytic behavior of the catalysts was examined at relatively low temperature of 673 K with different contact times. The decrease in particle size of zirconia results in enhanced metal-support interaction, which accounts for the high activity of the catalyst. Regarding the impact of crystalline phase of zirconia on catalytic performance, tetragonal zirconia yields a higher activity in water gas shift reaction but a lower activity in methane steam reforming than that of monoclinic zirconia. Nevertheless, zirconia plays a secondary role in product distribution, especially at long contact times. Catalytic activity tests performed at elevated temperature demonstrated a high activity and stability of Ni/ZrO₂ catalyst for hydrogen production from steam reforming of ethanol.