Catalysis Today (v.116, #3)

Preface by J.L.G. Fierro Guest Editor; M.A. Peña Guest Editor (pp. 263-263).

Improvement of activity and stability of Ni–Mg–Al catalysts by Cu addition during hydrogen production by catalytic decomposition of methane by A. Monzón; N. Latorre; T. Ubieto; C. Royo; E. Romeo; J.I. Villacampa; L. Dussault; J.C. Dupin; C. Guimon; M. Montioux (pp. 264-270).

Catalytic decomposition of methane is a potential alternative route for the production of hydrogen and carbon nanofilaments from natural gas and other feedstocks. In the present paper, we report the results of characterization and catalytic behaviour of Ni–Cu–Mg–Al catalysts.The effect of the Cu addition in the catalyst composition on activity and stability has been investigated. The influence of operating temperature and feed composition on carbon content and carbon formation rate has also been studied. It has been shown that H₂ inhibits both the carbon filament formation and the encapsulation of metallic particles by coke. A higher reaction temperature increases both the deactivation rate and the growth rate of filaments. An increase in the methane concentration generates a rise of the rate of carbon filament formation.The size of metal particles and the carbon filaments as well as the nanofilament texture depends on the copper content of the catalyst. When the Cu content is 7.6wt.%, the carbon nanofilaments are nanofibers with a platelet texture, and the particles and CNFs sizes are widely distributed (50–400nm).

Keywords: Catalytic methane decomposition; Hydrogen production; Carbon nanofibers; Platelet nanofibers; Ni–Cu catalysts

Characterization of NiAl and NiCuAl catalysts prepared by different methods for hydrogen production by thermo catalytic decomposition of methane by I. Suelves; M.J. Lázaro; R. Moliner; Y. Echegoyen; J.M. Palacios (pp. 271-280).

NiAl and NiCuAl catalysts have been prepared by co-precipitation, fusion and impregnation methods to promote the Ni formation, as active phase, in different degrees of dispersion and crystal domain sizes as evidenced through the characterization study of fresh catalysts. Performance tests show that the hydrogen production was not highly dependent on the preparation method used but the presence of Cu as a dopant in NiCuAl catalysts enhanced the catalytic activity substantially. The catalyst deactivation was never reached at the fixed times used in the reactivity tests. The Ni properties, mostly derived from thermal sintering and chemical-induced faceting were substantially altered during the process of methane decomposition, and the properties of the deposited carbon were highly dependent on the presence of Cu as a dopant in NiCuAl catalysts. NiCuAl catalysts enhances the formation of a well-ordered graphitic carbon while NiAl catalysts promote the deposition of a turbostratic carbon suitable as catalytic supports or hydrogen storage.

Keywords: Methane; Hydrogen production; Ni catalysts; Carbon; Structural properties

Autothermal catalytic pyrolysis of methane as a new route to hydrogen production with reduced CO₂ emissions by Nazim Muradov; Franklyn Smith; Cunping Huang; Ali T-Raissi (pp. 281-288).

Hydrogen production plants are among major sources of CO₂ emissions into the atmosphere. The objective of this paper is to explore new routes to hydrogen production from natural gas (or methane) with drastically reduced CO₂ emissions. One approach analyzed in this paper is based on thermocatalytic decomposition (or pyrolysis) of methane into hydrogen gas and elemental carbon over carbon-based catalysts. Several heat input options to the endothermic process are discussed in the paper. The authors conduct thermodynamic analysis of methane decomposition in the presence of small amounts of oxygen in an autothermal (or thermo-neutral) regime using AspenPlus™ chemical process simulator. Methane conversion, products yield, effluent gas composition, process enthalpy flows as a function of temperature, pressure and O₂/CH₄ ratio has been determined. CO₂ emissions (per m³ of H₂ produced) from the process could potentially be a factor of 3–5 less than from conventional hydrogen production processes. Oxygen-assisted decomposition of methane over activated carbon (AC) and AC-supported iron catalysts over wide range of temperatures and O₂/CH₄ ratios was experimentally verified. Problems associated with the catalyst deactivation and the effect of iron doping on the catalyst stability are discussed.

Keywords: Hydrogen; Carbon; Methane; Catalyst; Autothermal pyrolysis

Hydrogen production via CH₄ pyrolysis: Regeneration of ex hydrotalcite oxide catalysts by R. Guil-López; V. La Parola; M.A. Peña; J.L.G. Fierro (pp. 289-297).

Pure hydrogen was obtained by catalytic methane decomposition over thermally stable nickel-based catalysts prepared from hydrotalcite-like precursors. Two different Ni–Mg–Al catalyst compositions were tested in the catalytic pyrolysis reaction of methane. The catalytic results were compared with those of a catalyst prepared by conventional impregnation of Ni–Mg phases on an alumina support. The high thermal stability of these catalysts was demonstrated in several reaction–regeneration cycles. The regeneration processes were performed with CO₂ and O₂ as regenerating agents. Using either CO₂ or O₂ gas, hydrogen production after regeneration increased with regard to the fresh catalyst. Upon catalyst regeneration, larger amounts of hydrogen were obtained on catalysts regenerated with CO₂ than with O₂. The high thermal stability of the Ni particles of the catalysts from hydrotalcite-like precursors was improved in the presence of Mg. This high Ni-stability is a key factor for increasing hydrogen production after consecutive reaction–regeneration cycles.

Keywords: Methane pyrolysis; Nickel catalysts; Hydrotalcite precursors; Regeneration

A basic assessment of the reactivity of Ni catalysts in the decomposition of methane for the production of “CO_x-free�? hydrogen for fuel cells application by G. Bonura; O. Di Blasi; L. Spadaro; F. Arena; F. Frusteri (pp. 298-303).

The hydrogen production through the decomposition of methane into hydrogen and carbon on Ni supported catalysts followed by catalyst regeneration in oxidative atmosphere was evaluated. Typical temperature programmed catalytic reaction (TPCR) results revealed that the nature of the carrier slightly affects the onset temperature of CH₄ decomposition, while catalytic performance and regeneration capacity in O₂ or CO₂ streams depend on dispersion and morphology of the active phase. The “structure-sensitive�? character of methane decomposition reaction has been confirmed. TEM analyses of the “spent�? catalysts revealed that both “filamentous�? and “encapsulating�? carbon species were formed under isothermal conditions at 823K, the last being responsible for catalyst deactivation.

Keywords: Nickel catalysts; Hydrogen production; Methane decomposition; Carbon deposition; Catalyst regeneration

Nickel/alumina catalysts modified by basic oxides for the production of synthesis gas by methane partial oxidation by J. Requies; M.A. Cabrero; V.L. Barrio; J.F. Cambra; M.B. Güemez; P.L. Arias; V. La Parola; M.A. Peña; J.L.G. Fierro (pp. 304-312).

In the present work, Ni/α-Al₂O₃ catalysts modified with different amounts of CaO and MgO were used for the production of hydrogen by catalytic partial oxidation (CPO) and wet-CPO processes of methane. In the wet-CPO process, small additions of water were introduced into the feed of the reactor to improve both the H₂ yield and methane conversion. The addition of water is also beneficial because coke formation becomes thermodynamically unfavorable. The catalysts were characterized before and after the reaction with XRD, XPS, TPR and TPO techniques. Several methane decomposition tests and methane pulse experiments were carried out with a view to correlating the ability of metal sites to activate methane in the absence of oxygen with the performance for CPO and wet-CPO reactions.

Keywords: Magnesium and calcium additives; Catalytic partial oxidation; Nickel catalysts; Catalyst characterization

The oxygen-assisted transformation of propane to CO_x/H₂ through combined oxidation and WGS reactions catalyzed by vanadium oxide-based catalysts by N. Ballarini; A. Battisti; F. Cavani; A. Cericola; C. Lucarelli; S. Racioppi; P. Arpentinier (pp. 313-323).

This paper reports about the gas-phase oxidation of propane catalyzed by bulk vanadium oxide and by alumina- and silica-supported vanadium oxide. The reaction was studied with the aim of finding conditions at which the formation of H₂ and CO₂ is preferred over that of CO, H₂O and of products of alkane partial oxidation. It was found that with bulk V₂O₅ considerable amounts of H₂ are produced above 400°C, the temperature at which the limiting reactant, oxygen, is totally consumed. The formation of H₂ derived from the combination of: (i) oxidation reactions, with generation of CO, CO₂, oxygenates (mainly acetic acid), propylene and H₂O, all occurring in the fraction of catalytic bed that operated in the presence of gas-phase oxygen, and (ii) WGS reaction, propane dehydrogenation and coke formation, that instead occurred in the fraction of bed operating under anaerobic conditions. This combination of different reactions in a single catalytic bed was possible because of the reduction of V₂O₅ to V₂O₃ at high temperature, in the absence of gas-phase oxygen. In fact, vanadium sesquioxide was found to be an effective catalyst for the WGS, while V₂O₅ was inactive in this reaction. The same combination of reactions was not possible when vanadium oxide was supported over high-surface area silica or alumina; this was attributed to the fact that in these catalysts vanadium was not reduced below the oxidation state V⁴⁺, even under reaction conditions leading to total oxygen conversion. In consequence, these catalysts produced less H₂ than bulk vanadium oxide.

Keywords: Vanadium oxide; Supported vanadium oxide; Propane oxidation; Hydrogen production; WGS reaction

Design of a diesel reformer coupled to a PEMFC by F. Rosa; E. López; Y. Briceño; D. Sopeña; R.M. Navarro; M.C. Alvarez-Galván; J.L.G. Fierro; C. Bordons (pp. 324-333).

A strategic alliance has been established between Spanish partners to develop a 5kW diesel fuel processor for an integrated operation with a PEMFC. Oxidative Steam Reforming followed by a novel WGS reactor in one step and a PROX delivers a stream with a maximum CO of 20ppm, able to feed PEM without poisoning the anodes. Paper presents a detailed description of the work carried out to obtain novel catalyst (main section of this paper), design of the reformer and preliminary operational results. Data concerning how catalysts were prepared and catalytic activity measurements for OSR, WGS and PROX is presented as well design of test bench and control. From an experimental point of view some results, at laboratory scale, are presented concerning OSR, WGS and PROX and as well preliminary results concerning global operation of the prototype.

Keywords: Diesel; Reformer; PEMFC

Integration of gasoline prereforming into autothermal reforming for hydrogen production by Yazhong Chen; Hengyong Xu; Xianglan Jin; Guoxing Xiong (pp. 334-340).

An integrated process for hydrogen production which couples gasoline prereforming and autothermal reforming (ATR) over nickel-based catalysts was investigated using stainless steel fixed-bed reactors. Meanwhile the integrated process was compared with the gasoline ATR process without prereforming. The results indicate that in the gasoline ATR process without prereforming, the nickel-based ATR catalyst deposited with coke after short reaction time-on-stream under the following working conditions ( T=770°C, P=5.0bar, steam-to-carbon feed ratio (S/C, mol/mol) of 2.7, oxygen-to-carbon feed ratio (O₂/C) of 0.5 and gas hourly space velocity (GHSV) of 28,000mlg⁻¹h⁻¹). Quite the contrary, in the integrated process, almost 100% gasoline conversion and 99.4% selectivity to hydrogen were obtained and maintained well under similar working conditions during 100h reaction time-on-stream. Actually, almost coke-free operation of the process was achieved, which was confirmed by scanning electron microscopy (SEM) and O₂-TPSR characterizations of the used ATR catalyst. Reformate that contains no light alkenes or other higher hydrocarbons could be obtained from the ATR reactor. In addition, the nickel-based prereforming catalyst prepared by a coprecipitation method had high catalytic activity and promising stability.

Keywords: Gasoline; Prereforming; Autothermal reforming; Coke deposition; Nickel-based catalyst

Spillover of labile OH, H, and O species in the H₂ production by steam reforming of phenol over supported-Rh catalysts by K. Polychronopoulou; A.M. Efstathiou (pp. 341-347).

The aim of this work was to probe the back-spillover of labile O, OH and H species during steam reforming of phenol towards H₂ production in the 773–1028K range over Rh supported on MgO and Mg-Ce-Zr-O mixed-metal oxides. This was made possible through steady state isotopic transient kinetic analysis (SSITKA) and other transient isotopic experiments (use of D₂O and¹⁸O₂) combined with temperature-programmed desorption ones. The size of the active pool of H-containing intermediate species (H and/or OH) present in the H-path of reaction as a function of reaction T was measured over the 0.1wt% Rh/50Mg-25Ce-25Zr-O catalyst by SSITKA experiments. It was found that the size of this pool decreases by 18% in the 773–928K range ( θ=68.9–56.3), whereas a significant decrease (by a factor of 10) was observed between 928 and 1028K. These results demonstrate that most of the active H and OH species reside on the support and metal-support interface. Two kinds of H-containing intermediate species are likely to participate in the H-path of reaction. An inverse D kinetic isotopic effect was measured for the H₂ formation in the phenol steam reforming reaction in the 773–1028K range.

Keywords: Oxygen spillover; OH spillover; Phenol steam reforming; Hydrogen production; SSITKA; Kinetic isotope effect

Optically accessible channel reactor for the kinetic investigation of hydrocarbon reforming reactions by Marcello Bosco; Frédéric Vogel (pp. 348-353).

A new experimental reactor concept for studying heterogeneously catalyzed gas phase reactions was developed, which allows true surface temperature measurements along the reactor through a quartz window without affecting the flow in the reactor using IR thermography. The catalyst is coated as a thin layer onto a metal plate. The laminar flow field is similar to the one in a monolith channel. A small stream of gas can be withdrawn with a moveable capillary to measure the concentration profile in the reactor. The spatial resolution of the gas sampling is ≤0.1mm. Two- and three-dimensional fluid dynamic modeling of the channel reactor was performed to check the velocity field in the channel for different operating conditions. Buoyancy forces were insignificant at the conditions studied; the parabolic inlet flow profile was maintained along the reactor channel. The heat loss by radiation from the quartz glass top surface was found to be three times larger than the heat loss by free convection. The methanation of carbon monoxide and carbon dioxide was studied at 550 and 500°C, respectively. For these reactions nearly isothermal conditions were observed. The partial oxidation of methane, performed without diluting the feed, was also studied at 500 and 550°C. The measured hot spots correlated well with the concentration profile measurements. Film diffusional limitations were found only significant for the oxidation reaction.

Keywords: Kinetics; Hydrocarbon reforming; Experimental reactor; Catalytic plate; IR thermography

Nanosized catalysts for the production of hydrogen by methanol steam reforming by T. Valdés-Solís; G. Marbán; A.B. Fuertes (pp. 354-360).

Nanoparticulate ternary oxides (perovskites and spinels) and mixtures of oxides have been prepared via a template technique using a sodium silicate-based silica xerogel as template. The oxides prepared by this method were tested as catalysts for the methanol steam reforming reaction at 250°C and a very high space velocity (WHSV=52–57h⁻¹). Copper-based catalysts (CuMn₂O₄ and CuCr₂O₄ spinels or CuO/CeO₂ and CuO/ZnO) exhibit a high activity and selectivity for the steam reforming process, whereas the other formulations employed (LaFeO₃, LaMnO₃, NiMn₂O₄) are not active in the experimental conditions of this work. The favourable effect of increasing the surface area on the activity of the catalysts is clearly observed for CuMn₂O₄, which exhibits the highest initial reaction rate and a selectivity to CO₂ formation of over 90%. The catalytic activity values of the copper-based catalysts are similar to or greater than those found in the literature for common methanol steam reforming catalysts including noble metal-based catalysts. Deactivation of the catalysts seems to be independent of the preparation method and can be attributed to the concomitant effect of coke deposition and sintering.

Keywords: Spinel; Template; Methanol steam reforming; Coke deposition; CuMn; ₂; O; ₄

Low-temperature steam-reforming of ethanol over ZnO-supported Ni and Cu catalysts by Narcís Homs; Jordi Llorca; Pilar Ramírez de la Piscina (pp. 361-366).

ZnO-supported Ni and Cu as well as bimetallic Co-Ni and Co-Cu catalysts containing ca. 0.7wt% sodium promoter and prepared by the co-precipitation method were tested in the ethanol steam-reforming reaction at low temperature (523–723K), using a bioethanol-like mixture diluted in Ar. Monometallic ZnO-supported Cu or Ni samples do not exhibit good catalytic performance in the steam-reforming of ethanol for hydrogen production. Copper catalyst mainly dehydrogenates ethanol to acetaldehyde, whereas nickel catalyst favours ethanol decomposition. However, the addition of Ni to ZnO-supported cobalt has a positive effect both on the production of hydrogen at low temperature (<573K), and on catalyst stability. Evidence for alloy formation as well as mixed oxides at the microstructural level was found in the bimetallic systems after running the ethanol steam-reforming reaction by HRTEM–EELS.

Keywords: Ethanol-reforming; Hydrogen; Bimetallic catalysts; Nickel catalysts; Copper catalysts

Hydrogen formation in ethanol reforming on supported noble metal catalysts by András Erdőhelyi; János Raskó; Tamara Kecskés; Mariann Tóth; Márta Dömök; Kornélia Baán (pp. 367-376).

The formation and stability of surface species generated in the interaction of ethanol and ethanol–water mixture with Al₂O₃ and CeO₂-supported noble metal catalysts were studied by FT-IR, TPD and TPR methods. It was found that water enhanced the stability of ethoxide surface species formed in the dissociation of ethanol. Dehydrogenation of molecularly adsorbed ethanol was proposed as a key reaction step. The TPD spectra of ethanol adsorbed on supported noble metals exhibited a high temperature desorption stage which was explained by the formation and decomposition of surface acetate species. Ethylene (product of the dehydration of ethanol) was mainly formed on Al₂O₃-supported noble metals, while on CeO₂-supported noble metals significant amount of acetaldehyde (originated from the dehydrogenation of ethanol) was also formed. In the steam reforming of ethanol the selectivity of H₂ formation decreased but that of C₂H₄ increased in time, while the conversions were stable on alumina-supported noble metals. These observations were explained by the inhibiting effect of surface acetate species.

Keywords: Ethanol steam reforming; Surface acetate species; TPD of ethanol; Reaction of ethanol with water; Oxide-supported noble metal catalysts

A comparative study of catalysts for the preferential CO oxidation in excess hydrogen by Eun-Yong Ko; Eun Duck Park; Kyung Won Seo; Hyun Chul Lee; Doohwan Lee; Soonho Kim (pp. 377-383).

Selective CO oxidation in the presence of excess hydrogen was studied over metal oxides (CoO and CuO–CeO₂), supported gold catalysts (Au/γ-Al₂O₃, Au/CuO, Au/CeO₂/γ-Al₂O₃, Au/CuO–CeO₂ and Au/CeO₂), and supported Pt catalysts (Pt/γ-Al₂O₃, Pt–Ni/γ-Al₂O₃, and Pt–Co/γ-Al₂O₃). The methanation was dominant over CoO in the presence of excess H₂. CuO–CeO₂ was quite selective for CO oxidation at low temperatures. However, the presence of CO₂ and H₂O retarded its catalytic activity. No beneficial effect to CO₂ selectivity was observed when Pt, Ru, Ni, and Co was added to CuO–CeO₂ as a modifier. Supported gold catalysts showed the high CO conversion at low temperatures. However, the CO₂ selectivity decreased noticeably with increasing H₂ concentration in a reactant. Pt–Ni/γ-Al₂O₃ showed the highest CO conversion with a high CO₂ selectivity over a wide reaction temperature among above catalysts examined at the same reaction condition. This catalyst also showed the best performance in the presence of 2vol.% H₂O and 20vol.% CO₂.

Keywords: CO oxidation; PROX; Pt–Ni/γ-Al; ₂; O; ₃; Fuel cell; PEMFC

Physico-chemical properties and reactivity of Au/CeO₂ catalysts in total and selective oxidation of CO by F. Arena; P. Famulari; N. Interdonato; G. Bonura; F. Frusteri; L. Spadaro (pp. 384-390).

The effects of the preparation method (deposition–precipitation, incipient-wetness, combustion) on the structure and redox properties of 1% Au/CeO₂ catalyst have been probed by TPR, XRD, and TEM techniques. The catalytic pattern in total (COX) and selective (SCOX) CO oxidation has been assessed by temperature programmed reaction tests in the range 273–473K. Controlling residual chlorine, the synthesis route determines the strength of the Au–CeO₂ interaction which affects both the reduction of the active phase and the CO oxidation functionality. Removal of chlorine by washing in a diluted alkaline solution enables then an easy reduction of Au precursor levelling off the reactivity of the Au/CeO₂ catalysts.

Keywords: Au/CeO; ₂; catalyst; Preparation method; Total and selective CO oxidation; Chlorine effect

Selective CO oxidation over Ce_XZr1−_XO₂-supported Pt catalysts by J.L. Ayastuy; M.P. González-Marcos; A. Gil-Rodríguez; J.R. González-Velasco; M.A. Gutiérrez-Ortiz (pp. 391-399).

CO oxidation on Pt/Ce_XZr1−_XO₂ ( X=0, 0.15, 0.5, 0.68, 0.8 and 1) was studied, both in the absence of H₂ and in H₂-rich streams. Catalyst activity was correlated with support reducibility and Pt content. A certain excess of oxygen ( λ>1) with respect to CO had to be fed to the system in order to obtain complete CO conversion in the presence of H₂. Three catalysts were found capable of complete CO depletion with effective oxygen use at λ=2: Pt/Ce_0.8Zr_0.2O₂, Pt/Ce_0.68Zr_0.32O₂ and Pt/Ce_0.5Zr_0.5O₂. More demanding working conditions, by increasing GHSV from 12,000 up to 18,000h⁻¹, reduced the adequate catalysts to just two: Pt/Ce_0.68Zr_0.32O₂ and Pt/Ce_0.5Zr_0.5O₂, and only the latter would be adequate if the conditions were still more demanding. The presence of CO₂ and H₂O, produced a general decrease of CO conversion for the catalysts supported on mixed oxides and, among them, only Pt/Ce_0.5Zr_0.5O₂ remained capable of complete CO removal with effective oxygen use at λ=2. However, the presence of CO₂ and H₂O increases CO conversion of Pt/CeO₂ such that this catalyst arises as an alternative. Choice between Pt/CeO₂ and Pt/Ce_0.5Zr_0.5O₂ requires further research, and may depend on the actual application.

Keywords: CO oxidation; Selective CO oxidation; Ceria-zirconia mixed oxides; PROX; Pt catalysts

Water–gas shift reaction over sulfided molybdenum catalysts supported on TiO₂–ZrO₂ mixed oxides by M. Laniecki; M. Ignacik (pp. 400-407).

Supported sulfided molybdenum and nickel–molybdenum catalysts were applied in the water–gas shift (WGS) reaction with sulfided feed. TiO₂, ZrO₂ and binary systems of TiO₂–ZrO₂, in which composition was changed in 10wt.% intervals, were used as the supports for sulfided Mo and Ni–Mo catalysts. The concentration of Mo (8wt.%) and Ni (3wt.%) was the same in all studied catalysts. Supports and selected catalysts were characterized with XRD, BET, TPR (H₂), TPD of ammonia, FTIR and NO adsorption measurements. The comparison of pure TiO₂ or ZrO₂ with TiO₂–ZrO₂ systems shows that introduction of the second component always resulted in almost duplication of the surface area of the supports. No simple relationship between surface area and catalytic activity was found. The choice of the support with appropriate ratio of surface acid–base sites, high dispersion of supported Ni–Mo–S surface species as well as much easier reductivity of Mo⁶⁺ ions in the presence of nickel ions can lead towards high activity in the WGS reaction with sulfided feed. The highest activity was obtained for Ni–Mo–S catalysts supported on TiO₂ (40)–ZrO₂ (60).

Keywords: Hydrogen; Water–gas shift; Molybdenum sulfide; Ni–Mo–S; TiO; ₂; –ZrO; ₂; support

New approach to prepare Pt-based hydrogen diffusion anodes tolerant to CO for polymer electrolyte membrane fuel cells by Francisco Alcaide; Óscar Miguel; Hans-Jürgen Grande (pp. 408-414).

A new approach to prepare Pt-based hydrogen diffusion anodes for PEMFCs based on galvanostatic pulsed electrodeposition is demonstrated to be a reliable alternative to the conventional electrode preparation methods. The performance of the PtRu electrodeposited anodes depends on the electrodeposition parameters such as the peak current, on time, off time, and the total charge applied. The peak current density and the relaxation time are crucial in the control of electrode performance. Electrodes prepared using a cathodic peak current of 0.400Acm⁻², a duty cycle of 5.66% and a charge density of 6Ccm⁻² demonstrate high catalytic performance towards hydrogen oxidation.

Keywords: Platinum–ruthenium; CO tolerance; Pulse electrodeposition; PEMFC; Hydrogen oxidation

CO tolerant catalysts for PEM fuel cells by G. García; J.A. Silva-Chong; O. Guillén-Villafuerte; J.L. Rodríguez; E.R. González; E. Pastor (pp. 415-421).

CO tolerance of carbon-supported Pt₈₀Ru₂₀, Pt₈₀Os₂₀ and Pt₈₅Co₁₅ electrocatalysts has been studied in 0.1M perchloric acid solution applying cyclic voltammetry and in situ Fourier transform infrared spectroscopy (FTIRS), and the results were compared with those for a commercial Pt ETEK catalyst. CO stripping is used for the normalization of the area of the electrodes. It is shown that FTIR spectra can be acquired during CO oxidation at these technical materials in an electrochemical cell, obtaining valuable information on the reactivity, which allows predicting their behaviour in a polymer electrolyte membrane fuel cell (PEMFC). Linear adsorbed CO is the main adsorbate, but also small amounts of bridge bonded CO are formed. Moreover, COH species seem to be also present for Pt₈₀Os₂₀ and Pt₈₅Co₁₅. On the other hand, the onset potential for CO oxidation to CO₂ is established and compared for the four catalysts. All bimetallic alloys are able to oxidise adsorbed CO at lower potentials than platinum and a shift of about 0.20V is determined.

Keywords: Bimetallic Pt alloys; Carbon-supported catalysts; In situ FTIRS; Cyclic voltammetry; CO tolerance

Methanol electrooxidation on PtRu nanoparticles supported on functionalised carbon black by J.L. Gómez de la Fuente; M.V. Martínez-Huerta; S. Rojas; P. Terreros; J.L.G. Fierro; M.A. Peña (pp. 422-432).

The effect of the preparation method of PtRu electrocatalysts and the chemical treatment of support on the performance for methanol electrooxidation has been studied. Carbon supported PtRu catalysts were synthesized from aqueous solution of H₂PtCl₆ and RuCl₃ precursors by two different methods: colloidal (using NaHSO₃) and impregnation. The carbon black Vulcan XC-72R was functionalised with H₂O₂ and HNO₃. A commercial PtRu/C catalyst purchased from Johnson and Matthey was used as reference. The obtained electrocatalysts were characterized by XPS, XRD, TEM, EGA-MS, TGA and TXRF. Chronoamperometry in methanol and CO_ads stripping experiments were conducted to check their electrocatalytic activity. Electrocatalysts obtained by the colloidal method and supported on functionalised carbon black with HNO₃ and especially with H₂O₂, showed better performances (CO tolerance and superior methanol oxidation ability) than those obtained by the impregnation method and the commercial one.

Keywords: Pt–Ru catalysts; Direct methanol fuel cells; Carbon

Plate-like zinc oxide microcrystals: Synthesis and characterization of a material active toward hydrogen adsorption by D. Scarano; S. Bertarione; F. Cesano; J.G. Vitillo; A. Zecchina (pp. 433-438).

ZnO-based materials have been synthesized by means of hydrothermal method from aqueous solutions of ZnOH₄²⁻ in the presence of sodium-dodecyl sulphate (SDS). By means of a variety of analyses (SEM, AFM, IR, UV–vis and XRD) it is shown that this synthesis method allows to obtain ZnO microcrystals with well defined morphology and active toward hydrogen adsorption. The adsorption of hydrogen on these zinc oxide platelets has been investigated by FTIR spectroscopy and the results are compared with those obtained on ZnO, synthesized by combustion of zinc metal.

Keywords: Plate-like zinc oxide; Microcrystals; Hydrothermal synthesis; Hydrogen adsorption; XRD; Atomic force microscopy; Scanning electron microscopy; FTIR; UV–vis analyses

Kinetic study of the redox process for storing hydrogen by J.A. Peña; E. Lorente; E. Romero; J. Herguido (pp. 439-444).

The redox process, the reduction of metal oxides and subsequent oxidation by steam to release hydrogen, is an interesting alternative to other methods of storing hydrogen. In order to evaluate the suitability of different metallic oxides for this purpose, either alone (Fe₂O₃) or as mixed oxides (NiFe₂O₄, CuFe₂O₄), a kinetic study has been carried out by means of a thermogravimetric system.The kinetic parameters of the reduction of the oxides by hydrogen have been calculated by fitting experimental data with suitable “ad hoc�? models for non-catalytic gas–solid reactions. The addition of a second metal to form double oxides has a positive effect, since these exhibit greater reaction rates.

Keywords: Hydrogen storage; Redox process; Iron oxides; Kinetic study; Hydrogen purification

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