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Applied Catalysis B, Environmental (v.98, #1-2)
Direct hydrazine fuel cells: A review by Alexey Serov; Chan Kwak (pp. 1-9).
Low-temperature fuel cells operating on hydrazine fuel in acid and alkaline media comprise a promising class of new, non-conventional sources of energy. High battery performance is expected of hydrazine-based cells. The electrooxidation of hydrazine on the surface of different catalysts has been extensively studied recently. Examples of Direct Hydrazine Fuel Cells (DHFC) with anion or cation-exchange membranes show notable power densities. These aspects of DHFC development with analysis of future improvements in their performance based on changes such as an increase in catalytic activity, membrane type selection and MEA fabrication, are summarized in the present review.
Keywords: Hydrazine oxidation; Fuel cell; Anode; Catalyst
Heterogeneous photo-Fenton oxidation with pillared clay-based catalysts for wastewater treatment: A review by J. Herney-Ramirez; Miguel A. Vicente; Luis M. Madeira (pp. 10-26).
Due to their excellent properties, pillared clays (PILCs) have been widely used in several applications, particularly in catalysis. In this paper, their use in heterogeneous photo-Fenton-like advanced oxidation for wastewater treatment, employing either model/synthetic effluents or real streams, is reviewed. Particular attention is given to the effect that the main operating conditions have on process performance, namely wavelength of the light source and power, initial H2O2 or parent compound concentration, catalyst load, pH and temperature. Emphasis is also given to the type of catalyst used and its synthesis conditions (e.g. thermal aging or acid treatment). Several important technological aspects that should be accounted for in real practice are also discussed in detail, particularly the catalyst stability, the use of continuous-flow fixed-bed reactors, the mode of oxidant addition, the environmental impact/integration with biological processes and the possibility of using visible light instead of UV only. Then, some simple mechanistic studies reported are summarized, as well as modeling works.
Keywords: Pillared clays; Heterogeneous catalyst; Photo-Fenton; Wastewater treatment; Advanced Oxidation Processes
A review of the mechanisms and modeling of photocatalytic disinfection by Omatoyo K. Dalrymple; Elias Stefanakos; Maya A. Trotz; D. Yogi Goswami (pp. 27-38).
This paper is a review of the fundamental disinfection mechanisms of photocatalysis and the models used to fit the disinfection process. Photocatalysis is an attractive technology for water treatment largely due to its potential to utilize solar energy directly and achieve both disinfection and chemical detoxification. Many papers have been published on photocatalytic disinfection, but there is still considerable debate on disinfection mechanisms and a general lack of mechanistic models for the process. The fundamental photocatalytic disinfection mechanisms as they relate to the inactivation of bacteria are comprehensively surveyed here. The process of lipid peroxidation of membrane fatty acids, particularly polyunsaturated fatty acids, is gaining momentum in the literature. In recent papers, an increasing number of researchers are paying close attention to the products of lipid peroxidation.The mathematical models, empirical and mechanistic, used to fit the disinfection process have also been thoroughly reviewed. In this regard, most of the proposed models are empirical in nature and rooted in traditional chemical disinfection principles, which are often not representative of the heterogeneous photocatalytic process. The theoretical development of a mechanistic model for photocatalytic disinfection based on lipid peroxidation is explored with due consideration to the interaction between microbes and photocatalyst particles. The extensive literature on autooxidation of lipids in such fields as biology and medicine is informative to the development of the model.
Keywords: Titanium dioxide; Water disinfection; Solar applications; Lipid peroxidation
New Mo–V based oxidic precursor for the hydrotreatment of residues by Deana Soogund; Philippe Lecour; Antoine Daudin; Bertrand Guichard; Christelle Legens; Carole Lamonier; Edmond Payen (pp. 39-48).
In order to understand the role of vanadium and its interaction with molybdenum atoms in the catalysts used for the hydrotreatment of residues, mixed heteropolyanion (HPA) precursors PMo(12− x)V xO40(3+ x)− have been prepared and deposited by incipient wetness impregnation on an alumina support. The evolution of the compounds in the impregnating solutions till their deposition on the support has been analysed using various spectroscopic techniques such as Raman,31P and51V NMR, XPS as well as TEM. Activity measurements on model molecules (toluene and cyclohexane) and on real feedstock (vacuum residue) have been performed after activation step ( ex situ sulphidation). Hydrogenation (HYD), isomerisation (ISOM), hydrodemetallation (HDM), hydrodesulphurisation (HDS), hydrodeasphaltenisation (HDAsC7) were assessed. During tests (2h) on a Safaniya vacuum residue feed, interesting HDM activity was observed compared to reference promoted and unpromoted catalysts (NiMo and Mo/Al2O3). It can be concluded that the use of vanadium in the impregnating solution may promote HDM and HDAsC7 (increase of vanadium removal rate around 15% compared to Mo-catalyst without vanadium). Furthermore HDM and HDAsC7 catalytic performances turned out to be close to the ones of NiMo catalyst. The increase in HDM/HDAsC7 activity may be related to the improvement of hydrogenation and/or isomerisation, the latter being improved by the presence of vanadium.
Keywords: Catalysis; Hydrodemetallation; Heteropolyanions; Vanadium; Molybdenum; Sulphide
Palladium–vanadium alloy electrocatalysts for oxygen reduction: Effect of heat treatment on electrocatalytic activity and stability by Shee-Yen Ang; Darren A. Walsh (pp. 49-56).
Carbon black (Vulcan XC72R)-supported palladium–vanadium electrocatalysts for the oxygen reduction reaction (ORR) were synthesized by wet chemical reduction of metal chloride salts. The nominal compositions of the electrocatalysts were 60:40, 70:30 and 80:20 (Pd/V atomic ratio). The electrocatalysts were treated at a range of temperatures in 10% H2 in Ar and the effect of heat treatment on particle morphology was characterised using powder X-ray diffraction and transmission electron microscopy. These analyses showed that high temperatures caused an increase in the average particle size. The electrocatalytic activities of the electrocatalysts for the ORR were determined using rotating disk electrode voltammetry, which revealed a marked enhancement in the electrocatalytic activity of the Pd70V30 electrocatalyst after heat treatment. The electrochemical stability of the electrocatalysts was examined using an accelerated stability test, which showed a loss of electrochemical surface area upon electrochemical cycling, the extent of which depended on the nominal composition of the electrocatalysts. Electrocatalyst testing after the stability test showed a loss of electrocatalytic performance and microscopic analysis revealed significant morphological changes in the electrocatalyst particle dimensions and dispersion on the carbon support after the stability test.
Keywords: Oxygen reduction; Fuel cell; Palladium alloy; Rotating disk electrode
Hydrogen production by auto-thermal reforming of ethanol over nickel catalysts supported on metal oxides: Effect of support acidity by Min Hye Youn; Jeong Gil Seo; Howon Lee; Yongju Bang; Jin Suk Chung; In Kyu Song (pp. 57-64).
Hydrogen production by auto-thermal reforming of ethanol over nickel catalysts supported on pure metal oxides (ZnO, MgO, ZrO2, TiO2, and Al2O3) and mixed metal oxides (Ti XZr1− XO2) was conducted. Hydrogen yield over supported nickel catalysts showed a volcano-shaped curve with respect to acidity of the support. Among the catalysts, Ni/Ti0.2Zr0.8O2 with an intermediate acidity of support exhibited the best catalytic performance.Nickel catalysts supported on pure metal oxides (ZnO, MgO, ZrO2, TiO2, and Al2O3) with different acidity were prepared by an incipient wetness impregnation method, and they were applied to the hydrogen production by auto-thermal reforming of ethanol. The effect of support acidity on the catalytic performance of supported nickel catalysts was investigated. It was revealed that acidity of support played an important role in determining the reaction pathway and catalytic performance in the auto-thermal reforming of ethanol. Among various pure metal oxides, ZrO2 and TiO2 with an intermediate acidity were found to be efficient supporting materials for nickel catalysts in the auto-thermal reforming of ethanol. On the basis of this result, a series of TiO2–ZrO2 mixed metal oxides (Ti XZr1− XO2) with different Ti content ( X) were prepared by a sol–gel method for use as supporting materials for nickel catalysts. In hydrogen production by auto-thermal reforming of ethanol, an optimal Ti content was required for suitable acidity of Ti XZr1− XO2 support and favorable reducibility of Ni/Ti XZr1− XO2 catalyst. Hydrogen yield over nickel catalysts supported on metal oxides showed a volcano-shaped curve with respect to acidity of the support. Among the catalysts tested, Ni/Ti0.2Zr0.8O2 with an intermediate acidity of support exhibited the best catalytic performance.
Keywords: Hydrogen; Auto-thermal reforming of ethanol; Support acidity; Supported nickel catalyst; Metal oxides
Electroreduction of carbon dioxide at a lead electrode in propylene carbonate: A spectroscopic study by B. Eneau-Innocent; D. Pasquier; F. Ropital; J.-M. Léger; K.B. Kokoh (pp. 65-71).
The electrochemical reduction of carbon dioxide at a lead electrode was studied in propylene carbonate (PrC) containing tetraethylammonium perchlorate (TEAP) as electrolyte. Different electrochemical techniques such as cyclic voltammetry and chronoamperometry were used to evaluate the catalytic activity of this material towards CO2 electrodimerization. The electroreduction process was also investigated by in situ infrared reflectance spectroscopy in order to determine adsorbed intermediates and reaction products. The peak of reduction observed in cyclic voltammetry starting at −2.05V vs. Ag/AgCl has been clearly ascribed to the carbon dioxide reduction by SPAIRS technique. Infrared reflectance spectroscopy also confirmed the absence of CO at the lead cathode during chronoamperometric measurements and that oxalate has been formed concurrently to the CO2 consumption. Combining the analytic and spectroscopic results, a reaction mechanism was proposed for the reduction of carbon dioxide to oxalate ions on a lead cathode in a nonaqueous aprotic medium.
Keywords: Pb electrode; CO; 2; reduction; In situ; IR reflectance spectroscopy; Propylene carbonate; Oxalate
An eco-friendly synthesis of 1,2-methylenedioxybenzene in vapour phase by A. Giugni; D. Impalà; O. Piccolo; A. Vaccari; A. Corma (pp. 72-78).
An environmentally friendly synthesis of 1,2-methylenedioxybenzene (MDB) was carried out, avoiding the use of any dihalomethane, reacting 1,2-dihydroxybenzene (DHB, also called catechol) with formaldehyde acetals in the vapour phase and in the presence of suitable heterogeneous catalysts. Ti-silicalite (TS-1) or some Ti-, Sn- or Zr-doped MCM-41 were extensively investigated for this role. Catalysts were characterised using different techniques, including BET surface area, X-ray diffraction, FT-IR spectroscopy and thermal gravimetric analysis. Some interesting results were obtained with either TS-1 or Sn-doped MCM-41, which shed light on the role of surface acidity, reaction temperature and residence time on the reactivity and catalyst deactivation. The subsequent regeneration of a spent catalyst was shown to be possible. Among the formaldehyde acetals investigated (dimethoxymethane, diethoxymethane, dipropoxymethane or 1,3-dioxolane), the results showed diethoxymethane to be the most suitable reagent, giving rise to selectivity values higher than 80% in MDB. Finally, a possible reaction pathway was proposed by indicating the role of 2-(ethoxymethoxy)phenol as a reaction intermediate and explaining the origin of observed by-products.
Keywords: Vapour phase; 1,2-Methylenedioxybenzene; Ti-silicalite; MCM-41 catalysts; Formaldehyde acetals; 1,2-Dihydroxybenzene; Reaction pathway
Hydrodechlorination of dichloromethane with a Pd/AC catalyst: Reaction pathway and kinetics by Zahara M. de Pedro; Jose A. Casas; Luisa M. Gomez-Sainero; Juan J. Rodriguez (pp. 79-85).
The kinetics of gas-phase hydrodechlorination (HDC) of dichloromethane (DCM) with a Pd on activated carbon commercial catalyst has been studied in a fixed bed reactor within the 200–350°C temperature range. Different kinetic equations have been checked for describing the evolution of DCM. Statistical and physical reliable parameters were found for a Langmuir–Hinshelwood type expression with DCM adsorption as the controlling step. The reaction pathway and the kinetic model have been elucidated from the evolution of dichloromethane and the identified reaction products (methane, monochloromethane, ethane and ethylene). Adsorbed CH2Cl* radical, CH2** and C2H4** carbene species are proposed as the three intermediates evolving to the final reaction products. An apparent activation energy of 23.9±2.3kJmol−1 has been obtained for dichloromethane disappearance.
Keywords: Dichloromethane; Palladium/activated carbon catalyst; Catalytic hydrodechlorination; Kinetic model; Hydrodechlorination mechanism
Effect of preparation atmosphere of Pt–SnO x/C catalysts on the catalytic activity for H2/CO electro-oxidation by Guoxiong Wang; Tatsuya Takeguchi; Toshiro Yamanaka; Ernee Noryana Muhamad; Motofumi Mastuda; Wataru Ueda (pp. 86-93).
Pt–SnO x/C catalysts were prepared in a polyol process under Ar, sequential Ar and air, and air atmospheres in combination with a high temperature reduction treatment. The composition, structure, morphology and oxidation state of the prepared catalysts were characterized by Inductively Coupled Plasma-Atom Emission Spectroscopy, X-ray diffraction, scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by CO stripping voltammetry and single cell test in combination with in situ IR reflection absorption spectroscopy (IRRAS). The polyol-synthesized Pt–SnO x/C catalysts prepared under different atmospheres had a similar bulk composition, particle size and lattice parameter, however, the Pt–SnO x/C catalyst prepared under Ar atmosphere possessed a greater proportion of Sn(II) species than the other Pt–SnO x/C catalysts. Electrochemical and in situ IRRAS measurements indicated that the Pt–SnO x/C catalyst under Ar atmosphere had the greatest CO tolerance in proton electrolyte fuel cell among the Pt–SnO x/C catalysts.
Keywords: Pt–SnO; x; /C catalyst; Preparation atmosphere; CO tolerance
Valorisation of glycerol by condensation with acetone over silica-included heteropolyacids by P. Ferreira; I.M. Fonseca; A.M. Ramos; J. Vital; J.E. Castanheiro (pp. 94-99).
The acetalisation of glycerol was studied using heteropolyacids, immobilized in silica, as catalysts, at 70°C. The main product of glycerol acetalisation was solketal. The tungstophosphoric (PW), molybdophosphoric (PMo), tungstosilisic (SiW) and molybdosilisic (SiMo) acids were immobilized in silica by sol–gel method.It was observed that the catalytic activity decreases in the series: PW_S>SiW_S>PMo_S>SiMo_S. All catalysts exhibited good values of selectivity to solketal (about 98% near complete conversion). The effect of different parameters, such as catalyst loading, molar ratio of glycerol to acetone and temperature on the glycerol acetalisation, over PW_S catalyst, was studied. Catalytic stability of the PW_S, SiW_S, PMo_S and SiMo_S catalysts was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch, it was observed a stabilisation of the initial activity.
Keywords: Glycerol; Acetalisation; Heteropolyacids; Silica