Applied Catalysis B, Environmental (v.55, #1)


Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (R n ―COOH + O2 → R n −1 ―COOH +CO2) yielding essentially CO2 (route A). It may also be oxidized after C―C bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO2 (route B). Pt/CeO2 is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via C―C bond splitting is much more marked on Ru/CeO2. The catalyst characterization indicates that both noble metal and CeO2 particles remain stable during the reaction.
Keywords: Catalytic Wet Air Oxidation; Stearic acid; Acetic acid; Fatty acids; Ruthenium; Platinum; Cerium oxide;

Supported platinum catalysts for nitrogen oxide sensors by S. Benard; L. Retailleau; F. Gaillard; P. Vernoux; A. Giroir-Fendler (11-21).
The aim of this study was to select, to test and to optimise supported Pt catalysts for nitrogen oxide sensors application in order to improve their selectivity. A series of catalysts based on platinum dispersed onto different supports: SiO2, γ-Al2O3, Al2O3–SiO2, ZrO2, TiO2, CeO2 and YSZ (formulae: (ZrO2)0.92(Y2O3)0.08) were prepared and tested for NO oxidation. The effect of the nature of the support, and of the Pt dispersion and loading on the catalytic activity has been examined under operating conditions similar to those encountered by NO x sensors, i.e. traces of NO in air. Catalytic activity and TPD measurements have clearly shown the prevailing role of the support. Silica is the most adequate support because it weakly adsorbed NO and did not store NO2 as nitrates, then favouring the reaction between NO molecules coming from the support and oxygen adsorbed on Pt. The effect of the Pt particles sizes was also important and our results have shown that larger particles exhibit the highest activity. Finally, the most effective catalyst was found to be Pt/SiO2 containing 2 wt.% of platinum and presenting a low Pt dispersion. This kind of catalyst enables to fix a determined value of the NO/NO2 ratio near the sensing layer of the sensor by reaching the thermodynamic equilibrium over the whole working temperature range.
Keywords: NO oxidation; NO x sensor; Platinum; Temperature-programmed desorption; TPD; Nitrate;

Photocatalytic degradation of the natural oestrogens 17β-oestradiol and oestriol and the synthetic oestrogen 17α-ethynyloestradiol in water were investigated. The reactions were carried out in a quartz coil reactor coated internally with titanium dioxide (Degussa P-25). Degradation by UV light alone was also investigated. Reactions were monitored using fluorescence spectroscopy. The effect of initial concentration and the effect of light intensity on the photocatalysis and photolysis of 17β-oestradiol in water were also investigated. The results showed that photocatalysis and photolysis are capable of degrading all three oestrogens in water. Photocatalysis is much more effective than UV light alone and all reactions follow pseudo first order kinetics. The rate was found to be proportional to the square root of light intensity for photocatalysis of 17β-oestradiol. The relationship between light intensity and the rate of degradation by photolysis is linear up to a point when it starts to level off.
Keywords: Photocatalysis; Titanium dioxide; Photolysis; Water treatment; Endocrine disrupters; 17β-Oestradiol; Oestriol; 17α-ethynyloestradiol; Fluorescence spectroscopy;

Catalytic soot oxidation in microscale experiments by Martin Seipenbusch; Jan van Erven; Tobias Schalow; Alfred P. Weber; A. Dick van Langeveld; Jan C.M. Marijnissen; Sheldon K. Friedlander (31-37).
The oxidation of soot agglomerates over catalytically active surfaces is of interest for the development of catalytic reactors for the control of soot emissions. The process involves the transport and deposition of nanoparticle aggregates to a surface on which catalyst particles are deposited. To simulate this process, graphitized carbon nanoparticles and platinum nanoparticles were separately deposited on an oxidized silicon wafer by laser ablation and electro hydro dynamic atomization. Changes in particle morphology produced by the reaction were visualized ex situ by scanning electron microscopy. In this way chemical reaction data could be correlated with the local surface coverage and particle size of the catalytically active material and the morphology of the reacting particles, resulting in detailed local information on their interaction, which is not available in studies on bulk samples. The contact between catalyst and soot particles was loose, simulating the behavior of catalyst systems used in practice. The activation energy of the oxidation in air was found to be 40 kJ/mol whereas the activation energy in air/NO was found to be 160 kJ/mol, both in presence of Pt deposited on a SiO2 support. Notwithstanding the higher activation energy, the reaction rate of soot oxidation in air/NO is about two to three orders of magnitude higher than in air. A linear relationship between the relative Pt surface and reaction rate was found for the oxidation in an air/NO atmosphere. In air, the relationship has a minimum which indicates that there are different simultaneous mechanisms of reaction. Although activation energies are different from other studies, the oxidation temperatures are comparable. The EHDA and laser ablation produced platinum catalysts behave similarly and show potential to be used as model catalyst.
Keywords: Soot agglomerates; EHDA; Platinum catalysts;

Liquid phase hydrodechlorination of dieldrin and DDT over Pd/C and Raney-Ni by Sergei S. Zinovyev; Natalia A. Shinkova; Alvise Perosa; Pietro Tundo (39-48).
Selectivity and product distribution of hydrodechlorination (HDCl) of dieldrin and DDT are studied in different liquid phase systems, namely in: (1) in ethanol; and (2) in the supported ionic liquid heterogeneous catalytic system (multiphase system), composed by the organic phase and aqueous KOH, a quaternary ammonium ionic liquid promoter (Aliquat 336), and a metal catalyst, e.g. 5% Pd/C, 5% Pt/C, or Raney-Ni. At 50 °C and atmospheric pressure of hydrogen, a quantitative hydrodechlorination of DDT in the biphasic system with ionic liquid layer is achieved in 40 min and in 4 h with Raney-Ni and Pd/C, respectively, while the reaction on Pt/C or on Pd/C without Aliquat 336 is slow. Dieldrin undergoes partial dechlorination, with high selectivity achievable only for its mono- and bi-dechlorination products. Dechlorination pathways and reactivity of different types of organic chlorine atoms versus the catalyst nature and other conditions are discussed.
Keywords: Dieldrin; DDT; Hydrodechlorination; Detoxification; Multiphase system; Supported ionic liquid; Aliquat 336; Pd/C; Pt/C; Raney-Ni;

Phase-transfer promotion of hydrodechlorination of chlorophenoxy-pesticides over Pd/C and Raney-Ni by Sergei S. Zinovyev; Natalia A. Shinkova; Alvise Perosa; Pietro Tundo (49-56).
Hydrodechlorination of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), pentachlorophenol (PCP), and p-chlorobenzoic acid with hydrogen gas over 5% Pd/C or Raney-Ni was studied in different liquid phase systems: (1) ethanol or ethanol–aqueous KOH; (2) in the multiphase system, composed by an organic phase and aqueous KOH and containing a quaternary ammonium salt (Aliquat 336). Under mild conditions (50 °C and atmospheric pressure of hydrogen) quantitative hydrodechlorination of 2,4,5-T is achieved in 1–4 h over Raney-Ni or Pd/C in the multiphase system or in the ethanol–aqueous KOH solution. PCP reacts selectively giving the dechlorinated phenolate in several hours in the system made of aqueous KOH (with Raney-Ni or Pd/C) or in several minutes in the presence of a small amount of Aliquat 336 solution in isooctane (1–4 molar% of Aliquat 336), where Aliquat 336 promotes the phase-transfer of polychlorinated anion. The reaction rates versus conditions, process localization, and the role of the ionic liquid environment are discussed.
Keywords: 2,4,5-Trichlorophenoxyacetic acid; 2,4,5-T; Pentachlorophenol; PCP; p-Chlorobenzoic acid; Hydrodechlorination; Multiphase system; Phase-transfer; Supported ionic liquid; Aliquat 336; Pd/C; Raney-Ni;

Rh/γ-Al2O3–sepiolite monolithic catalysts for decomposition of N2O traces by S. Suárez; C. Saiz; M. Yates; J.A. Martin; P. Avila; J. Blanco (57-64).
The behaviour of Rh/γ-AlO3–sepiolite monolithic systems in the N2O decomposition reaction using catalysts with rhodium contents between 0.2 and 0.8 wt.% were analysed. The observed increase of the catalytic activity with the metal loading was related to an enhancement in the number of active sites. The SEM–EDX results showed that rhodium was mainly located on the alumina particles. The variation of the reaction rate values with the inlet N2O and O2 concentrations, suggested an apparent first order equation with respect to N2O and zero order for O2. The presence of NH3 traces or water vapour in the feed decreased the catalytic activity, probably due to the competitive adsorption of NH x or OH species. The ammonia oxidation reaction took place, producing N2O as a secondary product. The monolithic catalysts developed operate with a low pressure drop achieving a N2O conversion higher than 90% at 773 K in the presence of oxygen, ammonia or water vapour in the stream.
Keywords: N2O decomposition; Rh/γ-Al2O3; Monolithic catalysts; Sepiolite; Ammonia oxidation;

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs by Shuqin Song; Weijiang Zhou; Zhenxing Liang; Rui Cai; Gongquan Sun; Qin Xin; Vaios Stergiopoulos; Panagiotis Tsiakaras (65-72).
In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion®-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion®-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltammetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.It was found that ethanol shows lower cross-over rates than methanol through the Nafion® membrane in spite of the higher membrane porosity resulted in presence of ethanol aqueous solutions. Furthermore, it was found that ethanol presents less negative effect on the cathode performance due to both its smaller permeability through Nafion® membrane and its slower electrochemical oxidation kinetics over Pt/C cathode.
Keywords: PEMFC; Methanol cross-over; Ethanol cross-over; Direct alcohol fuel cells (DAFCs);