Applied Catalysis B, Environmental (v.80, #3-4)

Contents (CO4).

New PVDF microcapsules for application in catalysis by M.G. Buonomenna; A. Figoli; I. Spezzano; M. Davoli; E. Drioli (185-194).
Novel polyvinylidene fluoride (PVDF) porous microcapsule membranes were successfully prepared with non-solvent induced phase inversion method for the immobilization of catalyst ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O).The chemical–physical analysis of the new PVDF catalytic microcapsules was carried out by means of SEM, EDX, IR, DSC and XRD techniques.Catalytic activity of the PVDF catalytic microcapsules has been evaluated in the oxidation of benzyl alcohol to benzaldehyde in solvent free conditions. The polymeric microcapsules “keep in contact” the two phases: the organic phase, containing the substrate and the product, and the aqueous phase with the oxidant, H2O2. In literature, ((NH4)6Mo7O24·4H2O) was reported to be effective in the oxidation of alcohols with H2O2 in combination with a phase transfer catalyst in chlorinated solvents.The effect of reaction temperature, substrate:oxidant ratio, swelling of polymeric microcapsules on the reaction progress was investigated.PVDF catalytic microcapsules have given proof of their complete stability under oxidation conditions and their good recycle.
Keywords: Catalytic polymeric microcapsules; Selective oxidation; Polyvinylidene fluoride; Ammonium molybdate tetrahydrate; Phase inversion;

Hydrogen effect on the preferential oxidation of carbon monoxide over alumina-supported gold nanoparticles by Elodie Quinet; Franck Morfin; Fabrice Diehl; Priscilla Avenier; Valérie Caps; Jean-Luc Rousset (195-201).
Although alumina-supported gold nanoparticles are poor catalysts for the oxidation of carbon monoxide, they have turned out to be promising candidates for the preferential oxidation of CO in hydrogen-rich streams (PrOx), as hydrogen apparently enhances the CO oxidation rate. The mechanism of this promotion effect is unclear. In this study, we carry out kinetic measurements on the PrOx reaction catalyzed by a 0.9% Au/Al2O3 catalyst, which is prepared by direct anionic exchange. We show that the apparent activation energy of the oxidation of CO is lower than that of the oxidation of H2, whatever the hydrogen content in the feed. On the other hand, the hydrogen partial reaction order is higher in the oxidation of H2 than in the oxidation of CO. Thus, the CO oxidation rate is significantly increased at low temperature by the introduction of only a small amount of hydrogen in the reactant mixture. At higher temperatures, the selectivity to CO2 decreases due to competition with the oxidation of H2. Higher hydrogen concentrations cause the competition between CO and H2 oxidations to start at lower temperatures. It is proposed that hydrogen reacts with oxygen to yield highly oxidizing intermediates that selectively react with CO as long as the energetic barrier to produce water from these intermediates is not crossed.
Keywords: Hydrogen; Gold; Alumina; PrOx; CO oxidation; H2  + O2 intermediates;

Ag-based catalysts supported on various metal oxides, Al2O3, TiO2, and TiO2–Al2O3, were prepared by the sol–gel method. The effect of SO2 on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO2–Al2O3 in comparison to Ag/Al2O3 and Ag/TiO2, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO2–Al2O3. NO3 rather than NO2 or NOx reacted with the carboxylate species to form CN or NCO. NO2 was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO2–Al2O3. More amount of formate (HCOO) and CN were generated on the Ag/TiO2–Al2O3 catalyst than the Ag/Al2O3 catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO2 oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO2–Al2O3 system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO2 toleration to the Ag/Al2O3 catalyst.
Keywords: Selective catalytic reduction of NO; Ag/TiO2–Al2O3; Activity enhancement; SO2 poisoning; Lewis acid sites;

Pt–Ba–Al2O3 for NO x storage and reduction: Characterization of the dispersed species by Irene Malpartida; Maria Angeles Larrubia Vargas; Luis J. Alemany; Elisabetta Finocchio; Guido Busca (214-225).
Pt–Ba–Al2O3 active and selective for NO x storage and selective reduction to N2 has been prepared and tested. Characterization of the parent Al2O3, Pt–Al2O3 and Ba–Al2O3 materials, as well as of Pt–Ba–Al2O3 catalyst in the oxidized, reduced and sulphated state has been performed by FT-IR spectroscopy of low-temperature adsorbed carbon monoxide and of adsorbed acetonitrile. XRD, TEM and XPS analyses have also been performed. Evidence for the predominance of Ba species, which are highly dispersed on the alumina support surface, and may be carbonated or sulphated, has been provided. Competitive interaction of Pt and Ba species with the surface sites of alumina has also been found.
Keywords: NO x storage and reduction; Pt–Ba–Al2O3 catalysts; IR spectroscopy; CO adsorption; TEM Pt–Ba–Al2O3; XPS Pt–Ba–Al2O3; Sulfation NSR catalysts;

The N2O decomposition activity of the Fe-ZSM-5 catalysts, prepared by chemical vapor deposition (CVD) and aqueous ion exchange (IE), was studied after steaming and high temperature treatment at 1218 K (HT) and compared with the activity of the corresponding non-steamed catalysts after pretreatment at 873 K. FTIR spectra showed that dehydroxylation and/or dealumination took place during steaming and high temperature treatment of the catalysts, which leads to the formation of oxygen vacancies (i.e. lattice defect). These lattice defects leads to a change in electronic properties of the iron sites, which are associated with electron withdrawing Al Lewis centers. The iron sites in close proximity of defects are responsible for the initial higher N2O decomposition (transient activity) of the steamed and HT catalysts. The increase in steady-state activity over steamed and HT catalysts can be mainly attributed to an increase in the number of active sites created by autoreduction of the iron centers during steaming and high temperature treatment. The above-mentioned trends are valid for both CVD and IE samples.
Keywords: Iron zeolite; Isotope labeling; Step response; Dealumination; Defects; Autoreduction;

A series of noble metal (Pt, Pd, Ru) loaded Ce0.33Zr0.63Pr0.04O2 catalysts were used in the Catalytic Wet Air Oxidation (CWAO) of 2-chlorophenol (2-CP) at relatively low temperature (393 K). Among the investigated noble metals, Ru exhibited the best activity. To optimize the reaction conditions, the effects of different parameters, such as the nature of the ruthenium precursor, the reaction temperature, the total pressure, the initial 2-CP concentration and the initial pH of the 2-CP solution on the catalytic performances of 3 wt.% Ru/Ce0.33Zr0.63Pr0.04O2 were evaluated. It was confirmed that the nature of the ruthenium precursor had nearly no effect on the activity of Ru/Ce0.33Zr0.63Pr0.04O2. The activation energy for the 2-CP CWAO over Ru/Ce0.33Zr0.63Pr0.04O2 was calculated to be 34 kJ mol−1. Unexpectedly, the 2-CP removal rate was 0.5 order with respect to the initial 2-CP concentration. Furthermore, the CWAO of 2-CP changed from first order (“oxygen diffusion control”) to zero order (“kinetic control”) with respect to the oxygen partial pressure, when the total pressure was higher than 4 MPa. The 2-CP conversion increased with the pH of the initial 2-CP solution. The dechlorination reaction is promoted at higher pH. However, too high pH hindered the total mineralization of 2-CP due to the possible poisoning effect of adsorbed carbonate and hydroxycarbonate species. The optimum initial pH was about 6.
Keywords: Catalytic wet air oxidation (CWAO); Chlorophenol; Ru;

Study of the reaction of NO x and soot on Fe2O3 catalyst in excess of O2 by D. Reichert; H. Bockhorn; S. Kureti (248-259).
This study addresses the catalytic reaction of NO x and soot into N2 and CO2 under O2-rich conditions. To elucidate the mechanism of the soot/NO x /O2 reaction and particularly the role of the catalyst α-Fe2O3 is used as model sample. Furthermore, a series of examinations is also made with pure soot for reference purposes. Temperature programmed oxidation and transient experiments in which the soot/O2 and soot/NO reaction are temporally separated show that the NO reduction occurs on the soot surface without direct participation of the Fe2O3 catalyst. The first reaction step is the formation of CC(O) groups that is mainly associated with the attack of oxygen on the soot surface. The decomposition of these complexes leads to active carbon sites on which NO is adsorbed. Furthermore, the oxidation of soot by oxygen provides a specific configuration of active carbon sites with suitable atomic orbital orientation that enables the chemisorption and dissociation of NO as well as the recombination of two adjacent N atoms to evolve N2. Moreover, carbothermal reaction, high resolution transmission electron microscopy and isotopic studies result in a mechanistic model that describes the role of the Fe2O3 catalyst. This model includes the dissociative adsorption of O2 on the iron oxide, surface migration of the oxygen to the contact points of soot and catalyst and then final transfer of O to the soot. Moreover, our experimental data suggest that the contact between both solids is maintained up to high conversion levels thus resulting in continuous oxygen transfer from catalyst to soot. As no coordinative interaction of soot and Fe2O3 catalyst is evidenced by diffuse reflectance infrared Fourier transform spectroscopy a van der Waals type interaction is supposed.
Keywords: Simultaneous catalytic conversion; NO x reduction; Soot oxidation; Mechanism; Fe2O3 catalyst; Oxygen transfer; Isotope labelling; DRIFTS; HRTEM;

A comparative study of the selective catalytic reduction of NO by propylene over supported Pt and Rh catalysts by Areti Kotsifa; Dimitris I. Kondarides; Xenophon E. Verykios (260-270).
The catalytic performance of Pt and Rh catalysts for the selective catalytic reduction (SCR) of NO by propylene in the presence of excess oxygen has been investigated over catalysts supported on six different metal oxide carriers (CeO2, Al2O3, TiO2, YSZ, ZrO2 and W6+-doped TiO2). It has been found that the nature of the dispersed metal affects strongly the light-off temperature of propylene, the maximum NO conversion to reduction products and the selectivity towards nitrogen. For a given support, Pt catalysts are always more active for both NO reduction and propylene oxidation, but are much less selective towards N2, compared to Rh catalysts. Rhodium catalysts are able to selectively reduce NO even in the absence of oxygen in the feed. However, their activity is suppressed with increasing oxygen feed concentration possibly due to the formation of less reactive rhodium oxides. In contrast, oxygen promotes the de-NO x activity of platinum catalysts but decreases selectivity towards nitrogen. Results are explained by considering the effects of the nature of the metallic phase and the support on the elementary steps of the propylene-SCR reaction. It is concluded that the catalytic performance of both metals may be improved by proper selection of the support.
Keywords: Nitrogen monoxide; Propylene; Selective catalytic reduction; Platinum; Rhodium; Effect of support; Effect of oxygen concentration;

Photocatalytic activity of TiO2/ZSM-5 composites in the presence of SO4 2− ion by W. Panpa; P. Sujaridworakun; S. Jinawath (271-276).
TiO2/ZSM-5 composites were prepared from SiO2 of rice husk ash and TiO2 sol from hydrolyzed TiOSO4 salt. The combined effect of these two materials greatly enhanced the photocatalytic decolorization of methylene blue dye solution. The instant decolorization of the dye solution in the dark by the composite, TiO2/ZSM-5 (wt ratio 1:1), resulted from the combination of the adsorption by ZSM-5 zeolite and TiO2 nano-particles, and of Na2SO4 salt adhering to the composite surface. As a strong flocculating agent, the SO4 2− ion caused the precipitation of the dye onto the composite surface which consequently enhanced the photocatalytic decolorization of the dye under UV irradiation. The composite, TiO2/ZSM-5 (wt ratio 1:5), completely decolorized the methylene blue dye in 2.5 h, giving an equivalent performance to that of TiO2, P-25 powder.
Keywords: TiO2; TiO2/ZSM-5; Photocatalyst; Adsorption; Decolorization;

Applications of anodized TiO2 films for environmental purifications by Kinji Onoda; Susumu Yoshikawa (277-285).
The high performance photocatalytic TiO2 films were successfully obtained by a galvanostatic anodization of metallic titanium using the optimum anodization condition, subsequent to pre-nitridation treatment. The optimized anodization parameters on the formation of high photocatalytic TiO2 film were investigated. The pre-nitridation treatment was performed by annealing metallic Ti under a nitrogen atmosphere of 0.1 MPa. The anodized TiO2 film showed the high photocatalytic activities to decompose not only gaseous acetaldehyde but also tetrachloroethylene, which revealed that the anodized TiO2 film is a possible candidate of the photocatalyst for environmental purifications comparable to the best photocatalyst of fine crystalline powder.
Keywords: TiO2; Anodization; Pre-nitridation; Photocatalytic activity; Tetracholoroethylene;

Template synthesis of various nitrogen containing carbon nanotubes using different nitrogen containing polymers and the variation of nitrogen content in carbon nanotube (CNT) on the behaviour of supported Pt electrodes in the anodic oxidation of methanol in direct methanol fuel cells was investigated. Characterizations of the as-prepared catalysts are investigated by electron microscopy and electrochemical analysis. The catalyst with N-containing CNT as a support exhibits a higher catalytic activity than that carbon supported platinum electrode and CNT supported electrodes. The N-containing CNT supported electrodes with 10.5% nitrogen content show a higher catalytic activity compared to other N-CNT supported electrodes. This could be due to the existence of additional active sites on the surface of the N-containing CNT supported electrodes, which favours better dispersion of Pt particles. Also, the strong metal-support interaction plays a major role in enhancing the catalytic activity for methanol oxidation.
Keywords: Template synthesis; Methanol oxidation; Nitrogen containing carbon nanotubes;

Plasma/catalyst combination is an active solution to reach high conversion rates at low energetic cost. TiO2 is one of the catalysts frequently used in dielectric barrier discharges. Plasma/TiO2 synergy was already exhibited but the mechanisms still have to be understood. This work distinguishes three main effects involved in the synergy: (a) effect of catalyst on the injected power, (b) the effect of porosity on C2H2 oxidation, and (c) the photocatalytic degradation of C2H2 on TiO2 under plasma exposure. Different glass fibres-based catalytic materials coated with SiO2 and/or TiO2 nano-particles are used to separate these three contributions regarding to C2H2 conversion. It is reported that at constant voltage the injected power is mainly increased by the presence of glass fibres. C2H2 oxidation is mainly enhanced by the macroporosity of glass fibres and in a minor way by the nano-particles. The production of O atoms close to the surface is probably responsible for the higher C2H2 removal efficiency with porous material. The photocatalytic activity of TiO2 is negligible in the plasma except if additional UV lamps are used to activate TiO2. With external UV, photocatalytic activity is more efficient in the plasma phase than in a neutral gas phase. This plasma/photocatalysis synergy is due to the use of O atoms in photocatalytic mechanisms.
Keywords: Plasma photocatalysis combination; Dielectric barrier discharge; TiO2; Porosity; O atoms; C2H2 oxidation; Air treatment;

Promotion of palladium-based catalysts on metal monolith for partial oxidation of methane to syngas by Jae-Hong Ryu; Kwan-Young Lee; Hak-Joo Kim; Jung-Il Yang; Heon Jung (306-312).
Four different modifications of alumina were prepared for use as the support for a Pd catalyst used for the partial oxidation of methane to syngas. The catalysts were washcoated on a metallic monolith in order to determine their activities at high gas flow rates. Compared with the Pd/Al2O3 catalyst, enhanced partial oxidation activities were observed with the Pd/CeO2/Al2O3, Pd/CeO2/BaO/Al2O3 and Pd/CeO2/BaO/SrO/Al2O3 catalysts. The palladium particles were better dispersed in the presence of CeO2 and SrO. Adding BaO, CeO2 and BaO–CeO2 to γ-Al2O3 prevented the transformation of the alumina phase during the 3-day aging process at 1000 °C, providing the support with some level of thermal stability. The addition of small amounts of SrO to the CeO2/BaO/Al2O3 support enhanced the thermal stability of the Pd particles and minimized their sintering. The triply promoted Pd catalyst studied in this work was effective in carrying out partial oxidation at high temperatures, with BaO and CeO2 promoting the thermal stability of the support, CeO2 and SrO dispersing the Pd particles and SrO anchoring the Pd particles strongly to the support. The composition of the catalyst which gave both the highest partial oxidation activity and the best thermal stability was Pd(2)/CeO2(23)/BaO(11)/SrO(0.8)/Al2O3.
Keywords: Partial oxidation; Palladium; Ceria; Barium; Strontium;

Visible-light enabling titanium oxide/tin indium oxide (TiO2/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (2 1 1) and the Raman peak intensity at ∼640 cm−1 dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2 h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231 h−1. Hydrophilic conversion rate was estimated to be 8.14 × 10−3  deg−1  min−1 and long-term UV-induced hydrophilicity of ∼10° in the dark storage up to 72 h was observed. In addition to its inherent characteristics of the layered TiO2/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.
Keywords: Titanium oxide/tin indium oxide (TiO2/ITO) films; Visible-light; Hydrophilicity;

Molecular structure effects in photodegradation of phenol and its chlorinated derivatives with phthalocyanines by P. Kluson; M. Drobek; S. Krejcikova; J. Krysa; A. Kalaji; T. Cajthaml; J. Rakusan (321-326).
In this work we report on possible utilisation of sulphonated phthalocyanines as efficient oxidation catalysts for the removal of various traces of chlorinated compounds from an aquatic environment. Photocatalytic oxidations were carried out with visible and ultraviolet light in agreement with location of their distinctive absorption bands in both these regions. The reaction rate of decomposition of the substrate was measured as a function of pH. Special attention was paid to describe aggregation of the photocatalyst resulting in significant decreasing of the photooxidation activity. Suppression of this undesirable phenomenon by addition of some alcohol to the reaction mixture was studied in detail. Photocatalytic efficiency was verified according to calculated quantum yields.
Keywords: Phthalocyanines; Phenol; Chlorophenols; Photodegradation; Singlet oxygen;

Our previous study on the electrocatalytic dechlorination of 2-chlorobiphenyl at a Pd-loaded granular graphite-packed electrode demonstrated that the process did not follow the first-order kinetics. The rate constant varied with the applied potential at the beginning, but later became irrelevant to the potential. The electrocatalytic kinetic was investigated in this study, in which several experiments were conducted to dechlorinate 2-chlorobiphenyl using a Pd-loaded granular graphite-packed electrode at different potentials and in methanol–water solutions. Analysis of the experimental results reveals that the electrocatalytic process had reached equilibrium in these experiments. The apparent equilibrium constants, as well as the rate constants for the overall forward and backward reactions, were related to the applied potential. These relationships follow the Tafel equation, but the apparent charge transfer coefficients are very small values. The potential dependence of the overall rate constants suggests a reaction mechanism in which the electrocatalytic reaction is the rate-determining step. The influence of methanol on (together with the potential dependence of) the overall rate constants and the apparent equilibrium constant suggests a Langmuir–Hinshelwood mechanism.
Keywords: Polychlorinated biphenyls (PCBs); Electrocatalytic dechlorination; Kinetics; Equilibrium; Reaction mechanism; Rate law;

This work investigates the effect of treatments under different CH4-containing atmospheres on the reactivity of fresh and S-poisoned 2% w/w Pd/Al2O3/CeO2 catalysts for methane combustion.Over the fresh catalyst the decomposition/reformation processes of PdO occurring during cycles of CH4-reducing/lean combustion pulses allowed the complete recovery of activity losses possibly associated with H2O poisoning which were observed during prolonged exposure under lean combustion conditions. The presence of CeO2 markedly enhances both the activity losses under lean combustion conditions and the rate of PdO reoxidation/reactivation upon Pd redox cycle.Under lean combustion conditions, regeneration of catalyst deactivated by exposure to SO2-containing atmosphere required very high temperatures (above 750 °C) in order to decompose stable sulphate species adsorbed on the support. Treatments consisting of alternate CH4-reducing/lean combustion pulses allowed a complete recovery of activity at much lower temperatures (550–600 °C) due to the reduction of sulphates by CH4 activated on the surface of Pd metal. A protecting role of CeO2 on Pd poisoning due either to exposure to SO2-containing atmosphere or to spill-back of support sulphates species was also evidenced.
Keywords: Pd-catalysts; CH4 emission abatement; CH4 combustion; Sulphur poisoning; Catalyst regeneration; Ceria;

Performance of NO x traps after high-temperature treatments in different redox environments was studied. Two types of treatments were considered: aging and pretreatment. Lean and rich agings were examined for a model NO x trap, Pt–Ba/Al2O3. These were done at 950 °C for 3 h, in air and in 1% H2/N2, respectively. Lean aging had a severe impact on NO x trap performance, including HC and CO oxidation, and NH3 and N2O formation. Rich aging had minimal impact on performance, compared to fresh/degreened performance. Deactivation from lean aging was essentially irreversible due to Pt sintering, but Pt remained dispersed with the rich aging. Pretreatments were examined for a commercially feasible fully formulated NO x trap and two model NO x traps, Pt–Ba/Al2O3 and Pt–Ba–Ce/Al2O3. Pretreatments were done at 600 °C for 10 min, and used feed gas that simulated diesel exhaust under several conditions. Lean pretreatment severely suppressed NO x , HC, CO, NH3 and N2O activities for the ceria-containing NO x traps, but had no impact on Pt–Ba/Al2O3. Subsequently, a relatively mild rich pretreatment reversed this deactivation, which appears to be due to a form of Pt–ceria interaction, an effect that is well known from early work on three-way catalysts. Practical applications of results of this work are discussed with respect to NO x traps for light-duty diesel vehicles.
Keywords: NO x storage; NO x reduction; Pt–Ba/Al2O3; Pt–Ba–Ce/Al2O3; Ceria; Thermal deactivation;