Applied Catalysis B, Environmental (v.63, #1-2)

IFC (CO2).



Tungstated zirconia catalyzed bromination of phenol red under nearly neutral solution by She-Tin Wong; Chi-Chau Hwang; Chung-Yuan Mou (1-8).
The performance of tungstated zirconia catalysts prepared by co-precipitation (WZ) and impregnation (W/m-ZrO2) techniques in phenol red bromination reaction was tested. Both types of catalysts showed excellent activity in this reaction in aqueous solution. The activity of WZ increases as the W loading decreases and the most active 0.6WZ catalyst contained highly dispersed WO x of low surface density on zirconia. The W/m-ZrO2 catalysts showed even higher activity in this reaction but maximum performance is observed for 1.3W/m-ZrO2 instead. The active site for the redox reaction is probably the monomer or dimer of WO x with a single oxo group whereas low surface density of WO x provides enough space on zirconia for the adsorption of phenol red without blocking the redox sites.
Keywords: Tungstated zirconia; Mesoporous zirconia; Phenol red; Bromination; XPS; EXAFS;

Methane combustion over PdO-alumina catalysts: The effect of palladium precursors by Lílian Maria Tosta Simplício; Soraia Teixeira Brandão; Emerson Andrade Sales; Luca Lietti; François Bozon-Verduraz (9-14).
The role of palladium precursors and the preparation route in the catalytic properties of PdO/Al2O3 catalysts toward methane oxidation was investigated in this paper. The catalysts were prepared using palladium chloride, nitrate and acetylacetonate as precursors and the preparation routes employed were impregnation of alumina with solutions of these precursors and the polyol method, in which palladium deposition is carried in a liquid polyol, e.g. ethylene glycol. All catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), surface area measurements and temperature programmed desorption of O2 (TPD). Unsteady-state methane oxidation was carried out by temperature-programmed surface reaction (TPSR). The results obtained suggested that the use of different palladium precursors and preparation routes played an important role on the properties of the catalysts, as palladium particle size, thermal stability of PdO and catalytic properties toward methane combustion. The use of palladium acetylacetonate as precursor by the impregnation method generated well-dispersed PdO particles on alumina. Regarding the PdO thermal stability and the activity toward methane combustion, this catalyst also presented the highest thermal stability and catalytic activity.
Keywords: Methane combustion; Pdo-alumina catalysts; Palladium precursors;

Phenol degradation using hydroxyl radicals generated from zero-valent iron and hydrogen peroxide by David H. Bremner; Arthur E. Burgess; Didier Houllemare; Kyu-Cheol Namkung (15-19).
The degradation of the model pollutant phenol with hydroxyl radicals generated from zero-valent iron and hydrogen peroxide has been investigated by means of HPLC analysis of the intermediates. The optimum conditions for degradation utilise the continuous presence of iron metal, acidic pH and relatively concentrated hydrogen peroxide (9.5 M). When less stringent conditions were used, the products obtained from the decomposition are broadly the same but are formed over a much longer timescale. The intermediates in the oxidation were identified as catechol, hydroquinone, benzoquinone, maleic acid and a relatively stable product, tentatively identified as an organic complex of iron and oxidised catechol.
Keywords: Fenton reaction; Oxidation; Organic pollutants;

Sodium titanate nanorods: Preparation, microstructure characterization and photocatalytic activity by Václav Štengl; Snejana Bakardjieva; Jan Šubrt; Eva Večerníková; Lorant Szatmary; Mariana Klementová; Vladimir Balek (20-30).
A method for the preparation of sodium titanate nanorods with diameter around 50 nm and lengths up to 2–3 μm is described. The precursor prepared by the reaction of sodium titanate with ethylene glycol readily aggregated into 1D nanostructures. During heating of this precursor up to 900 °C the glycolate complex of sodium titanate decomposed and a crystalline product of the chemical composition Na2Ti6O13 with the morphology of nanorods was formed. The initial sodium titanate sample as well as samples heat treated to 550–900 °C, respectively, were characterized by X-ray diffraction, infrared spectroscopy, electron microscopy (SEM, TEM, HRTEM) thermal analysis methods (DTA–TG-coupled with mass spectroscopy and emanation thermal analysis) as well as by surface area and porosity measurements. It was demonstrated that the nanorods formed by heating of the precursor at 900 °C/2 h exhibit a good photacatalytic activity for the decomposition of 4-chlorophenol in an aqueous slurry under UV radiation.
Keywords: Sodium titanate; Nanorods; Ethylene glycol; Photocatalytic activity; Surface area; Porosity; SEM; HRTEM; XRD; 4-Chlorophenol;

A fine route to tune the photocatalytic activity of TiO2 by S. Sakthivel; M.C. Hidalgo; D.W. Bahnemann; S.-U. Geissen; V. Murugesan; A. Vogelpohl (31-40).
Different nanocrystalline photoactive TiO2 catalysts were prepared by the hydrolysis of titanyl sulphate (TiOSO4). Some important parameters in the preparation procedure, such as pH, calcination temperature, hydrolysing agent and temperature and ageing time were varied, leading to TiO2 with very different physical properties, i.e. crystalline phase composition, crystallite size, surface area, light absorption properties and bandgap energy. The photocatalytic activity of the TiO2 catalysts was evaluated using the photooxidation of dichloroacetic acid (DCA) as probe reaction. The experimental results revealed that the photocatalytic activity of the samples was greatly affected by their physical properties and therefore by the experimental conditions employed in their preparation. Using the optimum preparation parameters, TiO2 with an activity notably higher than the commercial TiO2 Degussa P-25 was obtained. Photoelectrochemical properties of both materials were studied for the hypothesis of enhanced activity.
Keywords: Titanium dioxide; Titanyl sulphate; Photocatalysis; Flatband potential; DCA;

Preparation of nanocrystals hydroxyapatite/TiO2 compound by hydrothermal treatment by Hu Anmin; Lei Tong; Li Ming; Chang Chengkang; Ling Huiqin; Mao Dali (41-44).
Hydroxyapatite/TiO2 compound had been successfully synthesized by hydrothermal treatment of HAp powders and Ti(OH)4 solutions at 100–190 °C with different hydroxyapatite/TiO2 proportion. The hydroxyapatite/TiO2 compounds were characterized by various methods including FT-IR, BET, TEM, EDX, XRD and ICP. TEM observation showed that small granule TiO2, identified as anatase crystals of 3–5 nm, were deposited on HAp rod-like crystals. X-ray diffraction results indicated that hydroxyapatite and anatase phase appeared and with higher colloidal TiO2 added into the HAp/TiO2 compound, there was more anatase appeared. With increasing colloidal TiO2 addition, FT-IR spectroscopy revealed PO4 3− band at 572, 602, 962, 1046, 1090 cm−1 became decreasingly, and ICP spectrometry revealed the content of Ti4+ increased. The photocatalytic activity of the hydroxyapatite/TiO2 particles was examined by decomposition of methylene blue (MB). The results showed that photocatalytic properties of hydroxyapatite/TiO2 compound are more effective than that of hydroxyapatite and TiO2.
Keywords: Hydroxyapatite; TiO2; Hydrothermal; Photocatalytic activity; Nanocrystal;

Structural and surface approach to the enhanced photocatalytic activity of sulfated TiO2 photocatalyst by G. Colón; M.C. Hidalgo; G. Munuera; I. Ferino; M.G. Cutrufello; J.A. Navío (45-59).
TiO2 materials prepared by sol–gel method and then impregnated with sulfuric acid and further calcined at different temperatures show high photon efficiencies for the photocatalytic degradation of phenol under UV-illumination. Best photocatalyst was obtained after calcination around 700 °C, giving specific activities (i.e. per m2) significantly higher than those exhibited by similarly prepared non-sulfated TiO2 or by pure Degussa P25. Structural analysis of these new materials by XRD, TG–DTG and Raman spectroscopy shows that once calcined at 700 °C the material was a well-crystallized, high surface area and sulfate-free 90% anatase. Surface characterization in this work by XPS, LEIS and 1H MAS-NMR confirms a complete loss of the sulfate and OH-groups, and a low XPS O/Ti-atomic ratio with the O(1s) peak shifted to higher binding energies (1.7 versus 2 ± 0.1 and 530.4 eV versus 529.8 eV, respectively, against the reference materials). This indicates the existence of oxygen vacancies, which give a broad band at 400–600 nm in the reflectance spectra. However, LEIS spectra show an O/Ti composition at the topmost exposed atomic surface layer similar to that of TiO2 reference materials. Adsorption microcalorimetry of pyridine gives a profile of acid sites quite similar to those found for reference anatase samples, what discards the presence of superacid sites as the origin of its enhanced UV-photoefficiency. A mechanism is proposed, on the basis of earlier results in the literature for acidic TiO2 surfaces, to explain the nature of these materials. We also try to correlate the contribution of the oxygen vacancies within the anatase sub-surface layers to the high photon UV-efficiency of the system and, likely, to an enhanced vis-photoactivity of these materials.
Keywords: Sulfated TiO2; Rietveld refinement; Surface acidity; Anatase–rutile; Oxygen vacancies; Photocatalysis;

This study describes the application of novel chemistry methods for the fabrication of robust nanostructured titanium oxide (TiO2) photocatalysts. Such materials can be applied in the development of efficient photocatalytic systems for the treatment of water. Mesoporous photocatalytic TiO2 films and membranes were synthesized via a simple synthesis method that involves dip-coating of appropriate substrates into an organic/inorganic sol composed of isopropanol, acetic acid, titanium tetraisopropoxide, and polyoxyethylenesorbitan monooleate surfactant (Tween 80) followed by calcination of the coating at 500 °C. Controlled hydrolysis and condensation reactions were achieved through in-taking of water molecules released from the esterification reaction of acetic acid with isopropanol. The subsequent stable incorporation of Ti–O–Ti network onto self-assembled surfactants resulted in TiO2 photocatalysts with enhanced structural and catalytic properties. The properties included high surface area (147 m2/g) and porosity (46%), narrow pore size distribution ranging from 2 to 8 nm, homogeneity without cracks and pinholes, active anatase crystal phase, and small crystallite size (9 nm). These TiO2 photocatalysts were highly efficient for the destruction of methylene blue and creatinine in water. High water permeability and sharp polyethylene glycol retention of the prepared photocatalytic TiO2/Al2O3 composite membranes evidenced the good structural properties of TiO2 films. In addition, the multi-coating procedure made it possible to effectively control the physical properties of TiO2 layer such as the coating thickness, amount of TiO2, photocatalytic activity, water permeability and organic retention.
Keywords: Titania; Photocatalyst; Photocatalysis; Photocatalytic; Thin film; Membrane; Sol–gel; Nanostructure; Surfactant; Dip-coating; Water permeability; Organic retention; Surface area; Porosity; Tween 80; Creatinine; Methylene blue;

Degradation of olive oil mill effluents by catalytic wet air oxidation by Doan Pham Minh; Pierre Gallezot; Michèle Besson (68-75).
The objective of this work was to investigate the catalytic wet air oxidation of p-coumaric acid, a biorecalcitrant phenolic compound typically found in olive oil wastewaters in the presence of Pt and Ru supported catalysts. The influence of the operating variables were established. The most important intermediates determined by HPLC measurements suggest a rapid attack by oxygen of the side-chain of p-coumaric acid, and the mineralization proceeds through different aromatic compounds reacting further to aliphatic intermediates (mainly acids). Important mineralization yields were achieved in the presence of the catalysts at 140 °C and 50 bar air. The importance of the nature of the support (TiO2, ZrO2) on the adsorption of p-coumaric acid was demonstrated.
Keywords: Catalytic wet air oxidation; Platinum and ruthenium heterogeneous catalysts; p-Coumaric acid; Olive oil mill effluents;

Thirteen different commercial TiO2 powders with specific surface areas varying from 9 to 335 m2/g and with isoelectric points (IEP) from 3 to 7.5 were investigated for their catalytic activity in E. coli inactivation. The TiO2 samples zeta potential, attenuation sizes and isoelectric points (IEP) were measured by the electroacoustic method. The influence of the initial pH of the TiO2 suspension was followed during the bacterial inactivation. It was observed that TiO2 Degussa P-25 consisting of an anatase-rutile powder inactivated E. coli with high kinetics that did not vary with the initial pH of the suspension. This was not the case for the other TiO2 samples used in this study. The IEP could be correlated with the catalytic activity of the commercial samples for most of TiO2 powders investigated. The lower the IEP of the TiO2, the lower the bacterial inactivation activity. By electron microscopy it is shown that the clusters of TiO2 Degussa P-25 are only in partial contact with E. coli K-12 (diameter 1 μm). The reasons for this behavior are discussed in terms of the interaction of the E. coli with TiO2.
Keywords: TiO2 photocatalysis; E. coli; Bacterial inactivation; Zeta potentials; TiO2 isoelectric points (IEP); Electron microscopy; Light intensity; Attenuation size; IEP;

A novel oxidative desulfurization process to remove refractory sulfur compounds from diesel fuel by Jeyagowry T. Sampanthar; Huang Xiao; Jian Dou; Teo Yin Nah; Xu Rong; Wong Pui Kwan (85-93).
Manganese and cobalt oxide catalysts supported on γ-Al2O3 have been found to be effective in catalyzing air oxidation of the sulfur impurities in diesel to corresponding sulfones at a temperature range of 130–200 °C and atmospheric pressure. The sulfones were removed by extraction with polar solvent to reduce the sulfur level in diesel to as low as 40–60 ppm. Oxidation of model compounds showed that the most refractory sulfur compounds in hydrodesulfurization of diesel were more reactive in oxidation. The oxidative reactivity of model impurities in diesel follows the order: trialkyl-substituted dibenzothiophene > dialkyl-substituted dibenzothiophene > monoalkyl-substituted dibenzothiophene > dibenzothiophene.
Keywords: Oxidative desulfurization; Diesel; Sulfur; Catalyst; MnO2/γ-Al2O3; Co3O4/γ-Al2O3; Solvent extraction;

Pure hydrogen production on a new gold–thoria catalyst for fuel cell applications by T. Tabakova; V. Idakiev; K. Tenchev; F. Boccuzzi; M. Manzoli; A. Chiorino (94-103).
A new gold catalyst was synthesized by deposition-precipitation of gold hydroxide on thoria. The catalyst showed extremely high catalytic activity at the lowest possible temperature for carrying out of water-gas shift reaction (WGSR) under experimental conditions. The measured degree of CO conversion at 393 K (GHSV = 4000 h−1) was 84%. The effect of space velocity and water vapor partial pressure on WGS activity was studied at different temperatures. The catalytic measurements testified high stability of Au/ThO2. HRTEM combined with EDS, X-ray diffraction and H2-TPR techniques were used for the catalyst characterisation. Detailed FTIR measurements of adsorbed CO at different temperatures on oxidized and reduced catalyst were performed. FTIR spectra were also collected during CO + O2 interaction at different temperatures, CO oxidation in the presence of hydrogen (PROX) and WGSR. Preliminary catalytic tests for CO oxidation in hydrogen-rich gas stream revealed that Au/ThO2 could be of interest as potential catalyst for the PROX process.
Keywords: Gold catalysts; Thoria; WGSR; PROX; HRTEM; TPR; FTIR spectroscopy;

The V2O5-WO3 catalysts loaded on the Ti-rich TiO2-SiO2-SO4 2− prepared by the coprecipitation method were investigated for the influences of the active components and the supports on the activities in SCR of NO by NH3 and in the oxidation of SO2 in comparison with a commercial V2O5-WO3/TiO2-SO4 2− catalyst. The physico-chemical properties of the catalysts were characterized by BET, XRD, IR, Raman, NH3-TPD, XPS and acidity measurements. The incorporation of sulfate to TiO2-SiO2 considerably increases the acidity of TiO2-SiO2, especially Brønsted acidity of the corresponding catalyst, resulting in the remarkable increase of the SCR activity and simultaneously, the addition of WO3 significantly enhances the SCR activity. The SCR activity changes depending on the calcination temperature of TiO2-SiO2-SO4 2−, which influences its acidity, surface area and titania crystallinity. The higher SCR activity was observed at high vanadia loadings above 2 wt.% as compared with the V2O5-WO3/TiO2-SO4 2− catalyst. This seems to be due to the fact that polymeric vanadates on the catalyst, which cause the oxidation of NH3 to N2O, are almost absent as evidenced by Raman analysis. The SO2 oxidation activity is increased by elevating the calcination temperature of TiO2-SiO2-SO4 2−, which shifts the oxidation state of vanadium species to the higher state, and the activity is slightly enhanced by WO3 but not changed by sulfate. The tendency of the increase in the SO2 oxidation activity with increasing V2O5 loadings is significantly smaller than the V2O5-WO3/TiO2-SO4 2− catalyst. This was attributed to the lower oxidation state of vanadium species, almost the absence of polymeric vanadates responsible for the SO2 oxidation and also a more strongly inhibiting effect of ammonia on the oxidation of SO2.
Keywords: SCR; SO2 oxidation; Sulfate; TiO2-SiO2-SO4 2−; V2O5-WO3/TiO2-SiO2-SO4 2−; Acidity;

Photocatalytic oxidation by oxygen of air in water suspension of TiO2-based catalysts was carried out for dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP)—simulants of warfare agents. Active photocatalysts were prepared via surface modification of standard photocatalyst Degussa P25 with platinum and palladium. The developed catalysts were about three-fold more active than traditionally best photocatalyst Degussa P25. Kinetic curves of DMMP oxidation on TiO2 and Pt/TiO2 are well approximated by the Langmuir–Hinshelwood model with competitive adsorption of oxygen and organophosphorus compound. The increase of activity of Pt/TiO2 is linked with higher oxygen adsorption constant or reaction rate coefficient. Photocatalytic oxidation can be scaled up to a larger reactor with the same reaction rates expressed as mmol l−1  min−1 in mineralization of DMMP. The batch recirculating reactor with total volume 3 l utilizes photocatalyst deposited over porous support and demonstrated higher oxidation rate and catalyst stability compared to suspended photocatalyst. Main criteria for mass-transfer process in the batch recirculating reactor were calculated to understand how concentration cross gradient depends on flow rate. The concentration of oxygen in reaction mixture changed with the stirring or recirculation rate and exerts strong influence on the oxidation rate.
Keywords: Batch reactor; Pt; TiO2; Pd; Phosphate; Phosphonate; CWA; Oxidation;

Photo-induced transformation of methylguanidine derivatives on titanium dioxide by Paola Calza; Claudio Medana; Claudio Baiocchi; Ezio Pelizzetti (124-130).
The photo-induced transformation of methyl and methyl acetic acid guanidine derivatives, which are the decomposition products of several pollutants, was studied adopting titanium dioxide as photocatalyst. The in-depth investigation of the overall process involved studying the evolution of intermediate compounds, the fate of organic nitrogen and the rate (and extent) of carbon mineralization. Intermediate products were identified with an HPLC/tandem MS instrument, thus enabling a transformation mechanism applicable to methyl-guanidinic derivatives to be defined. The derivatives are chiefly transformed through a combination of reductive and oxidative processes. Photocatalytically assisted hydrolysis, through sequential reactions involving •OH/e/H+, induces a demethylation process that, in all cases, leads to the formation of guanidine, then (very slowly) to its mineralization.Similarly, also with creatine and creatinine the main transformation pathway proceeds through a photocatalytically assisted hydrolysis that leads to the formation of 2-imino-imidazole-4-one (from creatinine) and guanidine acetic acid and methyl guanidine (from creatine). Guanidine is the ultimate intermediate compound recognized in these cases, too.The fate of nitrogen was also evaluated in all cases. The organic nitrogen is mainly released as nitrate ions, with [NH4 +]:[NO3 ] ratios ranging from 1:2 for creatine to 1:8 with methylguanidine.
Keywords: Methyl-guanidine; Photocatalysis; TiO2; Creatine; Creatinine; Intermediates; Fate of nitrogen;

The activity of honeycomb supported LaBOδ (B = Fe, Mn and Co) and La2NiO4 was tested for the catalytic flameless combustion (CFC) of methane and compared with their catalytic behaviour in powder form. Catalyst supporting brought about some modifications, mainly the complete loss of the suprafacial activity. Furthermore, thermal resistance of supported samples was checked through accelerated deactivation tests and showed to strongly depend on the nature of the B ion. Structural and morphological properties of fresh and aged catalysts, both in powder form (either pure or mixed with the primer precursor) and as honeycomb-supported samples, were compared to investigate the effect of each step of the dip-coating procedure. This allowed to shed light on the causes of the structural and chemical changes occurring during the wash-coating and leading to more or less severe decrease of performance and of thermal resistance of the final catalyst.
Keywords: Perovskites; Methane; Catalytic combustion; Lanthanum oxide; Supporting on honeycomb monoliths;

The methanol oxidation reaction on platinum alloys with the first row transition metals by Ermete Antolini; Jose R.C. Salgado; Ernesto R. Gonzalez (137-149).
In recent years there has been much activity in examining Pt alloys with first row transition metals as catalysts materials for DMFCs. In this work, the electrochemical oxidation of methanol on Pt–Co and –Ni alloy electrocatalysts is reviewed. The effect of the transition metal on the electrocatalytic activity of Pt–Co and –Ni for the methanol oxidation reaction (MOR) has been investigated both in half-cell and in direct methanol fuel cells. Conflicting results regarding the effect of the presence of Co(Ni) on the MOR are examined and the primary importance of the amount of non-precious metal in the catalyst is remarked. For low base metal contents, an enhancement of the onset potential for the MOR with increasing Co(Ni) amount in the catalyst is observed, whereas for high contents of the base metal, a drop of the MOR onset potential with increasing Co(Ni) is found. As well as the base metal content, an important role on the MOR activity of these catalysts has to be ascribed to the degree of alloying.
Keywords: Methanol oxidation; Platinum alloy catalysts; Nickel; Cobalt; Direct methanol fuel cell;

A novel scheme of integrated ion-exchange/catalytic denitrification process for the removal of excessive quantities of nitrate ions from groundwater is proposed, which employs two separate reactor units to considerably minimize the production of ammonium ions as a side product in subsequent regeneration cycles. In the first reactor unit, selective reduction of nitrates to nitrites is carried out at high pH value (above 11.0) in the presence of Pd-Cu/γ-Al2O3 bimetallic catalyst. At T  = 298 K and hydrogen partial pressure of 1.0 bar, up to 97% transformation of nitrates to nitrites was obtained, even at complete conversion of nitrate ions; the rest was found in the form of ammonium ions. In the second reactor unit, selective reduction of nitrites to nitrogen takes place at low pH value (4.5) over a Pd/γ-Al2O3 monometallic catalyst. A catalyst with higher dispersion (39%) of Pd clusters on the alumina carrier enables lower production of ammonium ions, the concentration of which was found below 0.5 mg/L for initial nitrite content up to 70 mg/L. Both Pd-Cu bimetallic and Pd monometallic catalysts were found chemically resistant in the investigated range of pH values (4.5–12.4). In comparison to the previous scheme of integrated ion-exchange/catalytic process, in which the denitrification step was conducted in a single, “liquid-full” reactor unit packed with a Pd-Cu/γ-Al2O3 bimetallic catalyst, the production of ammonium ions was reduced by an order of magnitude.
Keywords: Catalytic hydrogenation; Drinking water purification; Integrated process; Nitrate removal; Pd monometallics; Pd-Cu bimetallics;