A. Bahamonde

Photocatalytic destruction of toluene and xylene at gas phase on a titania based monolithic catalyst

Abstract Toluene and xylene were subjected to gas-solid heterogeneous photocatalytic oxidation on a titania based monolithic catalyst, in order to investigate the potential of solar-driven detoxification as a clean and safe method for air purification and gas phase waste destruction. Thus, gaseous streams with toluene or xylene were conducted through a monolithic catalysts based on titania dispersed on a fibrous silicate and irradiated with a Xenon lamp in the presence of air, at process temperatures from 150 to 450°C. Destructions levels higher than 96% were achieved for toluene and 99% for xylene at Area Velocity values in the range of 5–8 m h-1. A non-negligible number of undesirable sub-products (furans and benzofurans) were identified in partial oxidation conditions. The concentration of these sub-products was higher in the thermal process than with the photocatalytic system. Textural properties of the catalyst, the nature of phases and their distribution on the surface and light absorption properties were studied using techniques such as mercury intrusion porosimetry, scanning electron microscopy (SEM-EDX), X-ray diffraction and diffuse reflectance UV-Vis. spectroscopy.

Pillared clay and zirconia-based monolithic catalysts for selective catalytic reduction of nitric oxide by methane

Abstract New monolithic catalysts based on zirconia and pillared clays (PILC) have been studied for NOx removal by CH4 in the presence of oxygen. A comparative study of the influence of ZrO2 from various commercial sources for the system Pd–ZrO2 and the effect of the noble metal chosen for the system NM–PILC was carried out, trying to correlate the catalytic activity with the physico-chemical properties of these catalysts. The obtained results indicate that structure and surface acidity of the support plays an important role on the selectivity to NOx reduction, although properties such as the surface area or pore volume could also determine the overall activity of the monolithic catalysts.

Kinetic study of the selective reduction of nitric oxide over vanadia-tungsta-titania/sepiolite catalyst

A kinetic study of the reduction of nitric oxide by ammonia in the presence of oxygen on a novel catalyst prepared as a physical mixture of V2O5-WO3/TiO2 catalyst and a natural silicate (sepiolite) was carried out. The steady-state differential reactor data were fitted to several equations using a discriminating method based on physical and statistic criteria. The best fit was obtained from a model involving adsorption of ammonia and oxygen which react with nitric oxide from the gas phase following an Eley-Rideal mechanism. The equation considered for this model reproduces well the experimental results obtained in a differential regime. Important limitations by internal diffusion were determined when the reaction took place in an integral regime. (Less)

Influence of the binder on the properties of catalysts based on titanium-vanadium oxides

The influence of the nature of the binder and its concentration in V2O5/TiO2 catalysts on their mechanical and catalytic properties has been studied. The characterization analysis showed that the agglomeration mechanism is different when an inorganic acid, such as H3PO4, or a natural silicate, such as sepiolite, were used. Two different patterns are proposed, which explain the effect of these binders on the performance of this type of catalyst in the selective catalytic reduction of NOx with NH3.

Titania based platinum monolithic catalysts for lean-burn DeNOx process

Monolithic catalyst supports were prepared with mixtures of titanium dioxide and a natural magnesium silicate. Some properties of relevance to their scale-up for industrial applications using monoliths manufactured with various commercial titanias and treated at different temperatures were compared. Thus, their textural properties, anatase phase stability and axial strength were evaluated. Taking into account these results, a support was selected for the preparation of platinum catalysts, which were prepared by varying the impregnation time and the platinum solution concentration. Equations were obtained describing the dependence of the catalyst platinum content on each of these parameters. Catalyst activities were tested in the catalytic reduction of nitrogen oxide with propylene in lean-burn conditions.

Characterization of alumina:sepiolite monoliths for use as industrial catalyst supports

A series of honeycomb monolithic catalyst supports based on alumina, sepiolite and mixtures of the two were prepared. The textural characterization of these was carried out after heat treatments up to 1473 K, in order to assess the relative merits or drawbacks in the use of sepiolite as a possible admixture to improve the mechanical strengths of the monoliths, whilst preserving high specific surface areas and porosities.

Selectivity of hydrogen peroxide decomposition towards hydroxyl radicals in catalytic wet peroxide oxidation (CWPO) over Fe/AC catalysts

Two Fe/AC catalysts prepared with different iron precursors (iron nitrate and iron pentacarbonyl) and the same AC support have been tested in H(2)O(2) decomposition in presence and absence of methanol, a known strong scavenger of hydroxyl radicals, to investigate the selectivity towards .OH formation in this reaction and their behavior in the CWPO of phenol. The catalyst prepared with iron nitrate, with the most oxidized surface and the highest Fe surface content, seems to favor a higher selectivity towards .OH formation in CWPO allowing for complete phenol conversion and a significant TOC removal, with the highest mineralization degree at 50 degrees C and atmospheric pressure. Fe/AC catalysts were more efficient in the CWPO of phenol than in methanol presence due to a better use of the oxidant since adsorbed phenol on catalyst surface minimizes inefficient H(2)O(2) decomposition to H(2)O and O(2)(g). The influence of the initial H(2)O(2) concentration on phenol oxidation with this catalyst was also studied. A theoretical stoichiometric amount of H(2)O(2) for complete oxidation of phenol was chosen as the best starting concentration since auto-scavenging reactions can be minimized and it is sufficient for oxidizing phenol and the aromatic intermediates.

The use of sepiolite in the preparation of titania monoliths for the manufacture of industrial catalysts

Abstract In this work the merits of the use of a natural fibrous mineral, sepiolite, as a binder to produce titania based monoliths of high mechanical strength and abrasion resistance is discussed. The monoliths of square channels were conformed with an initial 7.5 channels cm −2 and 1 mm wall thickness. The textural characterization was made by mercury intrusion porosimetry (MIP), nitrogen adsorption/desorption (BET), and X-ray diffraction (XRD). The mechanical resistance, dimensional changes and weight losses at each stage of heat treatment were also determined. The thermal expansion coefficients (TEC) of the monoliths were determined between 200° and 400°C, since in practice the usual working temperature of DENOX catalysts lies between 250°–350°C.

Antimicrobial and antibiofilm efficacy of self-cleaning surfaces functionalized by TiO2 photocatalytic nanoparticles against Staphylococcus aureus and Pseudomonas putida

A photocatalytic sol of TiO2 nanoparticles has been used for creating self-cleaning antimicrobial flat and porous glass surfaces. The substrates were irradiated to study their photocatalytic properties and behavior in the presence of biofilm-forming bacteria. Smooth glass surfaces and glass microfiber filters were covered with 1.98×10-3±1.5×10-4gcm-2 and 8.55×10-3±3.0×10-4gcm-2 densities, respectively. Self-cleaning properties were analyzed using the methylene blue 365nm UV-A photodegradation test. TiO2-coated filters achieved rapid and complete photodegradation of methylene blue because of the better TiO2 dispersion with respect to the glass slides. The effect of functionalized surfaces on the growth and viability of bacteria was studied using the strains Staphylococcus aureus and Pseudomonas putida. After irradiation (2h, 11.2Wm-2, 290-400nm), the initially hydrophobic surface turned hydrophilic. The antibacterial effect led to extensive membrane damage and significant production of intracellular reactive oxygen species in all TiO2-loaded irradiated specimens. The reduction of cell viability was over 99.9% (>3-log) for TiO2 on glass surfaces. However, the polymeric extracellular matrix formed before the irradiation treatment was not removed. This study highlights the importance of bacterial colonization during dark periods and the difficulty of removing the structure of biofilms.

Effect of water composition on the photocatalytic removal of pesticides with different TiO2 catalysts.

The objective of this work is double—firstly to explore the photocatalytic efficiency of five different commercial TiO2 catalysts in the photodegradation of a mixture of pesticides classified by the EU as priority pollutants and secondly to analyze the correlation between their physicochemical properties and the inhibition of the studied photocatalytic process when natural water was employed. Photocatalytic efficiencies when ultrapure water was used seem to point out that surface area was not a prerequisite for the photodegradation of the selected mixture of pesticides. On the other hand, significant differences in total organic carbon (TOC) conversions were obtained with the two studied water compositions. On one side, Evonik materials appear to be mostly inhibited when natural water was employed, whereas on the other, it should be remarked that anatase Sigma-Aldrich (SA) and, particularly, Hombikat UV100 (HBK) materials presented a very limited photo-efficiency inhibition or even a higher initial rate of TOC removal when a natural water matrix was used, probably due to their specific surface properties (PZC, SBET). Therefore, heterogeneous photocatalysis has proved to be a promising technology for the degradation of the selected mixture of pesticides where the final photo-efficiency of the five commercial titania catalysts studied here responds to a complex balance between its surface and structural properties.