M. Faraldos

Partial oxidation of methane to formaldehyde on silica-supported transition metal oxide catalysts

Abstract This work describes the partial oxidation of methane on high surface area silica-supported redox oxide catalysts (MO x /SiO 2 ; M = V, Mo, W and Re). Formaldehyde, C 2 H n , and CO 2 are primary products obtained in this reaction, while CO originates from further oxidation of formaldehyde and hydrocarbons. Supported vanadium oxide was found to be the most reactive due to its higher reducibility, thus providing additional sites for oxygen activation. Rhenium oxide exhibited high specific activity and selectivity, however it deactivates from sublimation of metal oxide under on-stream operation at high temperatures, typically above 773 K. Results suggest a reaction scheme where oxygenates and oxygen-free intermediates are present yielding HCHO, CO x and C 2 H n hydrocarbons.

Hydrogen transfer on USY zeolites during gas oil cracking: Influence of the adsorption characteristics of the zeolite catalysts

Abstract In this work, the hydrogen transfer activity of two series of HY zeolites dealuminated by steam and by SiCl 4 (24.47-24.24 A unit cell) has been measured from the butene/butane ratio in the products obtained during the cracking of a vacuum gas oil at 756 K. With the steam-dealuminated zeolites, a sharp decrease in the ratio of hydrogen transfer to cracking is observed when the number of Al atoms per unit cell falls below 10. On the other hand, in samples dealuminated by SiCl 4 , this ratio changes very little with dealumination. These results cannot be explained assuming the need for adjacent acid sites for the hydrogen transfer. We have found, by adsorption measurements of n -butane and 1-butene, that the changes in the relative rates of bimolecular (hydrogen transfer) to monomolecular (cracking) reactions, observed with dealuminated HY zeolites, can be explained by the changes in the adsorption capacity and adsorption selectivity which occur on zeolites dealuminated at different levels by different dealumination procedures, and which are due to changes in the electric fields inside the pores.

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.

Bone Diagenesis at Azokh Caves

Bone diagenesis is a set of processes by which the organic and mineral phases and the structure of bone are transformed during fossilization. To understand how these processes have affected skeletal material recovered from Azokh Caves (particularly the organic preservation), we measured ‘diagenetic parameters’ of skeletal material from Holocene, Late Pleistocene and Middle Pleistocene deposits from Azokh Caves. Additionally, we used this study to further test the application of both nitrogen adsorption isotherm analysis and mercury intrusion porosimetry for measuring the porosity of fossil bone. The skeletal material from the Pleistocene layers of Azokh Caves can be characterized as generally poorly preserved (especially collagen preservation). Porosity values of the bones are lower than might be expected as many bones show evidence of extensive infilling of the pores with secondary minerals. The pore infilling in the Middle Pleistocene layers is most extensive and this type of preservation has not previously been described in archaeological material.

STRUCTURAL FEATURES OF SILICA-SUPPORTED VANADIA CATALYSTS AND THEIR RELEVANCE IN THE SELECTIVE OXIDATION OF METHANE TO FORMALDEHYDE

The direct conversion of methane to formaldehyde and methanol in a single catalytic step in sufficiently high yield is an extremely attractive process for the conversion of natural gas to other useful fuels and chemicals. Both the homogeneous and heterogeneous processes have been studied under varied conditions1–3 although progress towards obtaining a yield that would make such a process industrially viable has been very slow4–22. Nearly all of these studies have involved redox oxides4,5,7, and more specifically, silica supported heteropolyacids6 and metal oxide catalysts8–22. From this large body of work, there is a considerable range of conditions over which the CH4/oxidant stoichiometry has been varied (20 and 0.5), although the temperature has been kept in a narrow window (723–923 K) as a result of the extremely low reaction rate at low temperatures while above 900 K COx formation becomes much more dominant. These limited yields arise from the unfavourable ratio of the reactivity of formaldehyde and methanol to that of methane. As shown by Spencer et al..8,9, the rate constant for the HCHO oxidation to CO derived from their data is 50–100 times higher than the rate constant for methane conversion.