V. Ragaini

Sono-photocatalytic degradation of 2-chlorophenol in water: kinetic and energetic comparison with other techniques

The degradation of 2-chlorophenol in water was kinetically investigated using the following different techniques, employed either separately or simultaneously, always with the same experimental set-up: light irradiation (315-400 nm), sonication, photocatalysis with different types of TiO2, photocatalysis with sonication. The influence of the reaction volume and of different gas mixtures, containing Ar and O2, as well as O2/O3, was also investigated. Finally, an energetic comparison among these different techniques was performed, focused on an industrial application of some of them.

VOC removal by synergic effect of combustion catalyst and ozone

The synergic effects of the combustion catalyst BaCuOCr2O3/Al2O3 and ozone, used as strong oxidant species in the combustion of various VOCs, were studied. The experiments were performed with five different methods by feeding the organics with air (1000 ppmV) before (methods 2 and 4) and after the ozone generator (methods 1, 3 and 5), they entered into the catalytic reactor (methods 1, 2 and 3) or were directly analyzed (methods 4 and 5). The concentration profiles of the organics were compared as a function of the reaction temperature (from 100 to 500°C) for the methods 1, 2 and 3 and as a function of the peak voltage of the ozone generator (2–10 kV), that is the ozone concentration (up to 2000 ppm) for methods 4 and 5. Ozone strongly reacted in the gas phase with aromatic molecules and organics having functional groups. Moreover, a positive ionizing effect produced by the corona discharge in the ozone generator on the destruction of the organics was found too.

Dispersion measurement by the single introduction method coupled with the back-sorption procedure: A chemisorption and TPD study of the different chemisorbed hydrogen species: II. Pd on Alumina

Abstract In this work a comparison is made between values of the metal surface areas of several alumina-supported Ru, Rh, and Pt catalysts obtained by hydrogen adsorption isotherms, here defined as the “Multiple Introductions” method, and those calculated by a very simple technique defined as the “Single Introduction” method. With the systematic application of the procedure designated “Back-Sorption,” particularly good agreement is observed between the two techniques if dispersion is calculated on the basis of the irreversibly adsorbed hydrogen. “Back-Sorption” is a necessary practice because of the presence on the above-mentioned metals of more than one adsorbed species not to be considered for the calculation of dispersion, as shown in a more detailed manner for a Pt Al 2 O 3 catalyst using temperature-programmed desorption. Whenever the conditions for its applicability are satisfied, the Single Introduction method provides a faster and more reliable way to measure the dispersion of metal-supported catalysts than the Multiple Introductions technique.

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO2Prepared by Ultrasound

Nanocrystalline TiO2samples were prepared by promoting the growth of a sol–gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NOxin air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p3/2region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energyper volume (Etot/V) and not the acoustic intensity or the pulsed/continuous mode.

Preparation of highly dispersed CuO catalysts on oxide supports for de-NOx reactions

CuO based catalysts dispersed on silica-alumina supports at low (0.56 wt.%) and high (13 wt.%) Al(2)O(3) content were prepared by adsorption method with or without ultrasound treatment. The catalysts obtained were studied in their bulk (atomic absorption, X-ray diffraction, temperature programmed reduction) and surface (N(2) adsorption and X-ray photoelectron spectroscopy) properties. Significant differences between the series of catalysts prepared over the two supports in terms of size of the CuO aggregates and of their redox properties were evidenced. All the catalysts were tested in the selective catalytic reduction of NO(x) using C(2)H(4) as reducing species (HC-SCR process) in highly oxidant atmosphere. The CuO-catalysts prepared using ultrasounds were the most active. Moreover, they displayed a peculiar activity being able to activate NO both by reducing it to N(2), in larger extent, and by oxidizing it to NO(2).

An XPS study on ruthenium compounds and catalysts

Abstract The binding energy (BE) of the relevant peaks of several ruthenium compounds have been measured with a monochromatic small spot XPS. The BE of the 3d 5 2 level of ruthenium is in the range 279.91–282.88 eV. The variation of BE is due either to the variation of the oxidation state or to the different counter-ion. A series of catalysts with varying amounts of ruthenium supported on alumina and prepared using different precursors was also analyzed. The presence of more ruthenium species other than the metal was observed. On the basis of the values previously obtained on unsupported compounds, the species with higher BE were assigned to oxides. On all the samples prepared from RuCl3, an additional peak at a very high BE (283.79 eV) has been observed. This peak is related to the presence of chlorine on the surface: it is suggested that it is related to a charge transfer interaction. The influence of this species on the CO reactivity in the Fischer-Tropsch reaction is discussed.

Low temperature reduction of gallium in a Ga2O3/HZSM-5 catalyst

Abstract Several experiments were performed to provide convincing evidence for low temperature gallium reduction in a Ga2O3/HZSM-5 catalyst. XPS measurements showed the appearance of a GaI signal after in situ hydrogen reduction at temperatures ranging between 373 and 673 K. No transfer of reduced gallium species from Ga2O3 to the zeolite particles was detected. A revision of the existing reduction mechanism is thus proposed. It is suggested here that the actual role of the HZSM-5 zeolite could be to provide a kind of activated hydrogen able to reduce Ga2O3.

Ultrasound and microwave assisted synthesis of high loading Fe-supported Fischer–Tropsch catalysts

Supported iron-based Fischer-Tropsch (FT) catalysts with high loading of active metal have been prepared using both traditional and innovative methods. In these latter the impregnation of silica support has been performed by adding a step involving an ultrasound (US) or a microwave (MW) treatment to improve the metal deposition and to increase the catalyst activity. FT results have indicated the catalysts prepared by US as the most efficient, particularly when sonication is performed in argon atmosphere. MW prepared samples have given results very similar to those obtained with the traditional method. In order to explain the different catalytic activity, all the samples have been characterized by BET, TPR, SEM, TEM, XRD and micro-Raman analyses.

A new method to clean industrial water from acetic acid via esterification

Abstract The valorisation of very low concentration of acetic acid (6%, w/w) was investigated by reacting with n-butanol and 2-ethyl-1-hexanol taking advantage of the different solubilities of acetic acid and acetic ester in water. The esterification of very diluted solution of acetic acid with alcohol is a reversible reaction and the conversion is greatly restricted by equilibrium limitation. Therefore, the peculiarity of the present method is to shift the reaction equilibrium towards the ester and not towards the reagents, thermodynamically favourite, because of the large amount of water. Different acid catalysts were tested in both homogeneous (sulphuric acid) and heterogeneous phase (polymeric resins and sulphated zirconia) to optimise the process efficiency.

Fischer—Tropsch synthesis on alumina-supported ruthenium catalysts I. Influence of K and Cl modifiers

Abstract Fischer-Tropsch synthesis (FTS) has been studied at 5 · 103 Pa, at 508 K, an H2/CO=2/1 molar ratio on Ru/γ-Al2O3 catalysts (1% Ru wt./wt.), using Ru(AcAc)3 (AcAc standing for acetylacetonate), RuCl3 and K(AcAc) as precursors; K/Ru and Cl/Ru molar ratios ranged from 0.14 to 2.18 and from 1.31 to 3.71, respectively. As Ru catalysts for FTS undergo easy alteration resulting from coke deposition, the results from kinetic runs were collected using both fresh catalysts (at 5–10 min time-on-stream) and also when steady state conditions were reached (about 150 min time-on-stream). The influence of K/Ru and Cl/Ru ratios on CO conversion and on the selectivity of the formation of different products in the reaction has been examined. Changes in activity, during the regeneration procedures of the catalysts, differ significantly when the precursor is Ru(AcAc)3 (increase in activity after regeneration cycle) or RuCl3 (significant deactivation with a decrease in Ru surface concentration, as determined by XPS).