Antonella Gervasini

Study of the acidic character of modified metal oxide surfaces using the test of isopropanol decomposition

The evolution of the acid/base properties of a series of oxide supports (alumina, magnesia and silica) modified by increasing loadings of additive ions (Li+, Ni2+, and SO42-) from 1 to 50% of the support surface coverage is reported using the catalytic test of isopropanol decomposition, studied as a function of the reaction temperature. The calculated kinetic parameters Ea, A, and ΔS≠ permit interpretation of the reaction mechanism with relation to the acidity/basicity of the modified surfaces. The series of alumina oxides, due to the amphoteric properties of the surfaces, decomposed isopropanol through an E2 mechanism leading to propene and di-isopropyl ether formation. The selectivity to the two products was dependent on the strength of the basicity (addition of lithium and nickel) or on the acidity (addition of sulfate) of the surfaces. Magnesia series oxides dehydrated isopropanol through an E1b mechanism due to the presence of very strong basic surfaces possessing some weak acid sites. The very weak amphoteric character of silica was strengthened by the loading of the three additives; the modified silica surfaces displayed enhanced decomposition activity with respect to pure silica.

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.

Characterization of the textural properties of metal loaded ZSM-5 zeolites

Abstract The textural properties of metal ion over-exchanged zeolites, Co–, Cu–, Ni–ZSM-5, were compared with those of the parent ZSM-5 by nitrogen adsorption measurements and photoelectron spectroscopy. The treatment of the adsorption isotherms permitted a thorough characterization of the microstructure of the samples. A first estimation of the microporous volume was made by the Dubinin–Radushkevich method. The “ t -plot” method was used to determine the external surface and to obtain another estimation of the microporous volume. Effective micropore size distribution was obtained with the Horvath–Kawazoe approach. The Dubinin–Radushkevich method overestimated the microporous volume of the zeolites, in particular when the solid had an important external surface. It is shown that Cu–ZSM-5 had micropore size and micropore size distribution very close to those of ZSM-5, whereas Co–ZSM-5 and Ni–ZSM-5 had lower microporous volumes and larger external surfaces. The external to internal (microporous) surface ratios, r s , and the mesoporous to microporous volume ratios, r v , are proposed as practical parameters to classify the solids with respect to their microstructure. ZSM-5, a pure microporous solid, has low values of both r s and r v parameters. Ni– and Co–ZSM-5 have high r s ad r v parameters, indicative of some degree of mesoporous character. Cu–ZSM-5 has intermediate characteristics, typical for micro-mesoporous solid. XPS measurements confirmed that copper ions penetrated to a greater extent in the channels of ZSM-5 zeolite than cobalt and nickel ions, which merely deposited on the external surface of ZSM-5 zeolite as oxidic aggregates.

Hydrogenation of carbon monoxide: evidence of a strong metal-support interaction in Rh/ZrO2 catalysts

Abstract Temperature-programmed desorption (TPD) studies are reported on a series of Rh catalysts dispersed on ZrO2 and γ-Al2O3 and activated under H2 flow at 250, 400, and 600°C. While the high temperature of activation did not show any significant difference in the Rh γ-Al 2 O 3 samples, in the case or Rh ZrO 2 a pronounced effect is quite evident. The experimental observations have been associated to a modification of the metal-support interface, for which a possible model is suggested. Parallel experiments in the hydrogenation of carbon monoxide at 220°C and P = 1 atm have shown a sharp decrease in the overall activity while the selectivity was virtually unaffected by the temperature of reduction.

Gold on Carbon: Influence of Support Properties on Catalyst Activity in Liquid-Phase Oxidation

Gold-on-carbon catalysts have been prepared from a preformed metallic phase (metal sol). Using, as the support, active carbons of different microstructure and surface properties, we found that each carbon affected differently the reactivity of the same gold particle in a standard liquid-phase oxidation, indicating that a specific metal–support interaction does exist, probably connected to the density of phenolic groups at the surface.

Characterization of copper-exchanged ZSM-5 and ETS-10 catalysts with low and high degrees of exchange

Abstract Two different copper molecular sieve systems (Cu-ZSM-5 and Cu-ETS-10) have been prepared with different copper loadings from under- to overexchanged levels. The adsorption and surface properties have been studied using calorimetry of adsorbed NO, CO, C 2 H 4 and NH 3 probe molecules. The respective numbers and strengths of CO and NO adsorption sites on the surface, which are related to the ratio of Cu(I) to Cu(II), depend on the matrix type, location of the metal ions, and degree of Cu exchange. Cu(I) was the prominent copper species in Cu-ETS-10, and the number of Cu(I) species increased as the level of copper loading increased. In overexchanged Cu-ZSM-5, the Cu(I) sites were less prominent but more stable, as shown by temperature programmed reduction (TPR) experiments. The catalytic activity for NO reduction by C 2 H 4 in oxygen-rich atmosphere appeared to depend on the Cu(II)/Cu(I) ratio, but also on the adsorption properties towards the NO reactive gas. The samples presenting the best NO adsorption properties are the most active in the NOC 2 H 4 O 2 reaction.

Hexagonal and Cubic Thermally Stable Mesoporous Tin(IV) Phosphates with Acidic and Catalytic Properties

Thermally stable hexagonal and cubic mesoporous tin(IV) phosphates have been synthesised via a fluoride route using alkyl di- or tri-methylammonium bromide surfactants. X-ray powder diffraction and HREM show that the hexagonal phase exhibits a MCM-41 organisation while the structure of cubic phase is similar to those of the micellar cubic solid SBA-1. Removal of the surfactant by calcination under air atmosphere of both phases does not destabilise the framework and leads to mesoporous solids exhibiting surface area within the 200–630 m 2 /g range and pore sizes between 12 and 25 . Finally, microcalorimetric studies of the adsorption of NH 3 and SO 2 , indicated that both solids exhibit both a strong acidic and a weak basic character. First de-NOx catalytic tests have also shown positive results for both solids, which indicates that these porous solids represent an interesting family of materials with good catalytic properties.

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).

Structural, textural and acid–base properties of carbonate-containing hydroxyapatites

Carbonate-containing hydroxyapatites with different Ca/P ratios and optionally containing Na+ cations were successfully synthesized using a precipitation method. The solids were extensively characterized by XRD, LEIS, XPS, IR, TGA and NMR. Further, their acid–base properties were determined by NH3-TPD, PEA-XPS, CO2-TPD and by pulsed liquid chromatography using benzoic acid as a probe. The so-obtained structural, textural and acid–base properties could be finely correlated to give a clear picture of the system. The acidic properties of hydroxyapatites were attributed to Ca2+, surface HPO42− and OH− vacancies and the basic properties were attributed to PO43−, OH− and CaO species. The fine-tuning of the amount, of the nature and the strength of acid–base properties derived by varying the carbonate content in hydroxyapatites can find applications in catalysis, which was illustrated by isopropanol reactivity.

Hydrolysis of disaccharides over solid acid catalysts under green conditions

The hydrolysis of the three most important disaccharides: sucrose, maltose and cellobiose, has been comparatively studied in mild conditions (50-80°C) in water over several solid acid catalysts. Strong acidic resins (Amberlite A120 and A200), mixed oxides (silica-alumina and silica-zirconia), and niobium-containing solids (niobic acid, silica-niobia, and niobium phosphate) have been chosen as acid catalysts. The hydrolysis activity was studied in a continuous reactor with fixed catalytic bed working in total recirculation mode. Rate constants and activation parameters of the hydrolysis reactions have been obtained and discussed comparing the reactivity of the α-1,β-2-, α-1,4-, and β-1,4-glycosidic bonds of the employed disaccharides. The following order of reactivity was found: sucrose >> maltose > cellobiose. The sulfonic acidic resins, as expected, gave complete sucrose conversion at 80°C and good conversions for cellobiose and maltose. Among the other catalysts, niobium phosphate provided the most interesting results toward the disaccharide hydrolysis, which are here presented for the first time. Relations between activity and surface acid properties are discussed.