Environmental Reactions of Air-Quality Protection on Eco-Friendly Iron-Based Catalysts

A series of iron functionalized hydroxyapatite (Fe/HAP) samples with different metal loading (2 < wt.% Fe < 13) was prepared by a flash ionic exchange procedure from iron(III) nitrate as precursor and tested in some environmental air-quality protection reactions such as the catalytic reduction of NOx by NH3 (NH3-SCR), catalytic oxidation of NH3 (NH3-SCO) and catalytic N2O decomposition. The catalytic performances of the Fe/HAP catalysts were determined under flow conditions as a function of temperature and using reactant concentrations typical of polluting gaseous emissions from industrial vents. Physico-chemical characterization with various techniques of study (UV-DR and Mössbauer spectroscopies, NH3 titration, N2-physisorption, and XRPD analyses) provided valuable information on Fe-speciation, acidity, morphology, and structure of the samples. In general, highly dispersed Fe3+ centers were the predominant species, irrespective of Fe-loading, while just low percentage (≤15%) of FexOy nanoclusters (2 < size/nm < 4) was detected on the samples. As expected, the differences in iron concentration produced a diversified effect of both catalyst properties and catalytic activity, comprising the conversion and selectivity profiles, different for each reaction considered. The obtained results indicate a good potentiality for the eco-friendly Fe-catalysts for some environmental reactions of air protection.Fil: Greta Galloni, Melissa. Università degli Studi di Milano; ItaliaFil: Campisi, Sebastiano. Università degli Studi di Milano; ItaliaFil: Marchetti, Sergio Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; ArgentinaFil: Gervasini, Antonella. Università degli Studi di Milano; Itali

An Environmentally Friendly Nb–P–Si Solid Catalyst for Acid-Demanding Reactions

Here, we report the structural characteristics, the surface properties, and the catalytic performances of a Nb–P–Si ternary oxide material (2.5Nb2O5·2.5P2O5·95SiO2, 2.5NbP) in two reactions of importance for biomass valorisation and green industrial production: hydrolysis of inulin and esterification of oleic acid with polyalcohol for biolubricant production. High dispersion of the Nb centers, ascertained by UV–vis–DRS, 29Si, 31P, and 1H solid-state NMR spectroscopy, is the key point for the successful activity of 2.5NbP. Intrinsic and effective acidities of the sample were studied by FT-IR of adsorbed pyridine in the absence and presence of water and by volumetric titrations of the acid sites in cyclohexane and in water, to enlighten the nature and amount of acid sites in different environments. For both studied reactions, 2.5NbP catalyst exhibits water-tolerant acidic sites, mainly Brønsted ones, giving higher activity and better stability in the reaction medium than well-known niobium oxophosphate catalyst, which is considered one of the best water-tolerant acid catalysts

Kinetics of reduction of supported nanoparticles of iron oxides by temperature programmed reduction (tpr) analysis

Recently, supported iron oxide catalysts have received much attention because their potentiality for many applications in environmental catalysis (N2O decomposition and reduction) and in fine chemical industry for reactions requiring strong Lewis acid sites (e.g., Friedel-Crafts, isomerisations, etc.). [1-2]. Because nanostructured materials have unique physical and chemical properties completely different from those of bulk state, it is expected that catalytic systems consisting of nanosized iron oxide should have high performances. A series of catalysts prepared by dispersing iron oxide on supports of different nature and acidity have been studied in their surface and catalytic properties. Silica (S), with its neutral nature, zirconia (Z), possessing oxidizing, reducing, acid and basic properties, and mixed oxides of silica-zirconia (SZ) with different ZrO2 content (5, 15, 30 wt.%) were used as supports for the iron phase deposited by an equilibrium-adsorption method (Fe/S, Fe/Z, Fe/SZ-5, Fe/SZ-15 and Fe/SZ-30). Among the different techniques of thermal analysis used to characterize solids, temperature programmed reduction (TPR) found great success in catalysis. In this analysis, a reducing gas mixture flows through the sample while the sample temperature is linearly increased at fixed rate. Quantitative results in terms of maximum temperature of reduction (Tmax) and amount of reducible gas consumed are obtained from position and integration of the experimental peaks, respectively. In this work, the prepared Fe-catalysts have been analyzed by TPR (from 50\ub0C to 1000\ub0C at constant rate of 8\ub0C/min) using H2/Ar (5% v/v) as reducing mixture, to identify the supported iron phases and their interactions with the different supports. TPR profiles of the samples are characterized by two well defined and narrow peaks assignable to the two step reduction: 1) \uf061 Fe2O3 \uf0ae Fe3O4 \uf0ae FeO (around 400\ub0C) and 2) FeO \uf0ae Fe(0) (750-850\ub0C). The temperature of the second-step-peak increased with the zirconia content in the support, probably due to strong interaction of the iron phase with the support. A third peak at very high temperature (around 1000\ub0C) appeared, indicative of the presence of isolated Fe3+ species (Figure 1) [3]. The shape of TPR profile of all samples is typical of the presence of iron oxide aggregates of nanosized dimensions. A computational procedure has been applied to the experimental data for a deep investigation of the reduction kinetics of the samples. Moreover, relations have been individuated between the catalytic activity in a test reaction (\uf061-pinene-oxide isomerisation to \uf061-campholenic-aldheyde) and the nature of the iron species on the different supports

Study of the Influence of the Nature of the Support on the Properties of Ferric Oxide in Relation to its Activity in the Decomposition of N 2

Ferric oxide catalysts dispersed on silica and acidic silicas modified by the introduction of Al (SiO2-Al2O3), Nb (SiO2-Nb2O5) and Zr (SiO2-ZrO2) (ca. 30 mass%) were prepd. by wet impregnation from ferric acetylacetonate. The structural (by XRD studies), morphol. (by nitrogen adsorption/desorption studies) and electronic (by DRS/UV-vis) properties of both the fresh and used catalysts after their employment in the decompn. of N2O were studied. Ferric oxide species with different nuclearity, and in different relative proportions, were obsd. on the surface of each support, viz. isolated Fe(III) species, 2d FeOx dimer/oligomer aggregates and 3d Fe2O3 nanoparticles. Isolated Fe(III) species were most abundant on silica and silica-alumina, while 2d FeOx oligomers and 3d Fe2O3 predominated on silica-niobia and silica-zirconia. The nature of the support considerably influenced the speciation of iron, thereby affecting the activity of the catalyst and its stability in the N2O decompn. reaction. The introduction of Al2O3 into silica had a pos. effect on the course of the reaction but the catalytic activity was not maintained, while the presence of Nb2O5 substantially limited the course of the reaction