Papers by Barbara Bonelli
Turkish Journal of Chemistry
Materials capable of cost-effective on-board hydrogen storage and delivery are currently being so... more Materials capable of cost-effective on-board hydrogen storage and delivery are currently being sought worldwide as a means to facilitate a hydrogen-based energy transition in the transportation sector. Among the solutions proposed, hydrogen storage by physisorption on porous solids constitutes a main avenue of research, and for intelligent design of such materials a detailed knowledge of gas adsorption thermodynamics is of the utmost importance. Analysis of the available data for hydrogen adsorption on alkali and alkalineearth cation exchanged zeolites clearly shows that standard adsorption enthalpy (ΔH 0) and entropy (ΔS 0) are correlated, in the sense that larger ΔS 0 values correspond to larger ΔH 0 values. It was also shown that, referring to absolute values, the relative rate at which adsorption entropy changes decreases gradually as adsorption enthalpy increases thus resulting in a non-linear correlation between ΔH 0 and ΔS 0. These results are discussed and corresponding implications for hydrogen storage via physisorption are highlighted.
Among the many materials considered for propane ODH, V-containing mesoporous silicas characterize... more Among the many materials considered for propane ODH, V-containing mesoporous silicas characterized by high surface area, large pores and well-dispersed VOx species prove to be most effective [1,2]. V-based catalysts are usually obtained by impregnation: it has been observed, though, that V-containing mesoporous systems (i.e. V-SBA-15 and V-MCF) prepared by direct synthesis exhibit better V-dispersion and superior catalytic performances in both selective and total oxidation reactions, reactions both based on V reduction and subsequent reoxidation (MvK mechanism) [3,4]. As it is known, isolated V-species are beneficial in terms of propene selectivity, whereas higher activity is usually associated to polyvanadates (up to the formation of VOx monolayer) [1-5].In this work, a V-SBA-15 and a V-MCF sample [3,4] (V cont. 2.5 wt.%) prepared by direct synthesis were tested in propane ODH. Their physico-chemical and catalytic properties were compared with those of materials with the same V-content but prepared by different ways: i) two impregnated samples (V-SBA-15-i and V-MCF-i) and ii) a non-porous sample obtained by flame pyrolysis (V-SiO2), a high temperature synthesis technique allowing high V-dispersion to be achieved [2]. As a whole, both V-SBA-15 and V-MCF exhibited better textural properties (i.e. higher SSA) and higher V dispersion (isolated V-species), as compared to impregnated ones, in which polymeric VOx and micro-crystalline V2O5 were detected by TEM, H 2-TPR micro-Raman and DR UV-Vis [4,5]. On the other hand, both impregnated samples showed higher Br\uf8nsted acidity (related to V-OH groups), as shown by IR-spectroscopy of adsorbed CO and NH3 Better catalytic performances in terms of selectivity to propene were achieved with both samples directly synthesized, as consequence of higher V dispersion and lower surface acidity. Br\uf8nsted acidity seems indeed to be negatively correlated with the selectivity to propene, since stronger Br\uf8nsted acidic sites favor the formation of CO.. In contrast, samples directly synthesized show supported V species that can be converted into Lewis acidic sites by dehydroxylation much more easily than impregnated samples (Figure 1). x and other by-products. A similar correlation was previously observed with a set of non-porous VOx-SiO2 samples prepared by flame pyrolysis (results to be published). Moreover, higher selectivity to propene was obtained over V-MCF as compared to V-SBA-15 (a similar trend was observed with impregnated ones). This behavior was related to the different porous network of the two catalysts: the structure of MCF, featuring a 3-D network with ultra-large cells (20-40 nm), favors molecular diffusion along each direction, unlike cylindrical channels of SBA-15 (3-6 nm) occurring in one dimension mainly (axial diffusion). Molecules can be much more retained inside channels of SBA-15 (deeper oxidation) as compared to MCF. On the other hand, the non-porous sample, with V-species well dispersed and incorporated into the silica framework, exhibited worse catalytic results than mesoporous samples, confirming the important role of mesoporosity in oxidation processes. References [1] F. Cavani, N. Ballarini, E. Cericola, Catal. Today 127 (2007) 113. [2] I. Rossetti, L. Fabbrini, N. Ballarini, F. Cavani, A. Cericola, B. Bonelli, M. Piumetti, E. Garrone, H. Dyrbeck, E.A. Blekkan, L. Forni, J. Catal. 256 (2008) 45. [3] M. Piumetti, B. Bonelli, P. Massiani, S. Dzwigaj, I. Rossetti, S. Casale, L. Gaberova, M. Armandi, E. Garrone, Catal. Today, 176 (2011) 458. [4] M. Piumetti, B. Bonelli, P. Massiani, S. Dzwigaj, I. Rossetti, S. Casale, M. Armandi, C. Thomas, E. Garrone, Catal. Today doi:10.1016/j.cattod.2011.06.028 [5] H. Dai, A.T. Bell, E. Iglesia, J. Catal 221 (2004) 49
Chemical Communications
Mesoporosu (MCM-41 type) silica containing surfactant-embedded Congo Red has been prepared and te... more Mesoporosu (MCM-41 type) silica containing surfactant-embedded Congo Red has been prepared and tested against gas phase HCl and ammonia, as well as solutions of ionic species; it is shown that the hybrid (organic-inorganic) material is permeable to both gases and ionic species, and can act as a pH indicator and as a selective chelating agent.
Chimica oggi
Two sets of catalysts (VOx-SiO2 and VOx-Al2O3) were prepared by fl ame pyrolysis (FP) and tested ... more Two sets of catalysts (VOx-SiO2 and VOx-Al2O3) were prepared by fl ame pyrolysis (FP) and tested for the oxidative dehydrogenation (ODH) of propane. Better vanadium dispersion and superior catalytic performances (in terms of propene selectivity) were achieved with FP-samples compared to catalysts obtained by impregnation. Similarly, two V-containing mesoporous catalysts (V-SBA-15 and V-MCF) were directly synthesized to obtain highly dispersed V species in the silica. The latter catalysts performed better in both ODH of propane and dichloromethane decomposition compared to impregnated ones. In addition, better results in the ODH of propane were obtained with V-MCF, while higher activity in dichloromethane decomposition was achieved with V-SBA-15. These fi ndings seem to be related to the different porous network of the two catalysts
Studies in Surface Science and Catalysis, 2003
HMS materials with Si/Al ratio = 2.5 have been synthesised and characterized. 27A1 NMR spectra sh... more HMS materials with Si/Al ratio = 2.5 have been synthesised and characterized. 27A1 NMR spectra showed minimal occurrence of octahedral phase after template removal. FT-IR and microcalorimetric results showed that, though having the same chemical composition of Y zeolites, such materials exhibit drastically different acidic/basic properties.
Molecular Sieves: From Basic Research to Industrial Applications, Proceedings of the 3rd International Zeolite Symposium (3rd FEZA), 2005
Two ordered mesoporous carbons have been obtained by a casting procedure, starting from a SBA-15 ... more Two ordered mesoporous carbons have been obtained by a casting procedure, starting from a SBA-15 silica. XRD spectra showed that the ordered structure of the parent SBA-15 silica is maintained and that the samples are ordered carbon replicas. Micro-Raman spectra showed that rather homogeneous powders are obtained, exhibiting a consistent graphitized carbon phase along with an amorphous one, notwithstanding the relatively low temperature adopted during the carbonization process. BET surface area and pore diameter analysis indicate that these materials could have potential applications as media for gas storage for example CH4 and H2.
Studies in Surface Science and Catalysis, 2001
ABSTRACT
Studies in Surface Science and Catalysis, 2004
When adsorbed on the faujasite-type K-Y zeolite, carbon monoxide forms cationic C-bonded K(CO)+ c... more When adsorbed on the faujasite-type K-Y zeolite, carbon monoxide forms cationic C-bonded K(CO)+ carbonyls and also O-bonded K(OC)+ isocarbonyls. The carbonyl species gives a characteristic C-O stretching band at 2158 cm−1, while that of the isocarbonyl appears at 2124 cm−1. By means of variable-temperature infrared spectroscopy, these K(CO)+ and K(OC)+ species were found to be in a temperature-dependent isomerization equilibrium,
ACS Catalysis, 2013
Cobalt aluminum phosphate with AFI zeolitic structure (Co-APO-5) catalyzes light-driven water oxi... more Cobalt aluminum phosphate with AFI zeolitic structure (Co-APO-5) catalyzes light-driven water oxidation (WO) when both the ruthenium complex [Ru(bpy) 3 ] 2+ , as photosensitizer, and persulfate species S 2 O 8 2− , as sacrificial electron acceptor, are present. Measurements have been run in a flow reactor, allowing the amount of oxygen evolved to be evaluated and, in particular, the initial rate of WO reaction to be measured. The latter has been studied as a function of chemical composition, and some kinetic features have been established. Competitive reactions occur extensively, causing the oxidation of the Ru complex to the detriment of oxygen production. The initial rate of WO increases with the amount of catalyst until turbidity of the suspension sets in. A reaction order close to −1 with respect to persulfate was found, which indicates the occurrence of surface processes involving Co centers at the outer layer of Co-APO-5 particles (accessed by the bulky [Ru(bpy) 3 ] 2+ species, at variance with Co species in the core), for the adsorption onto which competition takes place between the Ru complex and persulfate species. A less pronounced negative order (ca. −0.4) for the sensitizer was also observed, for which an interpretation is proposed.
The Journal of Physical Chemistry C, 2012
Using a methylated Si precursor instead of tetraethoxysilane (TEOS), methyl-imogolite (Me−IMO), a... more Using a methylated Si precursor instead of tetraethoxysilane (TEOS), methyl-imogolite (Me−IMO), a nanotube material with formula (OH) 3 Al 2 O 3 SiCH 3 is obtained in place of the standard imogolite (OH) 3 Al 2 O 3 SiOH (IMO). 21 Postsynthesis grafting of the outer surface of Me−IMO with 3aminopropyltriethoxysilane (3-APS) yields a new hybrid material (Me−IMO−NH 2), with an entirely hydrophobic inner surface and a largely aminated outer surface. In this paper, the structure and stability of Me−IMO−NH 2 are studied in detail and compared with those of Me−IMO by means of (i) X-ray photoelectron spectroscopy (XPS), confirming the surface chemical composition of Me−IMO− NH 2 ; (ii) 1 H, 13 C, 27 Al, 29 Si, and heteronuclear correlation (HETCOR) 1 H− 13 C magic angle spinning nuclear magnetic resonance (MAS NMR) experiments, providing evidence for the occurrence of grafting and yielding an estimate of its extent; (iii) infrared spectroscopy, showing that most terminal −NH 2 groups are protonated; (iv) X-ray diffraction (XRD) measurements yielding information on the long-range order; and (v) N 2 adsorption at −196°C, yielding specific surface area and pore size distribution. Reaction with 3-APS brings about a limited loss in microporosity, probably caused by functionalization at the mouth of pores, and an increased disorder in the alignment of nanotubes, with neither a big loss of specific surface area nor a sizable change in the distance between nanotubes. As a whole, imogolite-type nanotubes appear to be rather prone to functionalization, which seems to allow the possible tailoring of the properties of both inner and outer surfaces.
The Journal of Physical Chemistry C, 2010
ABSTRACT
Physical Chemistry Chemical Physics, 2001
Microporous and Mesoporous Materials, 2011
This work reports the preparation and characterization of novel V-containing mesocellular foams (... more This work reports the preparation and characterization of novel V-containing mesocellular foams (MCF) obtained by direct synthesis: their physico-chemical properties were investigated by means of complementary techniques and comparison was made with V-containing MCF prepared by (traditional) impregnation method, figuring out the main differences in both textural and surface features of the two types of materials. Catalytic tests showed that V-MCF prepared by direct synthesis are more active towards dichloromethane decomposition, due to the presence of isolated vanadium sites, as detected by means of (complementary) spectroscopic techniques. Direct synthesis allows the formation of acidic VAOH groups and favours the incorporation of highly reducible tetrahedral vanadium species that are well dispersed inside silica walls. On the contrary, impregnation brings about an overall decrease of surface hydroxyls and preferential formation of highly acidic sites, most probably related to extra-framework VO x species, that are reduced at a higher temperature than isolated vanadium sites.
Uploads
Papers by Barbara Bonelli