Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe ...

University of Turin

Copper catalysts prepared by chemisorption-hydrolysis technique over silica (Cu/Si) and silica-alumina (Cu/SiAl) supports were studied to understand the role of the support on the nature and surface properties of the copper species stabilized on their surfaces. The morphological and surface properties of the copper phases have been characterized by complementary techniques, such as HRTEM, EXAFS-XANES, EPR, XPS, and FTIR. For the FTIR investigation, molecular probes (CO and NO) were also adsorbed on the surfaces to test the reactivity of the copper species. Moreover, the catalytic performances of the two catalysts have been compared in the HC-SCR reaction (NO reduction by C(2)H(4)) performed in highly oxidant conditions. The superior activity and selectivity of the supported silica-alumina catalyst with respect to that supported on silica could be related with the different nature of the copper species stabilized on the two supports, as emerged from the results obtained from the spectroscopic investigations. Small and well-dispersed CuO particles were present on silica, whereas isolated copper ions predominated on silica-alumina, likely in regions rich in alumina that made some exchangeable sites available, as indicated by FTIR spectra of adsorbed CO. The less positive global charge of copper species on Cu/SiAl than in Cu/Si has been confirmed by EPR, XPS, and EXAFS-XANES analyses.

Dependence of copper species on the nature of the support for dispersed CuO catalysts.

Fourier transform infrared spectra of CO adsorption from 120 K up to room temperature on two gold catalysts supported on different mixed ceria-titania oxides are discussed in comparison with those obtained on Au/TiO(2) and Au/Fe(2)O(3) reference catalysts provided by the World Gold Council. The spectra of adsorbed CO, run on the different samples before preliminary treatment, are shown and compared with those of the untreated catalysts and of the samples reduced either in CO or in hydrogen. Big differences have been found between the ceria-titania supported samples and the reference ones: unusual absorption bands, irreversible to outgassing, have been detected after CO interaction on the untreated and oxidized ceria containing samples. These absorptions are assigned to CO on Au(n)(+) small clusters stabilized at the ceria defects. By reduction in hydrogen, negatively charged Au(n)(-) species are produced on the same sample. Oxidized small particles are present on the reference catalysts, but only on the untreated samples; after treatment, only metallic step sites are evident.

CO adsorption on gold clusters stabilized on ceria-titania mixed oxides: comparison with reference catalysts.

Gold-loaded zirconia and sulfated zirconia catalysts were tested in the low-temperature water gas shift reaction. The samples were characterized by N2 adsorption analysis, temperature-programmed reduction, X-ray diffraction, pulse-flow CO chemisorption, FTIR spectroscopy, and high-resolution transmission electron microscopy. A reference catalyst, Au/TiO2, provided by the World Gold Council was investigated for comparison. CO chemisorption and FTIR data indicate the presence of only highly dispersed gold clusters on the sulfated sample and both small clusters and small particles on the non-sulfated sample. Both gold-zirconia catalysts are much more active than the Au/TiO2 reference sample over all the temperature range investigated. The sample prepared on sulfated zirconia exhibits higher stability than the catalyst on unmodified zirconia. The prominent role in the water gas shift reaction of gold clusters in close contact with the support was deduced.

Highly dispersed gold on zirconia: characterization and activity in low-temperature water gas shift tests.

The impact of ceria doping by Zn (atomic ratio Zn/(Zn + Ce) = 0.05) on the structural and catalytic properties of Au/CeO(2) catalyst was studied. The ceria modification influenced the catalytic activity toward purification of hydrogen via water-gas shift (WGS) and preferential CO oxidation (PROX) reactions in a different way: it diminished the WGS activity and improved the PROX performance. A characterization by FTIR spectroscopy was conducted to explain differences in the catalytic performance. The nature of gold active species after different pretreatments, under different atmospheres (H(2), D(2)), and after admission of CO and its subsequent interaction with (18)O(2) was investigated. Evidence has been found of the dissociation of hydrogen at room temperature on gold, producing on the oxidized sample a broad absorption assigned to Au-OH vibrations, whereas on the reduced one, bands at 3200 and 1800 cm(-1) ascribed, respectively, to Au-OH and Au-H species have been detected. For the first time, the formation of Au-hydride on supported heterogeneous catalysts was proposed. These features were stronger on the Au/CeO(2) sample than on the Au/Zn-CeO(2) sample. The availability of highly dispersed gold clusters in contact with oxygen vacancies on the ceria surface could contribute to higher WGS activity, whereas the steps of small gold particles are the active sites for both CO and oxygen activation during the PROX reaction.

CO-free hydrogen production for fuel cell applications over Au/CeO2 catalysts: FTIR insight into the role of dopant.

Single-site Re nanoparticles were produced by anchoring dirhenium organometallic clusters on to the inner walls of mesoporous silica. The presence of oxophilic atoms (Sb or Bi) is essential to obtain well dispersed Re(0) centers. The interaction between the organometallic cluster and the silica support is critical for the generation of well-defined and isolated Re(0) single sites. FTIR spectroscopy was used to track the decomposition of the organometallic precursors and the adsorption of probe molecules such as CO on the metal sites sheds valuable information on the catalytic potential of this new class of bimetallic nanocatalysts.

Synergistic behavior of bimetallic rhenium cluster catalysts: spectroscopic investigation into the nature of the active site.

Surface and inner defects in Au/CeO2 WGS catalysts: relation between Raman properties, reactivity and morphology.

Cluster-derived Ru(x)Pt(y)Sn(z) nanoparticles are active catalysts in the hydrogenation of nitrobenzene. The nature of the active sites has been elucidated by FTIR spectroscopy using CO and NO as probe molecules. A new metal carbonyl cluster precursor, Pt(2)Ru(2)(SnBu(t)(3))(2)(CO)(9)(μ-H)(2), has been synthesized to obtain a Ru(2)Pt(2)Sn(2)/SiO(2) catalyst, that displayed remarkably high levels of conversion and selectivities compared to other bi-and monometallic analogues. Spectroscopic comparisons with Ru(5)PtSn/SiO(2) indicate that both the nature and the stoichiometry of the metals play a key role in modulating the catalytic activities and selectivities. A multinuclear single-site containing Pt centers, which facilitate the hydrogen activation, coupled with a highly reactive Ru site, possibly involved in the nitrobenzene activation, can be hypothesized. The oxophilicity of tin helps with the anchoring of the nanoparticles, aids the dispersion of the other metals, and can play an important role in influencing the selectivity to aniline.

Ru(x)Pt(y)Sn(z) cluster-derived nanoparticle catalysts: spectroscopic investigation into the nature of active multinuclear single sites.

The ability to adroitly tailor acid-strength using specifically-engineered bimetallic nanoporous materials has been investigated with a view to exploiting their potential in solid-acid catalysed transformations. Further, it has been demonstrated that through site-specific interactions, extra-framework zinc ions can suitably modify the acidity of Brønsted acid sites, to stimulate diverse catalytic responses, when combined with isomorphously-substituted framework metal cations within porous architectures, for the Beckmann rearrangement of cyclohexanone oxime and in the isopropylation of benzene.

Investigating site-specific interactions and probing their role in modifying the acid-strength in framework architectures.

Among the metal organic framework materials proposed for CO2 separation, UTSA-16 possesses the highest CO2 volumetric density explained on the basis of favourable interactions between CO2 and structural water molecules in the material, as revealed by neutron diffraction. In this study, UTSA-16 was synthesised and extensively characterised by XRD, TEM combined with EDX analysis and DR-UV-Vis, Raman and FTIR spectroscopies, as well as by TGA measurements. The synthesised material shows XRD patterns, surface area, CO2 capacity and isosteric heat coincident to the ones reported for UTSA-16 in the original papers but a higher thermal stability and a complete removal of water upon activation under mild conditions (363 K). On the basis of EDX and IR measurements, the formula of UTSA-16 used in the present study is proposed to be K2Co3(cit)2. Infrared spectroscopy clearly shows that UTSA-16 described in this work reversibly interacts with water vapor, CO and CO2. The interaction is attributed to K(+) species, which are present as counterions in the pores. At 1 bar and 298 K a fraction of K(+) sites adsorbs 2 CO2 molecules.

New insights into UTSA-16.

Au-based catalysts have established a new important field of catalysis, revealing specific properties in terms of both high activity and selectivity for many reactions. However, the correlation between the morphology and the activity of the catalyst is not always clear although much effort has been addressed to this task. To some extent the problem relates to the complexity of the characterisation techniques that can be applied to Au catalyst and the broad range of ways in which they can be prepared. Indeed, in many reports only a few characterization techniques have been used to investigate the potential nature of the active sites. The aim of this review is to provide a critical description of the techniques that are most commonly used as well as the more advanced characterization techniques available for this task. The techniques that we discuss are (i) transmission electron microscopy methods, (ii) X-ray spectroscopy techniques, (iii) vibrational spectroscopy techniques and (iv) chemisorption methods. The description is coupled with developing an understanding of a number of preparation methods. In the final section the example of the supported AuPd alloy catalyst is discussed to show how the techniques can gain an understanding of an active oxidation catalyst.

Maela Manzoli

Department of Chemistry & NIS Interdepartmental Centre

University of Turin

Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties

Maela Manzoli

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Chemistry & NIS Interdepartmental Centre

University of Turin

Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties

Department of Chemistry & NIS Interdepartmental Centre