Adrian L. Bonivardi

Preparation of PdSiO2 cfor methanol synthesis III. Exposed metal fraction and hydrogen solubility

Tetramminepalladium complex was ion exchanged (IE) on purified, well characterized macro- and microporous Davison G-59 and G-03 silica gels (Pd loadings: 1.1–7.7% Pd w/w). These catalytic materials were reduced in hydrogen (473 to 723 K) after calcining them under both oxidating and inert atmospheres, in a wide range of experimental conditions. Two different regions were identified, each one showing its own dependence for the exposed metal fraction (FE) vs the maximum calcining temperature (Tc): (i) at Tc 423 K the FE is a function of the metal loading and the support structure, but not of the complex species mentioned. Hydrogen solubility on these Pd/SiO2 systems diminishes with the mean diameter of the metal crystallites, reaching a constant value for d < 20 A. The fraction of soluble hydrogen can be quantitatively decomposed into that of β-HPd and another one corresponding to hydrogen sorbed onto subsurface sites. It is shown that a suppression of H2 solubility exists for the metal crystallites occluded by the microporous support.

Stability of formate species on β-Ga2O3

Gallia (gallium oxide) has been proved to enhance the performance of metal catalysts in a variety of catalytic reactions involving methanol, CO and H(2). The presence of formate species as key intermediates in some of these reactions has been reported, although their role is still a matter of debate. In this work, a combined theoretical and experimental approach has been carried out in order to characterize the formation of such formate species over the gallium oxide surface. Infrared spectroscopy experiments of CO adsorption over H(2) (or D(2)) pretreated beta-Ga(2)O(3) revealed the formation of several formate species. The beta-Ga(2)O(3) (100) surface was modelled by means of periodic DFT calculations. The stability of said species and their vibrational mode assignments are discussed together with the formate interconversion barriers. A possible mechanism is proposed based on the experimental and theoretical results: first CO inserts into surface (monocoordinate) hydroxyl groups leading to monocoordinate formate; this species might evolve to the thermodynamically most stable dicoordinate formate, or might transfer hydrogen to the surface oxidizing to CO(2) creating an oxygen vacancy and a hydride group. The barrier for the first step, CO insertion, is calculated to be significantly higher than that of the monocoordinate formate conversion steps. Monocoordinate formates are thus short-lived intermediates playing a key role in the CO oxidation reaction, while bidentate formates are mainly spectators.

Preparation of Pd/SiO2 catalysts for methanol synthesis I. Ion exchange of [Pd(NH3)4)(AcO)2

Abstract An in-depth analysis of the adsorption via ion exchange (IE) of aminepalladium complexes prepared from palladium acetate on well-characterized commercial gels of silica (Davison, G-59 and G-03) in aqueous alkaline solutions is carried out. The nature of the exchanged species after different IE and washing treatments is scrutinized with diffuse reflectance spectroscopy. It is shown that (i) there is a maximum of IE at pH 10.3; (ii) IE occurs without any exchange of ligands; (iii) adsorption equilibrium is reached in about 1 h and (iv) IE follows a common Frumkin isotherm on both supports.

Preparation of Pd/SiO2 catalysts for methanoi synthesis: Part II. Thermal decomposition of [Pd(NH3)4]2+/SiO2

Abstract As a part of an experimental program aimed at the systematic analysis of the controlled deposition of Pd/SiO2 on well characterized macroporous and microporous silica gels (Davison G-59, 254 m2 g−1 and G-03, 558 m2 g−1) the nature of the surface species upon drying and thermal decomposition of the tetramminepalladium complex (TPSiO) obtained by ion exchange (IE) of palladium acetate in aqueous ammonium hydroxide (Pd loading: 0.5–11%Pd w w ), has been systematically followed by the combined use of diffuse reflectance spectroscopy (DRS), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). DRS indicates that drying in air (T ≈ 393 K) leaves a stable diammmepalladium complex (DPSiO) on the surfaces. Decomposition of DPSiO upon calcination in inert and oxidizing atmospheres was studied from 308 to 773 K, with heating rates of 4–64 K min−1 (N2) and 2–32 K min−1 (air). Two decomposition zones are identified with DSC and TG. (1) In the low-temperature region (308–473 K) endothennal signals which correspond to a liberation of NH3 around 359 K (G-59) or 371 K (G-03) were observed; (2) the high-temperature region (473–773 K) only shows endothennal peaks when N2 is used, but in air several signals indicate that a sequence of transformations of the Pd occurs. Ultradispersed Pdo is the final product on both catalyst types when N2 is the decomposing atmosphere, whereas either a mixture of Pd°+[(SiO)2]2−Pd2+ (on the microporous G-03) or pure [(SiO)2]2− Pd2+ (on the macroporous G-59) are the final products when air is employed.

Gluing ionic liquids to oxide surfaces: Chemical anchoring of functionalized ionic liquids by vapor deposition onto cobalt(II) oxide

Ionic liquids (IL) hold a great potential as novel electrolytes for applications in electronic materials and energy technology. The functionality of ILs in these applications relies on their interface to semiconducting nanomaterials. Therefore, methods to control the chemistry and structure of this interface are the key to assemble new IL-based electronic and electrochemical materials. Here, we present a new method to prepare a chemically well-defined interface between an oxide and an IL film. An imidazolium-based IL, which is carrying an ester group, is deposited onto cobalt oxide surface by evaporation. The IL binds covalently to the surface by thermally activated cleavage of the ester group and formation of a bridging carboxylate. The anchoring reaction shows high structure sensitivity, which implies that the IL film can be adhered selectively to specific oxide surfaces.

Infrared and Raman Investigation of Supported Phosphotungstic Wells- Dawson Heteropolyacid

Fil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico - Conicet- Santa Fe. Instituto de Desarrollo Tecnologico Para la Industria Quimica (i); Argentina

Interaction of Ester-Functionalized Ionic Liquids with Atomically-Defined Cobalt Oxides Surfaces: Adsorption, Reaction and Thermal Stability

Hybrid materials consisting of ionic liquid (ILs) films on supported oxides hold a great potential for applications in electronic and energy materials. In this work, we have performed surface science model studies scrutinizing the interaction of ester-functionalized ILs with atomically defined Co3 O4 (111) and CoO(100) surfaces. Both supports are prepared under ultra-high vacuum (UHV) conditions in form of thin films on Ir(100) single crystals. Subsequently, thin films of three ILs, 3-butyl-1-methyl imidazolium bis(trifluoromethyl-sulfonyl) imide ([BMIM][NTf2 ]), 3-(4-methoxyl-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([MBMIM][NTf2 ]), and 3-(4-isopropoxy-4-oxobutyl)-1-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([IPBMIM][NTf2 ]), were deposited on these surfaces by physical vapor deposition (PVD). Time-resolved and temperature-programmed infrared reflection absorption spectroscopy (TR-IRAS, TP-IRAS) were applied to monitor in situ the adsorption, film growth, and thermally induced desorption. By TP-IRAS, we determined the multilayer desorption temperature of [BMIM][NTf2 ] (360±5 K), [MBMIM][NTf2 ] (380 K) and [IPBMIM][NTf2 ] (380 K). Upon deposition below the multilayer desorption temperature, all three ILs physisorb on both cobalt oxide surfaces. However, strong orientation effects are observed in the first monolayer, where the [NTf2 ]- ion interacts with the surface through the SO2 groups and the CF3 groups point towards the vacuum. For the two functionalized ILs, the [MBMIM]+ and [IPBMIM]+ interact with the surface Co2+ ions of both surfaces via the CO group of their ester function. A very different behavior is found, if the ILs are deposited above the multilayer desorption temperature (400 K). While for [BMIM][NTf2 ] and [MBMIM][NTf2 ] a molecularly adsorbed monolayer film is formed, [IPBMIM][NTf2 ] undergoes a chemical transformation on the CoO(100) surface. Here, the ester group is cleaved and the cation is chemically linked to the surface by formation of a surface carboxylate. The IL-derived species in the monolayer desorb at temperatures around 500 to 550 K.

Kinetic analysis using two non-isothermal experiments. comparison among integral simple methods to determine kinetic reaction parameters

Abstract The kinetic parameters E and Z (apparent activation energy and global frequency factor) and the model function g (α) that best fits simulated experiments in non-isothermal analysis are determined by three integral simple methods. It is proved that one of these methods (method B) has the greatest potential to choose the model function g (α) that best fits the non-isothermal experiments. A statistic comparison is made among these methods in the calculation of E and log Z .

Structural Support Effects in The Systematic Preparation of Pd/SiO2 Catalyst for Methanol Synthesis by Ion Exchange Techniques

Abstract The activity (TOF) and selectivity for methanol and methane syntheses from CO/H 2 using Pd supported onto structurally different silicas (macro and microporous, DAVISON G-59 and G-03 types, resp.) has been evaluated. Reaction tests followed a careful follow-up of each of the preparation steps leading to the final catalysts. CH 3 OH is the main product on Pd/G-59 but with Pd/G-03 methane selectivity is much higher. In general the TOF CH 3 OH decreases smoothly, but TOF CH 4 shows a marked descent, by increasing the exposed metal fraction (FE) of Pd.