Leonarda F. Liotta

Activity of SiO2 supported gold-palladium catalysts in CO oxidation

Abstract Bimetallic Au-Pd catalysts supported on silica with different Au/Pd atomic ratios were prepared by simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polymer, polyvinylpyrrolidone (PVP). Formation of alloyed particles was detected by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and CO chemisorption measurements. The catalysts were tested in the catalytic oxidation of CO using a plug–flow reactor. The CO conversion was determined as a function of temperature. The monometallic palladium and the palladium-rich catalysts behaved quite similarly and were the most active catalysts. A drastic reduction of the CO oxidation activity was observed for the 50/50 Au/Pd catalyst and for samples with increasing amount of gold.

Co3O4 nanocrystals and Co3O4–MOx binary oxides for CO, CH4 and VOC oxidation at low temperatures: a review

Among the possible substitutes for noble metals, cobalt-based catalysts represent promising alternative systems. In recent years, many articles have been devoted to the synthesis, characterization and reactivity of cobalt oxides. This article provides a comprehensive review of the state-of-the-art activities that concentrate on the synthesis, structural properties and catalytic applications of Co3O4 nanocrystals and Co3O4–MOx binary oxides in CO, CH4 and VOC oxidation at low temperatures. It begins with the major synthetic approaches and basic properties of Co3O4 nanocrystals and Co3O4–MOx binary oxides and subsequently highlights the relationship between the peculiar structure of Co3O4 nanocrystals and their catalytic activity (or between the redox properties of Co3O4–MOx binary oxides and their catalytic activity). Finally, the active sites and key factors determining the catalytic oxidation over Co3O4 and Co3O4–MOx are discussed. The perspective with respect to future research on Co3O4 nanocrystals and Co3O4–MOx binary oxides is considered.

Multilayered supported ionic liquids as catalysts for chemical fixation of carbon dioxide: a high-throughput study in supercritical conditions

Multilayered, covalently supported ionic liquid phase (mlc-SILP) materials were synthesized by using a new approach based on the grafting of bis-vinylimidazolium salts on different types of silica or polymeric supports. The obtained materials were characterized and tested as catalysts in the reaction of supercritical carbon dioxide with various epoxides to produce cyclic carbonates. The material prepared by supporting a bromide bis-imidazolium salt on the ordered mesoporous silica SBA-15 was identified as the most active catalyst for the synthesis of cyclic carbonates and displayed improved productivity compared with known supported ionic liquid catalysts. The catalyst retained its high activity upon reuse in consecutive catalytic runs. This is the first report of the application of mlc-SILP materials as catalysts in a reaction for the fixation of carbon dioxide. Rapid, parallel screening and comparison of the catalysts was performed by means of high-throughput experimentation.

Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration

Catalytic and catalytic photo-assisted hydration of propene to form 2-propanol in gas-solid regime at atmospheric pressure and 85 °C were carried out by using a heteropolyacid (POM) supported on different oxides. Binary materials were prepared by impregnation of H3PW12O40 on different commercial and home prepared supports (TiO2, SiO2, WO3, ZrO2, ZnO, Al2O3). Some of the composites were active both for catalytic and catalytic photo-assisted reactions. The Keggin type POM was completely and partially degraded, when supported on ZnO and Al2O3, respectively, and these binary solids always resulted as inactive for both catalytic and catalytic photo-assisted reactions. The supported Keggin POM species played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary presence of heat and UV light improved the activity of almost all POM supported materials. All materials were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM), diffuse reflectance spectroscopy (DRS), determination of the conduction and valence band energy by photovoltage measurements, Fourier transform infrared spectroscopy (FTIR), NH3-TPD experiments and time resolved microwave conductivity (TRMC).

Palladium on pumice: new catalysts for the stereoselective semihydrogenation of alkynes to (Z)-alkenes

Abstract High selectivities (93–99%) and excellent stereoselectivities (>99%) in the semihydrogenation of CC triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the CC triple bond.

Efficient semihydrogenation of the CC triple bond using palladium on pumice as catalyst

Abstract An efficient semihydrogenation of CC triple bonds was achieved using palladium on pumice as the catalyst with a metal loading of 3 % wt. The results obtained showed better selectivity when compared with Pd/C and better activity when compared with Lindlars catalyst. Hydrogenation of sterically hindered alkynes is slow on Pd/pumice. The selectivity with respect to alkenes is probably due to the presence of sodium ions in the pumice structure that increases the electron density on the supported metal.

Fullerene-ionic-liquid conjugates: a new class of hybrid materials with unprecedented properties.

A modular approach has been followed for the synthesis of a series of fullerene-ionic-liquid (IL) hybrids in which the number of IL moieties (two or twelve), anion, and cation have been varied. The combination of C60 and IL give rise to new unique properties in the conjugates such as solubility in water, which was higher than 800 mg mL(-1) in several cases. In addition, one of the C60 -IL hybrids has been employed for the immobilization of palladium nanoparticles through ion exchange followed by reduction with sodium borohydride. Surprisingly, during the reduction several carbon nanostructures were formed that comprised nano-onions and nanocages with few-layer graphene sidewalls, which have been characterized by means of thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM-EDAX), and high-resolution transmission electron microscopy (HRTEM). Finally, the material thus obtained was successfully applied as catalyst in Suzuki and Mizoroki-Heck reactions in a concentration of just 0.2 mol %. In the former process it was recyclable for five runs with no loss in activity.

Combined sulfating and non-sulfating support to prevent water and sulfur poisoning of Pd catalysts for methane combustion

The appropriate combination of titania and silica, sulfating and non-sulfating support, respectively, results in Pd catalysts with improved water and sulfur tolerance in methane combustion. For the first time the catalyst recovers the initial activity after one cycle under lean-burn conditions without additional regenerating treatments.

Effect of sodium on the electronic properties of Pd/silica−alumina catalysts

Abstract The effect of the alkali ion content on the electronic properties of palladium, supported on natural pumice and on synthetic aluminosilicates, was studied by X-ray photoelectron spectroscopy (XPS) measurements. To this aim a series of catalysts of palladium supported on aluminosilicates with various amounts of sodium and potassium in the bulk structure were prepared and analysed. The Pd 3d 5/2 binding energy shifts of the different catalysts with respect to pure metal Pd 3d 5/2 binding energy were followed as a function of the Na/Pd atomic ratio. For reasons of comparison, a silica supported Pd catalyst whose surface had been doped with sodium was also studied. A correlation of the Pd 3d binding energy with the sodium content was found, regardless on whether sodium was present in the bulk structure or just at the surface of the catalyst. The effect was independent of the catalyst preparation procedure. The analysis of the intensity of the photoelectron peaks of Pd 3d and Si 2p of the lower surface area catalysts, using the Kerkhof-Moulijn model, yielded particle sizes in agreement with values obtained from small angle X-ray diffraction measurements (SAXS). For the large surface area supported catalysts a monolayer type of metal distribution was found. The intensity ratios of the Na 1s and Si 2p photoelectron peaks are in accordance with those estimated from the bulk Na/Si atomic ratios of the synthetic and natural pumice support. Therefore any segregation of the alkali ions on the palladium particle of the corresponding catalysts are ruled out. The electronic effect is thus discussed in terms of the formation of an electron donor composite formed by the metal, the oxygen and the alkali ion.

Cyclodextrin–calixarene co-polymers as a new class of nanosponges

Hyper-reticulated co-polymers jointly formed by cyclodextrin and calixarene units, which can be considered as a new class of nanosponges, were easily obtained by means of a click chemistry approach. In particular, we succeeded in preparing our materials by exploiting the copper-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction between heptakis-(6-deoxy)-(6-azido)-β-cyclodextrin and (5,11,17,23-tetra-tert-butyl)-(25,26,27,28-tetra-propargyloxy)-calix-[4]-arene, mixed in different proportions. These materials were fully characterized by means of combined FT-IR, thermogravimetric, 13C {1H} CP-MAS NMR and nitrogen adsorption/desorption techniques. In particular, 13C {1H} CP-MAS spectra allowed us to perform a quantitative analysis of the co-polymers obtained. Tests on their possible sequestering abilities towards some organic molecules, in particular nitroarenes and commercial dyes chosen as suitable pollutants or drug models, were successfully carried out. Results obtained point out that absorption abilities seem affected by polymer composition and porosity as well.