Stabilization of catalyst particles against sintering on oxide supports with high oxygen ion lability exemplified by Ir-catalyzed decomposition of N2O

Iridium nanoparticles deposited on a variety of surfaces exhibited thermal sintering characteristics that were very strongly correlated with the lability of lattice oxygen in the supporting oxide materials. Specifically, the higher the lability of oxygen ions in the support, the greater the resistance of the nanoparticles to sintering in an oxidative environment. Thus with γ-Al2O3 as the support, rapid and extensive sintering occurred. In striking contrast, when supported on gadolinia-ceria and alumina-ceria-zirconia composite, the Ir nanoparticles underwent negligible sintering. In keeping with this trend, the behavior found with yttria-stabilized zirconia was an intermediate between the two extremes. This resistance, or lack of resistance, to sintering is considered in terms of oxygen spillover from support to nanoparticles and discussed with respect to the alternative mechanisms of Ostwald ripening versus nanoparticle diffusion. Activity towards the decomposition of N2O, a reaction that displays pronounced sensitivity to catalyst particle size (large particles more active than small particles), was used to confirm that catalytic behavior was consistent with the independently measured sintering characteristics. It was found that the nanoparticle active phase was Ir oxide, which is metallic, possibly present as a capping layer. Moreover, observed turnover frequencies indicated that catalyst-support interactions were important in the cases of the sinter-resistant systems, an effect that may itself be linked to the phenomena that gave rise to materials with a strong resistance to nanoparticle sintering.

Base-free, one-pot chemocatalytic conversion of glycerol to methyl lactate using supported gold catalysts

We report an efficient one-pot conversion of glycerol (GLY) to methyl lactate (MLACT) in methanol in good yields (73 % at 95 % GLY conversion) by using Au nanoparticles on commercially available ultra-stable zeolite-Y (USY) as the catalyst (160 °C, air, 47 bar pressure, 0.25 M GLY, GLY-to-Au mol ratio of 1407, 10 h). The best results were obtained with zeolite USY-600, a catalyst that has both Lewis and Brønsted sites. This methodology provides a direct chemo-catalytic route for the synthesis of MLACT from GLY. MLACT is stable under the reaction conditions, and the Au/USY catalyst was recycled without a decrease in the activity and selectivity. From glycerol to green building blocks and solvents! An efficient, base-free conversion of glycerol to methyl lactate in methanol is reported, achieving good yields (73 % at 95 % glycerol conversion) using Au/ultra-stable zeolite-Y (USY) as the catalyst and environmentally benign oxygen as the oxidant by combining two separate reaction steps efficiently in a one pot procedure. The Au/USY catalyst can be recycled without a decrease in the activity and selectivity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A bimetallic catalyst on a dual component support for low temperature total methane oxidation

Palladium, platinum bimetallic catalysts supported on η-Al₂O₃, ZSM-5(23) and ZSM-5(80), with and without the addition of TiO₂, were prepared and used for low temperature total methane oxidation (TMO). The catalysts were tested under reaction temperatures of 200-500 °C with a GHSV of 100,000 mL g^-1 h^-1. It was found that all four components, palladium, platinum, an acidic support and oxygen carrier were needed to achieve a highly active and stable catalyst. The optimum support being 17.5% TiO₂ on ZSM-5(80) where the T_10% was observed at only 200 °C. On addition of platinum, longer time on stream experiments showed no decrease in the catalyst activity over 50 h at 250 °C.

Basalt Fibre Reinforced Polymer Strengthening of Normal Strength Reinforced Concrete Floor Slabs Subject to Arching Effects

With ever increasing demands to strengthen existing reinforced concrete structures to facilitate higher loading due to change of use and to extend service lifetime, the use of fibre reinforced polymers (FRPs) in structural retrofitting offers an opportunity to achieve these aims. To date, most research in this area has focussed on the use of glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP), with relatively little on the use of basalt fibre reinforced polymer (BFRP) as a suitable strengthening material. In addition, most previous research has been carried out using simply supported elements, which have not considered the beneficial influence of in-plane lateral restraint, as experienced within a framed building structure. Furthermore, by installing FRPs using the near surface mounted (NSM) technique, disturbance to the existing structure can be minimised.
This paper outlines BFRP NSM strengthening of one third scale laterally restrained floor slabs which reflect the inherent insitu compressive membrane action (CMA) in such slabs. The span-to-depth ratios of the test slabs were 20 and 15 and all were constructed with normal strength concrete (~40N/mm2) and 0.15% steel reinforcement. 0.10% BFRP was used in the retrofitted samples, which were compared with unretrofitted control samples. In addition, the bond strength of BFRP bars bonded into concrete was investigated over a range of bond lengths with two different adhesive thicknesses. This involved using an articulated beam arrangement in order to establish optimum bond characteristics for use in strengthening slab samples.

Catalytic reactions with palladium supported on mesocellular foam : Applications in hydrogenation, isomerization, and C-C bond forming reactions

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases.

Catalytic decomposition of formic acid using supported metal nanoparticles

Upgrade of hydrogen to valuable fuel is a central topic in modern research due to its high availability and low price. For the difficulties in hydrogen storage, different pathways are still under investigation. A promising way is in the liquid-phase chemical hydrogen storage materials, because they can lead to greener transformation processes with the on line development of hydrogen for fuel cells. The aim of my work was the optimization of catalysts for the decomposition of formic acid made by sol immobilisation method (a typical colloidal method). Formic acid was selected because of the following features: it is a versatile renewable reagent for green synthesis studies. The first aim of my research was the synthesis and optimisation of Pd nanoparticles by sol-immobilisation to achieve better catalytic performances and investigate the effect of particle size, oxidation state, role of stabiliser and nature of the support. Palladium was chosen because it is a well-known active metal for the catalytic decomposition of formic acid. Noble metal nanoparticles of palladium were immobilized on carbon charcoal and on titania. In the second part the catalytic performance of the “homemade” catalyst Pd/C to a commercial Pd/C and the effect of different monometallic and bimetallic systems (AuxPdy) in the catalytic formic acid decomposition was investigated. The training period for the production of this work was carried out at the University of Cardiff (Group of Dr. N. Dimitratos).

Adobe's Acrobat -- the Electronic Journal Catalyst?

Adobe's Acrobat software, released in June 1993, is based around a new Portable Document Format (PDF) which offers the possibility of being able to view and exchange electronic documents, independent of the originating software, across a wide variety of supported hardware platforms (PC, Macintosh, Sun UNIX etc.). The principal features of Acrobat are reviewed and its importance for libraries discussed in the context of experience already gained from the CAJUN project (CD-ROM Acrobat Journals Using Networks). This two-year project, funded by two well-known journal publishers, is investigating the use of Acrobat software for the electronic dissemination of journals, on CD-ROM and over networks.

Obtenção de óxidos a base de níquel e cobalto para reação de oxidação parcial do metano

Nickel-based catalysts supported on alumina have been widely used in various reactions to obtain synthesis gas or hydrogen. Usually, higher conversion levels are obtained by these catalysts, however, the deactivation by coke formation and sintering of metal particles are still problems to be solved. Several approaches have been employed in order to minimize these problems, among which stands out in recent years the use of additives such as oxides of alkali metals and rare earths. Similarly, the use of methodologies for the synthesis faster, easier, applicable on an industrial scale and to allow control of the microstructural characteristics of these catalysts, can together provide the solution to this problem. In this work, oxides with spinel type structure AB2O4, where A represents divalent cation and B represents trivalent cations are an important class of ceramic materials investigated worldwide in different fields of applications. The nickel cobaltite (NiCo2O4) was oxides of spinel type which has attracted considerable interest due to its applicability in several areas, such as chemical sensors, flat panel displays, optical limiters, electrode materials, pigments, electrocatalysis, electronic ceramics, among others. The catalyst precursor NiCo2O4 was prepared by a new chemical synthesis route using gelatine as directing agent. The polymer resin obtained was calcined at 350°C. The samples were calcined at different temperatures (550, 750 and 950°C) and characterized by X ray diffraction, measurements of specific surface area, temperature programmed reduction and scanning electron microscopy. The materials heat treated at 550 and 750°C were tested in the partial oxidation of methane. The set of techniques revealed, for solid preparations, the presence of the phase of spinel-type structure with the NiCo2O4 NixCo1-xO solid solution. This solid solution was identified by Rietveld refinement at all temperatures of heat treatment. The catalyst precursors calcined at 550 and 750°C showed conversion levels around 25 and 75%, respectively. The reason H2/CO was around 2 to the precursor treated at 750°C, proposed reason for the reaction of partial oxidation of methane, one can conclude that this material can be shown to produce synthesis gas suitable for use in the synthesis Fischer-Tropsch process

Oxygen-Nonstoichiometric YBaCo4O7+δ as a Catalyst in H2O2 Oxidation of Cyclohexene

Here we present oxygen-nonstoichiometric transition metal oxides as highly prominent candidates to catalyze the industrially important oxidation reactions of hydrocarbons when hydrogen peroxide is employed as an environmentally benign oxidant. The proof-of-concept data are revealed for the complex cobalt oxide, YBaCo4O7+δ (0 < δ < 1.5), in the oxidation process of cyclohexene. In the 2-h reaction experiments YBaCo4O7+δ was found to be significantly more active (>60 % conversion) than the commercial TiO2 catalyst (<20 %) even though its surface area was less than one tenth of that of TiO2. In the 7-h experiments with YBaCo4O7+δ, 100 % conversion of cyclohexene was achieved. Immersion calorimetry measurements showed that the high catalytic activity may be ascribed to the exceptional ability of YBaCo4O7+δ to dissociate H2O2 and release active oxygen to the oxidation reaction.

Ir supported over carbon materials for the selective hydrogenation of chloronitrobenzenes

In the present work we have studied the effect of carbon supports with different graphitic character (carbon nanotubes, mesoporous graphite and activated carbon) on the catalytic performance of iridium nanoparticles on the liquid phase chemoselective hydrogenation of para-chloronitrobenzene at room temperature. The effect of the oxygen groups was also evaluated by oxidizing a portion of the carbon nanotubes. The Raman and XRD spectra showed that the mesoporous graphite displayed the strongest graphitic character. The characterization of the catalysts by HR-TEM, XPS and TPR-H2, showed that the catalysts had similar particle size and that the catalysts prepared over the previously oxidized support, Ir/CNTox, was not fully reduced. The activity and selectivity achieved with the catalyst Ir/CNT was the best among the samples and the presence of irdium oxide on Ir/CNTox diminished the yield to p-chloroaniline, being the worse catalyst. The reactivity of different isomers was also studied over Ir/CNT and it followed the order m > o > p.

A new post-metallocene-ti catalyst with maltolate bidentade ligand: an investigation in heterogeneous polymerization reactions in different mesoporous supports

A new titanium catalyst easily synthesized from ethylmaltol bidentate chelator ligand was studied in homogeneous and heterogeneous ethylene polymerization. The dichlorobis(3-hydroxy-2-ethyl-4-pyrone)titanium(IV) complex was characterized by 1H and 13C NMR (nuclear magnetic resonance), UV-Vis and elemental analysis. Theoretical study by density functional theory (DFT) showed that the complex chlorines exhibit cis configuration, which is important for the activity in olefin polymerization. The complex was supported by two methods, direct impregnation or methylaluminoxane (MAO) pre-treatment, in five mesoporous supports: MCM-41 (micro and nano), SBA-15 and also the corresponding modified Al species. All the catalytic systems were active in ethylene polymerization and the catalytic activity was strongly influenced by the method of immobilization of the catalyst and the type of support.

Supported metal nanoparticles for sustainable green catalytic processes

Preformed Au nanoparticles supported on activated carbon and TiO2 were synthesised by sol-immobilisation. Polyethylene glycol, polyvinyl pyrrolidone and polyvinyl alcohol were used as stabilisers for the gold nanoparticles at different polymer/Au wt/wt ratios for each polymer. The effect of polymer/Au wt/wt ratios was investigated on (i) the average nanoparticle size, (ii) catalytic activity for two reactions, 4-nitrophenol reduction and glucose oxidation to glucaric acid. 4-nitrophenol reduction is recognised as a model reaction for nanomaterial catalytic activity tests; glucose oxidation to glucaric acid is a reaction that is traditionally carried out with concentrated nitric acid, for which alternative reaction pathways are looked for in an effort to reduce its environmental impact. The catalysts were characterised from the nanoparticle synthesis by colloidal method by means of UV-vis spectroscopy and DLS analysis, to the immobilisation step by XRD and TEM. The effect of the polymer:Au wt/wt ratio on nanoparticle size depends on the polymer nature, and point out the need to optimise supported nanoparticle synthesis protocols in the future depending on the type of stabiliser. The catalytic tests revealed that the polymers interact with Au nanoparticles through different active sites. Activated carbon (AC) and TiO2 were compared as supports for Au nanoparticles stabilised by PVA at PVA/Au 0,65 wt/wt. AC-supported Au NPs were the most active for glucose oxidation while TiO2-stabilised Au NPs were five times more active in 4-nitrophenol reduction that AC-supported NPs. Hence support and stabiliser are important parameters that should be optimised in order to achieve high catalytic activity for a given reaction.

Catalytic reduction of organic pollutants using supported metal nanoparticles

Metal nanoparticle catalysts have in the last decades been extensively researched for their enhanced performance compared to their bulk counterpart. Properties of nanoparticles can be controlled by modifying their size and shape as well as adding a support and stabilizing agent. In this study, preformed colloidal gold nanoparticles supported on activated carbon were tested on the reduction of 4-nitrophenol by NaBH4, a model reaction for evaluating catalytic activity of metal nanoparticles and one with high significance in the remediation of industrial wastewaters. Methods of wastewater remediation are reviewed, with case studies from literature on two major reactions, ozonation and reduction, displaying the synergistic effects observed with bimetallic and trimetallic catalysts, as well as the effects of differences in metal and support. Several methods of preparation of nanoparticles are discussed, in particular, the sol immobilization technique, which was used to prepare the supported nanoparticles in this study. Different characterization techniques used in this study to evaluate the materials and spectroscopic techniques to analyze catalytic activities of the catalyst are reviewed: ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS) analysis, X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) imaging. Optimization of catalytic parameters was carried out through modifications in the reaction setup. The effects of the molar ratio of reactants, stirring, type and amount of stabilizing agent are explored. Another important factor of an effective catalyst is its reusability and long-term stability, which was examined with suggestions for further studies. Lastly, a biochar support was newly tested for its potential as a replacement for activated carbon.

Effect Of Platform Connection And Abutment Material On Stress Distribution In Single Anterior Implant-supported Restorations: A Nonlinear 3-dimensional Finite Element Analysis.

Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance. The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method. Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4×13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts. The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material. The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.

Influence of different catilever extensions and glass or polyamaramid reinforcement fibers on fracture strength of implant-supported temporary

In long-term oral rehabilitation treatments, resistance of provisional crowns is a very important factor, especially in cases of an extensive edentulous distal space. The aim of this laboratorial study was to evaluate an acrylic resin cantilever-type prosthesis regarding the flexural strength of its in-balance portion as a function of its extension variation and reinforcement by two types of fibers (glass and polyaramid), considering that literature is not conclusive on this subject. Each specimen was composed by 3 total crowns at its mesial portion, each one attached to an implant component (abutment), while the distal portion (cantilever) had two crowns. Each specimen was constructed by injecting acrylic resin into a two-part silicone matrix placed on a metallic base. In each specimen, the crowns were fabricated with either acrylic resin (control group) or acrylic resin reinforced by glass (Fibrante, Angelus) or polyaramide (Kevlar 49, Du Pont) fibers. Compression load was applied on the cantilever, in a point located 7, 14 or 21 mm from the distal surface of the nearest crown with abutment, to simulate different extensions. The specimen was fixed on the metallic base and the force was applied until fracture in a universal test machine. Each one of the 9 sub-groups was composed by 10 specimens. Flexural strength means (in kgf) for the distances of 7, 14 and 21 mm were, respectively, 28.07, 8.27 and 6.39 for control group, 31.89, 9.18 and 5.16 for Kevlar 49 and 30.90, 9.31 and 6.86 for Fibrante. Data analysis ANOVA showed statistically significant difference (p<0.05) only regarding cantilever extension. Tukey's test detected significantly higher flexural strength for the 7 mm-distance, followed by 14 and 21 mm. Fracture was complete only on specimens of non-reinforced groups.