Gold/Iron Carbonyl Clusters for Tailored Au/FeOx Supported Catalysts

A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt4]4[Au4Fe4(CO)16] and [NEt4][AuFe4(CO)16] as precursors of highly dispersed nanoparticles over different supports. A series of catalysts with different metal loadings were prepared and tested in the complete oxidation of dichlorobenzene, toluene, methanol and in the preferential oxidation of CO in the presence of H2 (PROX) as model reactions. The characterization by BET, XRD, TEM, H2-TPR, ICP-AES and XPS point out the way the nature of the precursors and the thermal treatment conditions affected the dispersion of the active phase and their catalytic activity in the studied reactions

Synthesis of Nanometric Oxide Powders for SOFC Applications

Fuel Cell are electrochemical devices that convert the chemical energy of a fuel (generally hydrogen) and oxygen in electrical energy producing at the same time water and heat. These systems are interesting not only for the possibility of producing "clean" energy but also for the benefit linked to the high conversion efficiency. The Solid Oxide Fuel Cells (SOFC) in particular, are considered the most promising among the new systems of energy production especially for their intrinsic fuel flexibility (hydrocarbon, hydrogen, biogas, etc.). For these reasons, basic as well as technological studies focused on the improvement of the materials and production paths are of paramount importance to obtain SOFC competitive with the traditional energy production systems. Part of ISTEC research is devoted to the development of chemical synthesis able to produce tailored nano-oxides with characteristics suitable for SOFC applications. In particular soft-chemical synthesis routs were optimized to synthesize ceria and gadolinium-doped ceria nano-powders. Nano-structured powders exhibit in fact several size-dependant properties; among those, their high reactivity allows milder sintering conditions and as a consequence, better performances and lower production costs. Cerium oxide has been extensively used in a wide range of applications ranging from three way catalysts to gas sensors. When doped with gadolinum oxide, ceria becomes an alternative electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). Nano-structured ceria has recently attracted extensive attention because of its properties which were found to be size, shape and orientation-dependent. Although several methods were proposed for the synthesis of ultrafine powders, most of them generally require a subsequent calcination step. This thermal treatment is known to promote the crystallisation of the amorphous phase; however it also induces aggregation, reducing the specific surface area of the powder. The aim of this work was to produce ultrafine, pure and Gd-doped CeO2 powders using standard chemical routes coupled with non-conventional heating processes. Nano-crystalline ceria and Ce1-xGdxO2- (GDC) particles were successfully produced under mild conditions with two different methods: i) applying infrared heating to a common sol-gel process (IR-SG); ii) assisting with microwaves a polyol precipitation method (MW-PP). The correlation of the synthesis parameters with the thermodynamic and kinetic factors involved, allowed the control of fundamental properties such as size distribution, purity and morphology. Nano-structured ceria of particle size in the micron range with complex morphology and high specific surface area was prepared by adjusting the MW-PP synthesis conditions (temperature, time and templating agents). These mesoporous aggregates were found to be active in the catalytic oxidation of toluene. Moreover the GDC obtained through the optimization of the IR-SG parameters exhibited values of ionic conductivity higher than the ones showed by commercial and conventional sol-gel produced powders of similar compositio

Microwave-assisted synthesis of cerium oxide nanoparticles

Cerium oxide has recently received a lot of attention as a consequence of its catalytic properties that make it attractive for a wide range of applications ranging from solid oxide fuel cell, to three way catalysts gas sensors, etc. Although several methods have been proposed for the synthesis of ultrafine powders, the majority of them do not allow the production of powder with high specific area and they all generally require a calcination step for the crystallisation of the amorphous phase produced. Nanocrystalline ceria particles were successfully produced by one-step microwave-assisted synthesis from a glycol solution of metal nitrates under mild conditions (140?C, 1 atm). The as-prepared powder showed a good crystallinity and nanometric particle size. This simple and economic soft chemical method leads to nanometric cerium oxide with an high specific surface area suitable for catalytic applications

MW-Assisted polyol mediated synthesis of gadolinium-doped ceria nanopowders

Gadolinia-doped ceria (GDC) is one of the most promising electrolyte for intermediate temperature solid oxide fuel cells (SOFCs). In particular, the production of GDC as nanopowders leads to an higher reactivity that allows better performances, milder sintering conditions and lower production costs. However, nanopowders can be produced only by carefully tailoring their production process. The choice and optimization of the synthesis process is therefore a key step for the production of powders suitable for efficient SOFC components. In this work nanocrystalline GDC (Ce0.8Gd0.2O2-delta ) particles were successfully obtained by one-step microwave-assisted synthesis from a diethylene glycol solution of metal nitrates under mild conditions (170?C, 1 atm). The as-prepared powder showed good crystallinity with specific surface area of 50 m2/g. The sintering and electrochemical properties were compared with a nanometric commercial powder. The MW-produced powder showed an improved sintering behaviour and a uniform sub-micronic microstructure. Electrochemical tests for the MW-produced GDC showed at 600?C twice the conductivity of the corresponding commercial sampl

Alternative route for the synthesis of Lanthanum Strontium Titanate as SOFC Ni-free anode material

Among the perovskite structures, lanthanum-doped strontium titanates have attracted a lot of attention as possible candidates for SOFC Ni-free anodes. In particular the composition LaxSr1-(3x/2)TiO3 with x = 0.4 (LST) was recently considered for its tolerance to redox cycles and sufficiently high conductivities values. In this work an extensive study on the synthesis of LST powders with low-cost and easy-scalable methods is reported. The solid state and chemical synthesis as well as a combination of solution-solid state synthesis were considered. The influence of either the nature of the precursors (oxides, carbonates or nitrates) and the calcination temperature (from 500 to 1350?C) onto the perovskite formation was evaluated. The as-synthesized powders were morphologically, structurally and chemically characterized. The Pechini method leads to pure perovskite phase at 700?C for 1h, but it allows the production of only few grams of powder for each batch. On the other hand the solid state synthesis is a more up-scalable method but the phase can be obtained only at 1100?C for 1h. In addition the high reactivity of the lanthanum towards the humidity leads to a difficult control of the system stoichiometry and therefore of the final phase composition. An alternative solution-solid state synthesis was considered to produce batch of 100g of LST powders with good phase purity and in relatively mild conditions. The pure perovskite phase with the correct stoichiometry was obtained starting from the La and Sr nitrate aqueous solutions, highly reactive TiO2 followed by freeze-drying and calcination at 900?C for 1

Water-Resistant Photo-Crosslinked PEO/PEGDA Electrospun Nanofibers for Application in Catalysis

Catalysts are used for producing the vast majority of chemical products. Usually, catalytic membranes are inorganic. However, when dealing with reactions conducted at low temperatures, such as in the production of fine chemicals, polymeric catalytic membranes are preferred due to a more competitive cost and easier tunability compared to inorganic ones. In the present work, nanofibrous mats made of poly(ethylene oxide), PEO, and poly(ethylene glycol) diacrylate, PEGDA, blends with the Au/Pd catalyst are proposed as catalytic membranes for water phase and low-temperature reactions. While PEO is a water-soluble polymer, its blending with PEGDA can be exploited to make the overall PEO/PEGDA blend nanofibers water-resistant upon photo-crosslinking. Thus, after the optimization of the blend solution (PEO molecular weight, PEO/PEGDA ratio, photoinitiator amount), electrospinning process, and UV irradiation time, the resulting nanofibrous mat is able to maintain the nanostructure in water. The addition of the Au-6/Pd-1 catalyst (supported on TiO2) in the PEO/PEGDA blend allows the production of a catalytic nanofibrous membrane. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), taken as a water phase model reaction, demonstrates the potential usage of PEO-based membranes in catalysis

Heterocoagulation-spray drying process for the inclusion of ceramic pigments

The improvement of the physico-chemical resistance of hematite pigment in ceramic bodies has been pursued through its inclusion into a transparent and refractory matrix of silica or zirconia. The inclusion process was accomplished by heterocoagulation followed by spray-drying. The heterocoagulation process was optimised through an electrokinetic technique, that measured the potential of both matrix and pigment as a function of pH and of different amounts of dispersing agents. Suspensions of pigment and matrix were designed in order to achieve the maximum surface charges. The heterocoagulated mix was then spray-dried in order to avoid any separated coagulation of pigment and matrix and to obtain a well granulated powder suitable for application in ceramic bodies. A stable red-coloured ceramic pigment for low firing applications was obtained starting from amorphous silica as matrix and hematite as colorant

Investigation of the catalytic performance of Pd/CNFs for hydrogen evolution from additive-free formic acid decomposition

In recent years, research efforts have focused on the development of safe and efficient H2 generation/storage materials toward a fuel-cell-based H2 economy as a long-term solution in the near future. Herein, we report the development of Pd nanoparticles supported on carbon nanofibers (CNFs) via sol-immobilisation and impregnation techniques. Thorough characterisation has been carried out by means of XRD, XPS, SEM-EDX, TEM, and BET. The catalysts have been evaluated for the catalytic decomposition of formic acid (HCOOH), which has been identified as a safe and convenient H2 carrier under mild conditions. The influence of preparation method was investigated and catalysts prepared by the sol-immobilisation method showed higher catalytic performance (PdSI/CNF) than their analogues prepared by the impregnation method (PdIMP/CNF). A high turnover frequency (TOF) of 979 h−1 for PdSI/CNF and high selectivity (>99.99%) was obtained at 30 °C for the additive-free formic acid decomposition. Comparison with a Pd/AC (activated charcoal) catalyst synthesised with sol-immobilisation method using as a support activated charcoal (AC) showed an increase of catalytic activity by a factor of four, demonstrating the improved performance by choosing CNFs as the preferred choice of support for the deposition of preformed colloidal Pd nanoparticles

Pd/Au based catalyst immobilization in polymeric nanofibrous membranes via electrospinning for the selective oxidation of 5-hydroxymethylfurfural

Innovative nanofibrous membranes based on Pd/Au catalysts immobilized via electrospinning onto different polymers were engineered and tested in the selective oxidation of 5- (hydroxymethyl)furfural in an aqueous phase. The type of polymer and the method used to insert the active phases in the membrane were demonstrated to have a significant effect on catalytic performance. The hydrophilicity and the glass transition temperature of the polymeric component are key factors for producing active and selective materials. Nylon-based membranes loaded with unsupported metal nanoparticles were demonstrated to be more efficient than polyacrylonitrilebased membranes, displaying good stability and leading to high yield in 2,5-furandicarboxylic acid. These results underline the promising potential of large-scale applications of electrospinning for the preparation of catalytic nanofibrous membranes to be used in processes for the conversion of renewable molecules

Tandem Hydrogenation/Hydrogenolysis of Furfural to 2-Methylfuran over a Fe/Mg/O Catalyst: Structure–Activity Relationship

The hydrodeoxygenation of furfural (FU) was investigated over Fe-containing MgO catalysts, on a continuous gas flow reactor, using methanol as a hydrogen donor. Catalysts were prepared either by coprecipitation or impregnation methods, with different Fe/Mg atomic ratios. The main product was 2-methylfuran (MFU), an important highly added value chemical, up to 92% selectivity. The catalyst design helped our understanding of the impact of acid/base properties and the nature of iron species in terms of catalytic performance. In particular, the addition of iron on the surface of the basic oxide led to (i) the increase of Lewis acid sites, (ii) the increase of the dehydrogenation capacity of the presented catalytic system, and (iii) to the significant enhancement of the FU conversion to MFU. FTIR studies, using methanol as the chosen probe molecule, indicated that, at the low temperature regime, the process follows the typical hydrogen transfer reduction, but at the high temperature regime, methanol dehydrogenation and methanol disproportionation were both presented, whereas iron oxide promoted methanol transfer. FTIR studies were performed using furfural and furfuryl alcohol as probe molecules. These studies indicated that furfuryl alcohol activation is the rate-determining step for methyl furan formation. Our experimental results clearly demonstrate that the nature of iron oxide is critical in the efficient hydrodeoxygenation of furfural to methyl furan and provides insights toward the rational design of catalysts toward C–O bonds' hydrodeoxygenation in the production of fuel components