Metal Precursor Solution Research Articles

A new and generic preparation method of mesoporous clay composites containing dispersed metal oxide nanoparticles

Nanosized oxide precursors of various transitional metals, including iron, chromium, cobalt, manganese and cerium, were prepared by dissolving their corresponding hydroxides in acetic acid solutions. These precursors were used to substitute the sodium ions in laponite clay like the way to prepare pillared clays, forming mesoporous solids with high surface areas of ca. 510–640 m 2/g. Stabilised by the adsorbed acetic acid molecules, the nanoparticle precursors of the metal oxides were well dispersed on the silicate platelets during the synthesis. The increase in the porosity after the intercalation of nanoparticles is primarily interpreted in terms of further delamination of the laponite clay caused by the reaction between the acidic metal precursor solutions and the silicate platelets. The clay composites containing nanoparticles of cobalt oxide appeared much more active than the impregnated cobalt catalysts in the deep oxidation of volatile organic compounds.

Preparation of Multicomponent Metal Oxides Using Nozzle Spray and Microwaves

AbstractMulticomponent metal oxide (MMO) crystallites are prepared by spraying a reactant solution into a receiving solution or into air under microwave radiation at atmospheric pressure. The injection of a nitric acid solution through an ultrasonic nozzle into a receiving solution of metal precursor and the use of microwave radiation are combined to form a novel preparation technique called the nozzle‐spray/microwave (NMW) method. The inclusion of an additional step, the in situ mixing of precursor solutions prior to their injection through the ultrasonic nozzle spray, leads to another procedure called the in situ/nozzle‐spray/microwave (INM) method. For comparison, MMO materials with the same metal constituents as those prepared by our novel techniques are prepared by conventional hydrothermal (CH) methods. Fresh materials prepared by NMW, INM, and CH methods were heat treated to study the effect of calcination. All materials were characterized before and after calcination using X‐ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller surface area, and inductively coupled plasma elemental analysis. The NMW method produces particles with rodlike morphologies different from those obtained using CH methods. The INM method produces an amorphous material that crystallizes after calcination into small (ca. 200 nm) particles with interesting morphologies. Notably, calcination of materials prepared by both NMW and INM reduces the particle size and increases the surface area. The work presented in this paper paves the way to use NMW and INM to prepare MMOs with unique morphologies.

High-throughput preparation and testing of ion-exchanged zeolites

A high-throughput research platform was developed for the preparation and subsequent catalytic liquid-phase screening of ion-exchanged zeolites, for instance with regard to their use as heterogeneous catalysts. In this system aqueous solutions and other liquid as well as solid reagents are employed as starting materials and 24 samples are prepared on a library plate with a 4 × 6 layout. Volumetric dispensing of metal precursor solutions, weighing of zeolite and subsequent mixing/washing cycles of the starting materials and distributing reaction mixtures to the library plate are automatically performed by liquid and solid handlers controlled by a single common and easy-to-use programming software interface. The thus prepared materials are automatically contacted with reagent solutions, heated, stirred and sampled continuously using a modified liquid handling. The high-throughput platform is highly promising in enhancing synthesis of catalysts and their screening. In this paper the preparation of lanthanum-exchanged NaY zeolites (LaNaY) on the platform is reported, along with their use as catalyst for the conversion of renewables.

Novel transparent conducting sol–gel oxide coatings

This work focuses on the preparation of novel ternary transparent conducting oxide coatings on glass by the sol–gel method. The coatings were deposited by spin-coating from solutions of appropriate metal precursors and heat-treated at different heat-treatment procedures. An increase in electrical conductivity was achieved by a final forming gas treatment. Best electrical and optical properties have been obtained for coatings of crystalline Zn 2SnO 4, Zn 3In 2O 6 and Zn 5In 2O 8 and X-ray amorphous ZnSnO 3 with resistivities in the order of 10 − 2 –10 − 1 Ω cm, an average transmission in the visible of 85% and an average surface roughness of ∼ 1 nm. ZnGa 2O 4 and GaSbO 4 coatings showed no electrical conductivity. For Zn 2SnO 4 coatings, a restricted crystallite growth was observed probably due to phase segregation effects. Electrical properties of coatings in the system ZnO–In 2O 3 were interpreted on the basis of the percolation theory.

Performance of ternary PtRuRh/C electrocatalyst with varying Pt:Ru:Rh ratio for methanol electro-oxidation

Highly dispersed ternary PtRuRh/C anode catalysts for direct methanol fuel cells were prepared with various contents and their electro-catalytic activities towards methanol oxidation at 25 °C and 60 °C were examined to investigate the influence of the catalyst composition. Electrocatalysts were prepared by a co-impregnation method using ethanolic solutions of metal precursors and carbon black followed by pyrolysis under reducing conditions. X-ray diffraction analysis revealed that the fcc peaks shifted to higher diffraction angles with increasing Rh content, indicating the alloying of Rh into the fcc structure. In terms of the mass specific current density, the activity towards methanol oxidation differed significantly depending on the catalysts composition and cell temperature. The catalyst prepared at a ratio of Pt:Ru:Rh = 1:1:2 exhibited the highest activity at 60 °C of 155 A (g-Pt)−1 at 0.5 V vs. RHE.

Methane activation on superacidic catalysts based on oxoanion modified zirconium oxide

A series of metal promoted catalysts was prepared by impregnation of metal precursor solutions on oxoanion modified zirconias (sulfated, molybdated and tungstated), well recognized, in the literature, for their ability in catalyzing the isomerization of light alkanes at low temperatures. Structural characterization and nature of surface active sites were attempted to explain the methane activation reaction on these catalysts. Although Lewis and Brönsted acid sites were observed on the oxoanion modified zirconias, as detected by infrared of pyridine adsorption, the methane activation occurred only when promoted with specific metals, such as Fe-Mn, Co-Mn, Al, Ni and Cu, for sulfated zirconias, and Ni for molybdated and tugstated zirconias. The results obtained suggest different kinds of active surface sites, depending on the oxoanion present and thus different mechanisms could be proposed for the methane activation reaction. It was suggested that on metal promoted sulfated zirconias, methane was converted into ethane by an acid catalyzed mechanism, more specifically, by S OH groups as proton donors. On NiO promoted molybdated and tungstated zirconias, methane was not simultaneously converted into ethane but only after an induction period. The XRD patterns of tugstated zirconias after the reaction with methane, showed only reflections at 2 θ = 42.6°, 53.8° and 77.6°, characteristics of nickel on zero oxidation state. Although these reflections were absent for Ni promoted molybdated zirconias, these catalysts were black in color after reaction. TPR experiments using CH 4 as reduction gas gave support to the proposal for a mechanism catalyzed by metal for the methane conversion into ethane on Ni promoted molybdated and tungstated zirconias.

Facile In Situ Synthesis of Noble Metal Nanoparticles in Porous Cellulose Fibers

In situ synthesis of noble metal (Ag, Au, Pt, Pd) nanoparticles was carried out under ambient conditions in porous cellulose fibers as nanoreactors. Particles of less than 10 nm were readily prepared using the described approach, and monodisperse nanoparticles were obtained under an optimized concentration of the metal precursor solution. The nanoporous structure and the high oxygen (ether and hydroxyl) density of the cellulose fiber constitute an effective nanoreactor for in situ synthesis of metal nanoparticles. The nanopore is essential for incorporation of metal ion and reductant into cellulose fibers as well as for removal of unnecessary byproducts from fibers. This was endorsed by negligible adsorption of metal ion onto nonporous films of poly(vinyl alcohol) and starch. The ether oxygen and the hydroxyl group not only anchor metal ions tightly in cellulose fibers via ion−dipole interactions, but they also stabilize metal nanoparticles by strong bonding interaction with their surface atoms. The preparative procedure is facile and versatile, and provides a simple route to manufacturing of useful noble metal nanoparticles.

Ordered Macroporous Particles by Colloidal Templating

Ordered macroporous particles of silica and titania were fabricated by colloidal templating. The colloidal templates were assembled through colloidal crystallization of suspended polystyrene latex sphere particles in aqueous droplets straddling an air−oil interface. The procedures involve first preparing spherical colloidal crystalline particles of polystyrene latex spheres and then infusing them with metal precursor solutions that form silica or titania in the interstices. Finally, calcination decomposes the polystyrene latex spheres, leaving macropores at their sites. The shape of the template was controlled by the presence of additive surfactant or by the action of an applied electric field. Specifically, spherical, concaved disklike, and ellipsoidal colloidal crystals were prepared successfully and used as templates for the fabrication of ordered macroporous particles. The SEM images of the prepared macroporous particles showed that the pores were interconnected and ordered into a hexagonal arrangement.

Preparation and Catalytic Properties of Amphiphilic Copolymer-Stabilized Platinum Metals Colloids

Several metal colloids stabilized by an amphiphilic copolymer, poly(1-vinylpyrrolidone-co-acrylic acid) (abbreviated as PVPAA), were prepared by refluxing alcohol–water mixed solutions of the corresponding metal precursors. They had small particle sizes and narrow size distributions. Their catalytic activity was tested by hydrogenation of cyclooctene, 1-dodecene, and ortho-chloronitrobenzene (o-CNB). With the introduction of nickel(II) ions to a PVPAA-stabilized platinum catalytic system, selective hydrogenation of o-CNB to ortho-chloroaniline (o-CAN) with 97.1% selectivity and 100% conversion was obtained.

Nanostructural evolution of high loading Rh/lanthana catalysts through the preparation and reduction steps

A detailed high resolution electron microscopy investigation of different Rh/lanthana catalysts has been carried out. Samples prepared by wet impregnation using either aqueous or acetone solutions of rhodium nitrate and metal deposition by evaporation under high vacuum have been studied. The nanostructural evolution of the support and the metal phase through the different preparation steps has been tracked. Thus, the effects of reduction treatments in a wide range of temperatures (473–973 K) have been taken into consideration. Scanning electron microscopy images evidence an intense dissolution of the lanthanide sesquioxide crystallites during the impregnation step with the rhodium nitrate aqueous solution. Such an effect could not be detected in the catalyst prepared using an acetone solution of the same metal precursor. On its hand, HREM indicates the presence of a highly dispersed metal phase in the catalyst prepared in water after reduction at low temperatures. Increasing the reduction temperature leads to a significant sintering of rhodium present both on the surface and the bulk of the support. Decorated rhodium particles are clearly visible in the three catalysts in the whole range of reduction temperatures. The drastic structural rearrangements which take place in the support during the reduction treatment and support dragging during sintering, are most likely the driving force for the decoration of the metal particle surfaces.

Electrically Conductive Molecular Composites Based Upon Ppbt and Metallophthalocyanines: Processing, Microstructure, and Electrochemistry

ABSTRACTMechanically strong, environmentally stable, and electrically conductive polymeric films and fibers can be fabricated by processing (dry-jet, wet-spinning) solutions of PPBT and metallophthalocyanine molecular metal precursors, followed by chemical or electrochemical oxidation. X-ray diffraction, and resonance Raman measurements on (PPBT)-[Ni(Pc)I]x fibers indicate a microstructure consisting of small Ni(Pc)I crystallites imbedded in a PPBT matrix. Cyclic voltammetry and controlled potential coulometry indicate that PPBT/NiPc films can be reversibly doped.