We demonstrate an ultrafast method for the formation of graphene supported Pt catalysts by the co-reduction of graphene oxide and Pt salt using ethylene glycol under microwave irradiation conditions. Detailed analysis of the mechanism of formation of the hybrids indicates a synergistic co-reduction mechanism whereby the presence of the Pt ions leads to a faster reduction of GO and the presence of the defect sites on the reduced GO serves as anchor points for the heterogeneous nucleation of Pt. The resulting hybrid consists of ultrafine nanoparticles of Pt uniformly distributed on the reduced GO susbtrate. We have shown that the hybrid exhibits good catalytic activity for methanol oxidation and hydrogen conversion reactions. The mechanism is general and applicable for the synthesis of other multifunctional hybrids based on graphene.

Ce 1-x Sn x O 2 (x ) 0.1-0.5) solid solution and its Pd substituted analogue have been prepared by a single step solution combustion method using tin oxalate precursor. The compounds were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and H 2 /temperature programmed redution (TPR) studies. The cubic fluorite structure remained intact up to 50% of Sn substitution in CeO 2 , and the compounds were stable up to 700 °C. Oxygen storage capacity of Ce 1-x Sn x O 2 was found to be much higher than that of Ce 1-x Zr x O 2 due to accessible Ce 4+ /Ce 3+ and Sn 4+ /Sn 2+ redox couples at temperatures between 200 and 400 °C. Pd 2+ ions in Ce 0.78 Sn 0.2 Pd 0.02 O 2-δ are highly ionic, and the lattice oxygen of this catalyst is highly labile, leading to low temperature CO to CO 2 conversion. The rate of CO oxidation was 2 µmol g -1 s -1 at 50 °C. NO reduction by CO with 70% N 2 selectivity was observed at ∼200 °C and 100% N 2 selectivity below 260 °C with 1000-5000 ppm NO. Thus, Pd 2+ ion substituted Ce 1-x Sn x O 2 is a superior catalyst compared to Pd 2+ ions in CeO 2 , Ce 1-x Zr x O 2 , and Ce 1-x Ti x O 2 for low temperature exhaust applications due to the involvement of the Sn 2+ /Sn 4+ redox couple along with Pd 2+ /Pd 0 and Ce 4+ /Ce 3+ couples.

Semiconductor based nanoscale heterostructures are promising candidates for photocatalytic and photovoltaic applications with the sensitization of a wide bandgap semiconductor with a narrow bandgap material being the most viable strategy to maximize the utilization of the solar spectrum. Here, we present a simple wet chemical route to obtain nanoscale heterostructures of ZnO/CdS without using any molecular linker. Our method involves the nucleation of a Cd-precursor on ZnO nanorods with a subsequent sulfidation step leading to the formation of the ZnO/CdS nanoscale heterostructures. Excellent control over the loading of CdS and the microstructure is realized by merely changing the initial concentration of the sulfiding agent. We show that the heterostructures with the lowest CdS loading exhibit an exceptionally high activity for the degradation of methylene blue (MB) under solar irradiation conditions; microstructural and surface analysis reveals that the higher activity in this case is related to the dispersion of the CdS nanoparticles on the ZnO nanorod surface and to the higher concentration of surface hydroxyl species. Detailed analysis of the mechanism of formation of the nanoscale heterostructures reveals that it is possible to obtain deterministic control over the nature of the interfaces. Our synthesis method is general and applicable for other heterostructures where the interfaces need to be engineered for optimal properties. In particular, the absence of any molecular linker at the interface makes our method appealing for photovoltaic applications where faster rates of electron transfer at the heterojunctions are highly desirable.

Microwave-based methods are widely employed to synthesize metal nanoparticles on various substrates. However, the detailed mechanism of formation of such hybrids has not been addressed. In this paper, we describe the thermodynamic and kinetic aspects of reduction of metal salts by ethylene glycol under microwave heating conditions. On the basis of this analysis, we identify the temperatures above which the reduction of the metal salt is thermodynamically favorable and temperatures above which the rates of homogeneous nucleation of the metal and the heterogeneous nucleation of the metal on supports are favored. We delineate different conditions which favor the heterogeneous nucleation of the metal on the supports over homogeneous nucleation in the solvent medium based on the dielectric loss parameters of the solvent and the support and the metal/solvent and metal/support interfacial energies. Contrary to current understanding, we show that metal particles can be selectively formed on the substrate even under situations where the temperature of the substrate is lower than that of the surrounding medium. The catalytic activity of the Pt/CeO(2) and Pt/TiO(2) hybrids synthesized by this method for H(2) combustion reaction shows that complete conversion is achieved at temperatures as low as 100 °C with Pt-CeO(2) catalyst and at 50 °C with Pt-TiO(2) catalyst. Our method thus opens up possibilities for rational synthesis of high-activity supported catalysts using a fast microwave-based reduction method.

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Tetragonal ZrO(2) was synthesized by the solution combustion technique using glycine as the fuel. The compound was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and BET surface area analysis. The ability of this compound to adsorb dyes was investigated, and the compound had a higher adsorption capacity than commercially activated carbon. Infrared spectroscopic observations were used to determine the various interactions and the groups responsible for the adsorption activity of the compound. The effects of the initial concentration of the dye, temperature, adsorbent concentration, and pH of the solution were studied. The kinetics of adsorption was described as a first-order process, and the relative magnitudes of internal and external mass transfer processes were determined. The equilibrium adsorption was also determined and modeled by a composite Langmuir-Freundlich isotherm.

CO 2 methanation is an important probe reaction to understand CO 2 interactions with catalytic surfaces. Importance of this reaction is further increased by its association with CO 2 utilization. This study reports mechanistic aspects of CO 2 methanation over combustion synthesized Ru-substituted CeO 2 catalyst. Temperature programmed reaction experiments were carried out to understand the interaction of CO 2 , H 2 and their stoichiometric mixture with the catalyst surface. In situ FTIR spectroscopy was used to identify the intermediates of the reaction. It was observed that CO 2 adsorption took place on the surface of Ce 0.95 Ru 0.05 O 2 and the formation of surface carbonate intermediates took place only when H 2 was present in the gas phase. In absence of H 2 , CO 2 did not show any indication for chemisorption. This behavior was explained in terms of the reaction between CO 2 and the surface hydroxyls leading to formation of vacancy. Upon dissociation, carbonates led to chemisorbed CO which eventually formed methane upon reaction with gas phase H 2 . The exact identity of carbonate species and the pathway for methanation step were ambiguous following purely experimental studies. Density functional theory calculations were carried out to augment the experimental observations. Complete energy landscapes developed on the basis of differentiation of oxidized and reduced forms of the catalyst showed that the reaction followed a pathway consisting of surface carbonate species formed by the interaction of oxide surface and chemisorbed CO, and a sequential methanation via the surface methoxy species formation. The study provides physical insights into the role of oxidation state of the catalyst and the surface anionic vacancies in governing the reaction pathway.2

An efficient, cost-effective, and earth-abundant catalyst that could drive the production of hydrogen from water without or with little external energy is the ultimate goal toward hydrogen economy. Herein, nanoplates of tungsten oxide and its hydrates (WO 3 ·H 2 O) as promising electrocatalysts for the hydrogen evolution reaction (HER) are reported. The square-shaped and stacked WO 3 ·H 2 O nanoplates are synthesized at room temperature under air in ethanol only, making it as a promising green synthesis strategy. The repeated electrochemical cyclic voltammetry cycles modified the surface of WO 3 ·H 2 O nanoplates to WO 3 as confirmed by X-ray photoelectron and Auger spectroscopy, which leads to an improved HER activity. Hydrogen evolution is further achieved from distilled water (pH 5.67) producing 1 mA cm –2 at an overpotential of 15 mV versus the reversible hydrogen electrode. Moreover, WO 3 ·H 2 O and WO 3 nanoplates demonstrate excellent durability in acidic and neutral media, which is highly desirable for practical application. Improved hydrogen evolution by WO 3 (200) when compared to that by Pt(111) is further substantiated by the density functional theory calculations.