Arup Gayen

Nanofaceted PdO Sites in PdCe Surface Superstructures: Enhanced Activity in Catalytic Combustion of Methane†

An open superstructure: A Pd/CeO2 catalyst prepared by solution combustion synthesis is three to five times more active for CH4 combustion than the best conventional palladium-based systems. The catalyst contains an ordered, stable Pd-O-Ce surface superstructure (see picture; cyan arrow is a square-planar Pd site, red arrow is an undercoordinated O atom) and is an example of ultra-highly dispersed, stable PdO within an oxide carrier.

Influence of Different Palladium Precursors on the Properties of Solution-Combustion-Synthesized Palladium/Ceria Catalysts for Methane Combustion

A series of Pd/CeO2 catalysts was prepared by solution combustion synthesis (SCS) using different Pd precursors. The powders were characterized by complementary techniques such as BET surface area measurements, X‐Ray diffraction analysis, X‐Ray photoelectron spectroscopy, temperature‐programmed reduction, temperature‐programmed oxidation, and high‐resolution TEM. The results obtained evidenced the formation of a Pd‐Ce solid solution on all SCS samples. This solid solution is in the form of an ordered supercell structure only in the SCS catalyst prepared from palladium nitrate. This was correlated to the heat of reaction between Pd(NO3)2 and the fuel. The samples were tested for methane catalytic combustion, and the reaction rates on all SCS samples were approximately twice that of the impregnated counterpart, irrespective of the precursor. This was attributed to the presence of the Pd‐O‐Ce solid solution, which gave rise to strong Pd–ceria interactions.

Albumin matrix assisted wet chemical synthesis of nanocrystalline MFe2O4 (M = Cu, Co and Zn) ferrites for visible light driven degradation of methylene blue by hydrogen peroxide

Spinel MFe2O4 (M = Cu, Co and Zn) ferrites have been successfully synthesized via a wet chemical process assisted by albumin matrix and employed as catalyst for methylene blue (MB) degradation. The materials have been characterized by different techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FESEM), Raman spectroscopy, Mossbauer spectroscopy, vibrating sample magnetometry (VSM) and N2 adsorption–desorption isotherm. The crystallite size is found to vary from 13 to 43 nm depending on the calcination temperature and they exhibit low BET surface area. Spherical and rod like surface morphology is obtained for porous copper and zinc ferrite. Copper and cobalt ferrite exhibit ferromagnetic properties typical of nanomaterials. On the other hand zinc ferrite shows superparamagnetic behavior. The current ferrites, specifically copper ferrite, are reported to exhibit significant catalytic activity for the photodegradation of methylene blue in the presence of H2O2 under visible light. All the ferrite materials show better activity in acidic medium.

Selective liquid phase benzyl alcohol oxidation over Cu-loaded LaFeO3 perovskite

Copper loaded LaMO3 (M = Mn, Fe and Co) perovskites have been synthesized by a single-step solution combustion method. These materials have been investigated for liquid phase oxidation of benzyl alcohol using tertiary butyl hydrogen peroxide (TBHP) as oxidant in air at 80 °C under ambient pressure. Among these, the 10 at% Cu-loaded LaFeO3 has shown the best activity i.e., ∼99% conversion with complete benzaldehyde selectivity. The formation of perovskite phase was confirmed from XRD and the presence of Cu2+ was confirmed by XPS analysis. The higher activity of the combustion synthesized catalyst has been ascribed to the presence of a poorly defined surface structure containing an amorphous CuO phase wrapping the LaFeO3 particle, as evidenced from the HRTEM analysis. The catalyst recycling tests have shown a negligible loss of activity in the consecutive cycles.

Synthesis and magnetic properties of nano-dimensional Fe1−xCuxAl2O4 (0.3 ≤ x ≤ 0.8)

Here we report, the sol–gel synthesized, microstructural analysis, surface and magnetic properties of solid solutions of Fe1−xCuxAl2O4. The singular phase of the samples for x values varied between 0.3 and 0.8 at 700 °C has been obtained. The powder X-ray diffraction, electron diffraction and HRTEM analysis reveal that the particle size systemically increases with the increase in x value. The XPS studies have confirmed the presence of Cu2+ species with a (Fe + Cu)/Al surface atomic ratio close to the bulk stoichiometric value. Unlike the common magnetic spinels with B-site magnetic cations, Fe1−xCuxAl2O4 shows only A-site magnetism in a diamond-type lattice. The samples with smaller particle size, namely the samples for x = 0.3 and 0.4 exhibit small magnetization. The origin of such magnetism is attributed to the inversion in the spinel structure and the defect induced magnetism. Except for the x = 0.7 sample, all other samples show spin glass behavior.

Chemoselective hydrogenation of cinnamaldehyde at atmospheric pressure over combustion synthesized Pd catalysts

A series of Pd-supported metal oxides (Al2O3, Fe2O3 and CeO2) have been prepared by a single step solution combustion synthesis (SCS) method. Their catalytic performance was evaluated forxa0the selective hydrogenation of cinnamaldehyde (CAL) to hydrocinnamaldehyde (HCAL) under atmospheric pressure of hydrogen at 100xa0°C. Among these materials, combustion synthesized Pd (2 at.%)/Al2O3 catalyst exhibits the highest CAL conversion (69%) with complete HCAL selectivity. The analogous catalyst prepared by the incipient wetness impregnation (IWI) method shows an initially similar activity. X-ray diffraction and high resolution transmission electron microscopy analyses of the as prepared SCS sample show fine dispersion of PdO over the γ-Al2O3 support. On ageing, a major portion of PdO is reduced to metallic Pd (Pd2+:Pd0xa0=xa036:64 for the SCS catalyst and Pd2+:Pd0xa0=xa026:74 for the IWI catalyst from X-ray photoelectron spectroscopy studies) suggesting comparatively more ionic character of palladium in the SCS catalyst. In the hydrogen atmosphere, without distinguishing the reductive pretreatment of catalyst and the beginning of hydrogenation subsequent to CAL addition, the Pd-species undergoes rearrangement to form a core–shell like structure of Pd (core)–PdO (periphery) covered with alumina layer, bringing in additional stability to the Pd-species in the SCS catalyst and making it highly recyclable. The analogous IWI catalyst, on the contrary, contains a mixed Pd–PdO ensemble that does not increase the stability causing continuous loss of activity in the consecutive cycles of hydrogenation.

Single step combustion synthesized Cu/Ce0.8Zr0.2O2 for methanol steam reforming: Structural insights from in situ XPS and HRTEM studies

Abstract Single step combustion synthesized Cu (5–15 at.-%)/Ce0.8Zr0.2O2 materials containing highly dispersed copper have been assessed for methanol steam reforming (MSR). The activity patterns suggest Cu (10 at.-%)/Ce0.80Zr0.20O2 as the most active formulation, converting ~51% methanol at 300 °C at a gas hourly space velocity of 40,000 h-1 (W/F = 0.09 s). The in situ XPS experiments carried over the most active sample show a sharp falloff of Cu-surface concentration from a considerably high value of 26% before to 7.4% after the in situ MSR tests and it is associated with the complete reduction of oxidized Cu-species (Cu2+) to metallic copper (Cu0). These findings point to the sintering of copper during MSR which is attributed to be responsible for the deactivation observed with time on stream. Interestingly, the MSR activity is shown to be regenerated nearly completely through an intermediate in situ oxidation step in the consecutive cycles of methanol reforming.

Microstructure, morphology, and methylene blue degradation over nano-CuFe2O4 synthesized by a modified complexometric method

Nanodimensional copper ferrite has been successfully synthesized via a modified complexometric method using ethylenediaminetetraacetic acid and citric acid as the complexing agent and the fuel, respectively. The physical and chemical behaviors of this spinel ferrite material have been explored by using different kinds of techniques including thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), vibrating sample magnetometry (VSM), and N2 adsorption–desorption isotherm. The crystallite size falls in the range 13–30xa0nm depending on the calcination temperature required for phase formation. The surface morphology of the polycrystalline ferrite material is almost spherical. The band gap value and BET-specific surface area are determined to be 1.40xa0eV and 32xa0m2xa0g−1, respectively. This spinel ferrite behaves as a mesoporous (2–50xa0nm) material, and the material formed at a higher calcination temperature has agglomeration tendency. The CuFe2O4 exhibits typical soft ferromagnetic behavior with saturation magnetization value of 52xa0emuxa0g−1. Of interest, it has the capability to degrade 96% of methylene blue in acidic medium (pHu2009=u20094) in 45xa0min under the visible light in presence of H2O2 as oxidant.

Ultra-high sensitivity of luminescent ZnCr2O4 nanoparticles toward nitroaromatic explosives sensing

Here, we report the luminescence based sensing of trace amounts of nitroaromatic explosive organic compounds. The luminescence emission of nanosized spinel oxide ZnCr2O4 with high chemical and thermal stabilities has been used as a potential probe to detect such organic explosives. Low temperature solution combustion synthesized ZnCr2O4 oxide with an average particle size of ∼9 nm exhibits strong luminescence emission at 410 nm upon excitation at 260 nm in an aqueous suspension. The presence of nitroaromatics in ZnCr2O4 suspension dramatically suppresses the luminescence emission providing an opportunity to detect it quantitatively. The detection limit for 2,4,6-trinitrophenol (TNP) is as low as 23 ppb. A number of organic compounds have been investigated for a comprehensive understanding. The astonishing sensitivity of ZnCr2O4 nanoparticles towards nitro explosives is appealing for sensing application. A plausible explanation of such luminescence quenching has been ascribed to a two-fold mechanism. The underling mechanism is further substantiated by a similar study on ZnO nanoparticles.