• G Ranga Rao

      Articles written in Journal of Chemical Sciences

    • XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

      G Ranga Rao H Ranjan Sahu

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      A series of ceria-incorporated zirconia (Ce1−xZrxO2,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce3+ ← O2−and Ce4+ ← O2− charge transfer transitions. The two vibrational bands in 6960 cm−1 and 5168 cm−1 in the NIR region indicate the presence of surface hydroxyl groups on these materials.

    • Hydrogen transfer reaction of cyclohexanone with 2-propanol catalysed by CeO2-ZnO materials: Promoting effect of ceria

      Braja Gopal Mishra G Ranga Rao B Poongodi

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      Ce-Zn-O mixed oxides were prepared by amorphous citrate process and decomposition of the corresponding acetate precursors. The resulting materials were characterised by TGA, XRD, UV-Vis-DRS, EPR, SEM and surface area measurements. XRD and DRS results indicated fine dispersion of the ceria component in the ZnO matrix. EPR results clearly indicate the presence of oxygen vacancy and defect centres in the composite oxide. Addition of CeO2 to ZnO produced mixed oxides of high surface area compared to the pure ZnO. Hydrogen transfer reaction was carried out on these catalytic materials to investigate the effect of rare earth oxide on the activity of ZnO. Addition of ceria into zinc oxide was found to increase the catalytic activity for hydrogen transfer reaction. The catalytic activity also depended on the method of preparation. Citrate process results in uniformly dispersed mixed oxide with higher catalytic activity.

    • Investigation of hybrid molecular material prepared by ionic liquid and polyoxometalate anion

      T Rajkumar G Ranga Rao

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      A solid hybrid molecular material containing 1-butyl 3-methyl imidazolium cations and Keggin anions of phosphotungstic acid has been synthesized. It is fully characterized by CHN analysis, FTIR, XRD, UV-Vis-NIR DRS, 31P MAS NMR, TGA and SEM. The FTIR spectrum of the compound shows the fingerprint vibrational bands of both Keggin molecular anions and imidazolium cations. The aromatic C-H stretch region (2700-3250 cm-1) of imidazolium cation is split due to the interaction between the ring C-H and bulky Keggin anion. The red-shift in the UV-Vis spectra and the downfield 31P MAS NMR chemical shift also confirm the electrostatic interaction between the ions in the compound. Near IR spectral region (1000-2500 nm) shows the elimination of water in the compound which is hydrophobic.

    • Novel nanostructured CeO2 as efficient catalyst for energy and environmental applications

      Sumanta Kumar Meher G Ranga Rao

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      We report here versatile methods to engineer the microstructure and understand the fundamental physicochemical properties of CeO2 to improve its catalytic viability for practical applications. In this context, different morphologies of CeO2 are synthesized using tailored homogeneous precipitation methods and characterized by XRD, BET, SEM and TPR methods. The shuttle-shaped CeO2 prepared under hydrothermal condition shows higher surface area and low-temperature reducibility. The 0.5 wt% Pt-impregnated shuttle-shaped CeO2 shows lower-temperature CO oxidation behaviour as compared to its bulk-like CeO2 (with 0.5 wt% Pt) counterpart, synthesized by conventional-reflux method. Further, nanorod morphology of CeO2 prepared with Cl−as counter ion shows lower-temperature oxidation of soot as compared to the mesoflower morphology of CeO2, prepared with NO$^−_3$ as counter ion in the reaction medium. Further, linear sweep voltammetry, chronopotentiometry and CO-stripping voltammetry studies are performed to evaluate the promoting activity of CeO2 to Pt/C for ethanol electro-oxidation reaction in acidic media. Results show that CeO2 provides active triple-phase-interfacial sites for suitable adsorption of OH species which effectively oxidize the COads on Pt/C. The results presented here are significant in the context of understanding the physicochemical fine prints of CeO2 and CeO2 based hetero-nanocomposites for their suitability to important catalytic and energy-related applications.

    • Electrochemical behaviour of Cu(II)/Cu(I) redox couple in 1-hexyl-3-methylimidazolium chloride ionic liquid

      K Shakeela A Sri Dithya Ch Jagadeeswara Rao G Ranga Rao

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      The electrochemical behaviour of Cu(II)/Cu(I) redox couple in 1-hexyl-3-methylimidazolium chloride (C6mimCl) ionic liquid was studied using glassy carbon electrode at 375 K by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. In this electrochemical study, we have made an attempt to avoid the problem of water contamination in hygroscopic C6mimCl ionic liquid by setting the temperature at 375 K without glove box. This high temperature cyclic voltammetric study revealed two-step one electron reductions of Cu(II) to Cu(I) followed by Cu(I) to Cu metal. The reduction of Cu(II) to Cu(I) was found to be quasi-reversible at 375 K. The diffusion coefficients of Cu(II) and Cu(I), and the charge transfer rate constant of Cu(II) in C6mimCl were estimated by Randles-Ševčik equation and Nicholson’s method, respectively, and found to be consistent with the quasi-reversible process. Further, constant potential electrodeposition of metallic copper was carried out on a stainless steel electrode at 375 K and the deposit was characterised by X-ray diffraction and electron microscopy.

    • Textural and morphological studies of transition metal doped SBA-15 by co-condensation method

      P H K Charan G Ranga Rao

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      The 3d transition metals were incorporated into SBA-15 matrix by co-condensation synthesis method. Very low concentrations of metals were introduced into silica framework by maintaining the metal to silica ratio in the synthesis gel at 0.01. The difference in hydrolysis rates of metal and silica precursors have led to textural modifications while demonstrating the structural integrity akin to pristine SBA-15. The physicochemical properties obtained offer some insights into the P123 micelle aggregation and mechanism of formation of silica network in the presence of metal salts under similar synthesis conditions of pure SBA-15. The metal doping into SBA-15 leads to increased pore diameters. Higher lattice constants (a0) observed in these samples are attributed to the increased pore wall thickness. The significant retention of the hexagonal mesostructure seen in LXRD indicates diminutive influence of metal salts at lower concentrations.Macroscopic morphologies studied by SEM show the formation of spheres along with conventional fibre-like rods.

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