Abaji Govind Gaikwad

Nonhazardous Direct Oxidation of Hydrogen to Hydrogen Peroxide Using a Novel Membrane Catalyst

Nonhazardous and highly selective H2O2production! An H 2 -permselective membrane (2) has been developed which consists of thin films of Pd–Ag alloy (2b) and oxidized Pd (2c), and a hydrophobic polymer membrane (2d) supported on a tubular membrane (2a) within a reactor wall (1). Hydrogen atoms permeate through the membrane and react with molecular OH 2 in a liquid medium (LM; 2 M HH 2 SOH 4 ).

Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide

Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H2 to H2O2 (at 295 K) in acidic medium (0.02 M H2SO4) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H2O2, N2O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H2-to-H2O2 conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO2 < Pd/ThO2 < Pd/Ga2O3. The H2 oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H2O2 decomposition activity of the catalysts. There exists a close relationship between the H2-to-H2O2 conversion activity and/or H2O2 selectivity in the oxidation process and the H2O2 decomposition activity of the catalysts; the higher the H2O2 decomposition activity, the lower the H2-to-H2O2 conversion activity and/or H2O2 selectivity.

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H2O2 selectivity (or yield) in direct oxidation of H2-to-H2O2 (using 1.7 mol% H2 in O2 as a feed) and also the H2O2 decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H-β) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H2SO4, HCl, HNO3, H3PO4 and HClO4), and also by the form of palladium (Pd0 or PdO). The oxidized (PdO-containing) catalysts are active for the H2-to-H2O2 conversion and show very poor activity for the H2O2 decomposition. However, the reduced (Pd0-containing) catalysts show higher H2 conversion activity but with no selectivity for H2O2, and also show much higher H2O2 decomposition activity. No direct correlation is observed between the H2-to-H2O2 conversion activity (or H2O2 selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H2O2 yield and lower H2O2 decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.

Kinetics of hydrogen peroxide decomposition in aqueous sulfuric acid over palladium/carbon: effcet of acid concentration

Decomposition of H2O2 over Pd (5%)/carbon in an aqueous sulfuric acid solution at different acid concentrations (0-10 mol/L) and temperatures (281-313 K) in a magnetically stirred glass reactor has been investigated. The catalytic activity, activation energy and frequency factor for the decomposition decrease with increasing acid concentration; the decrease in the activation energy is, however, very small.

Studies of Ion Transport through a Liquid Membrane by Using Crown Ethers

Studies on ion transport through a liquid membrane system composed of two extraction processes have been carried out. Kinetic models based on extraction processes with consideration of the controlled parameters were developed for mediated ion transport through liquid membranes, especially those using crown ethers as the ion carrier. A study of the concentration change in the receiving or source phase envisages the determination of the equilibrium constant by a kinetic method corresponding to the chemical reaction at the interface as well as the maximum initial flux through the membrane. The equilibrium constant values determined by the kinetic process were checked by the solvent extraction method.

Kinetic Fluorimetric Method for the Determination of Tobramycin by Stopped-Flow Mixing Methodology

Abstract The reaction of tobramycin with o-phthaldialdehyde (OPA) in the presence of 2-mercaptoethanol was studied kinetically by using stopped-flow mixing methodology. New data on the kinetics of this reaction were exploited to develop a simple, fast method for tobramycin determination. The linear range (0.05–30.0 μg mL−1), detection limit (0.03 μg mL−1), precision (&RSD 1.92) and selectivity of the proposed kinetic method are quite acceptable. The method was satisfactorily applied to the analysis of pharmaceutical preparations with no pretreatment.

Solvent Extraction Studies of Metal-4-(2-pyridyl-azo)-Resorcinol Complexes with Potassium-Dicyclohexyl-18-crown-6 Complex

Abstract The solvent extraction studies of Pd(II), V(V), Co(III), Cu(II), Ni(II) and Fe(II)-PAR [4 - (2-pyridyl azo)-resorcinol] complexes with dicyclohexyl-18-crown-6 have been investigated in 1,2-dichloroethane as a solvent. It was observed that the complexes of Pd(II), V(V), Co(III), Cu(II), Ni(II) and Fe(II)-PAR were extracted into organic phase. In order to investigate the effect of enthalpy and entropy in the extraction of metal-PAR complexes, an attempt has been made to explore the temperature effect. In the extraction studies, it was observed that the entropy effect is one of the major factors for the selective extraction. The shape of the complexes may be one of the causes for the extractability of metal-PAR complexes with potassium dicyclohexyl-18-crown-6. The planar palladium-PAR-SCN− complex was easily extracted into organic phase in comparison with other complexes.