Parthasarathi Bera

An XPS study on binary and ternary alloys of transition metals with platinized carbon and its bearing upon oxygen electroreduction in direct methanol fuel cells

The present X-ray photoelectron spectroscopic study on carbon-supported Pt, Pt–Cr, Pt–Co, Pt–Ni, Pt–Co–Cr and Pt–Co–Ni electrocatalysts suggests that while Pt–Cr/C, Pt–Co/C and Pt–Ni/C binary alloy electrocatalysts are surface rich in platinum, both Pt–Co–Cr/C and Pt–Co–Ni/C ternary electrocatalysts happen to be surface rich in base metals. Among these electrocatalysts, Pt–Co/C electrocatalyst is found to possess a minimum amount of platinum oxides. Accordingly, Pt–Co/C exhibits a higher electrocatalytic activity towards oxygen-reduction reaction in the solid-polymer-electrolyte direct methanol fuel cells.

Characterization and Catalytic Properties of Combustion Synthesized Au/CeO2 Catalyst

Ceria-supported Au catalyst has been synthesized by the solution combustion method for the first time and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Au is dispersed as Au0 as well as Au3+ states on CeO2 surface of 20-30 nm crystallites. On heating the as-prepared 1% Au/CeO2 in air, the concentration of Au3+ ions on CeO2 increases at the expense of Au0. Catalytic activities for CO and hydrocarbon oxidation and NO reduction over the as-prepared and the heat-treated 1% Au/CeO2 have been carried out using a temperature-programmed reaction technique in a packed bed tubular reactor. The results are compared with nano-sized Au metal particles dispersed on α-Al2O2 substrate prepared by the same method. All the reactions over heat-treated Au/CeO2 occur at lower temperature in comparison with the as-prepared Au/CeO2 and Au/Al2O2. The rate of NO + CO reaction over as-prepared and heat-treated 1% Au/CeO2 are 28.3 and 54.0 μmol g-1 s-1 at 250 and 300 °C respectively. Activation energy (Ea) values are 106 and 90 kJ mol-1 for CO + O2 reaction respectively over as-prepared and heat-treated 1% Au/CeO2 respectively.

Catalytic partial-oxidation of methane on a ceria-supported platinum catalyst for application in fuel cell electric vehicles

Fuel cell developers are investigating the generation of hydrogen from light hydrocarbons, such as methane or natural gas, for fuelling polymer electrolyte fuel cells (PEFCs). This study demonstrates generation of H 2 and CO by catalytic partial-oxidation of CH 4 in air at atmospheric pressure on a ceria-supported platinum catalyst prepared by a novel solution-combustion method where platinum is present in ionically-substituted form. These catalysts at different platinum loadings showed methane conversion and hydrogen selectivity of 90 and 97%, respectively. Interestingly, there is little carbon deposition in the catalytic reactor even after prolonged reaction time.

Characterization of Ni–Pd alloy as anode for methanol oxidative fuel cell

Abstract Electrochemical deposition of Ni–Pd alloy films of various compositions from bath solution containing ethylenediamine (EDA) was carried out to use as anode material for methanol oxidative fuel cell in H2SO4 medium. Electronic absorption spectrum of bath solution containing Ni2+, Pd2+ ions and EDA indicated the formation of a four coordinate square planar metal–ligand complex of both the metal ions. X-ray diffraction (XRD) patterns of the deposited alloy films show an increase in Pd–Ni alloy lattice parameter with increase in Pd content, and indicate the substitution of Pd in the lattice. A nano/ultrafine kind of crystal growth was observed in the alloy film deposited at low current density (2.5xa0mAxa0cm−2). X-ray photoelectron spectroscopic (XPS) studies on the successively sputtered films showed the presence of Ni and Pd in pure metallic states and the surface concentration ratio of Ni to Pd is less than bulk indicating the segregation of Pd on the surface. Electro-catalytic oxidation of methanol in H2SO4 medium is found to be promoted on Ni–Pd electrodeposits. The anodic peak current characteristics to oxidation reaction on Ni–Pd was found typically high when compared to pure nickel and the relative increase in surface area by alloying the Ni by Pd was found to be as much as 300 times.

NO reduction, CO and hydrocarbon oxidation over combustion synthesized Ag/CeO2 catalyst

The n combustion technique produces ionically dispersed Ag on a nano-crystalline CeO2 surface. The catalysts n thus produced were characterized by X-ray diffraction, transmission electron microscopy and X-ray n photoelectron spectroscopy. Catalytic properties towards NO reduction, CO and hydrocarbon oxidation have n been investigated using the temperature programmed reaction technique in a packed bed tubular reactor. These n results are compared with α-Al2O3 supported finely divided Ag metal particles synthesized by the n same method. Both oxidation and reduction reactions over Ag/CeO2 have been observed to occur at n lower temperatures compared to Ag/Al2O3. The rate and turnover frequency of the NO+CO reaction over 1% Ag/CeO2 n are 56.3 μmol g−1 s−1 and 0.97 s−1 n at 225°C respectively. Activation energy (Ea) values are n 71 and 67 kJ mol−1 n for CO+O2 and NO+CO n reactions, respectively, over 1% Ag/CeO2 catalyst.

A solvothermal route to capped nanoparticles of γ-Fe2O3 and CoFe2O4

The decomposition of single or multiple transition metal cupferron complexes in organic solvents under solvothermal conditions and in the presence of long chain amines yields the corresponding oxide nanoparticles. The examples presented here are maghemite γ-Fe2O3 nanoparticles from an FeIII–cupferron complex and spinel CoFe2O4 nanoparticles starting from CoII–cupferron complex and FeIII–cupferron complex taken in suitable proportions. The nanoparticles are capped with n-octylamine or n-dodecylamine. The presence of amine in the reaction is found to be essential for the formation of the product. The magnetic behavior of pressed pellets of these nanoparticles is presented.

Thermal behaviour of hydroxides, hydroxysalts and hydrotalcites

Mass spectrometric analysis of gases evolved during thermal decomposition of divalent metal hydroxides, hydroxysalts and hydrotalcites show that all these compounds undergo dehydration in the temperature range 30 <T < 220°C followed by decomposition at temperatures above 250°C. The latter step involves simultaneous deanation and dehydroxylation of the layers. Our observations conclusively prove that alternative mechanisms which envisage CO2 evolution due to deanation at lower temperatures proposed by Kanezaki to be wrong.

Combustion synthesis of nanometal particles supported on α-Al2O3: CO oxidation and NO reduction catalysts

Nanoparticles of Pt, Pd, Ag and Au supported on alpha-Al2O3 have been synthesized by the combustion method for the first time and characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic activities of these nanosized materials have been investigated. For the CO+O-2 reaction, 100% CO conversion occurs below 300 degrees C over supported Pt, Pd and Ag metals whereas 90% conversion is observed over Au at 450 degrees C. Similarly 100% NO conversion is seen over 1% Pd/Al2O3 and 1% Pt/Al2O3 below 400 degrees C for the NO+CO reaction whereas approximate to 90% NO is converted into N-2 above 650 degrees C on 1% Ag/Al2O3 and 1% Au/Al2O3.

Low-temperature water gas shift reaction on combustion synthesized Ce1-xPtxO2-δ catalyst

Catalytic activity of Pt2+ ion substituted CeO2 synthesized by solution combustion method was tested for low-temperature water gas shift reaction in H2 rich steam reformate. XPS studies show that Pt is dispersed as ions and there is no change in Pt oxidation state after the reaction. CO conversion is found to be maximum at 200 °C over Ce1−xPtxO2−δ catalysts without any methanation. The values of rate are 1.86 and 4.66 μmol/g/s at 125 and 150°C respectively with a dry gas flow rate of 6 Lh−1 over 2% Pt/CeO2.

Investigation of surface composition of electrodeposited black chrome coatings by X-ray photoelectron spectroscopy

: Solar selective black chromium coating was electrodeposited on pre-treated electroformed nickel substrates from a hexavalent chromium containing bath. The composition of the film was investigated before and after annealing at 400 degreesC for different durations. In the as-deposited condition. the surface of the film was found to have trivalent chromium hydroxide and chromium in the chromate form contrary to previous studies which report the presence of hydroxides and metallic chromium. However in the present study, no evidence for metallic chromium was found. The major component. chromium hydroxide, was converted to Cr2O3 on annealing at 400 degreesC with the loss of water vapor. The chromate form remains but with a lowered concentration.