@article { ISI:000227016500007, title = {In situ XPS investigations of Cu1-xNixZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol}, journal = {Applied Catalysis B - Environmental}, volume = {55}, number = {4}, year = {2005}, month = {FEB}, pages = {287-299}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A series of CuNiZnAl-multicomponent mixed metal oxide catalysts with various Cu/Ni ratios were prepared by the thermal decomposition of Cu1-xNixZnAl-hydrotalcite-like precursors and tested for oxidative steam reforming of bio-ethanol. Dehydrogenation of EtOH to CH3CHO is favored by Cu-rich catalyst. Introduction of Ni leads to C-C bond rupture and producing CO, CO2 and CH4. H-2 yield (selectivity) varied between 2.6-3.0 mol/mol of ethanol converted (50-55\%) for all catalysts at 300 degreesC. The above catalysts were subjected to in situ XPS studies to understand the nature of active species involved in the catalytic reaction. Core level and valence band XPS as well as Auger electron spectroscopy revealed the existence of Cu2+, Ni2+ and Zn2+ ions on calcined materials. Upon in situ reduction at reactions temperatures, the Cu2+ was fully reduced to Cu-0. while Ni2+ and Zn2+ were partially reduced to Ni-0 and Zn-0, respectively. On reduction, the nature of ZnO on Cu-rich catalyst changes from crystalline to amorphous, relatively inert and highly stabilized electronically. Relative concentration of the Ni-0 and Zn-0 increases upon reduction with decreasing Cu-content. Valence band results demonstrated that the overlap between 3d bands of Cu and Ni was marginal on calcined materials, and no overlap due to metallic clusters formation after reduction. Nonetheless, the density of states at Fermi level increases dramatically for Ni-rich catalysts and likely this influences the product selectivity. (C) 2004 Elsevier B.V. All rights reserved.

}, keywords = {auger electron spectroscopy, Autothermal reforming, Bio-ethanol, copper oxide, fuel cell, Hydrogen, hydrotalcite, mixed metal oxides, nickel oxide, oxidative steam reforming, Steam reforming, XPS}, issn = {0926-3373}, doi = {10.1016/j.apcatb.2004.09.007}, author = {Velu, S. and Suzuki, K. and Vijayaraj, M. and Barman, S. and Gopinath, Chinnakonda S.} } @article { ISI:000227966600021, title = {Insight into the mechanism of selective mono-N-methylation of aniline on Cu1-xZnxFe2O4: a DRIFTS study}, journal = {Journal of Molecular Catalysis A - Chemical}, volume = {231}, number = {1-2}, year = {2005}, month = {APR}, pages = {169-180}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Mechanism of selective mono-N-methylation of aniline with methanol on Cu1-xZn2FeO4 catalysts was investigated in detail. The interaction of reactants (aniline. methanol and methanol: aniline) and possible products (N-methylaniline (NMA), N,N-dimethylaniline (DMA) and o-toluidine (OT)) on catalysts surface was studied by temperature-dependent in situ FTIR spectroscopy. Methanol adsorbs dissociatively over catalysts surface at 373 K as methoxy species and is oxidized to formate species at high temperature through dioxymethylene and/or formaldehyde as a surface intermediate species. On the other hand, adsorption of aniline:methanol mixtures shows that methanol oxidation was completely hindered in the presence of aniline. Aniline adsorbs on the Lewis acid sites at \<= 373 K with phenyl ring oriented in a perpendicular manner to the catalyst surfaced however, N-H bond scission occurs above 373 K. A comparison of adsorbed NMA and methanol: am line (3:1) mixture on Cu0.5Zn0.5Fe2O4 shows NMA forms from the reaction mixture at 473 K. However, maximum activity at 573 K in catalytic reaction studies suggests that desorption limits the methylation kinetics. FTIR study displays stable aniline and methyl species on ZnFe2O4 even at 573 K; however. no methyl species is detected on Cr0.95Zn0.05Fe2O4 at 473 K due to methanol reforming reaction and that limits the overall reaction and hence low catalytic activity. It is proposed that methanol is protonated on catalysts surface by the labile H+ due to N-H bond scission. Co-adsorption of acidity probes with aniline and methanol indicates that aniline methylation takes place at single acid-base site. (c) 2005 Elsevier B.V. All rights reserved.

}, keywords = {Aniline, Cu1-xZnxFe2O4, desorption limited, DRIFT, IR, Methanol, N-methylaniline, N-methylation, reaction mechanism}, issn = {1381-1169}, doi = {10.1016/j.molcata.2005.01.014}, author = {Vijayaraj, M. and Murugan, B. and Shubhangi B. Umbarkar and Hegde, S. G. and Gopinath, Chinnakonda S.} } @article { ISI:000230467900038, title = {Isothermal kinetic study of nitric oxide adsorption and decomposition on Pd(111) surfaces: molecular beam experiments}, journal = {Journal of Physical Chemistry B}, volume = {109}, number = {27}, year = {2005}, month = {JUL}, pages = {13283-13290}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The kinetics of NO adsorption and dissociation on Pd(111) surfaces and the NO sticking coefficient (S-NO) were probed by isothermal kinetic measurements between 300 and 525 K using a molecular beam instrument. NO dissociation and N-2 productions were observed in the transient state from 425 K and above on Pd(l 11) surfaces with selective nitrogen production. Maximum nitrogen production was observed between 475 and 500 K. It was found that, at low temperatures, between 300 and 350 K, molecular adsorption occurs with a constant initial SNO of 0.5 until the Pd(I 11) surface is covered to about 70-80\% by NO. Then SNO rapidly decreases with further increasing NO coverage, indicating typical precursor kinetics. The dynamic adsorption-desorption equilibrium on Pd(I 11) was probed in modulated beam experiments below 500 K. CO titration experiments after NO dosing indicate the diffusion of oxygen into the subsurface regions and beginning surface oxidation at \>= 475 K. Finally, we discuss the results with respect to the rate-limiting character of the different elementary steps of the reaction system.

}, issn = {1520-6106}, doi = {10.1021/jp050813f}, author = {Thirunavukkarasu, K and Thirumoorthy, K and Libuda, X and Gopinath, Chinnakonda S.} } @article { ISI:000340353100013, title = {In1-XGaXN@ZnO: a rationally designed and quantum dot integrated material for water splitting and solar harvesting applications}, journal = {Dalton Transactions}, volume = {43}, number = {33}, year = {2014}, month = {SEP}, pages = {12546-12554}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The highly desirable combination of the visible light absorption properties of In1-xGaxN Quantum dots (QD) along with the multifunctionality of ZnO into a single integrated material was prepared for solar harvesting. This is the first report on InGaN QD integrated with ZnO (InGaN@ZnO), synthesized by a highly reproducible, simple combustion method in 15 min. Structural, microstructural and electronic integration of the nitride and oxide components of InGaN@ZnO was demonstrated by appropriate characterization methods. Self-assembly of InGaN QD is induced in growing nascent zinc oxo nanoclusters taking advantage of the common wurtzite structure and nitrogen incorporation at the expense of oxygen vacancies. Direct integration brings about a single phase structure exhibiting extensive visible tight absorption and high photostability. InGaN@ZnO suggests synergistic operation of tight harvesting and charge conducting components for solar H-2 generation without using any co-catalyst or sacrificial agent, and a promising photocurrent generation at 0 V under visible light illumination. The present study suggests a direct integration of QD with the host matrix and is a potential method to realize the advantages of QDs.

}, issn = {1477-9226}, doi = {10.1039/c4dt01268b}, author = {Rajaambal, Sivaraman and Mapa, Maitri and Gopinath, Chinnakonda S.} } @article {47754, title = {In-situ experimental and computational approach to investigate the nature of active site in low-temperature CO-PROX over CuOx-CeO2 catalyst}, journal = {Applied Catalysis A-General}, volume = {624}, year = {2021}, month = {AUG }, pages = {118305}, type = {Article}, abstract = {Preferential oxidation (PROX) of carbon monoxide (CO) in presence of excess hydrogen is a necessity to prevent poisoning of the Pt-anode by CO in PEMFCs (Polymer Electrolyte Membrane Fuel Cell). A highly active catalyst, 5 wt\% Cu-CeO2 showed 100 \% CO conversion at 65 degrees C without any undesirable oxidation of H-2. The catalyst showed no deactivation even after 100 h on stream, making it viable for practical fuel cell application. Operando EPR in the PROX reaction condition revealed highly dispersed mixed valent cations with oxygen vacancies, responsible for the low-temperature PROX activity. At the active site, both Cu and Ce ions were shown to reversibly change their valence states to facilitate the abstraction of bridging lattice oxygen for CO oxidation to CO2. This surface oxygen mediated CO oxidation was found to be much faster than that of H-2 to H2O, which could explain the complete selectivity of oxygen for CO2 formation.}, keywords = {CuOx-CeO2, interface, Oxygen vacancy, PROX, Synergistic}, issn = {0926-860X}, doi = {10.1016/j.apcata.2021.118305}, author = {Adak, Shubhadeep and Rabeah, Jabor and Ranjan, Ravi and Khan, Tuhin Suvra and Poddar, Mukesh Kumar and Gupta, Rishi Kumar and Sasaki, Takehiko and Kumar, Sagar and Bordoloi, Ankur and Gopinath, Chinnakonda S. and Bruckner, Angelika and Bal, Rajaram} }