@article { ISI:000250234900007, title = {Fabrication of an effusive molecular beam instrument for surface reaction kinetics - CO oxidation and NO reduction on Pd(111) surfaces}, journal = {Catalysis Letters}, volume = {119}, number = {1-2}, year = {2007}, month = {NOV}, pages = {50-58}, publisher = {SPRINGER}, type = {Article}, address = {233 SPRING STREET, NEW YORK, NY 10013 USA}, abstract = {

A simple molecular beam instrument (MBI) was fabricated for measuring the fundamental parameters in catalysis such as, sticking coefficient, transient and steady state kinetics and reaction mechanism of gas/vapor phase reactions on metal surfaces. Important aspects of MBI fabrication are given in detail. Nitric oxide (NO) decomposition and NO reduction with carbon monoxide (CO) on Pd(111) surfaces were studied. Interesting results were observed for the above reactions and they support the efficiency of the MBI to derive the fundamental parameters of adsorption and catalysis. Sustenance of CO oxidation at 400 K is dependent mostly on the absence of CO-poisoning; apparently, CO + O recombination is the rate determining step \<= 400 K. NO adsorption measurements on Pd(111) surface clearly indicating a typical precursor kinetics. Displacement of the chemisorbed CO by NO on Pd(111) surfaces was observed directly with NO + CO beams in the transient kinetics. It is also relatively easy to identify the rate-determining step directly from the MBI data and the same was demonstrated for the above reactions.

}, keywords = {carbon monoxide, catalysis, kinetics, molecular beam, nitric oxide, Pd(111)}, issn = {1011-372X}, doi = {10.1007/s10562-007-9184-8}, author = {Thirunavukkarasu, Kandasamy and Gopinath, Chinnakonda S.} } @article { ISI:000271756700023, title = {Electronic decoupling of surface layers from bulk and its influence in oxidation catalysis: a molecular beam study}, journal = {Applied Surface Science}, volume = {256}, number = {2}, year = {2009}, note = {2nd International Conference on Physics at Surfaces and Interfaces (PSI2009), Puri, INDIA, FEB 23-27, 2009}, month = {OCT}, pages = {443-448}, publisher = {Inst Phys; Indian Assoc Cutivat Sci}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Interactions between oxygen and Pd-surfaces have important implications, especially towards oxidation reactions, and influence of subsurface oxygen to oxidation reactions is the focus of the present study. In our efforts to understand the above aspects, CO oxidation reactions have been carried out with mixed molecular beam (MB), consisting CO and O(2), on Pd(1 1 1) surfaces under a wide variety of conditions (T = 400-900 K, CO: O(2) = 7: 1 to 1: 10). A new aspect of the above reaction observed in the transient kinetics regime is the evidence for oxygen diffusion into Pd subsurface layers, and its significant influence towards CO oxidation at high temperatures (\>= 600 K). Interesting information derived from the above studies is the necessity to fill up the subsurface layers with oxygen atoms to a threshold coverage (theta(O-sub)), above which the reactive CO adsorption occurs on the surface and simultaneous CO(2) production begins. There is also a significant time delay (G) observed between the onset of oxygen adsorption and CO adsorption (and CO(2) production). Above studies suggest an electronic decoupling of oxygen covered surface and subsurface layers, which is slightly oxidized, from the metallic bulk, which induces CO adsorption at high temperatures and simultaneous oxidation to CO(2). (C) 2009 Elsevier B.V. All rights reserved.

}, keywords = {Electronic decoupling, heterogeneous catalysis, molecular beam, Oxidation, Pd(111), Subsurface diffusion}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2009.06.107}, author = {Thirunavukkarasu, Kandasamy and Nagarajan, Sankaranarayanan and Gopinath, Chinnakonda S.} } @article { ISI:000337074700019, title = {Towards a sustainable and near ambient DeNO(x) under lean burn conditions: a revisit to no reduction on virgin and modified pd(111) surfaces}, journal = {ACS Catalysis}, volume = {4}, number = {6}, year = {2014}, month = {JUN}, pages = {1801-1811}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Catalytic conversion of NO in the presence of H-2 and O-2 has been studied on Pd(111) surfaces, by using a molecular beam instrument with mass spectrometry detection, as a function of temperature and reactants composition. N-2 and H2O are the major products observed, along with NH3 and N2O minor products under all conditions studied. Particular attention has been paid to the influence of O-2 addition toward NO dissociation. Although O-2-rich compositions were found to inhibit the deNO(x) activity of the Pd catalyst, some enhancement in NO reduction to N-2 was also observed up to a certain O-2 content. The reason for this behavior was determined to be the effective consumption of the H-2 in the mixture by the added O-2 and O atoms from NO dissociation. NO was proven to compete favorably against O-2 for the consumption of H-2, especially \<= 550 K, to produce N-2 and H2O. Compared with other elementary reaction steps, a slow decay observed with the 2H + 0 -\> H2O step under SS beam oscillation conditions demonstrates its contribution to the rate-limiting nature of the overall reaction. Pd(111) surfaces modified with O atoms in the subsurface (Md-Pd(111)) induces steady-state NO reduction at near-ambient temperatures (325 K) and opens up a possibility to achieve room temperature emission control. A 50\% increase in the reaction rates was observed at the reaction maximum on Md-Pd(111), as compared with virgin surfaces. Oxygen adsorption is severely limited below 400 K, and effective NO + H-2 reaction occurs on Md-Pd(111) surfaces. Valence band photoemission with a UV light source (He I) under different oxygen pressures with APPES clearly identified the characteristics of the Md-Pd(111) surfaces and PdO. The electron-deficient or cationic nature of Md-Pd(111) surfaces enhances the NO dissociation and inhibits oxygen chemisorption \<= 400 K under lean-burn conditions.

}, keywords = {deNO(x), heterogeneous catalysis, Hydrogen, lean burn, molecular beam, nitric oxide, Palladium, surface modification}, issn = {2155-5435}, doi = {10.1021/cs500342a}, author = {Roy, Kanak and Jain, Ruchi and Gopinath, Chinnakonda S.} }