STRUCTURE-SENSITIVITY IN THE DYNAMICS OF CO OXIDATION OVER Pd SURFACES: INFRARED CHEMHEMILUMINESCENCE OF THE PRODUCT CO2

1997 ◽  
Vol 04 (06) ◽  
pp. 1359-1363 ◽  
Author(s):  
H. UETSUKA ◽  
K. WATANABE ◽  
H. OHNUMA ◽  
K. KUNIMORI
Keyword(s):  
Steady State ◽  
Surface Temperature ◽  
Co Oxidation ◽  
Surface Reaction ◽  
Reaction Dynamics ◽  
Structure Sensitivity ◽  
Surface Structures ◽  
Flat Surfaces ◽  
Structure Sensitive ◽  
Stepped Surface

Infrared-chemiluminescence spectra of CO 2 molecules formed by steady-state CO oxidation on Pd (111), Pd (110), Pd (100) and polycrystalline- Pd surfaces have been measured to get information on the surface reaction dynamics. In all cases, the product CO 2 was vibrationally and rotationally excited. The CO 2 molecules desorbed from Pd (100) and Pd (111), which have flat surfaces, were vibrationally more excited than those from Pd (110) (stepped surface) and polycrystalline Pd . These results show that the dynamics of CO oxidation on Pd surfaces are structure-sensitive, i.e. the structure of the activated CO 2 complex depends on the surface structures of the reaction sites. Furthermore, the activities of steady-state CO oxidation as a function of surface temperature were different among these Pd surfaces, which indicates that the CO oxidation on Pd is also structure-sensitive in the kinetics.

scholarly journals How the anisotropy of surface oxide formation influences the transient activity of a surface reaction

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
P. Winkler ◽  
J. Zeininger ◽  
Y. Suchorski ◽  
M. Stöger-Pollach ◽  
P. Zeller ◽  
...  
Keyword(s):  
Hydrogen Oxidation ◽  
Surface Oxidation ◽  
Surface Reactivity ◽  
Surface Oxide ◽  
Surface Structures ◽  
Oxide Formation ◽  
Reaction Fronts ◽  
Transient Activity ◽  
Surface Oxide Formation ◽  
Stepped Surface

AbstractScanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H2 oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.

Steady-State Investigation of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. K. Mallik ◽  
G. P. Peterson
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Surface Temperature ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Temperature Gradients ◽  
Bottom Surface ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

An experimental investigation of vapor deposited micro heat pipe arrays was conducted using arrays of 34 and 66 micro heat pipes occupying 0.75 and 1.45 percent of the cross-sectional area, respectively. The performance of wafers containing the arrays was compared with that of a plain silicon wafer. All of the wafers had 8 × 8 mm thermofoil heaters located on the bottom surface to simulate the active devices in an actual application. The temperature distributions across the wafers were obtained using a Hughes Probeye TVS Infrared Thermal Imaging System and a standard VHS video recorder. For wafers containing arrays of 34 vapor deposited micro heat pipes, the steady-state experimental data indicated a reduction in the maximum surface temperature and temperature gradients of 24.4 and 27.4 percent, respectively, coupled with an improvement in the effective thermal conductivity of 41.7 percent. For wafers containing arrays of 66 vapor deposited micro heat pipes, the corresponding reductions in the surface temperature and temperature gradients were 29.0 and 41.7 percent, respectively, and the effective thermal conductivity increased 47.1 percent, for input heat fluxes of 4.70 W/cm2. The experimental results were compared with the results of a previously developed numerical model, which was shown to predict the temperature distribution with a high degree of accuracy, for wafers both with and without the heat pipe arrays.

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