ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
A Pt single crystal of cylindrical shape (axis II [001]) whose surface exhibits all orientations of the [001] zone has been used to study coupling effects between orientations which exhibit kinetic oscillations in catalytic CO oxidation. On the clean surface, one can distinguish between an orientational range in between (110) and (320) which exhibits a 1×2 reconstruction, a nonreconstructed surface range around (210) and a hex reconstructed surface range around (100). Structural transitions proceed continuously via atomic steps between (110) and (210), while the orientational range extending from (210) to (100) is faceted. With a rotatable Kelvin probe, the orientational dependence of the work function could be followed. The results revealed that the variation of the oxygen sticking coefficient sO2 displays a mirror-like behavior with respect to the work function variation of the clean surface such that the orientation with the lowest work function (210) exhibits the highest sO2. Kinetic oscillations were studied in the 10−5 and 10−4 Torr range. By means of two Kelvin probes, the Δφ oscillations could be followed simultaneously at two different orientations, while the integral behavior of the cylinder surface was monitored via the CO2 production rate. A strong broadening of the oscillatory region in parameter space, as compared to a flat surface, was detected for the oscillatory range around (100). In the vicinity of this orientation, spatial coupling is provided via reaction fronts which propagate from (210) toward (110). Gas-phase coupling is only observed with the (110) orientations. Prolonged oscillation experiments cause faceting resulting in an increase of catalytic activity around (100), while the orientations around (210) lose catalytic activity by faceting.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.463818
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