Patterns in the NO + H2 Reaction on Rh(110) Modified by Coadsorbed Potassium

Abstract

Adding potassium as coadsorbate to the pattern forming system Rh(110)/NO + H2 generates new types of chemical wave patterns that have been investigated in the 10−6 and 10−5 mbar range using photoelectron emission microscopy as spatially resolving method. The modified patterns were studied for varying K coverages with θK = 0.03, 0.05, 0.07, and 0.12. As in the unpromoted system, one finds elliptically and rectangular shaped target patterns, but in addition one observes stationary Turing-like concentration patterns, fingering instabilities, and the mass transport of potassium by propagating pulses. Large scale (a few tenths of a millimeter) redistribution of potassium by the chemical waves is seen. The propagation direction of traveling wave fragments is rotated by 90° in the presence of coadsorbed potassium. At high K, coverages the existence range for patterns is shifted drastically toward higher pH2.