Parameter-dependent anisotropy of front propagation in the H2 + O2 reaction on Rh(110)

Front propagation in the H2 + O2 reaction on Rh(110) has been studied for 480 < T < 780 K in the 10−5 mbar range using photoemission electron microscopy as a spatially resolving method. Depending on the temperature and the hydrogen partial pressure (for fixed pO2) the anisotropy of front propagation was found to vary drastically from a front which was elliptical in the [110]-direction at high pH2/low T to a front which was elliptically deformed in the [001]-direction at low pH2/high T. The change in surface anisotropy is seemingly in contradiction with the anisotropy of the surface structures which are involved since these are all anisotropic in the [110]-direction.