Chemical Wave Patterns and Oxide Redistribution during Methanol Oxidation on a V-Oxide Promoted Rh(110) Surface

Chemical wave patterns and the formation of macroscopic vanadium oxide islands have been investigated in the 10^-4 mbar range during catalytic methanol oxidation on ultrathin VO_x films (θ_V ≤ 1 monolayer equivalent) supported on Rh(110). At temperatures around 800 K, wave fragments traveling along the [110] direction and oxidation/reduction fronts exhibiting different front geometries are observed with photoemission electron microscopy. At ≈1000 K, a redistribution of VO_x leads to the growth of macroscopic oxide islands under reaction conditions. On these macroscopic V-oxide islands chemical waves including traveling wave fragments propagate. Under conditions close to equistability of oxidized and reduced phase, a dendritic growth of the V-oxide islands is observed. In contrast to Rh(111)/VO_x, almost no catalytic activity in formaldehyde production is found on Rh(110)/VO_x.