Decomposition of Methanol on Mixed CuO-CuWO₄ Surfaces

Mixed CuO(2 × 1)-CuWO₄ layers on a Cu(110) surface have been prepared by the on-surface reaction of the CuO(2 × 1) surface oxide with adsorbed (WO₃)₃ clusters. The adsorption and decomposition of methanol on these well-defined CuO-CuWO₄ surfaces has been followed by high-resolution X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and temperature-programmed desorption (TPD) to assess the molecular surface species and their concentration, while the state of the surface oxide phases before and after methanol decomposition has been characterized by scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and XPS. Surface methoxy species form the primary methanol decomposition products, which desorb partly by recombination as methanol at 200-300 K or decompose into CH_x and possibly CO. The most reactive surfaces are mixed CuO-CuWO₄ phase, with CuWO₄ coverages 0.5-0.8 monolayer, thus pointing at the importance of oxide phase boundary sites. In a minority reaction channel, a small amount of formaldehyde is detected on the CuWO₄ surface. The CuWO₄ oxide phase becomes modified as a result of reduction and a morphology transition triggered by the methanol decomposition, but the pristine surface state can be recovered by a postoxidation treatment with oxygen.