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Adsorption and Decomposition of Methanol on mixed CuO-CuWO4 oxide surfaces The catalytic properties of methanol (CH3OH) adsorbed on clean and oxygen covered Cu(110) have been intensively investigated over the last thirty years. Besides of being generally important for the chemical industry (e.g.[1, 2]), methanol is of great interest as a “smart” probe molecule to study the chemical nature of surface adsorption sites of mixed oxides.[3] Recently the creation of a thin ternary Cu tungstate (CuWO4) oxide layer has been reported.[4] By varying the CuWO4 coverage different CuO-CuWO4 mixed surfaces with well-defined morphology and structure can be prepared. Here we investigate the adsorption and catalytic properties of methanol on this CuO-CuWO4 model system and determine possible adsorption sites, adsorption intermediates and desorption products. For this purpose we have applied state-of-the-art surface science techniques to unlock information on structural and morphological information (STM & LEED), surface species (XPS & HREELS) and desorption products (TPD). We find that methoxy (CH3O) surface species are the main decomposition products while on surfaces with CuWO4 present also formaldehyde (CH2O) forms at low temperatures in a minority reaction channel. Mixed CuO – CuWO4 surfaces with Cu-tungstate coverages of 0.5 - 1 ML are the most active phases for methoxy formation. This suggests that the most active sites are W (Cu) and O atoms at the CuO - CuWO4 phase boundary. Through the interaction with methanol the CuWO4 phase is modified showing reduction (loss of oxygen) and a morphology transition. However, the pristine surface state can be recovered by a post-oxidation treatment in oxygen. The CuO-CuWO4 surfaces may therefore be suitable as a robust system in catalytic cycling situations. |