Adsorption and reaction of methanol on supported palladium catalysts:: microscopic-level studies from ultrahigh vacuum to ambient pressure conditions

We investigated the decomposition and ( partial) oxidation of methanol on Pd based catalysts in an integrated attempt, simultaneously bridging both the pressure and the materials gap. Combined studies were performed on well-defined Pd model catalysts based on ordered Al2O3 and Fe3O4 thin films, on well-defined particles supported on powders and on Pd single crystals. The interaction of Pd nanoparticles and Pd( 111) with CH3OH and CH3OH/O-2 mixtures was examined from ultrahigh vacuum conditions up to ambient pressures, utilizing a broad range of surface specific vibrational spectroscopies which included IRAS, TR-IRAS, PM-IRAS, SFG, and DRIFTS. Detailed kinetic studies in the low pressure region were performed by molecular beam methods, providing comprehensive insights into the microkinetics of the reaction system. The underlying microscopic processes were studied theoretically on the basis of specially designed 3-D nanocluster models containing similar to 10(2) metal atoms. The efficiency of this novel modelling approach was demonstrated by rationalizing and complementing pertinent experimental results. In order to connect these results to the behavior under ambient conditions, kinetic and spectroscopic investigations were performed in reaction cells and lab reactors. Specifically, we focused on ( 1) particle size and structure dependent effects in methanol oxidation and decomposition, ( 2) support effects and their relation to activity and selectivity, ( 3) the influence of poisons such as carbon, and ( 4) the role of oxide and surface oxide formation on Pd nanoparticles.