Methane oxidation over oxide-supported Pd nanoparticles observed in-situ by ambient-pressure XPS

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A fundamental microscopic understanding of heterogeneous catalysis under working conditions is key to further developments in catalyst design and control of chemical processes. Heterogeneous catalysis happens at the catalyst surface; we therefore need meaningful experimental data about the chemical composition and molecular arrangement at the surfaces under investigation. In general, surface-specific information is best provided by electron-based photoemission spectroscopy such as X-ray photoelectron spectroscopy (XPS). The property that makes electrons ideal surface probes is their short penetration depth of only a few atomic layers in solid matter. This poses, however, a big problem when these systems are to be studied under realistic pressure environments in the range of millibar or higher. The mean free path of electrons is then only a few millimetres or less and conventional electron energy analysers cannot be used anymore.This so-called "pressure gap" between conventional electron spectroscopy and actual catalytic reactions, which usually take place at high reactant pressures or even in solution, is bridged to some extent by "near-ambient pressure electron analysers". Such instruments have become available very recently at synchrotron radiation facilities, such as the Advanced Light Source (ALS) in Berkeley, USA.The applicant is seeking funding for travelling to ALS in Berkeley in order to perform near-ambient pressure photoemission experiments on oxide-supported Pd nanoparticle catalysts for partial oxidation of methane under reaction conditions. This reaction produces syn-gas, a mixture of carbon monoxide and hydrogen which is used as basis for a whole range of useful bulk chemicals. The significance of the planned experiments is that they involve real industrial catalysts as opposed to model catalysts. Therefore the results can be fed into improvement of chemical plants much more directly.