Interaction of CO 2 with MnO x /Pd(111) Reverse Model Catalytic Interfaces.

Understanding the activation of CO 2 on the surface of the heterogeneous catalysts comprised of metal/metal oxide interfaces is of critical importance since it is not only a prerequisite for converting CO 2 to value-added chemicals but also often, a rate-limiting step. In this context, our current work focuses on the interaction of CO 2 with heterogeneous bi-component model catalysts consisting of small MnO x clusters supported on the Pd(111) single crystal surface. These metal oxide-on-metal 'reverse' model catalyst architectures were investigated via temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) techniques under ultra-high vacuum (UHV) conditions. Enhancement of CO 2 activation was observed upon decreasing the size of MnO x nanoclusters by lowering the preparation temperature of the catalyst down to 85 K. Neither pristine Pd(111) single crystal surface nor thick (multilayer) MnO x overlayers on Pd(111) were not capable of activating CO 2 , while CO 2 activation was detected at sub-monolayer (∼0.7 ML) MnO x coverages on Pd(111), in correlation with the interfacial character of the active sites, involving both MnO x and adjacent Pd atoms.