title: Surface modification processes during methane decomposition on Cu-promoted Ni-ZrO2catalysts.
abstract: The surface chemistry of methane on Ni-ZrO2and bimetallic CuNi-ZrO2catalysts and the stability of the CuNi alloy under reaction conditions of methane decomposition were investigated by combining reactivity measurements andin situsynchrotron-based near-ambient pressure XPS. Cu was selected as an exemplary promoter for modifying the reactivity of Ni and enhancing the resistance against coke formation. We observed an activation process occurring in methane between 650 and 735 K with the exact temperature depending on the composition which resulted in an irreversible modification of the catalytic performance of the bimetallic catalysts towards a Ni-like behaviour. The sudden increase in catalytic activity could be explained by an increase in the concentration of reduced Ni atoms at the catalyst surface in the active state, likely as a consequence of the interaction with methane. Cu addition to Ni improved the desired resistance against carbon deposition by lowering the amount of coke formed. As a key conclusion, the CuNi alloy shows limited stability under relevant reaction conditions. This system is stable only in a limited range of temperature up to ~700 K in methane. Beyond this temperature, segregation of Ni species causes a fast increase in methane decomposition rate. In view of the applicability of this system, a detailed understanding of the stability and surface composition of the bimetallic phases present and the influence of the Cu promoter on the surface chemistry under relevant reaction conditions are essential.
authors: Institute of Materials Chemistry , Vienna University of Technology , Getreidemarkt 9 , 1020 Wien , Austria . Email: karin.foettinger@tuwien.ac.at ; ; Tel: +43 1 165110.
authors: Astrid
authors: A
authors: Wolfbeisser
authors: Institute of Physical Chemistry , University of Innsbruck , Innrain 52a , 6020 Innsbruck , Austria.
authors: Bernhard
authors: B
authors: Klötzer
authors: Institute of Physical Chemistry , University of Innsbruck , Innrain 52a , 6020 Innsbruck , Austria.
authors: Lukas
authors: L
authors: Mayr
authors: Institute of Physical Chemistry , University of Innsbruck , Innrain 52a , 6020 Innsbruck , Austria.
authors: Raffael
authors: R
authors: Rameshan
authors: Purdue University , Brick Nanotechnology Center , 1205 West State Street , West Lafayette , IN 47907-2057 , USA.
authors: Dmitry
authors: D
authors: Zemlyanov
authors: University Service Center for Transmission Electron Microscopy , Vienna University of Technology , Wiedner Hauptstraße 8-10 , 1040 Wien , Austria.
authors: Johannes
authors: J
authors: Bernardi
authors: Institute of Materials Chemistry , Vienna University of Technology , Getreidemarkt 9 , 1020 Wien , Austria . Email: karin.foettinger@tuwien.ac.at ; ; Tel: +43 1 165110.
authors: Karin
authors: K
authors: Föttinger
authors: Institute of Materials Chemistry , Vienna University of Technology , Getreidemarkt 9 , 1020 Wien , Austria . Email: karin.foettinger@tuwien.ac.at ; ; Tel: +43 1 165110.
authors: Günther
authors: G
authors: Rupprechter