On the contribution of X-ray absorption spectroscopy to explore structure and activity relations of Pt/ZrO2 catalysts for CO2/CH4 reforming

X-ray absorption spectroscopy (XAS) has proven to be a very useful techniqu e in characterizing metal-based catalysts exposed to extreme operating cond itions. The technique allows in situ evaluation of structural parameters (X AFS) and electronic properties (XANES). The elucidation of the nature and s tate of Pt-based catalysts in dry reforming of methane with carbon dioxide is presented as case study to show the contribution and potential of XAS to explore property/performance relationships for heterogeneous catalysts. Pt /ZrO2 is an active and stable catalyst for the reaction between CH4 and CO2 to synthesis gas (H-2/CO). The activity and stability of the catalyst is s trongly influenced by the catalyst pretreatment (calcination/reduction). Th e combination of hydrogen chemisorption, IR spectroscopy, XPS and XAS is sh own to be suitable to track the changes of the state of the catalyst. In pa rticular, it will be demonstrated, how XAFS helped to correctly attribute v ariations in the chemisorptive properties of Pt/ZrO2 after severe temperatu re treatment to partial and reversible decoration of the small Pt particles with fragments of the oxide support. In situ tracking of the reduction of the catalysts by XANES additionally helped to semiquantitatively assess the partial reduction of the ZrO2. Finally, XANES helped to demonstrate that C O2 exposure under these severe conditions did not lead to detectable levels of surface oxidation of Pt. Based on XANES, IR spectroscopy and kinetic me asurements it is concluded that in dry reforming activation of methane occu rs on Pt, while CO2 is activated on the support and the two entities react at the metal-support interface.