Invited Paper AS-ThM10
Unraveling the Dynamic Nature of Mixed-Metal Oxides Nanocatalysts: An In Situ Multiple-Technique Approach

Thursday, October 22, 2015, 11:00 am, Room 212D

Catalysts have traditionally been characterized before or after reactions and analyzed based on static representations of surface structures. It is shown here how dynamic changes on a catalyst’s chemical state and morphology can be followed during a reaction by a combination of in situ microscopy (AP-STM) and spectroscopy (AP-XPS and AP-IRRAS). In addition to determining the active phase of the catalyst by in situ methods, the presence of weakly adsorbed surface species or intermediates generated only in the presence of reactants can be determined, allowing in turn the comparison of experimental results with first principle modeling of specific reaction mechanisms. Three reactions are used to exemplify the approach: CO oxidation (CO + 1/2O₂ → CO₂), water gas shift reaction (CO + H₂O → CO₂ +H₂) and methanol synthesis (CO₂ + 3H₂ → CH₃OH + H₂O). During CO oxidation, the full conversion of Cu⁰ to Cu⁺² deactivates an initially outstanding catalyst. This can be remedied by the formation of a TiCuO_x mixed-oxide that protects the presence of active partially oxidized Cu⁺ cations. We also show the switch from a redox mechanism on Cu(111) to a more efficient associative mechanism pathway for the WGSR at the interface of ceria nanoparticles deposited on Cu(111) [1]. Similarly, the activation of CO₂ at the ceria/Cu(111) interface allows its facile hydrogenation to methanol [2]. Our combined studies emphasize the need of searching for optimal metal/oxide interfaces, where multifunctional sites can lead to new efficient reaction pathways.

[1] Angew. Chem. Int. Ed. 52, 5101–5105 (2013)

[2] Science, 345, 546-550 (2014)