Role of powders and coatings for relating catalytic activity and structure of Pt in emission control catalysis

Abstract

Packed powder beds and coatings are two relevant forms of catalysts, applied in industrial heterogeneous catalysis and multiple fundamental studies including operando spectroscopy. Both types have their individual advantages and disadvantages in regard to the performance and characterisation causing some complexity in the resulting flow patterns, possible temperature inhomogeneities in the reactor and the dynamic evolution of chemical state of the noble metal during the reaction along the catalytic bed. The well-known CO oxidation reaction over Pt/Al₂O₃ catalysts was used in this study to uncover the influence of the gas phase compositions and the temperature on the evolution of the electronic structure of Pt for powdered and coated catalysts at comparable length scales. Advanced operando investigations were used to demonstrate the influence of spatial gradients in the gas phase for washcoats in contrast to packed powder beds. Additionally, transient gradients in the chemical state of Pt, which occurred more pronounced for packed powder beds than for coated monoliths were followed and traced back to heat and mass transfer effects. Finally, the catalytic activity can be linked to the temperature distributions for both types of samples. These findings will be valuable for planning and evaluating future combinations of spectroscopic and catalytic experiments on industrially relevant systems.