Operando Infrared Spectroscopy of Rh/Al2O3 Washcoated Monolithic Catalysts: Influence of Preparation and Aging

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is widely used to investigate surface species and metal–support interactions in heterogeneous catalysis, but is typically applied to powder samples. In contrast, industrial catalysts are often used as structured bodies, for which differences in preparation, geometry, and flow behavior may affect both catalytic performance and spectroscopic observations. Here, we present a proof-of-concept operando DRIFTS study of CO oxidation over intact 3 × 3-channel Rh/Al2O3 washcoated cordierite monolith cores. The catalytic light-off behavior of monolith cores and corresponding washcoat powders was comparable. However, the *NCO bands associated with nitric acid used during catalyst preparation were observed predominantly for the monolith cores, demonstrating that preparation-dependent features can be underrepresented in powder analogues. Reversing the gas-flow direction changed the position of the DRIFTS sampling region relative to the reaction zone without substantially affecting the overall CO oxidation activity, showing an additional capability of measurements on intact structured catalysts. To mimic catalyst deactivation during industrial operation, samples were subjected to aging in H2, air, and hydrothermal redox-cycling (HRC; alternating H2/O2 in the presence of water vapor). While H2 aging resulted in little change in catalytic activity and IR spectra, air aging led to a decrease in adsorbed CO IR band intensity and an increased light-off temperature, consistent with a change in the Rh-containing surface species, potentially involving Rh incorporation into the alumina support. HRC aging resulted in slight deactivation, and enhanced IR bands of CO adsorbed on metallic Rh, due to Rh nanoparticle sintering. These results demonstrate that operando DRIFTS on intact washcoated monolith cores can reveal preparation- and aging-dependent surface-chemistry differences while retaining features of the structured catalyst geometry.