Complementary and Spatially Resolved Operando Spectroscopic Investigation of Pt/Al$_2$O$_3$ and Pt/CeO$_2$ Catalysts during CO/NO Conversion

The composition of reaction mixtures strongly influences the structural evolution and performance of noble metal-based catalysts. In this work, we compared the effect of the simultaneous presence of CO and NO on the noble metal state and CO oxidation activity of Pt/Al$_2$O$_3$ and Pt/CeO$_2$ catalysts under close-to-stoichiometric conditions using complementary in situ/operando X-ray and infrared spectroscopic techniques. For the utilized catalysts, the integral catalytic performance data indicated a diminished CO oxidation activity in the presence of NO, which is due to a competitive adsorption of CO and NO, as elucidated by the diffuse reflectance infrared Fourier transform spectroscopy and high-energy resolution X-ray fluorescence X-ray absorption near-edge structure results. Spatially resolved operando X-ray absorption spectroscopy investigations and extended X-ray absorption fine structure analysis unraveled that the addition of NO led to a higher oxidation state of Pt along the entire catalyst bed for both samples. Moreover, NO was found to delay the reduction of Pt particles on Al$_2$O$_3$ and hinder the formation of active Pt clusters on CeO$_2$. As a result, a more oxidized Pt state at the beginning of the catalyst bed and a low overall activity were observed for Pt/CeO$_2$. However, the CO oxidation activity could be enhanced by a reductive pretreatment of the Pt/CeO$_2$ catalyst, resulting in a similar reduced Pt state along the entire catalyst bed and minimizing the negative impact of NO during the combined reaction.