In situ probing of Pt/TiO2 activity in low-temperature ammonia oxidation

The improvement of the low-temperature activity of the supported platinum catalysts in selective ammonia oxidation to nitrogen is still a challenging task. The recent developments in in situ/operando characterization techniques allows to bring new insight into the properties of the systems in correlation with their catalytic activity. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando X-ray absorption spectroscopy (XAS) techniques were applied to study Pt/TiO2 catalysts in ammonia oxidation (NH3 + O-2 reaction). Several synthesis methods were used to obtain samples with different size of Pt particles, oxidation state of Pt, and morphology of the support. Metal platinum particles on titania prepared by pulsed laser ablation in liquids exhibited the highest activity at lower temperatures with the temperature of 50% conversion of NH3 being 150 degrees C. The low-temperature activity of the catalysts synthesized by impregnation can be improved by the reductive pretreatment. NAP-XPS and operando XANES data do not show formation of PtOx surface layers or PtO/PtO2 oxides during NH3 + O-2 reaction. Despite the differences in the oxidation state of platinum in the as-prepared catalysts, their treatment in the reaction mixture results in the formation of metallic platinum particles, which can serve as centers for stabilization of the adsorbed oxygen species. Stabilization of the bulk platinum oxide structures in the Pt/TiO2 catalysts seems to be less favorable due to the metal-support interaction.

Automated summary

The improvement of low-temperature activity of supported platinum catalysts in selective ammonia oxidation remains a challenging task. Recent developments in in situ/operando characterization techniques have provided new insights into the correlation between system properties and catalytic activity. This study used NAP-XPS and operando XAS techniques to investigate Pt/TiO2 catalysts in ammonia oxidation, revealing that different synthesis methods can affect the catalyst's performance in the reaction.