Abstract

Catalysts for the selective oxidation of ammonia to molecular nitrogen are essential for the fight against environmental pollution due to vehicle and industrial emissions. This work reports a study of Pt/TiO₂-based K-modified catalysts for the selective oxidation of ammonia. The Pt/TiO₂ catalysts are prepared by impregnating a commercial TiO₂ support (Degussa, P25 Aeroxide) by a platinum nitrate precursor followed by depositing small amounts of potassium with variation of the precursor nature (KOH, KNO₃, KCl). The influence of a promoting additive on the catalysts properties is considered using a complex of physicochemical and kinetic methods such as powder XRD, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of NH₃ (NH₃-TPD), NH₃+O₂ temperature programmed reaction (NH₃+O₂-TPR). According to the XRD data, dispersed platinum particles with a coherent scattering region of no more than 5 nm are formed in the samples. The XPS data indicate that the oxidation state of platinum can be changed by varying the potassium precursor. It is shown that the potassium chloride precursor enhances the selectivity to molecular nitrogen in the temperature range up to 200 °C. The changes in the acidic properties of the sample surfaces are revealed using the NH₃-TPD data, and the changes are compared with catalytic characteristics of the samples in the reaction of ammonia oxidation.