H2-SCR of NO on Pt–MnOx catalysts: Reaction path via NH3 formation Original Research Article

Pt–MnOx catalysts without any alkali or transition metals were prepared and their performance in the selective catalytic reduction (SCR) of NO by H2 was examined. Their physicochemical properties were investigated using X-ray diffraction (XRD), extended X-ray adsorption fine structure (EXAFS), and X-ray photoelectron spectroscopy (XPS). The adsorption and removal of NO during H2-SCR were monitored by an in situ FT-IR spectrophotometer. The co-presence of MnO and MnO2 on Pt–MnOx was confirmed by EXAFS and XPS. NO was adsorbed on them as nitrate and nitrite, which were subsequently transformed to NHx species by the introduction of H2. The NHx species adsorbed on the acid sites of manganese oxide were active in the reduction of NO, although a direct reduction by H2 was also possible. The conversion of NO over the Pt(2.0)–MnOx catalyst was maximized to 64% at around 100 °C and fell with further increases in temperature. The N2 yield over the Pt(2.0)–MnOx catalyst was 30% at the same condition, indicating that about a half of NO was converted to N2. On the contrary, the Pt(2.0)/SiO2 catalyst exhibited very low N2 yield, 10%, because N2O was highly produced. The reaction between the hydrogen atoms activated on the platinum and the activated NO on the manganese oxide was considered essential for H2-SCR, and NH3 that formed as an intermediate effectively participated to the selective reduction.