Insight into the Nature of Active Species of Pt/Al 2 O 3 Catalysts for low Temperature NH 3 Oxidation

Two series of Pt/γ‐Al 2 O 3 catalysts for low temperature NH 3 oxidation were prepared using Pt(NO 3 ) 4 and H 2 PtCl 6 precursors. Using both precursors results in the formation of small Pt particles (d<1.5 nm), however, Cl‐containing Pt precursors give a higher fraction of highly dispersed Pt species. Such species show high stability against thermal or H 2 treatment probably due to the presence of a substantial amount of chlorine on the surface. Treatment of the samples prepared from Pt(NO 3 ) 4 with H 2 leads to the formation of metallic Pt nanoparticles accompanied by the improvement of catalytic activity in NH 3 oxidation at T<200 °C. The main products of ammonia oxidation at temperatures below 250 °C were molecular nitrogen and nitrous oxide with the N 2 selectivity reaching 80 %. Operando XANES/EXAFS revealed that even after H 2 pretreatment at least 40 % of Pt surface remains in oxidized state under reaction conditions resulting in the appearance of N 2 O as a by‐product.