The interaction of oxygen with high loaded Ru/γ-Al2O3 catalyst

Abstract The interaction of oxygen with the Ru/γ-Al 2 O 3 catalyst comprising metal particle with sizes of 1–16 nm, was examined over a temperature range 20–400 °C. The catalyst loaded with 10.8 wt.% Ru was prepared by incipient wetness from RuCl 3 precursor. The structure of the Cl-containing catalyst and the catalyst after elimination Cl − ions was characterized using H 2 and O 2 chemisorption, O 2 uptake, BET, XRD and TEM. The Cl − ions in the catalyst decreased the H 2 and O 2 chemisorption capacity of Ru and caused large discrepancies between the mean particle size calculated from gas chemisorption and from TEM. Exposure to O 2 at 100–200 °C caused oxidation of small Ru particles, while larger particles were covered with very thin Ru x O y skin (undetected by XRD and TEM). The O/Ru ratio increased up to 200 °C implying high affinity of the small Ru particles to oxygen. Oxidation at 250 °C led to the formation of poorly crystalline RuO 2 particles with a mean size of 4 nm, and coverage of large Ru particles with 1.6 nm thick oxide layer. At 300 and 400 °C crystallization of the RuO 2 phase, as well as significant agglomeration of oxide particles was observed. However, even at 400 °C, metallic Ru was detected by XRD, TEM and SAED suggesting that large metal particles were not fully oxidized under the used conditions. Also, the O 2 uptake at 400 °C was lower than expected for oxidation of Ru metal to RuO 2 . For the catalyst after elimination Cl ions the O 2 uptake (O/Ru ratio = 1.50) was higher, than for sample with large amount of Cl ions (O/Ru ratio = 1.34), indicating that the presence of Cl inhibits ruthenium oxidation in the Ru/Al 2 O 3 catalyst.