Mechanistic Investigation of Deactivation of Ru/Al₂O₃ Catalyst for Preferential CO Oxidation in the Presence of NH₃

Abstract

The preferential CO oxidation (PROX) on a Ru/Al2O3 catalyst was investigated at 115−185 °C in the presence of 21−75 ppm NH3. With an increase in [O2]/[CO] ratios, the CO conversion decreased, though it increased in the absence of NH3. In the presence of NH3, the catalytic activity was high at high temperature, which indicates that O2 was consumed over the upstream of the catalyst bed and that the reaction atmosphere in most portions of catalyst bed was reductive. Thus, a reduction atmosphere kept the catalyst active. For the H2 oxidation without CO, the catalyst was immediately deactivated in the presence of NH3, which indicates that the activation of oxygen was suppressed. In the in-situ IR spectra, a band assigned to nitrosyls appeared during the poisoning, and the intensity increased with time on stream. In addition, the band intensity of monocarbonyls decreased with an increase in that of multicarbonyls and nitrosyls. The presence of multicarbonyls indicates that the nitrosyls stabilized the oxidized Ru. In the presence of NH3, the oxidized Ru catalyst showed a low activity under an oxidation atmosphere, while the reduced Ru catalyst exhibited a high activity under a reduction atmosphere.

Operando Spectroscopic Study of the Dynamics of Ru Catalyst during Preferential Oxidation of CO and the Prevention of Ammonia Poisoning by Pt

“… 34 , 35 This results in the reformate containing NH 3 (usually 10–80 ppm) that deactivates the catalyst. 32 , 33 …”

“…34,35 This results in the reformate containing NH 3 (usually 10−80 ppm) that deactivates the catalyst. 32,33 Previously, we studied the activities of two Ru-based PROX catalysts, the conventional Ru-based PROX catalyst Ru/α-Al 2 O 3 and a Pt−Ru bimetallic catalyst (Pt/Ru/α-Al 2 O 3 ), in the presence of NH 3 . 31 In the deactivated Ru/α-Al 2 O 3 catalyst, we found that the Ru was partially oxidized.…”

“…The influence of impurities in the reformate on the catalytic activity and durability of PROX catalysts is an important topic of research. − For example, ammonia (NH 3 ) deactivates the conventional Ru-based PROX catalyst Ru/α-Al 2 O 3 . In domestic PEFC systems, natural gas is subjected to steam reforming, also over an Ru catalyst; however, these catalysts catalyze the synthesis of NH 3 from hydrogen and trace amounts of nitrogen that are also present in natural gas. , This results in the reformate containing NH 3 (usually 10–80 ppm) that deactivates the catalyst. , …”

Dynamic Modeling To Study Reversible Poisoning of a Catalytic Bed

“…Chemical feedstocks are often contaminated with minor quantities of undesirable compounds such as ammonia or sulfur-containing compounds, and these trace compounds can compete with the primary reactant for active sites, thereby reducing catalyst activity. In some cases these trace compounds can also desorb under changing process conditions (temperature or partial pressures) making the activity loss reversible. − …”