Improved Performance of Ru/γ‐Al₂O₃ Catalysts in the Selective Methanation of CO in CO₂‐Rich Reformate Gases upon Transient Exposure to Water‐Containing Reaction Gas

Abstract

To better understand the role of water in the selective methanation of CO in CO2-rich reformate gases on Ru/Al2O3 catalysts, the influence of exposing these catalysts to H2O-rich reformate gases on their reaction characteristics in transient experiments was investigated by employing kinetic and in situ spectroscopic measurements as well as ex situ catalyst characterization. Transient exposure of the ruthenium catalyst to wet reaction gas (5 or 15% H2O) results in significantly enhanced activity and selectivity for CO methanation in subsequent reactions in dry reformate compared with activation and reaction in dry reformate directly. Operando X-ray absorption spectroscopy results reveal that this is in accordance with a significant decrease in ruthenium particle size, which is stable during subsequent reaction in dry reformate. The implications of these data and additional results from in situ IR spectroscopy on the role and influence of H2O on the reaction, also in technical applications, are discussed.

Selective CO Methanation on Highly Active Ru/TiO2 Catalysts: Identifying the Physical Origin of the Observed Activation/Deactivation and Loss in Selectivity

“…3c). On the catalyst the spectra resolve a number of different modes related to CO adsorbed on the surface of the Ru NPs (see also 12 ). Bands at 2135 and 2078 cm -1 were previously attributed to CO coadsorbed with O ad or to CO ad at the Ru-oxide interface, possibly with multiply bonded carbonyl species, respectively.…”

“…Their preparation and details of their characterization were described elsewhere. 12 Prior to the reaction, the diluted Ru/TiO 2 catalysts (see section 2.2) were activated in the following way: i) heating up to 150°C in a flow of N 2 (40 Nml min -1 ), ii) calcination for 30 min in 10% O 2 /N 2 at this temperature, iii) purging in N 2 for 15 min at the same temperature, and finally iv) reduction in the respective reaction gas mixture (see Table 2) by heating up to 190°C in 10 min. According to previous XPS and energy dispersive X-ray (EDAX) characterization the calcination procedure is sufficient to minimize the residual Cl from the sample after 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 preparation to very low and similar concentration on all prepared samples, while keeping the thermal load of the catalyst at a minimum (see ref.…”

“…According to previous XPS and energy dispersive X-ray (EDAX) characterization the calcination procedure is sufficient to minimize the residual Cl from the sample after 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 preparation to very low and similar concentration on all prepared samples, while keeping the thermal load of the catalyst at a minimum (see ref. 12 ).…”

“…14 iv) Finally, for Ru/TiO 2 catalysts also the support surface area was found to strongly affect the (inherent) selectivity, with the highest selectivity observed for high-surface area Ru/TiO 2 catalysts. 12 This was attributed to increasing metal − support interactions (MSI). This effect, which was tentatively proposed to be valid also for other Ru catalysts supported on reducible oxide supports, provides additional opportuinities for controlling the catalytic performance and in particular the selectivity for CO methanation of supported Ru catalysts.…”

Morphologie‐optimierte hochaktive und ‐stabile Ru/TiO2‐Katalysatoren für die selektive CO‐Methanisierung

“…[1,2] Dabei haben sich insbesondere Oxidfixierte Ru-Katalysatoren als schon bei niedrigen Te mpera-turen hochaktive und selektive Katalysatoren erwiesen. [3][4][5][6] Neuere Arbeiten lassen darauf schließen, dass die intrinsische Selektivitätv on auf verschiedenen Oxiden fixierten Ru-Nanopartikeln (Ru-NPs) hauptsächlich durch die Ru-Partikelgrçße bestimmt wird, [7][8][9][10][11][12][13] während die Aktivitätm it der Reduzierbarkeit des Tr ägers variiert. [13] FürRu/TiO 2 zeigten sich zudem die spezifische BET-Oberfläche [9] und die damit korrelierten Veränderungen in den Metall-Träger-Wechselwirkungen als wesentlicher Faktor.…”