Boosting Ru atomic efficiency of LaFe0.97Ru0.03O3 via knowledge-driven synthesis design

Abstract

The exsolution of ruthenium from a 3 at% ruthenium-substituted LaFeO₃ (LFR3) perovskite oxide is meticulously designed to produce a high-performance ruthenium-supported catalyst with high atomic efficiency. A high-temperature redox pretreatment at 800 °C enriches the Ru concentration in the near-surface region of LFR3, while a subsequent mild reduction step with H₂ at 500 °C leads to the Ru exsolution from the Ru-enriched near-surface region (LFR3_Redox_500R), resulting in a high density of small particles that are not passivated by LaO _x . The performance of this catalyst is evaluated through its application in two prototypical catalytic reactions: the combustion of propane (oxidation reaction) and the reduction of CO₂ by hydrogenation (reduction reaction). For both reactions, the activity of the redox-pretreated sample LFR3_Redox_500R exhibits a significant increase compared to the activity of the untreated sample (LFR3_500R). In the catalytic hydrogenation of CO₂, the high selectivity profile undergoes a transition from CO for LFR3_500R to methane for LFR3_Redox_500R.

Fig. 1. (a) XRD patterns (blue diamonds are the position of orthorhombic LaFeO₃) and (b) Raman of the Ru-incorporated samples LFR3, LFR3_Redox and Ru-exsolved samples LFR3_500R, LFR3_Redox_500R. Fitted C 1s + Ru 3d ex situ XPS spectra of (c) LFR3, LFR3_500R and (d) high-temperature redox treated samples LFR3_Redox and LFR3_Redox_500R.

Fig. 2. Fitted C 1s + Ru 3d NAP-XPS of (a) the as-loaded LFR3 and (b) LFR3_Redox, carbon elimination after oxygen pretreatment at 0.5 mbar O₂ and 600 °C for 1 h (600O) and various reduction treatment at different temperatures (300 °C, 400 °C and 500 °C) under 1 mbar H₂ for 1 h (300R, 400R, 500R). (c) The derived total Ru content and (d) the fraction of Ru in different oxidation states. The fitting parameters are provided in Tables S1 and S2.

Fig. 3. Secondary electron (SE)-STEM images of (a) LFR3_500R and (b) LFR3_Redox_500R. The corresponding size distributions are presented in the right panel. The STEM images are representative.

Fig. 4. (a) H₂-TPR profiles of LFR3 and LFR3_Redox, (b) CO-DRIFTS of Ru-containing samples that collected in 2 vol% CO/Ar at room temperature, (c) CO pulse results of LFR3_500R and LFR3_Redox_500R.

Fig. 5. (a) The activity of Ru-containing perovskites in the propane combustion reaction (1 vol% C₃H₈, 10 vol% O₂ and 89 vol% N₂ at a total flow rate of 100 sscm), (b) the long-term stability of LFR3_500R and LFR3_Redox_500R at 260 °C. Three consecutive activity tests of (c) LFR3_500R and (d) LFR3_Redox_500R.

Fig. 6. (a) Activity and (b and c) selectivity of CO₂ hydrogenation over LFR3_500R and LFRO_Redox_500R as a function of temperature. Long-term stability in terms of (d) activity and (e and f) selectivity of LFR3_500R and LFRO_Redox_500R in the CO₂ hydrogenation reaction at 400 °C. The feeding gas consists of 4 sccm of CO₂ and 16 sccm of H₂ that is balanced by 20 sccm of Ar.