A novel hybrid route, combining simple co-precipitation and conventional solid state reaction, is proposed for the first time to synthesize BaCe 0.4 Zr 0.4 Y 0.2 O 3− δ powders at a temperature as low as 1150 °C. This temperature is much lower than that used for conventional solid state reaction method and even comparable to that used in sol–gel route. The reasons for the low calcination temperature are analyzed in detail from the macroscopic to microscopic viewpoints. Moreover, with the powders made by the novel method, dense ceramic could be easily obtained. Further, impedance data illustrated that its electrical conductivity in wet H 2 at 750 °C is up to 1.39 × 10 −2 S/cm, which is the highest among all the samples prepared by the three different methods and much higher than the reported results related to BCZY proton conductors . Also, the new method is particularly suitable for other multi-component oxides .
Ammonia (NH 3 ) is an excellent candidate for hydrogen storage and transport. However, producing NH 3 under mild conditions is a long-term, arduous task. Atomic cluster catalysts (ACCs) have been shown to be effective for catalytic N 2 -to-NH 3 conversion, opening the door to the development of efficient catalysts under mild conditions. Still, ACC formation with thermally stable catalytic sites remains a challenge because of their high surface free energy . Herein, we report anchoring Ba and/or Ce onto Ru ACCs (2 wt% Ru atomic clusters supported on N-doped carbon) to form so-called clusters–metal oxide promoters electronic interaction (CMEI) to stabilize the Ru atomic clusters. The resulting Ba/Ce/Ru ACCs significantly boost the NH 3 synthesis rate to 56.2 mmol NH3 g cat −1 h −1 at 400 °C and 1 MPa, which is 7.5-fold higher than that of Ru ACC. The strengthened CMEI between the Ba/Ce and Ru atomic clusters across the Ba/Ce/Ru ACC enables electron transfer from Ba and/or Ce to Ru atomic clusters. As such, the electron-enriched Ru atom could facilitate electron transfer to N≡N bond π* orbitals, which would weaken the N≡N bond and drive the eventual conversion of N 2 to NH 3 . This study offers insight into the role of CMEI in Ru ACCs and provides an effective approach for designing stable atomic cluster catalysts for NH 3 synthesis.
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