Dispersion of Au entities over Mo2N and MoC for the low-temperature water–gas shift reaction†

Abstract

Nitridation of an Au/MoO₃ precursor, 8 nm Au particles dispersed over MoO₃ nanobelts, by ammonia at 600 °C resulted in Au flat films of 4–27 nm wide over γ-Mo₂N, while further carburization with a CH₄/H₂ mixture at 700 °C converted γ-Mo₂N to α-MoC and simultaneously dispersed Au flat films into atomic layers and single-atoms. The Au/γ-Mo₂N catalyst was nearly inert for the low-temperature water–gas shift reaction at 120 °C and it became appreciably active at 200 °C. By contrast, the Au/α-MoC catalyst was readily highly active at 120 °C and further, the specific activity was nearly tenfold at 200 °C. Structure analysis regarding the dispersion of Au entities and the structure properties of γ-Mo₂N/α-MoC revealed that the support contributed significantly to the catalytic performance, in addition to the active Au species. The lower N vacancies of γ-Mo₂N favored the dispersion of Au thin layers, but weakened the ability to dissociate H₂O. Well-crystallized α-MoC anchored Au atomic layers and single-atoms and extended the Au–MoC interface, and thereby greatly facilitated H₂O dissociation.