Impregnated and Co-precipitated Pd–Ga2O3 Pd–In2O3 and Pd–Ga2O3–In2O3 Catalysts: Influence of the Microstructure on the CO2 Selectivity in Methanol Steam Reforming

摘要

AbstractTo focus on the influence of the intermetallic compound—oxide interface of Pd-based intermetallic phases in methanol steam reforming (MSR), a co-precipitation pathway has been followed to prepare and subsequently structurally and catalytically characterize a set of nanoparticulate Ga2O3- and In2O3-supported GaPd2 and InPd catalysts, respectively. To study the possible promoting effect of In2O3, an In2O3-doped Ga2O3-supported GaPd2 catalyst has also been examined. While, upon reduction, the same intermetallic compounds are formed, the structure of especially the Ga2O3 support is strikingly different: rhombohedral and spinel-like Ga2O3 phases, as well as hexagonal GaInO₃ and rhombohedral In₂O₃ phases are observed locally on the materials prior to methanol steam reforming by high-resolution transmission electron microscopy. Overall, the structure, phase composition and morphology of the co-precipitated catalysts are much more complex as compared to the respective impregnated counterparts. However, this induces a beneficial effect in activity and CO₂ selectivity in MSR. Both Ga₂O₃ and In₂O₃ catalysts show a much higher activity, and in the case of GaPd₂–Ga₂O₃, a much higher CO₂ selectivity. The promoting effect of In₂O₃ is also directly detectable, as the CO₂ selectivity of the co-precipitated supported Ga₂O₃–In₂O₃ catalyst is much higher and comparable to the purely In₂O₃-supported material, despite the more complex structure and morphology. In all studied cases, no deactivation effects have been observed even after prolonged time-on-stream for 12 h, confirming the stability of the systems.