Impregnated and Co-precipitated Pd–Ga(2)O(3), Pd–In(2)O(3) and Pd–Ga(2)O(3)–In(2)O(3) Catalysts: Influence of the Microstructure on the CO(2) Selectivity in Methanol Steam Reforming

ABSTRACT: To 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 Ga(2)O(3)- and In(2)O(3)-supported GaPd(2) and InPd catalysts, respectively. To study the possible promoting effect of In(2)O(3), an In(2)O(3)-doped Ga(2)O(3)-supported GaPd(2) catalyst has also been examined. While, upon reduction, the same intermetallic compounds are formed, the structure of especially the Ga(2)O(3) support is strikingly different: rhombohedral and spinel-like Ga(2)O(3) phases, as well as hexagonal GaInO(3) and rhombohedral In(2)O(3) 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 CO(2) selectivity in MSR. Both Ga(2)O(3) and In(2)O(3) catalysts show a much higher activity, and in the case of GaPd(2)–Ga(2)O(3), a much higher CO(2) selectivity. The promoting effect of In(2)O(3) is also directly detectable, as the CO(2) selectivity of the co-precipitated supported Ga(2)O(3)–In(2)O(3) catalyst is much higher and comparable to the purely In(2)O(3)-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. GRAPHICAL ABSTRACT: The presence of a variety of distinct supported intermetallic InPd and GaPd(2) particle phases is not detrimental to activity/selectivity in methanol steam reforming as long as the appropriate intermetallic phases are present and they exhibit optimized intermetallic-support phase boundary dimensions. [Image: see text]