Impregnated and Co-precipitated Pd-GaO, Pd-InO and Pd-GaO-InO Catalysts: Influence of the Microstructure on the CO 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 GaO- and InO-supported GaPd and InPd catalysts, respectively. To study the possible promoting effect of InO, an InO-doped GaO-supported GaPd catalyst has also been examined. While, upon reduction, the same intermetallic compounds are formed, the structure of especially the GaO support is strikingly different: rhombohedral and spinel-like GaO phases, as well as hexagonal GaInO and rhombohedral InO 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 selectivity in MSR. Both GaO and InO catalysts show a much higher activity, and in the case of GaPd-GaO, a much higher CO selectivity. The promoting effect of InO is also directly detectable, as the CO selectivity of the co-precipitated supported GaO-InO catalyst is much higher and comparable to the purely InO-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 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.