Abstract
To compare the inherent methanol steam reforming properties of intermetallic compounds and a corresponding intermetallic compound–oxide interface, we selected the Cu–In system as a model to correlate the stability limits, self-activation and redox activation properties with the catalytic performance. Three distinct intermetallic Cu–In compounds – Cu7In3, Cu2In and Cu11In9 – were studied both in an untreated and redox-activated state resulting from alternating oxidation–reduction cycles. The stability of all studied intermetallic compounds during methanol steam reforming (MSR) operation is essentially independent of the initial stoichiometry and all accordingly resist substantial structural changes. The inherent activity under batch MSR conditions is highest for Cu2In, corroborating the results of a Cu2In/In2O3 sample accessed through reactive metal–support interaction. Under flow MSR operation, Cu7In3 displays considerable deactivation, while Cu2In and Cu11In9 feature stable performance at simultaneously high CO2 selectivity. The missing significant self-activation is most evident in the operando thermogravimetric experiments, where no oxidation is detected for any of the intermetallic compounds. In situ X-ray diffraction allowed us to monitor the partial decomposition and redox activation of the Cu–In intermetallic compounds into Cu0.9In0.1/In2O3 (from Cu7In3), Cu7In3/In2O3 (from Cu2In) and Cu7In3/Cu0.9In0.1/In2O3 (from Cu11In9) interfaces with superior MSR performance compared to the untreated samples. Although the catalytic profiles appear surprisingly similar, the latter interface with the highest indium content exhibits the least deactivation, which we explain by formation of stabilizing In2O3 patches under MSR conditions.
Highlights
CH3OH(g) + H2O(g) ⇄ 3H2,(g) + CO2,(g)ΔHr0 = 49.6 kJ mol−1 (1)Competing side reactions lead to the formation of electrode-poisoning CO, where only a concentration in the low ppm regime is considered to be tolerable in most fuel 5518 | Catal
The present study aims at elucidating the specific stability limits of several selected intermetallic Cu–In compounds of different stoichiometry during methanol steam reforming operation and assessing the respective self-activation capability vs. redox activation by selected oxidation and reduction treatments
Inspired by the activity increase of a Cu/In2O3 catalyst at a stable CO2 selectivity in MSR upon formation of an Cu2In/ In2O3 interface by reactive metal–support interaction, the stability limits, self-activation and methanol steam reforming performance of three distinct intermetallic Cu–In compounds – Cu7In3, Cu2In and Cu11In9 – were assessed and compared to the performance after a targeted redox activation. The latter allows us to judge the inherent catalytic properties of a Cu–In intermetallic compound–oxide interface resulting from this redox activation
Summary
Competing side reactions lead to the formation of electrode-poisoning CO, where only a concentration in the low ppm regime is considered to be tolerable in most fuel 5518 | Catal. The present study aims at elucidating the specific stability limits of several selected intermetallic Cu–In compounds of different stoichiometry during methanol steam reforming operation and assessing the respective self-activation capability vs redox activation by selected oxidation and reduction treatments. This will allow assessing the intrinsic activity of the respective IMCs and directly relating it to the MSR performance of the potentially resulting metallic Cu (or intermetallic Cu–In compound)–oxide interface. Monitoring of the structural changes with respect to bulk stability of the IMCs, surface chemistry and segregation behavior was based on in situ X-ray diffraction (XRD), operando thermogravimetric analysis, quasi in situ X-ray photoelectron spectroscopy and electron microscopy combined with activity/selectivity and long-term stability measurements in methanol steam reforming
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