L. Mayr, N. Köpfle, B. Klötzer, T. Götsch, J. Bernardi, S. Schwarz, T. Keilhauer, M. Armbrüster, S. Penner:
"Microstructural and Chemical Evolution and Analysis of a Self- Activating CO2‑Selective Cu−Zr Bimetallic Methanol Steam Reforming Catalyst";
Journal of Physical Chemistry C,
The microstructure of the CO2-selective self-activating and self-stabilizing Cu-Zr bimetallic compound Cu51Zr14 has been studied by a combination of high-resolution electron microscopy and energy-dispersive X-ray spectroscopy both before and after entering the CO2 selective state in methanol steam reforming. Prior to catalysis, the phase composition of the catalyst is characterized by a microstructural mixture of Cu51Zr14 and metallic Cu. The structure appears in a distinct needle-like morphology with a characteristic microstucture of small Cu particles embedded in the intermetallic matrix. In contrast, entering the CO2-selective state goes along with oxidative decomposition-investigated by differential thermal analysis (DTA), thermogravimetry (TG), and mass spectrometry (MS)-and therefore massive structural and compositional changes of the Cu51Zr14 compound both in the near-surface and bulk regions. The final state is then composed of a structurally very heterogeneous sample with Zr-rich and Cu-rich regions within the material bulk with a characteristic lamellar structure. Most importantly, the catalytically relevant surface regions are drastically corroded and depleted in Zr and are characterized by a majority of Cu in intimate contact with oxidized ZrO2 exhibiting a well-ordered, predominantly tetragonal structure. This newly created Cu-ZrO2 interface is believed to be the most significant descriptor steering the CO2 selectivity. In due course, this new method for self-adjustment of the microstructure starting from well-defined intermetallic compounds in the catalytic reaction mixture might pave the way for a more systematic approach of controlled oxidative decomposition of intermetallic compounds acting as promising catalyst precursors.
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