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Abstract

In the present work improved Cu/ZrO₂ catalysts for the steam reforming of methanol (MSR) were investigated. Using various starting materials, templates and synthesis routes, nanostructured, mesoporous, and macroporous Cu/ZrO₂ catalysts were prepared and subsequently investigated under methanol steam reforming (MSR) conditions. XRD (X-ray diffraction) and XAS (X-ray absorption spectroscopy) combined with mass spectrometry were used to monitor structural changes, stability and catalytic activity under reaction conditions. Ex situ XAS measurements of the precursors identified very small or highly disordered CuO particles as the main copper phase. XRD measurements of the precursors showed that tetragonal ZrO₂ is the major zirconia phase, while various amounts of monoclinic ZrO₂ were also detectable depending on preparation and copper content. The copper oxide clusters in nearly all samples were reduced incompletely during heating in 2 vol-% H₂/He probably because of characteristic Cu metal support interactions in the Cu/ZrO₂ catalysts.
All catalysts studied were active for MSR. The initial low activity could be significantly improved by a temporary addition of oxygen to the feed. The microstructure of the copper phase in the activated catalysts strongly deviates from ideal copper metal. EXAFS analysis showed, that an increased amount of oxygen in the copper metal clusters correlates with an increasing activity for MSR. Furthermore, it was found that after extended times in the MSR feed at elevated temperatures (673 K, 2 vol-% H₂/He), the catalysts were still active or could be activated (via O₂ addition).
With regard to the influence of the preparation on the catalytic performance it was found, that the sequential formation of the ZrO₂ and CuO precursors, as well as the impregnation of a pre-formed (calcined) ZrO₂ support lead to stronger metal-support-interactions, and hence to improved MSR-activities. The copper concentration also plays a significant role, as with lower concentrations (less than ~ 15 %) better interactions are achieved.