Cross-section TEM investigation of quasicrystalline catalysts prepared by aqueous NaOH leaching

The Al-Cu-Fe quasicrystal (QC) has been shown to reveal high catalytic activity and thermal stability for steam reforming of methanol (SRM: CH3OH + H2O 3H2 + CO2), after leaching with NaOH aqueous solution. To investigate the origin of the high catalytic performance, cross-sectional transmission electron microscopy (TEM) observations of the catalyst particles were examined. By leaching with NaOH aq., a homogeneous composite structure, composed of Cu and Fe and/or their oxides or hydroxides, is formed at the outer layer of catalyst particles and the QC phase remains in the inner area. The homogeneous dispersion of Fe and/or the oxide/hydroxide in the composite suppresses sintering of Cu particles. In contrast, for the catalyst prepared from crystalline -phase (Al70Cu20Fe10), the original phase completely collapses and, instead, a complicated composite structure is formed. The inhomogeneity results in the formation of Cu-enriched regions at the rim of the catalyst particles. We suggest that the high catalytic performance of the Al-Cu-Fe QC catalyst prepared by leaching with NaOH aq. is due to the formation of a homogeneous composite region at the outer layer of the catalyst particles.