Abstract
Structure, morphology and composition of different tin oxide and germanium oxide thin film catalysts for the methanol steam reforming (MSR) reaction have been studied by a combination of (high-resolution) transmission electron microscopy, selected area electron diffraction, dark-field imaging and electron energy-loss spectroscopy. Deposition of the thin films on NaCl(0 0 1) cleavage faces has been carried out by thermal evaporation of the respective SnO 2 and GeO 2 powders in varying oxygen partial pressures and at different substrate temperatures. Preparation of tin oxide films in high oxygen pressures (10 −1 Pa) exclusively resulted in SnO phases, at and above 473 K substrate temperature epitaxial growth of SnO on NaCl(0 0 1) leads to well-ordered films. For lower oxygen partial pressures (10 −3 to 10 −2 Pa), mixtures of SnO and β-Sn are obtained. Well-ordered SnO 2 films, as verified by electron diffraction patterns and energy-loss spectra, are only obtained after post-oxidation of SnO films at temperatures T ≥ 673 K in 10 5 Pa O 2. Preparation of GeO x films inevitably results in amorphous films with a composition close to GeO 2, which cannot be crystallized by annealing treatments in oxygen or hydrogen at temperatures comparable to SnO/SnO 2. Similarities and differences to neighbouring oxides relevant for selective MSR in the third group of the periodic system (In 2O 3 and Ga 2O 3) are also discussed with the aim of cross-correlation in formation of nanomaterials, and ultimately, also catalytic properties.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have