A combined environmental scanning electron microscopy and Raman microscopy study of methanol oxidation on silver(I) oxide

• Published in: Catalysis letters Vol. 43; no. 1-2; pp. 97 - 105
• Main Authors: MILLAR, G. J, NELSON, M. L, UWINS, P. J. R
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 1997; Springer Nature B.V
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Crystal defects; Decomposition reactions; Environmental scanning; Exact sciences and technology; General and physical chemistry; Grain growth; Heating; High temperature; Hydroxyl groups; Methanol; Oxidation; Oxygen; Polycrystals; Raman spectroscopy; Scanning electron microscopy; Silver oxides; Sintering (powder metallurgy); Spectrum analysis; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Catalytic reaction; Catalysts; Group IB metal Compounds; Raman spectroscopy; Alcohols; Surface structure; Silver Oxides; Heterogeneous catalysis; Transition metals Compounds; Oxidation; SEM; Catalysis; Methanol
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1023/A:1018938522320

The techniques of environmental scanning electron microscopy (ESEM) and Raman microscopy have been used to respectively elucidate the morphological changes and nature of the adsorbed species on silver(I) oxide powder, during methanol oxidation conditions. Heating Ag2O in either water vapour or oxygen resulted firstly in the decomposition of silver(I) oxide to polycrystalline silver at 578 K followed by sintering of the particles at higher temperature. Raman spectroscopy revealed the presence of subsurface oxygen and hydroxyl species in addition to surface hydroxyl groups after interaction with water vapour. Similar species were identified following exposure to oxygen in an ambient atmosphere. This behaviour indicated that the polycrystalline silver formed from Ag2O decomposition was substantially more reactive than silver produced by electrochemical methods. The interaction of water at elevated temperatures subsequent to heating silver(I) oxide in oxygen resulted in a significantly enhanced concentration of subsurface hydroxyl species. The reaction of methanol with Ag2O at high temperatures was interesting in that an inhibition in silver grain growth was noted. Substantial structural modification of the silver(I) oxide material was induced by catalytic etching in a methanol/air mixture. In particular, "pin-hole" formation was observed to occur at temperatures in excess of 773 K, and it was also recorded that these "pin-holes" coalesced to form large-scale defects under typical industrial reaction conditions. Raman spectroscopy revealed that the working surface consisted mainly of subsurface oxygen and surface Ag=O species. The relative lack of subsurface hydroxyl species suggested that it was the desorption of such moieties which was the cause of the "pin-hole" formation.