Characterization of silver catalysts for the oxidation of methanol

• Published in: Applied catalysis Vol. 29; no. 2; pp. 261 - 283
• Main Authors: Plummer, H.K., Watkins, W.L.H., Gandhi, H.S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 1987; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; General. Nomenclature, chemical documentation, computer chemistry; Theory of reactions, general kinetics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Silver Chlorides; Scanning electron microscopy; X ray fluorescence; Carbon dioxide; X ray diffraction; Fourier spectrometry; Supported catalyst; Infrared spectrometry; Silver; Transmission electron microscopy; Oxidation; Silver Nitrates; Alumina; Methanol
• ISSN: 0166-9834
• DOI: 10.1016/S0166-9834(00)82897-3

The selection of a silver catalyst system for further study was determined on a basis of cost and its ability to oxidize formaldehyde selectively. In addition a silver catalyst can provide a low light off temperature for the conversion of methanol to carbon dioxide and water vapor. Silver catalysts were prepared by the deposition of solutions of silver nitrate or silver chloride on gamma alumina washcoat supported on cordierite monolith. These silver catalysts were characterized by a variety of analytical techniques including TEM, SEM, EMP, STEM, XRF, XRD and FTIR. It is concluded that the best silver catalyst is prepared by deposition of silver from a solution of silver ammnonium chloride onto a cordierite supported high surface area gamma alumina washcoat, drying at 100°C in air, followed by reduction in flowing 3% H 2 in N 2 at 500°C for 4 h. This procedure will produce a silver catalyst with highest activity, largest retention and most uniform distribution of silver. The procedure also retains the concentration of silver and the gamma phase of alumina at temperatures as high as 1000°C in air for as long as 6 h. Due to the inability of normal TEM imaqing modes to obtain silver particle size information in the presence of the small gamma alumina washcoat particles a model system was made to test the ability of a dedicated STEM to furnish that information. The model system consisted of silver particles in the range of 1 to 50 nm which had been evaporated onto a uniform thin film of alumina. High resolution X-ray maps obtained from the model system demonstrate the ability to determine location and size of silver particles > 5 nm. A number of catalysts containing noble and base metals supported on gamma alumina washcoat on a cordierite monolith have also been studied. Laboratory flow reactor studies and chassis dynamometer studies using a Mercury Lynx modified to burn neat methanol have shown the following order of activity for conversion of methanol burned in experimental or engine exhaust gas: Pd > Ag > Pt + Rh > CuO + ZnO + Cr 2O 3 > Ni.