Effect of drying conditions of Au-Mn co-precipitates for low-temperature CO oxidation

An-Mn co-precipitates were dried at different temperatures and in different atmospheres. The co-precipitates were tested for low-temperature CO oxidation without any additional thermal treatment. While samples dried at 120 degreesC in air exhibited the highest activity for CO oxidation, samples dried at room temperature under vacuum were less active. The catalytic properties of most fresh samples improved after the first light-off test, during which a temperature of 400 degreesC was reached. To investigate the physical and chemical state of gold and manganese support, dried samples were examined by Au-197 Mossbauer spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The Au-197 Mossbauer spectra showed that gold existed only in metallic form and was produced during the co-precipitation procedure. XRD and XPS analyses demonstrated that fresh samples contained manganese carbonate and oxides such as MnO2. The carbonate was converted to manganese oxides after the light-off test. TEM analysis indicated that the manganese support was present in plate-like shapes and the shape of gold particles was rectangular with rounded corners. Au particle sizes were in the range 4.5-6.5 nm before the light-off test. After heat treatment at 400 degreesC, catalytic activity improved and a strong interaction between gold particles and the MnOx support was induced. (C) 2001 Academic Press.