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 oxidat ion without any additional thermal treatment. While samples dried at 120 de greesC in air exhibited the highest activity for CO oxidation, samples drie d at room temperature under vacuum were less active. The catalytic properti es of most fresh samples improved after the first light-off test, during wh ich a temperature of 400 degreesC was reached. To investigate the physical and chemical state of gold and manganese support, dried samples were examin ed 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 d emonstrated that fresh samples contained manganese carbonate and oxides suc h 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 roun ded corners. Au particle sizes were in the range 4.5-6.5 nm before the ligh t-off test. After heat treatment at 400 degreesC, catalytic activity improv ed and a strong interaction between gold particles and the MnOx support was induced. (C) 2001 Academic Press.