Abstract

Epoxidation of styrene to styrene oxide (SO) by molecular oxygen was studied over cesium promoted silver nanowires, catalysts. Styrene oxide (SO) and phenylacetaldehyde (Phe) were the main products. The results showed that Cs plays an important role improving the efficiency of the catalyst. The effect of the reaction temperature and the O-2:C8H8 molar ratio on the catalytic epoxidation was also investigated. Low reaction temperatures or high 02:C8H8 ratios increase the selectivity to SO. The catalytic activity shows a maximum for silver nanowires promoted with 0.25 wt.% of Cs, achieving 94.6% of conversion and total selectivity to desired oxidation products (styrene oxide and phenylacetaldehyde). Besides, negligible deactivation of the catalyst was observed over 30 days of reaction. The experimental characterization was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The presence of cesium plays a strong role in reducibility of the silver as detected by temperature-programmed reduction analysis affecting the catalytic activity. The results also suggested the presence of two different species of oxygen formed on the silver nanowires surface after oxygen exposure. (c) 2006 Elsevier B.V. All rights reserved.