Dispersion of alkali on the surface of Co-MoS 2/clay catalyst: a comparison of K and Cs as a promoter for synthesis of alcohol

Abstract

The surface of alkali (K, Cs) promoted Co-MoS 2/clay catalysts were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The surface enrichment of K and Cs on the surface of catalysts increased with syngas exposure. XPS suggests that syngas treatment slightly shifted the K 2p lines of K-promoted catalyst (K 2p 3/2=292.9 and 2p 1/2=295.7 eV) to a higher binding energy (BE) (K 2p 3/2=293.2 and 2p 1/2=296 eV), and for Cs-promoted catalyst, the Cs 3d 5/2 (724.6 eV) and Cs 3d 3/2 (738.7 eV) were shifted slightly to a higher binding energy (0.2 eV). Co 9S 8 was formed during syngas exposure of Cs-promoted catalyst, but it was not formed during syngas exposure of the K-promoted catalyst. XPS, SEM and EDS analysis indicated that potassium and cesium distributions on the fresh catalysts were not uniform when a mortar and pestle was used to mix the active chemicals. The formation of Co 9S 8 on the surface of Cs-promoted Co-MoS 2/clay catalyst may result in a reduction of Co-Mo-S surface area and its activity toward alcohol production. The highest ethanol production rate (129 g/kg cat h −1) was achieved for K-promoted Co-MoS 2/clay catalyst at 300 °C and 2000 psig for gas hour space velocity (GHSV=2000 h −1). The total alcohol synthesis (AS) production rate increased upon increasing the reaction temperature, however, the total alcohol selectivity was decreased.