CO Hydrogenation to Light Alkenes Over Mn/Fe Catalysts Prepared by Coprecipitation and Sol-gel Methods

CO hydrogenation to light alkenes was carried out on manganese promoted iron catalysts prepared by coprecipitation and sol-gel techniques. Addition of manganese in the range of 1–4 mol.% by means of coprecipitation could improve notably the percentage of C2=~C4= in the products, but it was not so efficient when the sol-gel method was employed. XRD and H2-TPR measurements showed that the catalyst samples giving high C2=~C4= yields possessed ultrafine particles in the form of pure α-(Fe1-xMnx)2O3, and high quality in lowering the reduction temperature of the iron oxide. Furthermore, these samples displayed deep extent of carburization and different surface procedures to the others in the tests of Temperature Programmed Surface Carburization (TPSC). The different surface procedures of these samples were considered to have close relationship with the evolving of surface oxygen. It was also suggested that for the catalysts with high C2=~C4= yields, the turnover rate of the active site could be kept at a relatively high level due to the improved reducing and carburizing capabilities. Consequently, there would be a large number of sites for CO adsorption/dissociation and an enhanced carburization environment on the catalyst surface, so that the process of hydrogenation could be suppressed relatively to a low level. As a result, the percentage of the light alkenes in the products could be raised.