1998

Reinikainen, Matti

Cobalt and ruthenium-cobalt catalysts prepared from various precursors were studied in the activation of CO using CO hydrogenation and vapour phase hydroformylation as test reactions. The characteristics and activity were related to the precursor, composition, promoters and the method of preparation. Catalysts prepared from carbonyls exhibited the highest activity in CO hydrogenation. In addition to hydrocarbons, Co2(CO)8/SiO2 had a high (20%) selectivity for oxygenates such as alcohols and esters. Likewise, the Co2(CO)8/SiO2 catalyst was active in the hydroformylation of ethene, whereas the conventional cobalt catalysts prepared from inorganic salts were virtually inactive in this reaction. Promotion by alkali or alkaline earth cations affected the performance of the Co2(CO)8/SiO2 catalyst significantly: the activity decreased in both CO hydrogenation and ethene hydroformylation, but at the same time the selectivity for oxygenates and oxo-products, respectively, was tremendously increased. An exceptionally high selectivity for propanoic acid (47%) was observed on an alkaline earth oxide promoted Co2(CO)8/SiO2. The results for ruthenium containing catalysts indicated that the precursor and/or the combination of metals significantly influenced the interaction of the catalytic species with the support. The method of preparation also had a profound effect on the attachment of catalytic species to the support and their reducibility. In addition, the pretreatment exerted a significant influence on the catalyst, since the surface was restructured during the pretreatment resulting in changes in/losses of the active sites. As a result of the sensitivity to preparation, the performance of the catalysts differed significantly in CO hydrogenation, both in terms of activity and selectivity. Interestingly, the Co-Ru/SiO2 catalyst prepared by ionic adsorption exhibited unique selectivity in the Fischer-Tropsch synthesis, pronounced formation of methanol, compared with similar catalyst compositions prepared by impregnation or reflux methods. In all, the work clearly demonstrated the strong interrelation of catalyst preparation and performance. It also indicated that catalysts with very unusual performance could be prepared, particularly from Co2(CO)8 precursor. The commercial applicability of all the carbonyl based catalysts is, however, limited by their air sensitive nature and by the losses occurring during the catalyst pretreatment. Thus, the catalysts with a less sensitive preparation method but nevertheless unique characteristics, such as Co-Ru/SiO2 prepared by ionic adsorption, appear more interesting in the light of further development work.