Effect of novel metal nitrate calcination on the catalytic behavior of silica supported cobalt catalyst during Fischer-Tropsch synthesis, and impact on slurry phase kinetics

摘要

It is well known that water, possessing as high as about 50% of the total Fischer-Tropsch synthesis (FTS) products, can significantly affect the performance parameters (e.g., CO conversion rate, product selectivities, and catalyst deactivation rate) of supported cobalt catalysts. Water co-feeding studies indicate that the support type influences the size distribution of Co clusters, as well as their extent of reduction, as determined by the strength of the support-cobalt oxide interaction. This in turn in large part governs the way in which H2O affects catalytic behavior. Our group [1-6] and others [7-9] conducted water co-feeding studies and identified that at low H2O/He ratios that H2O exerts a reversible negative effect on CO consumption rate for Co/Al2O3, and this has been suggested to be due to adsorption inhibition. At higher H2O/He ratios, however, EXAFS/XANES results suggest that tiny Co crystallites, those influenced by the support, may oxidize to either CoO or irreducible cobalt aluminate-like species depending on the crystallite size (i.e., as determined by the Co loading).