The influence of metal-support interactions on the selectivities of cobalt catalysts for Co hydrogenation

Typescript (photocopy).XPS studies for SiO(,2)-, TiO(,2)-, La(,2)O(,3)-, Eu(,2)O(,3)-, and CeIO(,2)-supported Co catalysts showed that surface properties of cobalt change markedly with variation in pretreatment conditions and supports. Strong support interactions existed between the cobalt metal and the La(,2)O(,3) and Eu(,2)O(,3) supports as shown by the color change in the dispersion process of catalyst preparation, and the XPS spectra of Co 2p peaks indicate that the surface Co were existed primarily in the low-spin state, while the surface Co of rest of the supports were in the high-spin state. The ease of reduction of surface Co on the five supports following H(,2) treatment at 400(DEGREES)C is as follows: Co/CeO(,2) > Co/Eu(,2)O(,3) (DBLTURN) Co/La(,2)O(,3) > Co/TiO(,2) > Co/SiO(,2). In general, the surface reduction of supported cobalt among the five supports studied were very low except CeO(,2) which showed substantial surface reduction at 400(DEGREES)C pretreatment temperature. However, oxidation of Co('2+) to Co('3+) was observed on Co/CeO(,2) following H(,2) treatment at 500(DEGREES)C. The extents of reduction of surface Co, following exposure to H(,2)/Co mixtures, were substantially increase for all the lanthanide oxides supports, but less with TiO(,2) and SiO(,2) supports. Significant differences in catalytic behaviors, such as H(,2) adsorption and catalytic selectivities for CO hydrogenation have been observed. Eu(,2)O(,3)- and CeO(,2)-supported Co showed H(,2) adsorption corresponded to 20% of metal exposures, which may be due to H(,2) spillover rather than normal adsorption behaviors. All three of the lanthanides oxides-supported Co showed catalytic selectivities of substantially longer average HC product chain lengths and higher olefin/paraffin (O/P) ratios compare to SiO(,2) and TiO(,2) supports. In general, both the average HC product chain length and O/P ratio were in the following order: Co/Eu(,2)O(,3) (DBLTURN) Co/Ce(,2)O(,3)(?) (DBLTURN) Co/La(,2)O(,3) > Co/TiO(,2) (DBLTURN) Co/CeO(,2) > Co/SiO(,2), and which is in the same order observed with the relative amount of surface Co reduced under reaction conditions for the different supports