Study of the effect of water on alumina supported cobalt Fischer–Tropsch catalysts

Abstract The effect of water on Co/Al 2 O 3 and CoRe/Al 2 O 3 catalysts has been studied by adding water to the synthesis gas feed and by model studies exposing the catalysts to H 2 O/H 2 feeds using several characterization techniques such as TPR, gravimetry, XPS, TPD and pulse adsorption. It was found that the CoRe/Al 2 O 3 catalyst deactivates when water is added during Fischer–Tropsch synthesis and model-studies showed that this catalyst oxidizes in H 2 O/H 2 mixtures with a ratio much lower than expected for oxidation of bulk cobalt. The reoxidation increases with increasing H 2 O partial pressure and H 2 O/H 2 ratio. TPR and gravimetry showed only small amounts of bulk reoxidation, while pulse adsorption and TPD indicated large decreases in Co-surface metal. It is suggested that oxidation of highly dispersed phases or surface oxidation are the cause for the observed deactivation. Significant differences in behavior of the Co/Al 2 O 3 and the CoRe/Al 2 O 3 catalyst when exposed to H 2 O/H 2 /He were found by gravimetry, TPR, pulse adsorption and XPS. The CoRe/Al 2 O 3 catalyst was reoxidized more easily in H 2 O/H 2 /He mixtures than the Co/Al 2 O 3 catalyst. This is probably a result of the higher dispersion of the CoRe/Al 2 O 3 catalyst, but a direct influence of Re on the reoxidation cannot be excluded. A phase interacting strongly with the alumina support was found in both catalysts after H 2 O/He exposure, but also another oxide phase was formed. This second phase is reduced at lower temperature for the CoRe/Al 2 O 3 catalyst than for the Co/Al 2 O 3 catalyst.

[1]  F. Delannay.  Characterization of heterogeneous catalysts , 1984 .

[2]  M. Rosynek,et al.  Effect of cobalt source on the reduction properties of silica-supported cobalt catalysts , 1991 .

[3]  A. Holmen,et al.  Study of Pt-promoted cobalt CO hydrogenation catalysts , 1995 .

[4]  L. Guczi,et al.  Structure and catalytic activity of alumina supported platinum-cobalt bimetallic catalysts. 3. Effect of treatment on the interface layer , 1992 .

[5]  J. H. Scofield,et al.  Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV , 1976 .

[6]  A. Holmen,et al.  Fischer-Tropsch synthesis on supported cobalt catalysts promoted by platinum and rhenium , 1995 .

[7]  J. Zieliński.  Reductibility of silica supported nickel oxide , 1995 .

[8]  A. Holmen,et al.  Alkali promotion of alumina-supported cobalt Fischer-Tropsch catalysts studied by TPR, TPD and pulse chemisorption , 1993 .

[9]  A. Hughes,et al.  An XPS and TPR study of the reduction of promoted cobalt-kieselguhr Fischer-Tropsch catalysts , 1986 .

[10]  J. Moulijn,et al.  Temperature-programmed reduction of CoOAI2O3 catalysts , 1985 .

[11]  J. G. Goodwin,et al.  In-Situ XAFS Investigation of K-Promoted Co Catalysts , 1995 .

[12]  D. Hercules,et al.  Determination of the distribution of species in supported metal catalysts by X-ray photoelectron spectroscopy , 1987 .

[13]  D. R. Penn.  Quantitative Chemical Analysis by ESCA , 1976 .

[14]  H. Schulz,et al.  Effect of water partial pressure on steady state Fischer-Tropsch activity and selectivity of a promoted cobalt catalyst , 1997 .

[15]  D. Hercules,et al.  A surface study of cobalt-molybdena-alumina catalysts using x-ray photoelectron spectroscopy , 1976 .

[16]  R. Prins,et al.  Characterization of supported cobalt and cobalt-rhodium catalysts. I. Temperature-programmed reduction (TPR) and oxidation (TPO) of Co---Rh/Al2O3 , 1986 .

[17]  J. Zieliński.  The effect of water on the reduction of nickel/alumina catalysts , 1992 .

[18]  T. Paryjczak,et al.  Investigations of rhenium—hydrogen system within the wide temperature range , 1979 .

[19]  A. Holmen,et al.  Hydrogenation of carbon monoxide over iron catalysts on different supports , 1989 .

[20]  F. Habraken,et al.  Deactivation of Alumina Supported Catalysts Due to Spinel Formation , 1994 .

[21]  A. Holmen,et al.  TPR study of the mechanism of rhenium promotion of alumina-supported cobalt Fischer-Tropsch catalysts , 1996 .

[22]  Richard D. Jones,et al.  Improved flow technique for measurement of hydrogen chemisorption on metal catalysts , 1988 .

[23]  F. Massoth,et al.  Studies on molybdena-alumina catalysts: VII. Effect of cobalt on catalyst states and reducibility , 1980 .

[24]  J. Moulijn,et al.  Quantitative analysis of XPS intensities for supported catalysts , 1979 .

[25]  Enrique Iglesia,et al.  Selectivity Control and Catalyst Design in the Fischer-Tropsch Synthesis: Sites, Pellets, and Reactors , 1993 .

[26]  D. Hercules,et al.  Surface spectroscopic characterization of cobalt-alumina catalysts , 1982 .

[27]  G. Hutchings,et al.  Cobalt/manganese oxide water gas shift catalysts: I. Competition Between Carbon Monoxide Hydrogenation and Water Gas Shift Activity , 1988 .

[28]  C. H. Bartholomew.  Chemistry of nickel-alumina catalysts , 1976 .

[29]  Hans Schulz,et al.  Selectivity and mechanism of Fischer-Tropsch synthesis with iron and cobalt catalysts , 1994 .

[30]  J. Goodwin,et al.  The formation of cobalt silicates on Co/SiO2 under hydrothermal conditions , 1995 .