Carbon monoxide hydrogenation on Co--Rh/Nb{sub 2}O{sub 5} catalysts
Carbon monoxide hydrogenation activities and product distributions were investigated here for the first time on a series of seven Co-Rh/Nb{sub 2}O{sub 5} catalysts: two monometallics Co and Rh supported on Nb{sub 2}O{sub 5} and five bimetallics CO-RH supported on NB{sub 2}O{sub 5} with similar Co ({approximately}1.9 wt%) and variable Rh loadings (0.3--2.3 wt%). Catalytic performances at atmospheric pressure and 493 K were evaluated after low temperature reduction (LTR, 533--573 K) and after high temperature reduction (HTR, 773 K). Temperature-programmed reduction characterization revealed that the reduction temperature of the dominant Co phase on calcined catalysts, Co{sub 3}O{sub 4}, strongly decreased as the Rh/Co bulk atomic ratio increased, while the reduction temperature of the RH{sub 2}O{sub 3} phase (363 to 419 K) was not strongly influenced by the presence of Co{sub 3}O{sub 4}. It was observed that the activity decay effect caused by metal-support interaction was remarkably inhibited on the bimetallics with respect to the monometallics by comparing reaction rate after LTR and after HTR. The addition of Rh to the Co monometallic catalyst significantly altered the product distribution. An unusual promotion of the selectivity to long chain hydrocarbons were observed. This promotion was more intense after HTR on the bimetallic catalysts, reaching {approximately}56% in the diesel fraction on the bimetallic catalyst with higher Rh concentration. Alcohol selectivity was enhanced up to 3.5 and 5.4% for ethanol and propanol, respectively, on the bimetallic catalyst with lower Rh concentration. The total CO hydrogenation reaction rate and the selectivity for methane were approximately constant as the Rh concentration on the bimetallics increased, suggesting that the metal surface area did not vary considerably on these catalysts. This agrees with hydrogen adsorption measurements on the bimetallic catalysts and with the XPS surface structural characterization of the calcined CO-Rh/Nb{sub 2}O{sub 5} catalysts, which revealed that the specific surface area of active metal (Rh + Co) precursor oxide did not vary considerably as the Rh concentration increased.
- Research Organization:
- Univ. Federal do Rio de Janeiro (BR)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 20003846
- Journal Information:
- Journal of Catalysis, Vol. 188, Issue 1; Other Information: PBD: 15 Nov 1999; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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