Synthesis, Characterization And Catalytic Performance Of The Bifunctional Cobalt-Based Catalysts

Supported cobalt is the preferred catalyst for the F-T synthesis and the CH4-CO2reforming, because of their high activity for catalytic reaction. The nature of the cobalt precursor has a large influence on various properties of the catalyst. The catalysts derived from cobalt carbonyl cluster with good dispersion and higher catalytic activities due to cobalt carbonyl clusters have provided zero valent metal particles. There is currently a consensus in the literature that promoter can improve the cobalt-based catalyst reactivity, stability and selectivity. Lanthanide is an excellent promoter for cobalt-based catalyst as a result of its unique properties.In this paper, catalysts were prepared by introduced lanthanide promoter into cobalt carbonyl clusters as precursors. The cobalt atoms and lanthanide, therefore, can be arranged in orderly rows on the supports by linked organic-ligand skeleton, leading to higher dispersion of cobalt-Ln on catalysts. Rare earth can reduce the acidity of the supports, promote the dissociation of CO and improve the activity of catalytic. Specific results are as follows:1. A series of cobalt carbonyl clusters with different cobalt atoms has been synthesized. The organometallic carboxylic cluster (CO)9Co3CCH2COOH was first synthesized and structure of Co3(CO)9CCH2COOH has been determined by X-ray diffraction.2. Four heterobimetallic complexes containing cobalt carbonyl cluster and lanthanide [Ln3{-OOCCCCo3(CO)9}(-OOCCF3)6(THF)3]2Co(-OH)6·THF (Ln=La,Ce, Sm, Eu) have been synthesized by reaction of Co4(CO)10HCCCOOH with Ln(-OOCCF3)3(Ln=La, Ce, Sm, Eu), and structurally characterized by single-crystal X-ray diffraction.3. New type of Co-based catalysts were prepared using Co2(CO)6HCCCOOH, Co3(CO)9CCH2COOH and Co4(CO)10HCCCOOH as precursors supported on γ-Al2O3. The Co(NO3)2can be used as precursor for preparing reference catalyst. The F-T synthesis and CH4-CO2reforming performance were investigated. The dispersion, metal particle size and interaction with support of metal cobalt derived from cobalt carbonyl catalysts were researched. The F-T synthesis results suggest that the CO conversion and C5+selectivity decreased in the following:Co3(CO)9CCH2COOH>Co2(CO)6HCCOOH>Co4(CO)10HCCCOOH>Co(NO3)2.. The CH4-CO2reforming results indicated that the catalyst prepared by the precursor of trinuclear cobalt carbonyl clusters exhibited a superior anti-coking property.4. Catalysts were prepared using lanthanide-cobalt clusters bridging complexes as catalyst precursors supported on γ-Al2O3. The F-T synthesis and CH4-CO2 reforming performance were explored. The dispersion, metal particle size and interaction with support of metal cobalt species derived from lanthanide-cobalt clusters bridging complexes were researched. The F-T synthesis results suggest that the CO conversion and C5+selectivity decreased in the order:Co-Ce/γ-Al2O3> Co-Eu/γ-Al2O3>Co-Sm/γ-Al2O3>Co-La/γ-Al2O3>Co+Ce/γ-Al2O3>Co(N)/γ-Al2O3； The CH4-CO2reforming results revealed that the catalysts prepared by the lanthanide-cobalt clusters bridging complexes with similar structures showed similar activity for the catalysts with adjacent atomic numbers.5. Comparisons of catalytic performance for lanthanide-cobalt clusters bridging complexes and cobalt carbonyl clusters as catalyst precursors were explored. The results as follows:(1) The catalytic activity and C5+selectivity of the catalysts prepared by the lanthanide-cobalt clusters bridging complexes were superior to those prepared by the cobalt carbonyl cluster and the mixture of cobalt carbonyl cluster with lanthanide salt.(2) The CH4-CO2reforming catalytic activity of the catalysts prepared by the lanthanide-cobalt clusters bridging complexes were better than that of those prepared by cobalt carbonyl cluster, but anti-carbon deposition of the catalysts prepared by lanthanide-cobalt clusters bridging complexes decreased on support.