Characterization and reactivity of nanoscale La(Co,Cu)O3 perovskite catalyst precursors for CO hydrogenation

The characterization of La(Co,Cu)O-3 perovskites has been performed by several techniques including XRD, BET, H-2-TPR, O-2-TPO, TPRS, and the solids tested as catalysts for the hydrogenation of CO. The reducibility of the perovskites is strongly affected by the preparation route. calcination temperature, catalyst morphology. and the amount of remnant alkali. Compared with the citrate-derived perovskite, LaCoO3 sample prepared by mechano-synthesis has various distinct Co3+ ions in perovskite lattice, which are reduced at different temperatures. Under typical conditions, the reduction of cobalt ions occurs in two consecutive steps: Co3+/Co2+ and Co2+/Co-0. while the intra-lattice copper ions are directly reduced from Cu2+ to Cu-0. The reducibility of cobalt ions is promoted by the presence of metallic copper. which is formed at a lower reduction temperature. The re-oxidation of the reduced lanthanum cobaltite perovskite could regenerate the original structure, whereas that of the reduced Co-Cu-based samples is less reversible under the same experimental conditions. The cobalt atom in the reduced perovskites plays an important role in the dissociation of CO, but the presence of a neighboring copper along with remnant sodium ions on the catalyst surface has remarkably affected the reactivity of cobalt for CO hydrogenation. The addition of copper into the perovskite framework leads to at change in the product distribution of CO hydrogenation and a decrease in reaction temperature. An increased copper content leads to a substantial decline in the rate of methanation and an increase in the formation of higher alcohols. A close proximity between cobalt and copper sites on the Na+-modified catalyst surface of the reduced nanocrystalline Co-Cu-based perovskites plays a crucial role in the synthesis of higher alcohols from syngas. (C) 2007 Elsevier Inc. All rights reserved.