LaCo1−xCuxO3−δ perovskite catalysts for higher alcohol synthesis
Perovskite-type materials LaCoO3, LaCo1−xCuxO3−δ, and Cu2O/LaCoO3 were synthesized by the mechano-synthesis process known as reactive grinding. Their characterization was performed by BET, X-ray diffraction, SEM, O2-TPD, and H2-TPR. The partial cobalt substitution by copper in perovskite lattice gives rise to a distorted structure of LaCoO3 and influences the thermal stability and redox properties of perovskites. Temperature-programmed reduction (TPR) analysis showed a complete reduction of Co3+, Cu2+ to metallic state in the temperature range of 310–580 °C. A lower cobalt reduction temperature observed for LaCo1−xCuxO3−δ in comparison to LaCoO3 produces a finely dispersed bimetal on a La2O3 support. Quantitative TPR data showed that cobalt ions in the grain boundaries of the ground perovskites are directly reduced to metals at a relatively low temperature (310–450 °C). The existence of strong cobalt–copper interaction in perovskites could enhance the metallic dispersion of cobalt and prevent copper sintering. The reduced forms of LaCo1−xCuxO3−δ catalysts were tested as alcohol synthesis catalysts in a fixed bed flow reactor system at 275 °C and space velocity of 4000 h−1 (H2/CO = 2/1). A mixture of C1–C7 alcohols with the chain growth propagation factors of 0.34–0.42 was produced. The alcohol productivity is from 36.5 to 49.6 mg/gcat/h and selectivity towards higher alcohols took values in the range of 40–49.5%. The preliminary catalytic data indicated that copper located outside of the perovskite lattice is solely leading to the production of methanol and methane whereas its location in the octahedral position of the perovskite precursor framework is necessary for higher alcohol synthesis. Therefore, a uniform distribution of the metallic cobalt–copper atoms in the prereduced catalysts is crucial for the conversion of carbon monoxide and hydrogen into higher alcohols.
Journal: Applied Catalysis A: General - Volume 311, 1 September 2006, Pages 204–212