Conversion of syngas to higher alcohols over nanosized LaCo0.7Cu0.3O3 perovskite precursors

Abstract

Abstract Two LaCo 0.7 Cu 0.3 O 3 perovskite catalysts synthesized by reactive grinding and by the citrate complex method have been characterized by X-ray diffraction (XRD), BET, SEM, H 2 -temperature-programmed reduction (TPR) and tested for the synthesis of higher alcohols and hydrocarbons from syngas. The ground sample shows a rather high surface area and nanometric particles. The coexistence of copper and cobalt in the perovskite lattice provides a highly dispersed bimetallic phase after pretreatment under hydrogen. Both samples were reduced in situ prior to being tested for the synthesis of alcohols and hydrocarbons. The catalytic activity and product distribution depend strongly on the process variables, alkali promoter, preparation method, and catalyst morphology. While the ground perovskite is rather selective for the synthesis of higher alcohols, the citrate-derived precursor produces mainly methane and light hydrocarbons in addition to 10–15 wt.% of alcohols. The optimum parameters for catalyst preparation and for alcohol synthesis were determined. Under the optimal reaction conditions, the alcohol productivity is in a broad range of 70–140 mg/g cat /h and the selectivity towards alcohols is about 40–45 wt.%. Both alcohols and hydrocarbons produced obey a classical Anderson–Schulz–Flory (ASF) plot carbon number distribution. The nanocrystalline perovskite precursor shows a better catalytic performance compared to the citrate-derived sample in terms of both alcohol selectivity and productivity. The catalytic stability of the ground perovskite is dependent not only on the crystal domain size (or the size of nanoparticles) and the amount of remnant sodium ions, but also strongly on the compactness of nanoparticles. The existence of slit-shaped spaces between primary nanoparticles and/or grain boundaries hinders the formation of long carbon chains, which are precursors for the formation of coke on the catalyst surface.