Co-Cu Metal Alloys from LaCo1-xCuxO3 Perovskites as Catalysts for Higher Alcohol Synthesis from Syngas

Abstract

The specific surface area of ground perovskites is strongly dependent on the synthesis and pretreatment conditions. Calcining the ground LaCo1-xCuxO3-? perovskites at 5000C causes a decrease of their specific surface, but the further reductive pretreatment of the calcined sample in hydrogen leads to only a minor change in the specific surface area.The introduction of extra- and intra-perovskite lattice copper has different effects on the structure stability, reducibility and catalytic properties of LaCoO3 perovskites. Under the same pretreatment conditions the basic structure of both LaCoO3 and Cu2O/LaCoO3 samples is retained at the reduction temperature of 5000C (90 min) while that of Co-Cu based perovskites is completely collapsed producing a high dispersion of bimetallic metals and Co-Cu alloys supported on amorphous La2O3. For a series of LaCo1-xCuxO3 samples, increasing the copper content in the perovskite structure leads to an increase in the metal surface area of the reduced phase. The pretreated catalysts were tested for CO dissociation and for alcohol synthesis from syngas. The results indicated that the copper sites neighboring with cobalt atoms in the reduced perovskites decrease the activity in CO dissociation and increase the rate of higher alcohol synthesis while extra-perovkite lattice copper tends to produce methanol, methane and CO2. The overall activity in syngas conversion and higher alcohol productivity are proportional to the Co-Cu metal surface. The role of dual sites of Co and Cu for the synthesis of higher alcohols is discussed. The catalytic activity and alcohol productivity as well as product distribution depend strongly on reaction temperature and pretreatment conditions. The highest productivity of alcohols in the present study is about 73 mg/gcat/h for sample LaCo0.7Cu0.3O3.