The effect of substituting La and Co with Ca and Ti in LaCoO3/KIT-6 on its properties and possible catalytic application in syngas conversion

Abstract

Perovskite-type samples La1-xCaxCo1-xTixO3/KIT-6 (x = 0–0.5) were synthesized by citrate method. KIT-6 is partially embedded in the perovskite structure. The complete reduction of cobalt in perovskites in the presence of KIT-6 occurs at a temperature of ca. 670 °C due to the formation of a cobalt silicate phase. With the substitution of titanium for cobalt cations, the complete reduction of cobalt occurs at temperatures above 720 °C. The proportion of cobalt that is reduced at temperatures below 500 °C increases with an increase in the ratio of Co3+/Co2+ cations. Partial substitution of cobalt cations with titanium cations decreases the selectivity ratios SCH3OH/SC2+OH and SCH4/SC2-8. The introduction of calcium cations leads, proportionally to its content, to a strong decrease in selectivity to methanol and an increase in selectivity for light hydrocarbons C2-8 in syngas conversion. It was shown that the maximum selectivity for higher alcohols with a low selectivity for methanol is observed at x = 0.3 on a sample containing calcium. A significant amount of the cobalt carbide phase Co2C in the used KIT-6-free sample of LaCoO3 is accompanied by the predominance of the methanation reaction (CH4 selectivity 58.7%). The synthesized samples on KIT-6 have higher selectivity to alcohols compared to a conventional CoAl oxide catalyst and somewhat lower activity in syngas conversion.