Effects of phase composition and of potassium promotion on cobalt molybdate catalysts for the synthesis of alcohols from CO₂ and H₂

Cobalt molybdate and cobalt molybdate-potassium catalysts were found to exhibit activity for alcohol formation from CO₂/ H₂ at 3.0 MPa and 250°C and 300°C. Tetrahedrally coordinated Mo⁶⁺ ions favor the selectivity to alcohols. Addition of K₂CO₃ greatly enhances the selectivity of the reaction to methanol. The extent of this effect was dependent on the way the alkali metal was mixed with the catalyst. Catalysts obtained by mechanical mixing of α-CoMoO₄ and K₂CO₃ deactivate faster than the β-CoMoO₄/K mixture calcined at 550°C, where formation of a K₂MoO₄ phase was detected by XRD. Both catalysts show a similar maximum in selectivity to alcohols at around 90 min of reaction. Addition of potassium by coprecipitation along with Co and Mo, which leads to the formation of K₂Co₂(MoO₄)₃, also enhances alcohol production, but the effect is more attenuated than for the other promoted samples.