High temperature calcined K–MoO3/γ-Al2O3 catalysts for mixed alcohols synthesis from syngas: Effects of Mo loadings Original Research Article

One series of oxidized K–MoO3/γ-Al2O3 samples with different Mo loadings (MoO3/Al2O3 (wt ratio)=0.05–0.45) was prepared by impregnating K and Mo compounds and successive calcination in air at 800°C. The oxidized samples were sulfided and then utilized for mixed alcohols synthesis from syngas. The structural information from laser Raman spectroscopy (LRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ammonia saturation, temperature programmed desorption (TPD) and ethanol decomposition were studied to elucidate the reaction properties. The results indicated that with Mo loading increased from MoO3/Al2O3=0.05 to 0.25, the total yields of mixed alcohols and hydrocarbons decreased, but the selectivity to mixed alcohols was enhanced sharply from 3% to 50%. With Mo loading increased from MoO3/Al2O3=0.25 to 0.45, the CO conversion was enhanced, but the selectivity to mixed alcohols leveled off. On these catalysts, Fischer–Tropsch (FT) synthesis to linear alcohols and the condensation reaction of low alcohols to form branched i-C4OH occurred at the same time. With increased Mo loading, activity of the alcohols condensation became high. Structural studies demonstrated that on oxidized samples with increased Mo loading the same K–Mo–O species was formed, but the dispersion of these K–Mo species decreased. The catalystʹs acidity decreased remarkably with Mo loading up to MoO3/Al2O3=0.25, and stayed unchanged as Mo loading was further increased to MoO3/Al2O3=0.45. With increased Mo loading, the activity for ethanol dehydration changed parallel to the acidity. Results of the activity experiments for mixed alcoholsʹ synthesis and the structural measurements indicated that the dispersion state of Mo species and the content of unreduced Mo species influenced the total CO conversion, and that the acidity of the catalyst controlled the selectivity to mixed alcohols. Article Outline