HIGH-TEMPERATURE CALCINED K-MOO3 GAMMA-AL2O3 CATALYSTS FOR MIXED ALCOHOLS SYNTHESIS FROM SYNGAS - EFFECTS OF MO LOADINGS/

One series of oxidized K-MoO3/gamma-Al2O3 samples with different Mo lo adings (MoO3/Al2O3 (wt ratio)=0.05-0.45) was prepared by impregnating K and Mo compounds and successive calcination in air at 800 degrees C. The oxidized samples were sulfided and then utilized for mixed alcoho ls synthesis from syngas. The structural information from laser Raman spectroscopy (LRS), X-ray diffraction (XRD), X-ray photoelectron spect roscopy (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 hydroc arbons decreased, but the selectivity to mixed alcohols was enhanced s harply 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) synthes is to linear alcohols and the condensation reaction of low alcohols to form branched i-C4OH occurred at the same time. With increased Mo loa ding, activity of the alcohols condensation became high. Structural st udies demonstrated that on oxidized samples with increased Mo loading the same K-Mo-O species was formed, but the dispersion of these K-Mo s pecies decreased. The catalyst's 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 a ctivity for ethanol dehydration changed parallel to the acidity. Resul ts of the activity experiments for mixed alcohols' synthesis and the s tructural measurements indicated that the dispersion state of Mo speci es and the content of unreduced Mo species influenced the total CO con version, and that the acidity of the catalyst controlled the selectivi ty to mixed alcohols. (C) 1998 Elsevier Science B.V. All rights reserv ed.