A comparative study of supported MoO 3 catalysts prepared by the new “slurry” impregnation method and by the conventional method: their activity in transesterification of dimethyl oxalate and phenol

Abstract

A new preparation method for supported MoO 3 catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO 3/water is used instead of the solution ammonium heptamolybdate, AHM [(NH 4) 6Mo 7O 24]. The MoO 3/γ-alumina, MoO 3/active carbon, and MoO 3/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO 3 was sufficient to transport molybdenum species from solid MoO 3 to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO 3/γ-Al 2O 3 catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO 3/SiO 2 catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH 4) 6Mo 7O 24. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.