Anderson type heteropolyoxomolybdates in catalysis:: 1.: (NH4)3[CoMo6O24H6]•7H2O/γ-Al2O3 as alternative of Co-Mo/γ-Al2O3 hydrotreating catalysts

A new preparation method of Co-Mo/gamma-Al2O3 HDS catalyst has been developed by using the (NH4)(3)[CoMo6O24H6]. 7H(2)O Anderson type heteropolyoxomolybdate supported on gamma-Al2O3. The system can be considered as an interesting and simplified alternative to the traditional bimetallic catalyst. Diffuse reflectance spectroscopy measurements have been employed to confirm that the planar-arrangement of the heteropolyanion is not substantially altered by the adsorption process. The corresponding adsorption isotherm has been registered at room temperature due to the good solubility of the phase. In comparison with the traditional HDS catalysts, this new system shows the following relevant aspects: (a) the activity for the HDS of thiophene is similar in both cases, although the Co content is considerably lower than that of the impregnation of the ammonium heptamolybdate and cobalt nitrate hexahydrate solutions ([Co]/([Co]+[Mo])=0.14 in relation to 0.25-0.40 in the conventional system); (b) the phase adsorbs well onto the support; (c) the activity of molbydenum seems to be promoted by the presence of cobalt in the ordered distribution of the heteropolyanion on the surface of gamma-Al2O3 (synergy-like effect). The primary structure of supported heteropolyoxomolybdate is clearly preserved; (d) whereas the conventional catalysts can be prepared through a series of steps (two impregnation operations, one for drying and another for the calcination at 550 degrees C), the proposed method only requires one impregnation step and a drying step at 80 degrees C, suppressing the calcination at 550 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.