Anderson type heteropolyoxomolybdates in catalysis: 1. (NH4)(3)[CoMo6O24H6]center dot 7H(2)O/gamma-Al2O3 as alternative of Co-Mo/gamma-Al2O3 hydrotreating catalysts

A new preparation method of Co-Mo/gamma-Al2O3 HDS catalyst has been develop ed by using the (NH4)(3)[CoMo6O24H6]. 7H(2)O Anderson type heteropolyoxomol ybdate supported on gamma-Al2O3. The system can be considered as an interes ting and simplified alternative to the traditional bimetallic catalyst. Dif fuse reflectance spectroscopy measurements have been employed to confirm th at the planar-arrangement of the heteropolyanion is not substantially alter ed by the adsorption process. The corresponding adsorption isotherm has bee n 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 s imilar in both cases, although the Co content is considerably lower than th at of the impregnation of the ammonium heptamolybdate and cobalt nitrate he xahydrate 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 th e ordered distribution of the heteropolyanion on the surface of gamma-Al2O3 (synergy-like effect). The primary structure of supported heteropolyoxomol ybdate is clearly preserved; (d) whereas the conventional catalysts can be prepared through a series of steps (two impregnation operations, one for dr ying 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, sup pressing the calcination at 550 degrees C. (C) 2000 Elsevier Science B.V. A ll rights reserved.