The influence of Rh heteroatom on the molybdenum reducibility in the Anderson-type heteropolyoxomolybdate structure of formula (NH4)(3)[RhMo6O24H6]center dot 7H(2)O was investigated by means of TPR technique. With comparative purposes, the thermal behavior in non-reducing conditions was also carried out by means of TGA-DTA studies. The study was performed by XRD, SEM, EDAX and FTIR-Raman techniques. Results were related to those preliminary measurements over other XMo6 Anderson phases. Likewise, Rh(III)-Al(III) formal replacement in the RhMo6 structural arrangement was proved. The formation of a solid solution in a limited range of composition (up to 0.25 Rh) was,established in order to explore the catalytic performance of gamma-Al2O3 supported planar heteropolyoxomolybdate, aiming at optimizing the noble metal content in the catalytic system. Preliminary measurements of RhMo6/gamma-Al2O3 and (Rh, AI)Mo-6/gamma-Al2O3 activity for HDS and HYD processes were also performed. These results were compared to those obtained for CoMo6/gamma-Al2O3 system in similar operating conditions and other conventional catalytic systems. The potentiality and scope of RhMo6 catalytic system for the HDS and HYD processes were analyzed. (C) 2006 Elsevier B.V. All rights reserved.