EFFECT OF SURFACE OXIDATION OF THE SUPPORT ON THE THIOPHENE HYDRODESULFURIZATION ACTIVITY OF MO, NI, AND NIMO CATALYSTS SUPPORTED ON ACTIVATED CARBON

The present investigation attempts to provide a better understanding o f the influence of the nature of the carbon support on the HDS activit y of Mo, Ni, and NiMo catalysts. For this purpose a high purity activa ted carbon was subjected to oxidative treatments with HNO3 to modify i ts surface properties. NiMo catalysts supported on the resulting activ ated carbons were prepared and characterized by TPR, XRD, and SEM-EDX, and their activity for HDS of thiophene at 30 bars and 375 degrees C was evaluated. The results obtained showed that oxidation of the carbo n surface does not affect the HDS activity and other characteristics o f the supported Mo phase. In contrast, the HDS activity of the Ni cata lysts is enhanced by acid treatments of the carbon support. In this ca se, introduction of oxygen-containing functional groups (O-(S)) leads to a strong interaction of O-(S)-Ni during impregnation, which becomes essential to achieving and preserving high nickel dispersion. This ef fect on Ni dispersion is also reflected on the HDS activity of the bim etallic NiMo/C catalysts, The synergistic effect of the bimetallic cat alysts is observed only when oxygen functional groups are present on t he carbon surface, which are necessary for a good HDS activity, mainly because they enhance Ni-Mo interactions that produce the highly activ e Ni-Mo-S phase, A NiMoO4-like phase formed during impregnation seems to be the precursor for the active sulfide phase over the present NiMo /C catalysts. (C) 1996 Academic Press, Inc.