A novel type of TiO2-modified Al2O3 carrier was prepared to investigate the carrier effect of Mo-Co type hydrotreating catalysts as compared with Al2O3 using positron annihilation spectroscopic chem. anal. Three different molybdena surface species were located at three different sites on either the alumina carrier or the TiO2-modified alumina. However, the fraction and characteristics for each sort of surface site on the alumina carrier are quite different from those on TiO2-modified alumina. The interaction between MoO3 and the surface of the carrier was weakened remarkably by addition of TiO2, which leads to an increase of polymolybdate-like surface species (active phase). The synergism of Co-Ti was verified and the nature of it might be the electron interaction.

Key words: MODIFICATION, CATALYST, ALUMINIUM OXIDE, SURFACE STRUCTURE, SYSTEMS, ACTIVITY, TITANIUM OXIDE, COBALT OXIDE, HYDROFINING, MOLYBDENUM OXIDE