TEMPERATURE-PROGRAMMED REDUCTION OF MOOX/SIOX AND MOOX/AL2O3 CATALYSTS - SURFACE STRUCTURAL CONSEQUENCES OF IMPREGNATION ACIDITY

Conclusions derived from previous work on the surface structures of MoO(x)/SiO2 and MoO(x)/Al2O3 catalysts prepared by impregnation with heptamolybdate solutions of different pH, followed by calcination, are summarised and the results of their temperature-programmed reduction are recorded. These are consistent with the view that after impregnation at pH 11 most of the molybdenum in MoO(x)/SiO2 is present as MoO3 particles (more easily reduced than unsupported MoO3); after impregnation at pH 1, a dispersed SiMoO(x) phase is formed; and after impregnation at pH 6, both phases are present but the MoO3 phase is predominant. MoO(x)/Al2O3 samples made by impregnation at pH 6 and 11 show single reduction peaks at high temperature, associated with a mixed MoO3-Al2O3 surface phase, but in each case much of the molybdenum is sub-surface and is effectively irreducible.