Using a newly developed preparation procedure, well-dispersed silica-supported vanadium-phosphorus-oxide catalysts have been prepared, With different techniques, it was established that a mixed vanadium-phosphorus-oxide phase was well dispersed over the surface of the support material, The use of silica instead of titania enhanced the selectivity in the selective oxidation of n-butane to maleic anhydride, but decreased the activity. The lower activity is originating from the nature of the constituent components and the character of the interaction of silica with the applied active vanadium-phosphorus-oxide phase. It was indicated that the interaction of vanadium-phosphorus oxide with titania increased the number as well as the activity of the active sites. The interaction with silica, however, decreased the activity of the active sites present in the catalyst, With temperature-programmed reduction, it was observed that the nature of the interaction changes the reducibility of the applied vanadium-phosphorus-oxide phase.