The catalytic activity and selectivity of supported vanadia catalysts doped with alkali metal sulphates.: I. Structural re-organisations during pre-treatment and use

Abstract

Silica supported vanadium pentoxide catalysts with and without promoters have been prepared and characterised. Solid promoters used include the sulphates of lithium, sodium, potassium, rubidium and cesium added in the molar ratio Me 2SO 4:V 2O 5 = 2:1. Gaseous promotion examined included pre-treatment of the catalysts with sulphur trioxide and the addition of 0.01 mole % of sulphur dioxide to oxidising gases passed over the catalysts. Examination of a commercial V 2O 5-K 2SO 4-SO 3 catalyst was also carried out. Supported vanadia catalysts maintain surface area after sulphur trioxide pre-treatment and with sulphur dioxide in the feed. Alkali-doped vanadia catalyst undergo major loss of surface area as a result of sulphur trioxide pre-treatment. This loss of surface area begins to be significant at ca 573K and is apparently due to the formation of a low melting point eutectic in the system. Low surface area supports can give a higher active surface area in the final catalyst than high surface area supports as a result of pore blocking in the latter case. Characterisation of used material is important in determining specific activity of doped vanadia catalysts.