Vanadium sulfate, anhydrous

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Although the forward reaction is favored by increase in pressure, this is not employed in practice since 97 to 99% conversion of sulfur dioxide to sulfur trioxide can be accomplished at the temperature specified here, provided suitable catalysts are used. The first catalyst used for this reaction consisted of finely divided platinum dispersed in asbestos, anhydrous magnesium sulfate, or silica gel. Other catalysts were later discovered. Mixtures of ferric and cupric oxides are useful, but these are less efficient than platinum. Certain mixtures containing vanadium pentoxide (V205) and other compounds of vanadium appear to be as good as or better than platinum. There has been much controversy over the relative merits of platinum and vanadium catalysts, and only time will provide the answer as to which is best. 

Pure anhydrous vanadium(III) sulfate can be prepared by the reduction of vanadium(V) oxide dissolved in sulfuric acid with elemental sulfur as the reducing agent.The procedure given below is an adaptation of this method. 

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