As indicated above, the catalyst composition of the present invention has a BET surface area of from 5 to 95 m²/g. By keeping BET surface area on a moderate level, the tin oxide particles are efficiently covered by a noble metal oxide layer even at relatively low amounts of noble metal.

Preferably, the BET surface area of the composition is from 5 m²/g to 90 m²/g, more preferably from 10 m²/g to 80 m²/g. Even if the BET surface area of the composition is within the range of from 5 m²/g to 60 m²/g, or from 5 m²/g to 50 m²/g, the catalyst composition still shows a surprisingly high catalytic activity. In another preferred embodiment, the BET surface area of the composition is from 5 m²/g to 35 m²/g, in particular if the tin oxide is non-doped.

As indicated above, the catalyst composition has an electrical conductivity at 25° C. of at least 7 S/cm. High electrical conductivity promotes electron transfer to the reactants during the catalytic reaction.

Preferably, the electrical conductivity of the composition is at least 10 S/cm, more preferably at least 12 S/cm. Appropriate ranges are e.g. from 7 to 60 S/cm, more preferably from 10 to 50 S/cm, or from 12 to 40 S/cm.

Preferably, the ratio of the BET surface area (in m²/g) of the composition to the total amount (in wt %) of iridium and ruthenium in the composition is within the range of from 6.0 to 0.75, more preferably 4.0 to 1.0.