In a preferred embodiment, the tin oxide is doped with antimony in an amount of from 2.5 at % to 20 at %, more preferably from 2.5 at % to 10.0 at %; the amount of iridium in the composition is within the range of from 15 to 35 wt %, more preferably from 20 to 28 wt %, the remainder being the tin oxide particles and the oxygen of the iridium oxide layer; the BET surface area of the composition is from 15 m²/g to 90 m²/g, more preferably from 30 m²/g to 80 m²/g; and the electrical conductivity of the composition is at least 10 S/cm, more preferably at least 12 S/cm (e.g. 10 to 50 S/cm, or 12 to 40 S/cm).

In another preferred embodiment, the tin oxide is a non-doped tin oxide; the amount of iridium in the composition is within the range of from 15 to 35 wt %, more preferably from 20 to 28 wt %, the remainder being the tin oxide particles and the oxygen of the iridium oxide layer; the BET surface area of the composition is from 5 m²/g to 35 m²/g; and the electrical conductivity of the composition is at least 10 S/cm, more preferably at least 12 S/cm (e.g. 10 to 50 S/cm, or 12 to 40 S/cm).

Furthermore, the present invention relates to a process for preparing the catalyst composition as described above, which comprises

• • dispersing tin oxide particles and dissolving a noble-metal-containing precursor compound in an aqueous medium, wherein the noble metal is iridium or ruthenium or a mixture thereof,
  • adjusting pH of the aqueous medium to 5-10 and optionally heating the aqueous medium to a temperature of from 50° C. to 95° C., thereby depositing noble metal species on the tin oxide particles,