The present disclosures provides a catalyst composition comprising a mixed oxide support material and a platinum group metal supported on the mixed oxide support material, the mixed oxide support material comprising a solid solution mixed oxide having the formula CewZrxSnyMzOa, wherein: 0.05≤w≤0.90; 0.05≤x≤0.90; 0.001≤y≤0.25; 0.001≤z≤0.60; w+x+y+z=1.00; 1.0≤a≤2.0; and M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium.