Gold-titania (Au--TiO.sub.2) composite aerogels and ambigles were synthesized, characterized, and tested as ambient temperature catalysts for carbon monoxide. Adding alkanethiolate-monolayers-protected gold clusters (with .about.2 nm Au cores) directly to titania sol before gelation yields uniformly dispersed guests in the composite aerogel. The Au guests aggregate to 5 to 10 nm upon calcination to remove alkanethiolate and crystallize amorphous titania to anatase. The resulting composite aerogel exhibits high catalytic activity toward CO oxidation at room temperature at Au particle sizes that are essentially inactive in prior Au--TiO.sub.2 catalysts. Transmission electron microscopy illustrates the three-dimensional nature of the catalytic nanoarchitecture in which gold guests contact multiple anatase nanocrystallites.