A novel solution route has been developed that after heat-treatment to 500-600.degree. C. under inert atmosphere, yields highly porous composites of nano-sized metal (Ni) particle inclusions in ceramics (Al.sub.2O.sub.3). Metal loadings could be made from <1% to >95% Ni. The metal inclusion sizes in the Ni--Al.sub.2O.sub.3 system with the 10 atom % Ni sample were 4-7 nm, while for the 75 atom % Ni sample they were 5-8 nm. It was shown that the 10 atom % Ni sample could be used as a catalyst for the conversion of CO.sub.2 and CH.sub.4 in the temperature range 550-700.degree. C., while higher temperatures led to growth of the Ni particles and carbon poisoning over time. The solution routes could also be deposited as thin dense films containing <10 nm Ni particles. Such films with high Ni-particle loadings deposited on aluminium substrates have shown very good solar heat absorber proficiency and provide good substrates for carbon tube growth.