1889.  KNOBLOCH, W., AND SCHILLER, G. (I. G. Farbenindustrie A. G.) [Catalytic Reduction of Carbon Dioxide to Carbon Monoxide With Hydrogen.] German Patent 730,409, Dec. 10, 1942 (Cl. 12 i-34); Chem. Abs., vol. 38, 1944, p. 462.

Alkaline-earth oxides are used as catalysts.