Hydrocarbons are oxychlorinated by reaction with gaseous HCl and an oxygen-containing gas, in the presence of a catalytically effective amount of a ternary copper/molybdenum chalcogenide having the formula:Cu.sub.x Mo.sub.6 Ch.sub.8wherein x is a number ranging up to 4 and Ch is sulfur, selenium or tellurium, advantageously, in the added presence of a known oxychlorination catalyst and, optionally, a proportion of inert particulate solids; the ternary molybdenum chalcogenides of the formula M.sub.x Mo.sub.6 S.sub.8 are also prepared, wherein M is a metal, advantageously by the hydrogen gas reduction of intimate admixture of MoS.sub.2 and metal M, or precursors thereof.