PURPOSE: The catalytic reaction between carbon monoxide and hydrogen is effected in the presence of a catalyst that is prepared by impregnating a carrier with a transition metal compound in the absence of oxygen and reducing it with carbon monoxide in the presence of steam to produce the titled compounds, especially ethylene and propylene in high selectively.

CONSTITUTION: A carrier is impregnated with a compound containing a transition metal in VIII group of the periodic table such as rhodium chloride or rhodium nitrate under exclusion of oxygen and reduced in the presence of steam at 90W 200°C to prepare a catalyst. The reaction of carbon monoxide and hydrogen is effected in the presence of the resultant catalyst at 140W200°C under normal to elevated pressure to produce lower unsaturated hydrocarbons. The activated metal is dispersed on the carrier so that it has a special structure to prepare the catalyst of high selectivity. When this catalyst is further brought into contact with air at room temperature, the content of ethylene increases in the product mixture. Since the preparation and reactivation of the catalyst are simple, the process is economically valuable.