A study has been made of the possibility of synthesizing C2C3 olefins from CO and H2 at atmospheric pressure and temperatures below 700 K on membrane catalysts of two types: membranes permeable only to hydrogen atoms and porous membranes. In both cases the surface of the membrane was modified by applying finely dispersed particles or a porous layer of catalytically active metals. Ultrafine iron and nickel powders without supports have also been tested. It has been shown that, by introducing hydrogen through the walls of a PdRu alloy pipe, the ethylene formation rate is almost double the ethane formation rate and is 3-4 times higher than the rate of C2H4 synthesis when a mixture of CO and H2 comes into contact with this catalyst. Similar results were obtained with a PdNi alloy, and, after a porous nickel layer had been applied to it, propane, propylene and small quantities of butane and butylene appeared in the products of interaction of CO and H2. On some of the ultrafine nickel and iron powders, the predominant product of hydrocarbon synthesis from CO and H2 at 673 K and 0·1 MPa was propylene. Selectivity with respect to propylene reaches 37 at.%, and with respect to ethylene 32 at.%. Hydrocarbons C4 and above have not been found. Mixtures of iron powder with SiO2 and Al2O3 powder are just as selective, but their productivity is twice as high and stable in time. These systems are promising for the creation of solid block catalysts. © 1992.