An adsorbent for selective adsorption of unsaturated hydrocarbons from its mixture with saturated hydrocarbons, carbon dioxide, carbon monoxide, permanent gases or mixture thereof. The adsorbent includes a silver or copper compound in an amount of 1 to 70 wt % and a substrate in 30 to 99% wt %. Also a method for the manufacture of an adsorbent, which includes impregnating or dispersing a silver (I) or copper (I) compound on a mesoporous substrate or support to form a composite material and subjecting the composite material to heat treatment. Also, a process for separating ethylene and/or propylene from gas mixtures containing them by passing a stream of the gas mixture through a mass of the adsorbent at a temperature from 0° C. to 170° C. and a pressure from 0.1 to 100 atmospheres and releasing the adsorbed ethylene and/or propylene by lowering pressure and/or increasing temperature.