Catalytically active microporous thin film membranes were prepared by dip coating of an asymmetric ceramic support membrane in a Na2PtCl6 containing sol based on Ti(OiPr)(4). After drying and calcination, the membrane (thickness of the top layer, 0.2-0.4 mu m) shows separation properties typical for microporous membranes with low defect concentration (nanofiltration). After activation with hydrogen at 250 degrees C the membranes exhibit a hydrogenation activity significantly higher than those of comparable batch catalysts. At conditions of reaction control and limitation of hydrogen availability, 2-hexyne is semihydrogenated with such a membrane with 100% selectivity to cis-2-hexene. 1,3-Hexadiene is semihydrogenated selectively to l-hexene. The unusual selectivity observed is attributed to the prevention of back-mixing through the use of the membrane contactor.