The as-synthesized molybdenum nitrides and carbide has higher conversion of alkadienes and selectivity of alkenes for selective hydrogenation of longer chain afkadienes (C-10-C-13) than the supported palladium catalyst used in industry at higher temperature and pressure. The introduction of oxygen element to the surface of molybdenum nitride or carbide is favorable to improvement of selectivity of alkenes. The passivated molybdenum nitride or carbide catalyst pretreated in H-2 at 450 degreesC has higher yield of alkenes than corresponding unpassivated and passivated molybdenum nitride or carbide, respectively. It was proved by XPS that the modification of molybdenum nitride or carbide by oxygen results in the change of oxidation states of molybdenum and their content. Decreasing of Moo content and improvement of Mo2+ and Mo3+ are favorable to the elevation of selectivity of alkenes. (C) 2003 Elsevier B.V. All rights reserved.