Molybdenum carbide and/or boride are synthesized from MoO3, KBH4, and CCl4 by a thermosynthesis method at moderate temperature. The relative content of molybdenum carbide and boride in the product is changed by the molar ratio of MoO3, KBH4, and CCl4 and absorbing the produced HCl by CaO. Most of these catalysts show good activity, similar catalytic behavior to Mo2C prepared by conventional temperature-programmed carburization, and better selectivity for liquid-phase hydrogenation of longer chain alkadienes than Pd/Al2O3 at higher temperatures and pressures. The selectivity of the as-synthesized catalysts depends on relative abundance and distribution of Modelta+ (0 less than or equal to delta < 4) species on the surface of these catalysts.