The control and optimization of the catalytic properties of nonexpensive early transition metals is an important issue in the chemical industry. Density functional theory was employed to study the relative stability and chemical activities of molybdenum carbides, nitrides and phosphides. The results show that molybdenum phosphides display the highest reactivity toward CO and sulfur adsorption as compared to molybdenum carbides and nitrides. Considering the better catalysts, those that combine high stability and a reasonable chemical activity, we observe that the catalytic potential of these systems should increase following the sequence: Mo < MoC &AP; MoN < MoP. An electronic analysis is included to understand the better performance of molybdenum phosphide.