This paper presents the development of catalytic mechanochemical nitrogen fixation using molybdenum complexes. Atmospheric pressure dinitrogen reacted with samarium diiodide as a reductant and water or alcohols as proton sources in the presence of molybdenum catalysts using ball milling under solvent-free, near-ambient conditions. The process yielded up to 860 ammonia equivalents based on the catalyst, even using insoluble cellulose as a proton source. The reaction mechanism involves nitrogen-nitrogen bond cleavage at the gas-solid interface and nitrogen-hydrogen bond formation in the solid phase.