In the present work, we have extended some previously calculated bulk-based results of MCE to the scale of nanoparticles where the catalytic processes actually happen. With the aid of atomistic spin dynamics, we have successfully investigated the size dependence of the MCE. According to the finite-size effect of ferromagnetism, the effective magnetization of the surface atoms at the nanoscale catalysts can be significantly lower than its bulk status at the same temperature. Since MCE itself is observable at the range of 0 < 𝑀 < 𝑀 / , the interesting effect can be induced at more applicable conditions than the previous predictions. By rescaling our earlier ab initio results, the 1 nm Co NP can theoretically achieve the Sabatier optimal of the ammonia synthesis at a temperature of ~910 K. Although more efforts are still needed to optimize the whole framework and related methodologies, we B A still believe this work will bridge the gap between the bulk phase transition and interfacial chemical reaction and provide a feasible possibility for the practical application of MCE in heterogeneous catalysis.