<p>Single atom and nanocluster catalysts are extensively investigated in heterogeneous catalysis due to their high catalytic activity and atomic utilization, while their coexisting properties and potentially synergistic effect are yet to be clarified. Herein, we construct three systems of atomic-scale catalysts (<i>x</i>Ni/Mo₂TiAlC₂, <i>x</i> = 0.5, 1, and 1.5) for bio-ethanol reforming, which correspond to single atoms, single atoms mixed with nanoclusters, and nanoclusters. The respective hydrogen utilization efficiency of mixed-form catalyst increases by 43.7% and 29.3% compared to single atom and nanocluster catalysts. Results demonstrate that the adjacent Ni single atom facilitates electron transfer from Mo₂TiAlC₂ to Ni-Mo interface and raises the d-band center, thus enhancing bio-ethanol adsorption and activation; while the existence of Ni nanoclusters contributes to lowering the energy barriers of CH₃CHO* dehydrogenation. The catalytically active sites are Ni-Mo alloyed single atoms with adjacent Ni nanoclusters. This work provides new implications for highly activated catalytic site construction and advanced catalyst design.</p>