Enhancing the hydrogen spillover effect of catalysts is an effective method for optimizing hydrogen storage reactions. In this study, we report a catalyst consisting of Ru nanoclusters (1.2–2.7 nm) anchored on nitrogen-doped carbon (NC) that are highly dispersed on an Al2O3 substrate. Both experimental and density functional theory-based calculations indicate that these constrained, highly dispersed ultrafine nanoclusters significantly improve the intrinsic catalytic activity of Ru and reduce the reaction barriers. Moreover, the electron transfer between NC and Ru clusters increases the adsorption inertness of Ru with hydrogen, enhances hydrogen desorption, and promotes hydrogen spillover, synergistically improving the activity of catalytic hydrogen storage. Notably, the aromatic compounds in the ethylene tar narrow fraction were effectively converted at a low temperature of 80 °C, and the total cycloalkanes yield reached 99.04 %. The hydrogen storage capacity can be about 5.70 wt%. Liquid Organic Hydrogen Carriers model compounds were fully hydrogenated at temperatures no higher than 70 °C with low Ru loading (2 wt%). This work provides a potential utilization strategy of ethylene tar narrow fraction as hydrogen carriers based on its hydrogenation over the highly active and stable Ru nanocluster catalysts.