Synthesis of supported Pd-based bimetallic catalysts is of great importance in the heterogeneous catalysis field owing to their optimal geometric and electronic effects. Downsizing active metals to ultrasmall nanocluster (2 nm), which is mandatory for maximizing the metal atom utilization, however remains as formidable synthesis challenges. Here, we present a general synthetic approach to sub-2 nm Pd-based bimetallic nanoclusters on porous nitrogen-doped carbon supports, in which the strong chemical interaction between metal and nitrogen largely suppresses the metal aggregation during the H-2-reduction at 400-500 degrees C. Through the nitrogen-fixing strategy, we prepare 9 sub-2 nm Pd-based bimetallic nanocluster catalysts by conventional impregnation process. The prepared supported bimetallic Pd-Pb nanocluster catalyst exhibit a high turnover frequency of 1092 h(-1) for the semihydrogenation of phenylacetylene under a mild condition (30 degrees C, 5 bar H-2), along with a high selectivity of 93% to styrene, demonstrating the alloying and small-size effects in the bimetallic nanocluster catalysts. (c) 2020 Elsevier Inc. All rights reserved.