Size effect of PdC nanoparticles synthesized by S-containing silane coupling agents on semi-hydrogenation of acetylene

• PdC particles with different sizes can be synthesized by S-containing silane coupling agents. • The size of PdC particle affects the selectivity of acetylene hydrogenation. • Smaller PdC particles can inhibit ethane formation. • PdC particles around 2.0 nm favor the generation of C4 and green oil. S-containing silane coupling agents (SCA) with various structures were chosen as regulators to synthesize PdC nanoparticles in different sizes for semi-hydrogenation of acetylene. Characterization and catalytic performance demonstrate that the catalytic property of PdC is deeply influenced by particle size. PdC particles prepared by employing SCA containing sulfhydryl has a smaller size and narrow diameter distribution. They exhibited better inhibition on ethane formation than those by containing thioether bond. Catalysts with larger PdC particles have lower selectivity to C4 and green oil. Reaction paths on typical (1 1 1) surface of PdC nanoparticles with different dimensions were investigated by DFT calculations. It reveals that within a certain particle size range (∼2.6 nm), surfaces of smaller PdC particles have weaker adsorption strength of ethylene. As particle size exceeds 2.6 nm, the adsorption strength no longer increases. C4 and green oil are more likely to be generated when PdC particles are around 2 nm, and the size smaller or larger than 2 nm will weaken the tendency of C4 and green oil formation.