A new method for synthesis of carbon-supported catalysts where precursors were obtained by slow pyrolysis of whole (8 mm) and ground (4 and 2 mm) corn grains impregnated with nickel nitrate solution is described. Carbon-supported nickel catalysts prepared by precursor activation at three levels of maximum activation temperature (600, 680, and 750 degrees C) were characterized and tested in the liquid-phase cinnamaldehyde hydrogenation. The influence of corn grain size and maximum activation temperature on catalyst texture, nickel loading, nickel nanoparticle size, and hydrogenation reaction performances was evaluated. An increase in BET specific surface (92-379 m(2)/g), porosity (0.13-0.60), mean pore diameter (12.8-22 nm), nickel loading (3.56-25.41%), and nickel nanoparticle size (21-55 nm) was found with decreasing grain size and increasing activation temperature. The highest values of cinnamaldehyde conversion (97%) and initial turnover frequency (0.31 and 0.36 s(-1)) were obtained for supported catalysts prepared from ground grains activated at 750 degrees C.