Here, without using any organic stabilizer, via two-steps process, Pd-based catalysts supported on La-modified Al2O3 by a new colloid synthesis method using different reducing reagents were prepared. It was found that the reducibility and structure of reducer controlled the rate of nucleation and growth of Pd in its precursor solution supported on the modified Al2O3. The surface OH groups of alumina can stabilize the formed Pd nanoparticles and enhance Pd dispersion. The catalyst obtained by using the mild reducing reagent, ethylene glycol, had the highest dispersion (32.6%) and largest active metal surface area. This catalyst showed the best catalytic performance among the five as-synthesized catalysts for removing pollutants in a simulated natural gas vehicles (NGVs) exhaust. Compare to its counterpart by common impregnation method, the light-off temperature over the catalyst by colloid synthesis method can be significantly decreased by 39 degrees C for CH4 and 27 degrees C for NO, respectively. The study may provide a general method to control the formation of metal (oxide) nanoparticles for heterogeneous catalysis, especially for emission abatement of NGVs. [GRAPHICS] .