Over the past decade, to meet the ever increased demand on high-performance catalysts with excellent activity, selectivity and stability, the nanocatalysts and catalysis have been rigorously explored, resulting in a noticeable progress in new paradigm of nanoscience and nanotechnology for catalysis. Differing remarkably from conventional bulk catalysts, size shrinkage of active components to nanometer scale gives a rise to significantly increased catalytic activity, owing to the high surface-to-volume ratio of small particles as well as a large fraction of active atoms with dangling bonds exposed surfaces. In addition, other unique properties of nanomaterials such as surface- and strain-driven lattice distortion, variation in electronic state density and oxidation-induced charge redistribution could also benefit the catalytic performance.