Exploring the Size Effect of Pt Nanoparticles on the Photocatalytic Nonoxidative Coupling of Methane

The high inertness of the C–H bond makes the photocatalytic methane conversion a significant challenge. The platinum nanoparticle is a promising cocatalyst for CH4 activation, while the study of its structure characteristics and functionality remains in its infancy. Herein, the size effect of Pt on the photocatalytic nonoxidative methane conversion efficiency was systematically investigated over x-Pt/Ga2O3 with the particle size (x) ranging from 1.5 to 2.7 nm, where a volcano-shaped relation was observed. The smaller size is beneficial to the formation of Ptδ+ species, which is mainly distributed on the terrace sites according to the DFT calculation. The corner Pt atom is the geometric active site for the CH4 polarization, and the terrace Ptδ+ helps promote C–H activation since the activity is decreased on reduced x-Pt/Ga2O3 with a lower Ptδ+ content. Meanwhile, Ptδ+ species favors the oxidation of adsorbed −CH3 group to ·CH3. The volcano-shaped size effect on the NOCM activity was finally rationalized by the balance between C–H activation and C2H6 desorption from the corner sites on different sized Pt.