Photocatalytic decomposition of water for hydrogen generation is a promising way to obtain clean energy sources, and photon flux together with photon energy play particularly important roles in photocatalytic reactions. However, a study of their effects under real conditions is still limited, thus leaving a gap in our understanding. Herein, an operando NMR technique was proposed to systematically study the effects of photon flux and photon energy on TiO2 and Pd/TiO2-based photocatalytic methanol reforming reactions by changing the irradiation wavelength from 350 to 400 nm. Experimental results showed that the productivity of the methanol oxidation reaction can be obviously influenced by photon flux for the pure TiO2 and Pd/TiO2 sample, but longer wavelengths (lower photon energy) can slow down the reaction. Meanwhile, on the Pd/TiO2 catalyst a significantly enhanced activity in CH3OH oxidation was found at the irradiation with the wavelength of 380 nm, which activity in CH3OH oxidation is even higher than that observed under the irradiation with the wavelength of 365 nm. This enhanced oxidation activity can be attributed to the surface plasmon resonance of the cocatalyst. (C) 2019 Elsevier Inc. All rights reserved.