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Solar‐driven transfer hydrogenation of unsaturated bonds has received considerable attention in the research area of sustainable organic synthesis; however, water, the ultimate green source of hydrogen, has rarely been investigated due to the high barrier associated with splitting of water molecules. We report a carbon‐nitride‐supported palladium single‐atom heterogeneous catalyst with unparalleled performance in photocatalytic water‐donating transfer hydrogenation compared to its nanoparticle counterparts. Isotopic‐labeling experiments and operando nuclear magnetic resonance measurements confirm the direct hydrogenation mechanism using in situ‐generated protons from water splitting under visible‐light irradiation. Density functional theory calculations attribute the high activity to lower barriers for hydrogenation, facilitated desorption of ethylbenzene, and facile hydrogen replenishment from water on the atomic palladium sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Operando NMR combined with gas-probe method was used to study active sites transfer under the metal-support interaction. • The photocatalytic conversion efficiency of pure TiO 2 decreased, while that of Pt/TiO 2 was unaffected in gas conditions. • After loading metal-Pt, active sites changed from TiO 2 surface to Pt/TiO 2 interface. Recently metal-support interaction (MSI) has attracted considerable attention in photocatalysis. Some studies emphasize the importance of active sites on photocatalysts; however, there are no reports on site changes under MSI in real reactive conditions. Herein, an operando nuclear magnetic resonance technique was proposed to study such site changes on anatase TiO 2 and Pt/TiO 2 , through a gas-probe method, in CH 3 OH reforming. The photocatalytic oxidation efficiency of CH 3 OH by pure TiO 2 decreased immensely under extra-gas conditions, while that by Pt/TiO 2 was unaffected. The surface of pure TiO 2 were occupied by injected gas molecules, making CH 3 OH inaccessible to active sites. However, in Pt/TiO 2 , CH 3 OH adsorption sites changed from TiO 2 surface to metal-Pt/TiO 2 interface as confirmed by H 2 gas-probe experiments. This study provides a deeper understanding of active sites transfer by MSI and leverages the gas-probe method for its detection to guide the development of technology to test active-site positions in heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

Operando NMR has been exploited to probe the effects of photon flux and wavelength on photocatalytic reforming of methanol. • Operando NMR technique can be used to study the CH 3 OH photochemistry process. • CH 3 OH oxidation reaction could be enhanced by photon flux. • Photo energy had different effects on CH 3 OH photoreactions for TiO 2 and Pd/TiO 2. • SPR of the metal cocatalyst can be observed at 380 nm for the Pd/TiO 2 sample. • Operando NMR may help know the photoreactions in practical working conditions. 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 TiO 2 and Pd/TiO 2 -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 TiO 2 and Pd/TiO 2 sample, but longer wavelengths (lower photon energy) can slow down the reaction. Meanwhile, on the Pd/TiO 2 catalyst a significantly enhanced activity in CH 3 OH oxidation was found at the irradiation with the wavelength of 380 nm, which activity in CH 3 OH 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. [ABSTRACT FROM AUTHOR]

Operando NMR combined with the DFT calculations has been exploited to probe the crucial role of the bulk H 2 O in the CH 3 OH heterogeneous photochemistry processes on the surface of rutile-TiO 2. • Bulk H 2 O can significantly affect the CH 3 OH reforming products. • The participation ways of bulk H 2 O can vary from H 2 O molecule to H-atom. • The productivities of CH 3 OH reforming products vary with H 2 O concentration. • Operando NMR can be used to probe the kinetics of the CH 3 OH photocatalysis. Solid-liquid heterogeneous catalysis reactions play key roles in industrial catalytic reactions, throughout pollution control, fuel cell, methanol reforming and so on. But, few operando techniques have been performed to track the complex reaction processes, especially those in bulk liquid environment containing two or more liquid reactants, thus leaving a gap in our understanding of the reaction mechanisms deep into the working conditions. Here, we demonstrate an approach, using operando nuclear magnetic resonance (NMR) to probe the dynamics and kinetics of the methanol heterogeneous photochemistry processes in liquid condition with and without bulk water (H 2 O). It shows that not only can bulk H 2 O affect the types of methanol reforming products, but also its participation way can vary from H 2 O molecule to H-atom. Furthermore, the productivities of the main products - methylene glycol (HOCH 2 OH) and hemiacetal (CH 3 OCH 2 OH) – show different dependency on the H 2 O concentration, which is further supported by the density functional theory calculations (DFT). The operando NMR method opens up exciting opportunities for the mechanism studies of heterogeneous catalysis reaction in bulk liquid. [ABSTRACT FROM AUTHOR]