Size-Dependent Photocatalytic Activity of Silver Nanoparticles Embedded in ZX-Bi Zeolite Supports

In this study, the photocatalytic activity of highly dispersed silver (Ag) embedded into ZX-Bi zeolite during methanol (MeOH) photooxidation under visible light and at room temperature was investigated. The size and dispersion of Agnδ+ subnanoclusters (<1 nm) was studied by high-resolution transmission electron microscopy (HRTEM), diffuse-reflectance UV–vis, in situ Fourier transform infrared (FTIR), etc. Catalytic tests were performed using the operando FTIR technique during MeOH photooxidation as a model reaction. The results showed that the as-prepared Ag/ZX-Bi had very low activity, while the activated sample at 200 °C (Ag/ZX-Bi_200) exhibited the highest photocatalytic activity (49.60 mmol·g–1·cm–2 after 12 h of reaction) during MeOH photooxidation, more than 6 times higher than that of TiO2-P25 used as a reference. This activity originated from the migration and agglomeration of subnanosized Agnδ+ clusters into Ag nanoparticles (NPs) with a size of 6 nm. However, the catalyst experienced a partial desactivation when the particle size of sintered Ag NPs was below 20 nm. The activity and deactivation of Ag/ZX-Bi will be discussed on the basis of operando FTIR results and HRTEM analysis at different stages of the reaction.