Dynamic evolution of vanadia sites in dendritic mesoporous silica nanospheres for selective oxidation of methane to formaldehyde

• The highly dispersed vanadium is tailored over DMSN via a heterogeneous oil–water biphase stratification reaction. • Low-degree polymeric vanadium evolves into the isolated (≡SiO) 2 (OH)V=O via V-O-V bond cleavage under high temperature. • (≡SiO) 2 (OH)V=O species exhibits higher activity for methane oxidation compared to the (≡OSi) 3 V=O species. • The (≡OSi) 3 V=O species can transition into (≡SiO) 2 (OH)V=O species by co-feeding water. Selective oxidation of methane to valuable C1 oxygenates (e.g. CH 3 OH, HCHO) using O 2 is a compelling route for upgrading methane, but remains grand challenge in catalysis. Vanadium-based catalysts show promising activity for the selective oxidation of methane to HCHO, but optimizing the vanadium nanostructures to enhance the catalytic performance is difficult. Here, we reported on the in-situ dispersion of vanadium into three-dimensional dendritic mesoporous silica nanospheres (DMSN). The V-DMSN catalyst with 4.2 wt% vanadium loading shows exceptional performance in converting methane to HCHO and CO. Spectroscopic studies reveal that low-degree polymeric vanadia sites dynamically transition into isolated (≡OSi) 2 (OH)V=O sites to enhance catalytic activity. Additionally, isolated (≡OSi) 3 V=O sites in V-DMSN with low loadings can transform into (≡OSi) 2 (OH)V=O sites when co-feeding water, resulting in increased catalytic activity. However, co-feeding H 2 O to (≡OSi) 2 (OH)V=O sites results in the competitive adsorption of H 2 O, CH 4 and products, reducing the activity while enhancing the selectivity to HCHO and CH 3 OH.