CeO2 nanodots embedded in a porous silica matrix as an active yet durable catalyst for HCl oxidation

A unique architecture of CeO2 nanodots embedded in a porous SiO2 matrix (CeO2@SiO2) was successfully fabricated by a spontaneous deposition strategy and evaluated in the recycling of Cl-2 from HCl oxidation. The nano-sized CeO2 particles with a narrow size distribution (2-4 nm) were uniformly dispersed in the amorphous SiO2 matrix. Based on the characterizations from various techniques, including XRD, SEM/(HR) TEM, H-2-TPR, Raman, and XPS, it was revealed that the CeO2 nanodots in the SiO2 matrix exhibited a significant "size effect", with characteristics such as a considerably high concentration of Ce3+, a high fraction of oxygen vancant sites, and a notably enhanced oxygen reducibility, which all affect oxygen activation and surface Cl desorption. The current CeO2@SiO2 catalyst shows superior activity (1.60 g(Cl2) g(cat)(-1) h(-1)) and good durability (an on-stream time of 100 h at 703 K). The isolation of fine CeO2 nanodots by the SiO2 matrix is a key factor in the inhibition of sintering of CeO2 entities. Kinetic measurements indicate that catalytic activity is more dependent on the O-2 partial pressure than that of HCl, suggesting that enhancement in oxygen adsorption and surface Cl desorption is crucial for improving the catalytic activity.