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 Cl2 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, H2-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 gCl2 gcat−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 O2 partial pressure than that of HCl, suggesting that enhancement in oxygen adsorption and surface Cl desorption is crucial for improving the catalytic activity.