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

Abstract

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