Structure-performance relationship in CuO/SBA-15-type SOx adsorbent: evolution of copper-based species under different regenerative treatments

Abstract

Sulphur oxides (SO_x) represent a major air pollutant and are controlled by national and international regulations. CuO/SiO₂ materials are known as SO_x trap materials. However, their large-scale development is still hampered by the sintering of the active phase over multiple adsorption/regeneration cycles, leading to the progressive decrease in SO_x adsorption capacities of the adsorbent. In this work, SBA-15 organised mesoporous silica was functionalized with highly dispersed Cu²⁺-based species. The as-obtained adsorbent was then assessed as a regenerable SO_x trap material. An extended characterisation was performed along with adsorption/regeneration cycles to correlate the evolution of the copper species with the performance of the adsorbent under different regenerative treatments. Thermal regeneration at 600 °C under pure N₂ leads to the formation of Cu⁺-based species, enabling a significant increase in SO_x chemisorption efficiency, which nevertheless decreases during the subsequent cycles due to progressive sintering of the active phase, leading to bulky copper(II) oxide particles. Regeneration under reductive conditions (0.5 vol% of H₂ in N₂) was then investigated as a way to decrease the regeneration temperature and limit this sintering process. It was found that the general behaviour of the copper-based species was very sensitive to the regeneration temperature. At 600 °C, the active phase was completely converted into large metallic copper particles, giving rise to a fast decrease in SO_x adsorption capacity of the adsorbent due to partial obstruction of the SBA-15 silica porosity. Conversely, when this regeneration was performed at 280 °C, no decrease in performances was noticed, and the copper species remained as a highly dispersed phase on the silica support.