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

Sulphur oxides (SOx) represent a major air pollutant and are controlled by national and international regulations. CuO/SiO2 materials are known as SOx 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 SOx 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 SOx 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 degrees C under pure N-2 leads to the formation of Cu+-based species, enabling a significant increase in SOx 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 H-2 in N-2) 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 degrees C, the active phase was completely converted into large metallic copper particles, giving rise to a fast decrease in SOx adsorption capacity of the adsorbent due to partial obstruction of the SBA-15 silica porosity. Conversely, when this regeneration was performed at 280 degrees C, no decrease in performances was noticed, and the copper species remained as a highly dispersed phase on the silica support.