Total oxidation of benzene over cerium oxide-impregnated two-dimensional MWW zeolites obtained by environmental synthesis using Brazilian rice husk silica agro-industrial waste

Abstract

This work aimed to obtain sustainable catalysts for environmental catalysis. The ITQ-2 and MCM-22 layered zeolites impregnated with cerium (5 and 10%) were synthesized from a sustainable approach employing silica (R) from low-cost and abundant Brazilian agro-industrial waste, rice husks. The results indicate the type of support, porosity, surface defects and concentration of Ce influenced the size and dispersion of cerium oxide-nanoparticles (NPs). At the same Ce loading (5%), the porosity and surface defects followed the order R (46 m² g−1) < MCM-22 (341 m² g−1) < ITQ-2 (475) m² g−1) and resulted the decrease of NPs size (7.3 > 6.5 > 5.7 nm). The ITQ-2 and MCM-22 containing 10% of Ce resulted in the decrease of porosity of 422 and 329 m² g−1 and the increase of NPs size (7.5 and 8.3 nm), respectively. The DRS UV-Vis and XPS results indicated that Ce4+ and Ce3+species were present in all synthesized materials. The materials were evaluated for the gas-phase total oxidation of volatile organic compound (benzene) as a model reaction to reduce atmospheric pollutants. The best oxidation results were achieved at 350 °C for the Ce-impregnated ITQ-2 (5 and 10% of Ce) reaching benzene conversions of 84 and 91%, respectively, and followed by Ce-impregnated MCM-22 (5 and 10% of Ce) with 70 and 79%, respectively. No loss of activity was observed after 16 h of reaction for both Ce-impregnated ITQ-2 and MCM-22 with 10% of Ce.