Novel\nCore–Shell (ε-MnO₂/CeO₂)@CeO₂ Composite Catalyst with a Synergistic Effect\nfor Efficient Formaldehyde Oxidation

Abstract

A novel\ncore–shell (ε-MnO₂/CeO₂)@CeO₂ composite catalyst with a synergistic effect was\nprepared by hydrothermal reaction and thermal decomposition and its\napplication to high-efficiency oxidation removal of formaldehyde (HCHO)\nwas systemically investigated. The (MnCO₃/CeO₂)@CeO₂ precursor was prepared first by the one-pot hydrothermal\nreaction of Mn²⁺ and Ce³⁺ solutions with a CO₂-storage material (CO₂SM) without any external\ntemplates or surfactants required. The thermal decomposition of the\nprecursor afforded the core–shell (ε-MnO₂/CeO₂)@CeO₂ composite catalyst with excellent catalytic\nperformance. HCHO in the feed gas (180 ppm HCHO, 21% O₂, N₂ balanced) at a gas hourly space velocity of 100 L/(g_cat h) is 100% converted over the catalyst at 80 °C. The\nconversion rate remains above 95% in 72 h and above 73.8% in 140 h,\nsuggesting the strong stability of the catalyst at high gas flow rates\nand relatively low temperatures. The synergistic mechanism of the\ncatalyst was explored by X-ray diffraction, Raman, Brunauer–Emmett–Teller,\ntransmission electron microscopy, and X-ray photoelectron spectroscopy.\nThe number of defects in the catalyst and the strength of the Mn–O\nbond in ε-MnO₂ can be tuned by adjusting the synthesis\nconditions. More oxygen vacancies on the surface of CeO₂ can make the synergistic effect of the catalyst stronger, which\nsignificantly improves the lattice oxygen (O_latt) activity\non the surface of ε-MnO₂. Our work has provided new\ninsights into the preparation of the desired composite catalysts with\nexcellent performances.