HCHO oxidation over the δ-MnO2 catalyst: Enhancing oxidative activities of surface lattice oxygen and surface adsorbed oxygen by weakening Mn-O bond

Abstract

The usages of HCHO in construction and decoration materials lead to serious indoor air pollution, removing the indoor HCHO to improve air quality is urgently required. In this work, we developed a new procedure to synthesis ultra-thin nanosheet δ-MnO2 without using traditional templates. The Mn-O bond was much weaker in the ultra-thin nanosheet δ-MnO2 than those in the β- and γ-MnO2. As a consequence, surface oxygen lattice of the δ-MnO2 was the most removable, generating the most oxygen vacancy on the surface. The oxidative ability of the lattice oxygen was the most enhanced, active surface adsorbed oxygen species were the most present on the δ-MnO2 surface. These contributed to an unexpected performance that 100 ppm HCHO was fully oxidized at 35–45 °C depending on the relative humidity between 10 and 50% at high space velocity of 300 L/(gh). When compared with HCHO oxidation performance of MnO2 in literatures, the current ultra-thin nanosheet δ-MnO2 lists the most active HCHO oxidation catalyst as regards to the lowest activation energy, the lowest temperature of full HCHO conversion and the highest rate of HCHO oxidation, giving the most promising potential application for practical indoor HCHO elimination.