Crystal facets engineering of γ-MnO2 catalysts for remarkable enhancement of formaldehyde removal efficiency

Formaldehyde (HCHO) is a hazardous gas in indoor spaces because it is carcinogenic to human body. The removal of HCHO is of great significance for breathing safety. Facets engineering is a novel strategy to synthesize efficient catalysts, for which the selective exposed active facets on the catalysts can considerably improve catalytic performance. In this work, we synthesized three γ-MnO2 catalysts with selective exposures of (3 0 0), (1 6 0) and (1 3 1) crystal facets, the γ-MnO2-300 exposing (3 0 0) crystal facet had the best HCHO oxidation activity than the γ-MnO2-160 and γ-MnO2-131 exposing (1 6 0) and (1 3 1) crystal facets, respectively. 100 ppm HCHO was completely eliminated under high gas hourly space velocity at 40–45 °C catalyzed by the γ-MnO2-300, which was superior to other MnO2 reported in literatures. Through characterizations of BET, XPS, H2-TPR and O2-TPD etc., the highest surface area, the most active surface lattice oxygen and the most oxygen vacancy on the γ-MnO2-300 surface are assigned to its highest oxidation activity. The work provides a facet engineering method for γ-MnO2 catalyst to full eliminate HCHO at room temperature, which is applicable to facet-oriented catalysts development for other reactions.