Room-Temperature Oxidation of Formaldehyde by Layered Manganese Oxide: Effect of Water

Abstract

Layered manganese oxide, i.e., birnessite was prepared via the reaction of potassium permanganate with ammonium oxalate. The water content in the birnessite was adjusted by drying/calcining the samples at various temperatures (30 °C, 100 °C, 200 °C, 300 °C, and 500 °C). Thermogravimetry-mass spectroscopy showed three types of water released from birnessite, which can be ascribed to physically adsorbed H2O, interlayer H2O and hydroxyl, respectively. The activity of birnessite for formaldehyde oxidation was positively associated with its water content, i.e., the higher the water content, the better activity it has. In-situ DRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde, which is promoted by bonded water via hydrogen bonding, is transformed into formate and carbonate with the consumption of hydroxyl and bonded water. Both bonded water and water in air can compensate the consumed hydroxyl groups to sustain the mineralization of formaldehyde at room temperature. In addition, water in air stimulates the desorption of carbonate via water competitive adsorption, and accordingly the birnessite recovers its activity. This investigation elucidated the role of water in oxidizing formaldehyde by layered manganese oxides at room temperature, which may be helpful for the development of more efficient materials.

Progress of Catalytic Oxidation of Formaldehyde over Manganese Oxides

“…The Flower‐like MnO 2 nanospheres prepared by a redox method using KMnO 4 and (NH 4 ) 2 C 2 O 4 could remove 81.7% of HCHO (150 ppm) at 25 °C, (other conditions: 240 L(g cat h) −1 of GHSV: 60%RH, 60 min) . And 84.7% of HCHO removal was observed over the MnO x catalyst obtained by a redox method using KMnO 4 and (NH 4 ) 2 C 2 O 4 ⋅H 2 O as the raw materials at 25 °C (other conditions: 180 L(g cat h) −1 of GHSV, 200 ppm HCHO, 3 h) . However, one of shortages in these works is that the CO 2 conversion efficiency is lower than the removal efficiency of HCHO.…”

“…Also, the G−Mn hybrids could convert about 20% HCHO at 30 °C. A lot of work has been done by Zhang's group on the catalytic activity of MnO 2 with special structure at room temperature . A layered MnO 2 was prepared by hydrothermal method using Mn(CH 3 COO) 2 ⋅4H 2 O and KMnO 4 as the precursors .…”

“…Zhang's group investigated the mechanism of formaldehyde oxidation over manganese oxides in detail. They firstly proposed a four‐step mechanism for room temperature oxidation of HCHO .…”

“…Zhang's group investigated the mechanism of formaldehyde oxidation over manganese oxides in detail. They firstly proposed a four‐step mechanism for room temperature oxidation of HCHO . First, HCHO molecules are adsorbed on the surface of the catalyst by hydrogen bonding, and then react with the surface hydroxyl species of the birnessite to form formate and carbonate.…”

“…Here, the catalytic activity is mainly determined the different microstructures of three kinds of MnO 2 . Zhang et al [81] also [103] found that δ-MnO 2 exhibited the highest catalytic activity among α-MnO 2 , β-MnO 2 , γ-MnO 2 and δ-MnO 2 catalysts, which were prepared by hydrothermal method. The temperatures required for 100% conversion of formaldehyde over α, β, γ, δ-MnO 2 were 125°C, 200°C, 150°C, and 80°C, respectively (shown in Figure 2), indicating that the δ-type MnO 2 showed the lowest conversion temperature and the best catalytic activity.…”