The catalytic efficacy of modified manganese-cobalt oxides for room-temperature oxidation of formaldehyde in air.

Abstract

Formaldehyde (FA) is a hazardous indoor air pollutant with carcinogenic propensity. Oxidation of FA in the dark at low temperature (DLT) is a promising strategy for its elimination from indoor air. In this light, binary manganese-cobalt oxide (0.1 to 5 mol L^-1-MnCo₂O₄) is synthesized and modified in an alkaline medium (0.1-5 mol L^-1 potassium hydroxide) for FA oxidation under room temperature (RT) conditions. Accordingly, 1-MnCo₂O₄ achieves 100 % FA conversion at RT (50 ppm and 7022 h^-1 gas hourly space velocity (GHSV)). The catalytic activity of 1-MnCo₂O₄ is assessed further as a function of diverse variables (e.g., catalyst mass, relative humidity, FA concentration, molecular oxygen (O₂) content, flow rate, and time on-stream). In situ diffuse reflectance infrared Fourier-transform spectroscopy confirms that FA molecules are adsorbed onto the active surface sites of 1-MnCo₂O₄ and oxidized into water (H₂O) and carbon dioxide (CO₂) through dioxymethylene (DOM) and formate (HCOO^-) as the reaction intermediates. According to the density functional theory simulations, the higher catalytic activity of 1-MnCo₂O₄ can be attributed to the combined effects of its meritful surface properties (e.g., the firmer attachment of FA molecules, lower energy cost of FA adsorption, and lower desorption energy for CO₂ and H₂O). This work is the first report on the synthesis of alkali (KOH)-modified MnCo₂O₄ and its application toward the FA oxidative removal at RT in the dark. The results of this study are expected to provide valuable insights into the development of efficient and cost-effective non-noble metal catalysts against indoor FA at DLT.