Solvent-engineered copper cobaltite spinel thermocatalysts for the oxidative removal of gaseous formaldehyde

Abstract

Cost-effective thermocatalysts are essential for broadening the application of catalytic systems in environmental remediation. The broad application of many transition-metal oxides, nonetheless, remains constrained by their inherent limitations in catalytic activity or durability. In response, copper cobaltite (CuCo<inf>2</inf>O<inf>4</inf> (CCO)) is synthesized as a bifunctional mixed metal-oxide catalyst using various solvents: deionized water (DI), ethanol (ET), ethylene glycol (EG), and glycerol (GL). These CCO catalysts are then employed for the catalytic oxidation of gas-phase formaldehyde (FA) in air. In terms of reaction kinetics, the performances of catalysts are measured by the temperature (T<inf>90</inf>) required to achieve 90 % conversion of FA (100 ppm), using a 30 mg catalyst at a space velocity of 100,000 mL g-1h−1 under 0 % relative humidity. The T<inf>90</inf> values followed this order: CCO-DI (90 °C) < CCO-GL (114 °C) < CCO-ET (118 °C) < CCO-EG (148 °C). The enhanced performance of the optimized catalyst, CCO-DI, is attributed to a combination of its high reducibility, abundant oxygen vacancies, high surface area, and oxygen mobility/activation. The catalytic activity of CCO-DI has also been evaluated across various process variables. Its improved activity, even in the presence of low moisture, suggests facile oxygen adsorption and transfer, likely mediated by hydroxyl groups from the H<inf>2</inf>O dissociation. Furthermore, density functional theory simulations indicate that the catalytic oxidation of FA proceeds via the Mars–van Krevelen mechanism, while dioxymethylene and formate are identified as the key intermediates in the FA oxidation reaction. This work provides an effective strategy for catalyst design by demonstrating the effectiveness of solvent engineering in enhancing FA oxidation performance.