Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Abstract

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.