Noble-Metal-Based Catalysts on a Scale from Nanoparticles to Subnanoclusters and Single Atoms for Formaldehyde Oxidation at Room Temperature: A Review

As an extremely toxic pollutant, formaldehyde (HCHO) is a risk to human health. Catalytic oxidation with noble-metal-based catalysts is considered to be the most effective and promising strategy for HCHO removal at room temperature. Unfortunately, it usually exhibits high cost. In this review, we aim to establish comprehensive viewpoints for noble-metal-based catalysts including platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), and gold (Au) using in ambient-temperature HCHO oxidation. Because the catalytic performance highly depends on the metal particle size for supported catalysts, we summarize the recent significant progress focusing on metal species with dispersions from nanoparticles to subnanoclusters and single atoms, which can yield atomic-level insight and enhance the utilization efficiency of metal atoms. First, the impacts of the noble-metal species status as well as their support properties are summarized. Relative humidity as a critical impact factor for catalytic activity during HCHO oxidation is also discussed. Then, the reaction mechanisms in terms of typical intermediates and reaction pathways are demonstrated. Importantly, the emerging combination method of adsorption and oxidation for the tandem elimination of HCHO is briefly introduced and discussed. Finally, the perspective on the challenges and opportunities to design highly efficient but low-cost noble-metal-based catalysts is put forward in combination with the process optimization technologies.