A platinum ensemble catalyst for room-temperature removal of formaldehyde in the air

Abstract

Minimal use of noble metals is ideal in developing catalytic systems against carcinogenic formaldehyde (FA) in air. Although single-atom catalysts (SACs) have been proposed to maximize atomic utilization, metals dispersed to the single-atom limit are less durable in redox environments. A highly dispersed platinum (Pt) ensemble (Ptn) on titanium dioxide (TiO2) was synthesized and validated to achieve 100% conversion of 100 ppm FA in dry air at room temperature (RT) at a gas hourly space velocity of 47,771 h−1. In contrast, Pt SAC (Pt1/TiO2) and a reference Pt nanoparticle catalyst (PtNP/TiO2) exhibited much lower performances. The turnover frequencies (TOFs) of Ptn/TiO2, Pt1/TiO2, and PtNP/TiO2 for the RT FA oxidation reaction were 0.03, 0.01, and 0.005 s−1, respectively. The critical role of the surface lattice oxygen (Olatt) in the overall reaction was supported by the prominence of the Mars van Krevelen kinetics in FA oxidation by the Ptn catalyst. The performance of the PtNP catalyst matched with Ptn only when the Pt loading in the former was raised to 2 wt%. Hence, the Pt dose can be reduced by one-fourth through the ensemble form dispersed at the sub-nanometer scale. The density functional theory simulation also distinguished the roles of different Pt catalysts. The Ptn sites could serve as an oxygen reservoir (effective dissociation of molecular oxygen) to promote proximate reactions (between the adsorbed –CHO and surface Olatt species). Conversely, Pt1 is a single site that restricts proximate reactions with vulnerability to surface poisoning.