Review on noble metal-based catalysts for formaldehyde oxidation at room temperature

Catalytic oxidation of formaldehyde (HCHO) to CO2 and H2O under ambient condition is highly desired for purifying indoor air quality. In this work, it was found for the first time that TiO2 supported subnanometer Rh catalyst exhibited a remarkable activity with complete removal of HCHO at room temperature. The humidity under ambient condition can significantly improve the activity, stability and specific rates but result in lower activation energy for the oxidation of HCHO on this catalyst. A combination of characterizations, such as H2 temperature programmed reduction, adsorption microcalorimetry and in situ diffuse reflectance infrared Fourier transform spectroscopy, demonstrated the importance of Rh species for the dissociative adsorption of O2 and the key role of water on the oxidation of HCHO. The O atoms facilitated the transformation of HCHO adsorbed on TiO2 into intermediate of formates, while the presence of water led to the production of hydroxyl probably from the reaction with the adsorbed O species, which promoted the decomposition of formates to CO2. This study can provide an important implication into the design and fabrication of more economic Rh-based catalysts for ambient HCHO oxidation.

Complete oxidation of formaldehyde over TiO2 supported subnanometer Rh catalyst at ambient temperature

Two-dimensional (2D) layered MnO2 materials, composed of exotic electronic properties and accessible active sites with alkali metal ions, provide a comprehensive platform for developing catalysts w...

Unveiling the Effects of Alkali Metal Ions Intercalated in Layered MnO2for Formaldehyde Catalytic Oxidation

The redox-driven hydrolysis precipitation is developed to atomically disperse Pt on TiO2 by involving high-valence Mn cations as the “anchor” into TiO2. With multiple characterizations including Cs-HAADF-STEM and XAFS, single-atom state of Pt on the surface of support is evidenced. Due to high dispersion of Pt and strong interaction between Pt and MnOx-TiO2 (Mn-TiO2), the physicochemical properties of catalysts are obviously improved. With combination of theoretical calculation and characterization, it is revealed that metallic Pt atom is stabilized by lattice oxygen of support. As observed, only 0.5% nominal amount of Pt loading (actual amount = 0.47%) on Mn-TiO2 support can meet the demands of complete removal of HCHO with high/low concentrations and severe space velocity at low temperature. Through analysis of in-situ DRIFTS of HCHO, the catalytic oxidation of HCHO over Pt/Mn-TiO2 obeys Mars-van-Krevelen mechanism. By associating with H-D exchange, it is found that introduction of water vapor can inhibit side-reactions and facilitate deep oxidation of HCHO.

Incorporating Mn cation as anchor to atomically disperse Pt on TiO2 for low-temperature removal of formaldehyde

Formaldehyde (HCHO) is considered as a major indoor air pollutant, and may cause serious health problems for humans. Therefore, HCHO needs to be removed from indoor air. Several techniques have been developed for indoor HCHO removal, among which room-temperature HCHO oxidation is the most promising method. To obtain excellent catalytic performance, various well-designed hierarchical catalysts have been fabricated in recent years. In this review, we first summarize the strategies for gaseous HCHO removal with special regard to thermal catalytic oxidation. Then, the major influencing factors affecting the catalytic activities of supported noble metal catalysts are raised and discussed. Finally, we emphasize on hierarchical porous catalysts for room-temperature HCHO oxidation and propose the feasible mechanisms for supported noble metal catalysts. A comprehensive impression of catalysts for HCHO removal may bring a new understanding and opportunity for the design and fabrication of highly efficient and practical hierarchical catalysts for indoor HCHO oxidation.

Room-temperature formaldehyde catalytic decomposition

A series of titania nanowires containing different Na content (NaxTiO2) were prepared from sodium titanate by varying the pH value of ion-exchange. They were used to load the Pt nanoparticles for low temperature formaldehyde catalytic oxidation. As prepared samples were systematically characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature programmed reduction/desorption/oxidation (TPR/TPD/TPO) and so on. The results showed that NaxTiO2 were consisted of anatase and sodium titanate. As pH value increased, the surface area and anatase content of catalyst decreased. Pt particles on NaxTiO2 were more easily oxidized and had smaller size but less exposed atoms compared with those on pure TiO2. The HCHO catalytic oxidation result exhibited that Pt/NaxTiO2 catalysts possessed excellent HCHO catalytic oxidation at ambient temperature that were 8.9–52.8 times the activities as that of Pt/TiO2. Kinetic studies manifested the easy activation of HCHO reaction over Pt/NaxTiO2 catalysts. Structure-performance analysis showed that the enhanced performance of Pt/NaxTiO2 catalysts was mainly attributed to two factors: increase in HCHO adsorption amount and change in HCHO decomposition pathway. According to HCHO-DRIFTS, linearly adsorbed CO generated from formate can react with hydroxyls to be carbonate/bicarbonate over Pt/NaxTiO2 catalysts. Simultaneously, the formate in Pt/NaxTiO2 catalyst with high Na content was also decomposed into a weak adsorbed CO. Both reaction pathways avoided the strong adsorption of CO on Pt/NaxTiO2 catalysts, which can facilitate the HCHO decomposition.

Highly active Pt/NaxTiO2 catalyst for low temperature formaldehyde decomposition

Development of the environment-tolerant catalyst can contribute to pollutant treatment in extreme environment. In the present work, precursor of the silicate-decorated titania (SiOx-TiO2) was prepared by incorporating silica into hydrothermal synthesis of TiO2 nanowire (TNT). After loading Pt nanoparticles by impregnation, the as-prepared catalyst (Pt/SiOx-TiO2) possessed 7.2 times and 13.6 times the HCHO decomposition rate of Pt/TNT and conventional Pt/TiO2, respectively, at the temperature of 30 °C and the relative humidity of ∼5 %. Structure-performance relationship analyses showed that the excellent catalytic performance of Pt/SiOx-TiO2 was closely related to the presence of silicate and formation of sodium-stabilized Pt nanoparticles. The heterogeneously decorated silicate in Pt/SiOx-TiO2 had the excellent ability of capturing water from environment and even from HCHO decomposition itself. Consequently, the sodium-stabilized Pt nanoparticles of Pt/SiOx-TiO2 could be maintained in a wet microenvironment to exhibit the excellent HCHO decomposition performance in low temperature and dry environment.

Enhanced catalytic decomposition of formaldehyde in low temperature and dry environment over silicate-decorated titania supported sodium-stabilized platinum catalyst

Halogenation of organic semiconductors is an efficient strategy for improving the performance of organic solar cells (OSCs), while the introduction of halogens usually involves complex synthetic process and serious environment pollution problems. Herein, three halogen-free ternary copolymer donors (PCNx, x = 3, 4, 5) based on electron-withdrawing dicyanobenzotriazole are reported. When blended with the Y6, PCN3 with strong interchain interactions results in appropriate crystallinity and thermodynamic miscibility of the blend film. Grazing-incidence wide-angle X-ray scattering measurements indicate that PCN3 has more ordered arrangement and stronger π-π stacking than previous PCN2. Fourier-transform photocurrent spectroscopy and external quantum efficiency of electroluminescence measurements show that PCN3-based OSCs have lower energy loss than PCN2, which leads to their higher open-circuit voltage (0.873 V). The device based on PCN3 reaches power conversion efficiency (PCE) of 15.33% in binary OSCs, one of the highest values for OSCs with halogen-free donor polymers. The PCE of 17.80% and 18.10% are obtained in PM6:PCN3:Y6 and PM6:PCN3:BTP-eC9 ternary devices, much higher than those of PM6:Y6 (16.31%) and PM6:BTP-eC9 (17.33%) devices. Additionally, this ternary OSCs exhibit superior stability compared to binary host system. This work gives a promising path for halogen-free donor polymers to achieve low energy loss and high PCE.

Halogen-Free Donor Polymers Based on Dicyanobenzotriazole with Low Energy Loss and High Efficiency in Organic Solar Cells.

As one of the crystal phases of titania, TiO2(B) was first utilized as a catalyst carrier for the oxidation of formaldehyde (HCHO). The mesoporous TiO2(B) loaded with Pt nanoparticles enhanced the HCHO oxidation reaction whose reaction rate was 4.5–8.4 times those of other crystalline TiO2-supported Pt catalysts. Simultaneously, Pt/TiO2(B) exhibited long-term stable HCHO oxidation performance. The structural characterization results showed that in comparison with Pt/anatase, Pt/TiO2(B) had more abundant hydroxyls, facilitating increasing the content of oxygen species. Studies on the role of hydroxyls in HCHO oxidation of Pt/TiO2(B) illustrated that synergistic involvement of terminally bound hydroxyls and bridging hydroxyls in HCHO oxidation accelerated the transformation from HCHO to formate via dioxymethylene. Moreover, hydroxyls could avoid the accumulation of excessive formate on Pt/TiO2(B) and promote the rapid oxidation of CO. Accordingly, the hydroxyl groups could accelerate each substep of formaldehyde oxidation, which enabled Pt/TiO2(B) to exhibit excellent formaldehyde oxidation performance.

https://pubs.acs.org/doi/pdf/10.1021/acsomega.2c02490

Enhanced Formaldehyde Oxidation Performance of the Mesoporous TiO2(B)-Supported Pt Catalyst: The Role of Hydroxyls

High molecular weight polymeric acceptors based on semi-perfluoroalkylated perylene diimides for pseudo-planar heterojunction all-polymer organic solar cells

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