The Surface/Interface Modulation of Platinum Group Metal (PGM)-Free Catalysts for VOCs and CO Catalytic Oxidation.

Effective management of volatile organic compounds (VOCs) and carbon monoxide (CO) is critical to human health and the ecological environment. Catalytic oxidation is one of the most promising technologies for achieving efficient VOCs and CO emission control. Platinum group metal (PGM)-free catalysts are recently receiving sustainable attention in catalyzing VOCs and CO removal due to their low cost, superior catalytic activity, and excellent stability, but PGM-free catalysts face challenges in low-temperature catalytic efficiency. In this mini-review, starting with discussing the catalytic mechanism of VOCs and CO oxidation, we summarize the surface/interface modulation strategies of PGM-free catalysts to promote oxygen and VOCs/CO molecule activation for enhanced low-temperature oxidation activity, including oxygen vacancy engineering, heteroatom doping, surface acidity modification, and active interface construction. We highlight the currently remaining challenges and prospects of advanced PGM-free catalyst development for highly efficient VOCs and CO emission control in practical applications.

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter.

Particulate matter, represented by soot particles, poses a significant global environmental threat, necessitating efficient control technology. Here, we innovatively designed and elaborately fabricated ordered hierarchical macroporous catalysts of Ce0.8Zr0.2O2 (OM CZO) integrated on a catalyzed diesel particulate filter (CDPF) using the self-assembly method. An oxygen-vacancy-enriched ordered macroporous Ce0.8Zr0.2O2 catalyst (VO-OM CZO) integrated CDPF was synthesized by subsequent NaBH4 reduction. The VO-OM CZO integrated CDPF exhibited a markedly enhanced soot oxidation activity compared to OM CZO and powder CZO coated CDPFs (T50: 430 vs 490 and 545 °C, respectively). The well-defined OM structure of the VO-OM CZO catalysts effectively improves the contact efficiency between soot and the catalysts. Meanwhile, oxygen vacancies trigger the formation of a large amount of highly reactive peroxide species (O22-) from molecular oxygen (O2) through electron abstraction from the three adjacent Ce3+ (3Ce3+ + Vö + O2 → 3Ce4+ + O22-), contributing to the efficient soot oxidation. This work demonstrates the fabrication of the ordered macroporous CZO integrated CDPF and reveals the importance of structure and surface engineering in soot oxidation, which sheds light on the design of highly efficient PM capture and removal devices.

Role of the In-Situ-Formed Surface (Pt-S-O)-Ti Active Structure in SO2-Promoted C3H8 Combustion over a Pt/TiO2 Catalyst.

Typically, SO2 unavoidably deactivates catalysts in most heterogeneous catalytic oxidations. However, for Pt-based catalysts, SO2 exhibits an extraordinary boosting effect in propane catalytic oxidation, but the promotive mechanism remains contentious. In this study, an in situ-formed tactful (Pt-S-O)-Ti structure was concluded to be a key factor for Pt/TiO2 catalysts with a substantial SO2 tolerance ability. The experiments and theoretical calculations confirm that the high degree of hybridization and orbital coupling between Pt 5d and S 3p orbitals enable more charge transfer from Pt to S species, thus forming the (Pt-S-O)-Ti structure with the oxygen atom dissociated from the chemisorbed O2 adsorbed on oxygen vacancies. The active oxygen atom in the (Pt-S-O)-Ti active structure is a robust site for C3H8 adsorption, leading to a better C3H8 combustion performance. This work can provide insights into the rational design of chemical bonds for high SO2 tolerance catalysts, thereby improving economic and environmental benefits.

Rapid Ozone Decomposition over Water-activated Monolithic MoO3 /Graphdiyne Nanowalls under High Humidity.

Catalytic ozone (O3 ) decomposition at high relative humidity (RH) remains a great challenge due to the catalysts poison and deactivation under high humidity. Here, we firstly elaborate the role of water activation and the corresponding mechanism of the promoted O3 decomposition over the three-dimensional monolithic molybdenum oxide/graphdiyne (MoO3 /GDY) catalyst. The O3 decomposition over MoO3 /GDY reaches up to 100 % under high humid condition (75 % RH) at room temperature, which is 4.0 times as high as that of dry conditions, significantly surpasses other carbon-based MoO3 materials(≤7.1 %). The sp-hybridized carbon in GDY donates electrons to MoO3 along the C-O-Mo bond, facilitating water activation to form hydroxyl species. As a result, hydroxyl species dissociated from water act as new active sites, promoting the adsorption of O3 and the generation of new intermediate species (hydroxyl ⋅OH and superoxo ⋅O2 - ), which significantly lowers the energy barriers of O3 decomposition (0.57 eV lower than dry conditions).

Ultra-high-efficiency capture of lead ions over acetylenic bond-rich graphdiyne adsorbent in aqueous solution.

A satisfactory material with high adsorption capacity is urgently needed to solve the serious problem of environment and human health caused by lead pollution. Herein, hydrogen-substituted graphdiyne (HsGDY) was successfully fabricated and employed to remove lead ions from sewage and lead-containing blood. The as-prepared HsGDY exhibits the highest adsorption capacity of lead among the reported materials with a maximum adsorption capacity of 2,390 mg/g, i.e., ~five times larger than that of graphdiyne (GDY). The distinguished hexagonal hole and stack mode of HsGDY allows the adsorption of more lead via its inner side adsorption mode in one single unit space. In addition, the Pb 6s and H 1s hybridization promotes the strong bonding of lead atom adsorbed at the acetylenic bond of HsGDY, contributing to the high adsorption capacity. HsGDY can be easily regenerated by acid treatment and showed excellent regeneration ability and reliability after six adsorption-regeneration cycles. Langmuir isotherm model, pseudo second order, and density functional theory (DFT) demonstrated that the lead adsorption process in HsGDY is monolayer chemisorption. Furthermore, the HsGDY-based portable filter can handle 1,000 µg/L lead-containing aqueous solution up to 1,000 mL, which is nearly 6.67 times that of commercial activated carbon particles. And, the HsGDY shows good biocompatibility and excellent removal efficiency to 100 µg/L blood lead, which is 1.7 times higher than that of GDY. These findings suggest that HsGDY could be a promising adsorbent for practical lead and other heavy metal removal.

Dual Activation of Molecular Oxygen and Surface Lattice Oxygen in Single Atom Cu1 /TiO2 Catalyst for CO Oxidation.

The in-depth mechanism on the simultaneous activation of O2 and surface lattice O2- on one active metallic site has not been elucidated yet. Herein, we report a strategy for the construction of abundant oxygen activation sites by rational design of Cu1 /TiO2 single atom catalysts (SACs). The charge transfer between isolated Cu and TiO2 support generates abundant CuI and 2-coordinated Olat sites in Cu1 -O-Ti hybridization structure, which facilitates the chemisorption and activation of O2 molecules. Simultaneously, the Cu1 -O-Ti induced TiO2 lattice distortion activate the adjacent surface lattice O2- , achieving the dual activation of O2 and surface lattice O2- . The Cu1 -O-Ti active site switches the CO oxidation mechanism from Eley-Rideal (80 °C) to Mars-van Krevelen route (200 °C) with the increase of reaction temperature. The dual activation of O2 and surface lattice O2- can by modulating the electron properties of SACs can boost the heterogeneous catalytic oxidation activity.

Neighboring sp-Hybridized Carbon Participated Molecular Oxygen Activation on the Interface of Sub-nanocluster CuO/Graphdiyne.

Activation of O2 is a crucial step in oxidation processes. Here, the concept of sp-hybridized C≡C triple bonds as an electron donor is adopted to develop highly active and stable catalysts for molecular oxygen activation. We demonstrate that the neighboring sp-hybridized C and Cu sites on the interface of the sub-nanocluster CuO/graphdiyne are the key structures to effectively modulate the O2 activation process in the bridging adsorption mode. The as-prepared sub-nanocluster CuO/graphdiyne catalyst exhibited the highest CO oxidation activity and readily converted 50% CO at around 133 °C, which is 34 and 94 °C lower than that for CuO/graphene and CuO/active carbon catalysts, respectively. In situ diffused reflectance infrared Fourier transform spectroscopy and density functional theory calculation results proved that the neighboring sp-hybridized C is more favorable to promote the rapid dissociation of carbonate than sp2-hybridized C without overcoming any energy barrier. The gaseous CO directly reacts with the active molecular oxygen and tends to proceed through the E-R mechanism with a relatively low energy barrier (0.20 eV). This work revealed that sp-hybridized C of graphdiyne-based materials could effectively improve the O2 activation efficiency, which could facilitate the low-temperature oxidation processes.

Oxygen Vacancy-Governed Opposite Catalytic Performance for C3H6 and C3H8 Combustion: The Effect of the Pt Electronic Structure and Chemisorbed Oxygen Species.

Revealing the role of engineered surface oxygen vacancies in the catalytic degradation of volatile organic compounds (VOCs) is of importance for the development of highly efficient catalysts. However, because of various structures of VOC molecules, the role of surface oxygen vacancies in different catalytic reactions remains ambiguous. Herein, a defective Pt/TiO2-x catalyst is proposed to uncover the different catalytic mechanisms of C3H6 and C3H8 combustion via experiments and theoretical calculations. The electron transfer, originated from the oxygen vacancy, facilitates the formation of reduced Pt0 species and simultaneously interfacial chemisorbed O2, thus promoting the C3H6 combustion via efficient C═C cleavage. The reduced Pt nanoparticles facilitate the robust chemisorption of bridging dimer O22- (Pt-O-O-Ti) species. This chemisorbed oxygen inhibits the C3H8 combustion by depressing C3H8 adsorption. This work offers insights for the rational design of highly efficient catalysts for activating the C═C bond in alkene or C-H bond in alkane.

Oxygen Vacancies and Lewis Acid Sites Synergistically Promoted Catalytic Methane Combustion over Perovskite Oxides.

An in-depth understanding of the surface properties-activity relationship could provide a fundamental guidance for the design of highly efficient perovskite-based catalysts for the control of anthropogenic methane emission. Herein, both oxygen vacancies and Con+ Lewis acid sites were purposely introduced on ordered macroporous La0.8Sr0.2CoO3 monolithic catalysts by one-step reduction and selective etching in oxalic acid, and their synergistic effect on methane combustion was investigated. Combined with experimental and theoretical investigations, we revealed that the positively charged Con+ Lewis acid sites and single-electron-trapped oxygen vacancies (Vo·) formed an active pair, which enabled an effective localized electron cloud shift from Vo· to Con+. The characteristic electronic effect modulates surface electronic properties and coordination structures, thus resulting in superior oxygen activation capacity, lattice oxygen mobility, and reducibility, as well as favorable CH4 interaction and oxidation. Our work not only gives insights into surface properties-activity relationships on perovskite for hydrocarbon combustion but also sheds substantial light on future environmental catalyst design and modulation for hydrocarbon pollutants elimination.

Interfacial sp C-O-Mo Hybridization Originated High-Current Density Hydrogen Evolution.

High-current density (≥1 A cm-2) is a critical factor for large-scale industrial application of water-splitting electrocatalysts, especially seawater-splitting. However, it still remains a great challenge to reach high-current density due to the lack of active and stable intrinsic catalytic active sites in catalysts. Herein, we report an original three-dimensional self-supporting graphdiyne/molybdenum oxide (GDY/MoO3) material for efficient hydrogen evolution reaction via a rational design of "sp C-O-Mo hybridization" on the interface. The "sp C-O-Mo hybridization" creates new intrinsic catalytic active sites (nonoxygen vacancy sites) and increases the amount of active sites (eight times higher than pure MoO3). The "sp C-O-Mo hybridization" facilitates charge transfer and boosts the dissociation process of H2O molecules, leading to outstanding HER activity with high-current density (>1.2 A cm-2) in alkaline electrolyte and a decent activity and stability in natural seawater. Our results show that high-current density electrocatalysts can be achieved by interfacial chemical bond engineering, three-dimensional structure design, and hydrophilicity optimization.

Engineering the Nucleophilic Active Oxygen Species in CuTiOx for Efficient Low-Temperature Propene Combustion.

Industrialization has resulted in the rapid increase of volatile organic compound (VOC) emissions, which have caused serious issues to human health and the environment. In this study, an extensive Cu incorporating TiO2 induced nucleophilic oxygen structure was constructed in the CuTiOx catalyst, which exhibited superior low-temperature catalytic activity for C3H6 combustion. Thorough structural, surface characterization and density functional theory (DFT) calculations revealed that the Cu-O-Ti hybridization induced nucleophilic oxygen initiates C3H6 combustion by abstracting the C-H bond. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that incorporated copper species acted as the major adsorbent site for the propene molecule. In combination of the DRIFTS and DFT results, the promotion effect of the nucleophilic O on the C-H bond abstraction and CO2 formation pathway was proposed. The surface doping induced nucleophilic oxygen as strong Brønsted basic sites for low-temperature propene combustion exemplified an efficient strategy for rational design of next-generation environmental catalysts.

Nanostructured MoO3 for Efficient Energy and Environmental Catalysis.

This paper mainly focuses on the application of nanostructured MoO3 materials in both energy and environmental catalysis fields. MoO3 has wide tunability in bandgap, a unique semiconducting structure, and multiple valence states. Due to the natural advantage, it can be used as a high-activity metal oxide catalyst, can serve as an excellent support material, and provide opportunities to replace noble metal catalysts, thus having broad application prospects in catalysis. Herein, we comprehensively summarize the crystal structure and properties of nanostructured MoO3 and highlight the recent significant research advancements in energy and environmental catalysis. Several current challenges and perspective research directions based on nanostructured MoO3 are also discussed.