Mechanistic insights into NO-H2 reaction over Pt/boron-doped graphene catalyst

This work presents a systematical experimental and density functional theory (DFT) studies to reveal the mechanism of NO reduction by H 2 reaction over platinum nanoparticles (NPs) deposited on boron-doped graphene (denoted as Pt/BG) catalyst. Both characterizations and DFT calculations identified boron (in Pt/BG) as an additional NO adsorption site other than the widely recognized Pt NPs. Moreover, BG led to a decrease of Pt NPs size in Pt/BG, which facilitated hydrogen spillover. The mathematical and physical criteria of the Langmuir-Hinshelwood dual-site kinetic model over the Pt/BG were satisfied, indicating that adsorbed NO on boron (in Pt/BG) was further activated by H-spillover. On the other hand, Pt/graphene (Pt/Gr) demonstrated a typical Langmuir-Hinshelwood single-site mechanism where Pt NPs solely served as active sites for NO adsorption. This work helps understand NO-H 2 reaction over Pt/BG and Pt/Gr catalysts in a closely mechanistic view and provides new insights into roles of active sites for improving the design of catalysts for NO abatement

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

The catalytic ozonation of VOCs is a promising approach for degradation of indoor VOCs, such as gaseous toluene. However, the mechanism and relevant kinetic steps involved in this reaction remain unclear. In this study, the catalytic ozonation of toluene over MnO2/graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-Hs) mechanism. The apparent activation energy determined using the power law model was 29.3±2.5 kJ mol−1. This finding indicated that the catalytic ozonation of toluene over MnO2/graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-Hs mechanism did not fit the experimental data, suggesting that the reaction was non-single-site governed. A novel Langmuir-Hinshelwood dual-site (denoted as L-Hd) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO2/graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO2 was responsible for ozone decomposition and toluene adsorption on graphene; these two types of adsorption were coupled by an adjacent attack. Furthermore, XPS results confirmed the presence of a strong connection between MnO2 and graphene sites on the surface of MnO2/graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-Hd model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r2 = 0.9165). Moreover, the physical criterion was in accordance with both enthalpy and entropy of toluene adsorption constraints. Fulfillment of mathematical and physical criteria indicated the catalytic ozonation of toluene over MnO2/graphene can be well described by the L-Hd mechanism. This study helps understand the catalytic ozonation of toluene over MnO2/graphene in a closely mechanistic view

Iron-modulated nickel cobalt phosphide embedded in carbon to boost power density of hybrid sodium–air battery

Nickel cobalt phosphide (NiCoP) is emerging as a potential electrocatalyst towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, its ORR/OER activities are sluggish. Here, we investigated the roles of iron dopants in the Fe-doped NiCoP (Fe–NiCoP) in order to boost its ORR/OER kinetics. The density functional theory (DFT) calculations reveal that the Fe dopant effectively modulates the electron conductivity of NiCoP and reduces binding energies of the reaction intermediates towards rate-determining steps of ORR and OER. A binder-free 3D microflowers morphology of the Fe–NiCoP embedded in the amorphous carbon layer (Fe–NiCoP@C) catalyst on the nickel foam was prepared as the air cathode for the hybrid sodium-air battery (HSAB). The HSAB displays a discharge voltage of 2.74 V at 0.01 mA cm−2 with excellent round trip efficiency of 93.26 % at the 500th cycle and state-of-the-art power density of 621 mW g−1

Role of graphene in MnO2/graphene composite for catalytic ozonation of gaseous toluene

The degradation of gaseous toluene is of great significance to protect human health. In this work, a facile and environmentally friendly route for synthesis of different MnO2 loadings (14.2-94.8wt.%) on graphene composites was developed through the direct redox reaction between graphene oxide and potassium permanganate at 160°C for 12h under hydrothermal condition. The elemental composition, crystal structure, and material properties of the MnO2/graphene samples were characterized using ICP-AES, XRD, TEM, FTIR spectroscopy, Raman spectroscopy, N2 physisorption technique, and TG/DTA. The results show that the hydrothermal method is an effective way to prepare tightly anchored birnessite-type MnO2 on graphene. MnO2 nanoparticles were uniformly distributed throughout the surface of graphene nanosheets at 64.6wt.% MnO2 loading, whereas aggregation or erosion of graphene sheets occurred at low or high loading of MnO2. The activities of graphene, MnO2, and the MnO2/graphene samples in catalytic ozonation of gaseous toluene were determined at 22°C. The amount of MnO2 loaded on graphene showed a significant influence on the BET surface area, and the catalytic activity of the MnO2/graphene samples. The highest toluene degradation rate (7.89×10-6molmin-1g-1) over the 64.6wt.% MnO2/graphene sample was attributed to the synergetic effect of graphene and MnO2 which was attributed to the tight connection between the active sites on graphene for adsorption of toluene and decomposition of ozone, and the MnO2 on graphene for decomposition of ozone to form atomic oxygen species

Revolutionizing Fuel Cell Efficiency with Non-Metallic Catalysts for Oxygen Reduction Reactions

Platinum-based catalysts are widely used in oxygen reduction reactions, but platinum’s high cost and low reserves have restricted their sustainable development. With continuous in-depth research, it has been found that metal-free catalysts also have better catalytic activity in oxygen reduction reactions and have great potential for development due to the low cost and abundant reserves of metal-free catalysts, which has become a hot research direction. This paper reviews the application of metal-free catalysts in oxygen reduction reactions, including heteroatom-doped carbon-based catalysts, polymeric nitrogen catalysts, and emerging carbon catalysts. This work provides insights into developing non-platinum catalysts for oxygen reduction reactions by comparing the catalytic activity, selectivity, and prolonged stability

Recent Progress of Non-Pt Catalysts for Oxygen Reduction Reaction in Fuel Cells

In recent years, non-Pt-based ORR catalysts have been developing rapidly and have achieved performance comparable to or even surpassing Pt precious metal catalysts in specific reactions, offering new possibilities for Pt-based catalyst replacement and showing great promise for application. This paper reviews the recent research progress of non-Pt-based fuel cell ORR catalysts. The latest research progress of non-Pt-based ORR SACs (including single metal active site ORR SACs, multi-metal active site ORR SACs, and non-Pt-based noble metal catalyst ORR SACs), non-metallic ORR catalysts, alloy-based ORR catalysts, high-entropy alloy ORR catalysts, and other non-Pt-based fuel cell ORR catalysts are presented in detail. This paper discusses in detail the synthesis methods, characterization means, optimization of performance, and application prospects of these non-Pt-based ORR catalysts. In addition, this review details the excellent performance of these catalysts in terms of compositional and structural controllability, electrical conductivity, and chemical stability, as well as their ability to exhibit ORR activity comparable to that of commercial Pt/C catalysts. This field is full of opportunities and challenges. In summary, non-Pt-based fuel cells show great potential in ORR. With the continuous improvement of preparation and characterization technologies, catalysts have broad application and market prospects. In addition, the development trend of non-precious metal fuel cell catalysts is reviewed

Recent Progress of Non-Pt Catalysts for Oxygen Reduction Reaction in Fuel Cells

In recent years, non-Pt-based ORR catalysts have been developing rapidly and have achieved performance comparable to or even surpassing Pt precious metal catalysts in specific reactions, offering new possibilities for Pt-based catalyst replacement and showing great promise for application. This paper reviews the recent research progress of non-Pt-based fuel cell ORR catalysts. The latest research progress of non-Pt-based ORR SACs (including single metal active site ORR SACs, multi-metal active site ORR SACs, and non-Pt-based noble metal catalyst ORR SACs), non-metallic ORR catalysts, alloy-based ORR catalysts, high-entropy alloy ORR catalysts, and other non-Pt-based fuel cell ORR catalysts are presented in detail. This paper discusses in detail the synthesis methods, characterization means, optimization of performance, and application prospects of these non-Pt-based ORR catalysts. In addition, this review details the excellent performance of these catalysts in terms of compositional and structural controllability, electrical conductivity, and chemical stability, as well as their ability to exhibit ORR activity comparable to that of commercial Pt/C catalysts. This field is full of opportunities and challenges. In summary, non-Pt-based fuel cells show great potential in ORR. With the continuous improvement of preparation and characterization technologies, catalysts have broad application and market prospects. In addition, the development trend of non-precious metal fuel cell catalysts is reviewed

Structure and Thermal Stability of (H₂O)₄ Tetrahedron and (H₂O)₆ Hexagon Adsorbed on NaY Zeolite Studied by Synchrotron-Based Time-Resolved X‑ray Diffraction

Water adsorption and desorption features play an important role in determining the adsorptive and catalytic properties of zeolites. In this study, the extraframework structure (water and cations) in NaY faujasite zeolite was studied by synchrotron-based <i>in situ</i> time-resolved X-ray diffraction (TR-XRD) in combination with the Rietveld refinement method. It was observed that Na cations locating at different sites migrated between each other during the dehydration process. Water molecules at three separate sites showed interesting geometries: (H₂O)₄ tetrahedron W1, (H₂O)₆ ice-like hexagonal W2, and disordered triangle W3. Interactions between each form of water and Na cations were deeply investigated. The stability of the waters followed the sequence of W1 > W3 > W2. This work provides insights into both framework structure and cation positions of model zeolite under actual working conditions, which helps fully understand the properties of zeolites

Significant Enhancement of Photocatalytic Reduction of CO₂ with H₂O over ZnO by the Formation of Basic Zinc Carbonate

Electron–hole pair separation efficiency and adsorption performance of photocatalysts to CO₂ are the two key factors affecting the performance of photocatalytic CO₂ reduction with H₂O. Distinct from conventional promoter addition, this study proposed a novel approach to address these two issues by tuning the own surface features of semiconductor photocatalyst. Three ZnO samples with different morphologies, surface area, and defect content were fabricated by varying preparation methods, characterized by XRD, TEM, and room-temperature PL spectra, and tested in photoreduction of CO₂ with H₂O. The results show that the as-prepared porous ZnO nanosheets exhibit a much higher activity for photoreduction of CO₂ with H₂O when compared to ZnO nanoparticles and nanorods attributed to the existence of more defect sites, that is, zinc and oxygen vacancies. These defects would lower the combination rate of electron–hole pair as well as promote the formation of basic zinc carbonate by Lewis acid–base interaction, which is the active intermediate species for photoreduction of CO₂. ZnO nanoparticles and ZnO nanorods with few defects show weak adsorption for CO₂ leading to the inferior photocatalytic activities. This work provides new insight on the CO₂ activation under light irradiation

Highly Oriented Thin Membrane Fabrication with Hierarchically Porous Zeolite Seed

Nanosized zeolite is widely used as seed for high quality zeolite membranes fabrication, while its complicated synthesis routine limits large-scale productions. In this work, a non-nanosized cubic hierarchically porous TS-1 zeolite (HTS-1), obtained by basic hydrothermal treatment of conventional ellipsoid solid TS-1, is used as seed to prepare highly oriented thin membranes. A capillary condensation phenomenon resulting from the unique hierarchically porous structure benefits gel attachment. Moreover, abundant ledges, kinks, and terraces on the HTS-1 surface promote epitaxial growth of the membrane. In contrast, the solid TS-1 seed induces intergrowth dominantly, which results in a thick TS-1 membrane. The HTS-1 membrane demonstrates superior CO₂/N₂ separation properties compared to the TS-1 one. It associates with thin oriented membrane morphology, leading to exposure of a high Miller index surface and less diffuse distance and tortuosity. The results suggest beneficial effects of a hierarchically porous TS-1 zeolite seed on the interfacial crystal growth for membrane fabrication. A similar conclusion is applicable to the case of a hierarchically porous zeolite β. This work develops a facile approach to obtain a highly oriented thin zeolite membrane with enhanced separation properties