Tuning Interfacial Electronic Properties of Palladium Oxide on Vacancy-Abundant Carbon Nitride for Low-Temperature Dehydrogenation

CO2 reduction reaction on Sc-doped nanocages as catalysts

CONTEXT

The catalytic ability of Sc-doped C46 and Sc-doped Al23P23 as catalysts of CO2-RR to create the CH4 and CH3OH is investigated. The mechanisms of CO2-RR are examined by theoretical methods and ΔGreaction of reaction steps of CO2-RR mechanisms are calculated. The overpotential of CH4 and CH3OH production on Sc-doped C46 and Sc-doped Al23P23 is calculated. The Sc atoms of Sc-doped C46 and Sc-doped Al23P23 can adsorb the CO2 molecule as the first step of CO2-RR. The CH4 is produced from hydrogenation of *CH3O and the *CO → *CHO reaction step is the rate limiting step for CH4 production. The CH3OH can be formed on Sc-doped C46 and Sc-doped Al23P23 by *CO → *CHO → *CH2O → *CH3O → CH3OH mechanism and HCOOH → *CHO → *CH2O → *CH3O → CH3OH mechanism. The Sc-C46 and Sc-Al23P23 can catalyze the CO2-RR to produce the CH4 and CH3OH by acceptable mechanisms.

METHODS

Here, the structures are optimized by PW91PW91/6-311+G (2d, 2p) and M06-2X/cc-pVQZ methods in GAMESS software. The frequencies of nanocages and their complexes with species of CO2-RR are investigated by mentioned methods. The transition state of each reaction step of CO2-RR is searched by Berny method to find the CO2-RR intermediates. The ∆Eadsorption of intermediates of CO2-RR on surfaces of nanocages is calculated and the ∆Greaction of reaction steps of CO2-RR is calculated.

Atomically Dispersed Pd Sites on ZrO2 Hybridized N-Doped Carbon for Efficient Suzuki–Miyaura Reaction

Researchers studying heterogeneous catalysis are intrigued by single-atom catalysts (SACs) due to their ultrahigh atomic utilization. However, only a few reports on SAC-catalyzed classical organic transformations are available. In this work, atomically dispersed Pd sites are confined to a ZrO2 hybridized N-doped carbon skeleton with a smart design. UiO-66-NH2 is used to anchor Pd atoms by the coordination of the donor atoms including lone pairs of electrons and metal atoms. Subsequently, the in situ introduction of ZrO2 doping is achieved using pyrolysis, which helps improve the catalytic performance by modulating the electronic state. The Pd@ZrO2/N–C catalyst obtained from the unique design exhibits a high yield (99%) in eco-friendly media with an extremely low noble metal dosage (0.03 mol% Pd) for the Suzuki reaction. Moreover, Pd@ZrO2/N–C remains highly active after being reused several times and possesses versatility in a variety of substrates. This strategy offers a feasible alternative to designing SACs with atomically dispersed noble metals for heterogeneous reactions.

Phosphorus doped and defect modified graphitic carbon nitride for boosting photocatalytic hydrogen production

The enhancement of photogenerated carrier separation efficiency is a significant factor in the improvement of photocatalyst performance in photocatalytic hydrogen evolution. Heteroatom doping and defect construction have been considered valid methods to boost the photocatalytic activity of graphitic carbon nitride. Herein, we report graphitic carbon nitride modified with P doping and N defects (PCN_x), and the effects of doping and defects were investigated in photocatalytic H₂ evolution. Its hydrogen evolution rate can reach up to about 59.1 μmol h^-1, which is more than 123.1 times higher than pristine graphitic carbon nitride under visible light irradiation. Importantly, the apparent quantum efficiency reaches 8.73% at 420 nm. The excellent performance of the PCN_x photocatalyst was attributed to the following aspects: (I) the large BET surface area of PCN_x affords more active sites for H₂ production and (II) the introduction of P and N defects can accelerate the charge carrier separation and transfer efficiency, leading to more efficient photocatalytic hydrogen production. The photocatalyst showed obviously enhanced activities.

Boosting Photosynthetic H2O2 of Polymeric Carbon Nitride by Layer Configuration Regulation and Fluoride-Potassium Double-Site Modification

Photocatalytic hydrogen peroxide (H₂O₂) production will become a burgeoning strategy for solar energy utilization by selective oxygen reduction reaction (ORR). Polymeric carbon nitride (PCN) shows relatively high two-electron ORR selectivity for H₂O₂ production but still limited low H₂O₂ production efficiency due to slow exciton dissociation. Herein, we constructed a heptazine/triazine layer stacked carbon nitride heterojunction with fluorine/potassium (F/K) dual sites (FKHTCN). The introduction of F/K not only can regulate layer components to enhance the charge separation efficiency but, more importantly, also optimize the adsorption of surface oxygen molecules and intermediate *OOH during H₂O₂ production. Consequently, FKHTCN efficiently improves the photocatalytic H₂O₂ production rate up to 3380.9 μmol h^-1 g^-1, nearly 15 times higher than that of traditional PCN. Moreover, a production-utilization cascade system was designed to explore their practical application in environmental remediation. This work lays out the importance of engineering a layer-stacked configuration and active sites for enhancing photocatalysis.

Construction and excellent photoelectric synergistic anticorrosion performance of Z-scheme carbon nitride/tungsten oxide heterojunctions

The use of heterojunctions for metal corrosion protection is a highly innovative and challenging task. Based on the composition and structure of tungsten oxide-based heterojunctions, Z-scheme heterojunctions were designed and synthesized by the electrostatic self-assembly method using energy band-matched g-C₃N₄ and WO₃ materials. Applied in the field of anticorrosion, they overcame the problems of poor reduction ability and transmission inefficiency of traditional materials. The Z-scheme heterojunctions ensured unidirectional electron transfer, while the aggregation of the retained strongly reduced electrons on the surface of the iron substrates provided a strong driving force for retarding corrosion occurrence. Meanwhile, the inherent shielding properties of the two-dimensional material g-C₃N₄ and the confinement of chloride ions as an electroactive layer hindered the penetration of the corrosive solution. After being corroded for 72 h, the corrosion impedance of the g-C₃N₄/WO₃ heterojunction system was improved by 640.11% compared with the epoxy resin coating. In addition, the g-C₃N₄/W₁₈O₄₉ heterojunction was synthesized by using mixed valence tungsten oxide, which overcame the problems of photogenerated electron yield and lifetime, and enhanced the anticorrosion performance compared with a single g-C₃N₄ phase. This research provided ideas for designing efficient and environmentally friendly heterojunction anticorrosion materials.

Synthesis of Bifunctional Ru-Pd Catalysts Following the Double Reduction Method: Hydrogenation/Dehydrogenation of Liquid Organic Hydrogen Carriers

Catalytic hydrogenation and dehydrogenation of liquid organic hydrogen carriers (LOHCs) have attracted immense attention as this is the most attractive strategy for the storage and release of hydrogen. Heterogeneous catalysts...

Dehydrogenation of Cycloalkanes over N-Doped Carbon-Supported Catalysts: The Effects of Active Component and Molecular Structure of the Substrate

Efficient dehydrogenation of cycloalkanes under mild conditions is the key to large-scale application of cycloalkanes as a hydrogen storage medium. In this paper, a series of active metals loaded on nitrogen-doped carbon (M/CN, M = Pt, Pd, Ir, Rh, Au, Ru, Ag, Ni, Cu) were prepared to learn the role of active metals in cycloalkane dehydrogenation with cyclohexane as the model reactant. Only Pt/CN, Pd/CN, Rh/CN and Ir/CN can catalyze the dehydrogenation of cyclohexane under the set conditions. Among them, Pt/CN exhibited the best catalytic activity with the TOF value of 269.32 h⁻¹ at 180 °C, followed by Pd/CN, Rh/CN and Ir/CN successively. More importantly, the difference of catalytic activity between these active metals diminishes with the increase in temperature. This implies that there is a thermodynamic effect of cyclohexane dehydrogenation with the synthetic catalysts, which was evidenced by the study on the activation energy. In addition, the effects of molecular structure on cycloalkane dehydrogenation catalyzed by Pt/CN were studied. The results reveal that cycloalkane dehydrogenation activity and hydrogen production rate can be enhanced by optimizing the type, quantity and position of alkyl substituents on cyclohexane.