ChemCatChem最新文献

The cycloaddition of epoxides with CO₂ not only represents a crucial pathway for producing cyclic carbonates but also contributes to the reduction of CO₂ emissions. In this cycloaddition reaction, heterogeneous catalysts are urgently desired to facilitate product separation. Herein, a dual-functional heterogeneous catalyst was fabricated by covalently attaching crown ether units to graphene oxide support and subsequent complexation with KI. The as-synthesized heterogeneous catalyst (i.e., GO-DAB18C6-KI) possesses abundant hydroxyl groups and nucleophilic sites (I⁻), which can synergistically activate the epoxides. When applied to the cycloaddition of epoxides with CO₂, this GO-DAB18C6-KI heterogeneous catalyst exhibits high catalytic activity and excellent substrate suitability, affording up to 99% yield of ethylene carbonate under solvent-free conditions. Remarkably, this heterogeneous catalyst can be reused for at least five cycles without significant activity loss.

As a major byproduct of biodiesel production, the selective hydrogenolysis of glycerol into high-value 1,3-propanediol (1,3-PDO) has been brought into focus for sustainable biorefineries. Among various catalytic systems, Pt-WO_x-based catalysts have emerged as promising systems owing to their exceptional selectivity toward 1,3-PDO. In this work, a series of Pt/WO_x/Al₂O₃ catalysts with modulated WO_x loadings was synthesized to elucidate the structure-activity relationships governing Pt-WO_x synergy. Our findings reveal that WO_x not only modulates Pt dispersion and generates electron-deficient Pt sites but also promotes Brönsted acid species generation, and thus collectively enhances the selectivity toward 1,3-PDO, supported by structural characterization correlated with catalytic performance indicative of a bifunctional mechanism.

This study reports nitrogen-deficient CN (Nv-CN) derivatives, synthesized from various nitrogen-rich precursors, as highly efficient photocatalysts for the selective aerobic oxidation of benzyl alcohol to benzaldehyde under visible-light irradiation. Comprehensive structural and photophysical analyses confirmed that defect-engineering significantly alters both the framework and electronic structure of CN. Among the derivatives, Nv-CN(C) prepared from cyanamide exhibited the highest density of N-vacancies, mid-gap states, and polar surface functionalities, which collectively enhanced visible-light harvesting, charge separation, and the adsorption and electron transfer to molecular oxygen, leading to efficient generation and stabilization of reactive oxygen species. Compared to its pristine analogue, Nv-CN(C) achieved near-complete benzyl alcohol conversion (96%) with > 99% selectivity toward benzaldehyde. Mechanistic investigations employing ROS scavengers identified a cooperative pathway involving superoxide radicals ($$), singlet oxygen (¹O₂), and photogenerated holes as the dominant oxidative species, while hydroxyl radicals (•OH) played only a minor role. According to the ¹³C CP-MAS NMR analysis, the defective regions of CN(C) are mainly located at the outer nitrogen atoms of the heptazine rings, which play an important role as active sites. Substrate scope studies confirmed the broad applicability of Nv-CN(C) to both electron-rich and electron-deficient benzyl alcohol derivatives, maintaining high selectivity across diverse substrates.

Up to now, high performance high-temperature denitrification catalyst has been rarely systematically studied and elucidated. The reduction in the number of active sites, attributed to the agglomeration and growth of active nanoparticles at high temperature, which is a key factor limiting the activity of NH₃-SCR catalysts. In this work, a novel Ce/WZrTiO₂ catalyst is designed, and Zr, W species are doped into the lattice of the TiO₂, which effectively inhibits the phase transformation of TiO₂ from anatase to rutile and stabilizes the surface chemistry of the catalyst at high-temperature. Meanwhile, the interaction between Zr and W species increases the surface acidity of the catalyst, which is beneficial to improve the activity of the catalyst at high temperatures. Importantly, a new active site Ce³⁺-O-W⁶⁺ was formed on Ce₅/W₁₀Zr₁₀TiO₂ at high temperature, which compensated for the reduction in the number of active sites attributed to CeO₂ agglomeration, and enabled Ce₅/W₁₀Zr₁₀TiO₂ to realize the dynamic coordination of active sites, so that Ce₅/W₁₀Zr₁₀TiO₂ can maintain a high NO_x conversion. The NO_x conversion of Ce₅/W₁₀Zr₁₀TiO₂ exceeds 80% in a wide temperature range of 240–520 °C. Even when 20 vol% H₂O/150 ppm SO₂ was introduced, the NO_x conversion remained basically stable within 12 h. Combining with DFT calculation and in-situ DRIFTS analysis, the anti-poisoning mechanism of Ce/WZrTiO₂ catalyst in the high-temperature NH₃-SCR reaction process has been clearly elucidated. This study provides important theoretical basis for future exploration and design of high-temperature denitrification catalysts.

Amidst growing energy demands and environmental concerns, photocatalytic water splitting for hydrogen production offers a sustainable solution, yet efficient photocatalyst design remains challenging. This work addresses the limitations of graphitic carbon nitride (g-C₃N₄), such as restricted light absorption, low surface area, and poor charge separation, by innovatively engineering its nanostructure. In this study, we report a hydrogen bond-mediated strategy to construct hollow g-C₃N₄ nanotubes (HCNT) via supramolecular pre-organization of melamine and cyanuric acid (CA) within ethylene glycol (EG), followed by calcination. Synergistic hydrogen bonding between EG and CA directs precursor curvature, enabling the formation of well-defined nanotubes with a significantly enlarged specific surface area (102.24 m² g⁻¹), enhanced hydrophilicity, optimized band structure, and superior charge separation efficiency. Consequently, the developed HCNT catalyst achieves an exceptional visible-light photocatalytic H₂ evolution rate of 14,409 µmol g⁻¹ h⁻¹, representing an 11-fold enhancement over bulk g-C₃N₄ and surpassing most reported g-C₃N₄-based catalysts. Our work establishes a green, template-free morphology-engineering paradigm through rational hydrogen bond manipulation, advancing the design of efficient photocatalysts for solar fuel generation.

The transesterification reaction of glycerol with dimethyl carbonate (DMC) into glycerol carbonate presents an attractive route for simultaneous biodiesel by-product valorization and indirect CO₂ utilization. In this study, a heterogeneous catalyst was developed for this reaction by grafting 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) on mesoporous SBA-16 silica (TBD@SBA-16), combining strong basicity with high surface area and structural stability. Various physicochemical characterizations (BET, TGA, FTIR, NMR, SAXS, TEM) confirmed the successful formation, functionalization, and thermal stability of samples. The forward reaction was identified as endothermic and entropy-driven, with an activation energy of 23.3 kJ/mol in the presence of homogeneous TBD, as validated by kinetic and thermodynamic analyses. This reaction was monitored for the influence of reaction parameters, including catalyst loading, reaction time, temperature, and DMC/glycerol molar ratio. Under optimal conditions (3 wt% catalyst, 90 °C, 2 h, 4:1 DMC: glycerol molar ratio), glycerol conversion reached 97% with glycerol carbonate yield exceeding 98%. The grafted catalyst displayed higher selectivity and operational practicality compared to homogeneous TBD. Reusability studies over five successive cycles revealed just a minor activity loss (∼4%) and low TBD leaching. These findings highlight the efficiency and stability of TBD@SBA-16 as a viable heterogeneous catalyst for the selective synthesis of glycerol carbonate.

Surface modification of TiO₂ with single-atom catalysts (SACs) is an effective strategy for enhancing photocatalytic efficiency. However, thorough characterization of SACs at the atomic scale remains challenging. X-ray absorption spectroscopy (XAS) offers unique advantages for the in-depth analysis of TiO₂-supported SACs. By employing XAS, the local atomic structure, oxidation state, and electronic properties of the SACs, as well as the underlying photocatalytic mechanism, can be revealed. Herein, we present a short review on the application of XAS in studying TiO₂-supported SACs. We first elucidate the key role of XAS in simultaneously probing the structure and electronic properties of monometallic SACs across different periods. Next, we discuss XAS studies of bimetallic SACs from the perspective of each constituent element and highlight the element-specific capabilities of XAS for analyzing multi-element SACs. Finally, we demonstrate how in situ XAS can effectively monitor structural and electronic property changes in SACs under real photocatalytic reaction conditions. Overall, this review highlights the unique advantages of XAS in achieving a more comprehensive understanding of the structure−property relationships in SACs, ultimately aiding the rational design of future photocatalysts. Additionally, we provide practical suggestions for utilizing XAS more efficiently in the analysis of various SAC systems.

The oxidative fluorination of a ternary CZMg (Cu/ZnO/MgO) methanol catalyst resulted in a 5%–10% catalyst improvement within the first 3 to 4 days on a CO₂/3 H₂ stream reaching a stable and improved performance over 14 days on stream with respect to methanol productivity (at 40 bar, 250 °C, GHSV 19,800 NL kgcat⁻¹ h⁻¹). By contrast the powerful commercial (but more expensive) CZZ (Cu/ZnO/ZrO₂) and the industrially used CZA (Cu/ZnO/Al₂O₃) system optimized for CO/CO₂/H₂ streams lost 30% (CZA) / 12% (CZZ) of their initial methanol productivity and were surpassed in productivity by a fluorinated CZMg system within a few hours (CZZ) or after a few days on stream (CZA). This (fluorinated) CZMg catalyst system was characterized using methods including XPS, XAS, in situ pXRD, in situ EPR, and HRTEM. Hence, oxidative fluorination of the pristine CZMg system reduced the apparent activation energy for CO₂ hydrogenation E_A,app from 52 to 43 kJ mol⁻¹ (CZMg versus CZMg_F1250), removed the volcano shape of the methanol production under integral conversion in a stoichiometric (1 + x)H₂ / (CO_x)-variation stream (x = 1…2) and led to stable performance even with a CO₂-rich or pure CO₂-stream with stoichiometric amounts of H₂ present (at 40 bar, 250 °C, GHSV 19,800 NL kgcat⁻¹ h⁻¹). This long-term stability is most likely attributed to the formation of mixed oxo fluorides MgO_1-xF_2x during oxidative fluorination. Magnesium and fluoride are presumably incorporated into the ZnO_1-x overgrowths of the Cu nanoparticles, stabilize them against sintering and apparently prevent the catalyst from deactivation by water, thus acting as a structural support.

Electrocatalytic C–N coupling using gaseous pollutants NO and CO offers a promising alternative to conventional industrial urea synthesis. However, designing efficient electrocatalysts remains challenging due to the complexity of multi-step reactions, which yield diverse products. Herein, based on density functional theory (DFT) calculations, we explore Cu and p-block atoms (B, Al, and Ga) anchored on graphitic carbon nitride as novel heteronuclear double-atom catalysts (DACs) for urea synthesis from NO and CO. The reactants are stably adsorbed on the DACs, while strong d–p orbital hybridization facilitates effective activation and efficient C–N coupling. Among the candidates, CuB@g-C₃N₄ and CuGa@g-C₃N₄ exhibit particularly promising performance, with limiting potentials of −0.55 V and −0.36 V, respectively. Furthermore, these catalysts significantly suppress competing reactions, including the hydrogen evolution reaction (HER) and the formation of *NOH, *COH, and *CHO intermediates, ensuring high selectivity. Our work not only highlights highly efficient p-d DACs for electrocatalytic urea production but also provides a theoretical framework in catalyst design.

Conventional catalytic methodologies for the cycloaddition of CO₂ into epoxides predominantly rely on transition metal-based catalysts in conjunction with detrimental halide-containing cocatalysts. Thus, developing metal and halide-free catalysts that function under ambient conditions is highly desirable. The current research endeavours to synthesize a pyrimidine-based bifunctional organocatalyst via a facile one-step Schiff-base condensation reaction. The synthesized organocatalyst efficiently transforms a wide range of epoxides (35 different epoxides, including 6 challenging internal epoxides) into cyclic carbonates with a minimal catalyst loading of just 0.1 mol% under mild conditions (60 °C–100 °C, atmospheric CO₂ pressure) without solvents and cocatalysts. Comprehensive experimental investigations elucidate how the catalyst facilitates the reaction, emphasizing the intricate interplay of hydrogen (H) bonding, spatial arrangement, and catalyst-substrate interactions. The meticulous analysis, using advanced spectroscopic techniques and density functional theory (DFT) calculations, reveals that hydroxyl groups play a pivotal role in epoxide activation through H-bonding interactions, whereas the imine nitrogen facilitates CO₂ activation through the formation of a carbamate intermediate. These two interactions collectively accelerate the overall catalytic process. Furthermore, the catalyst exhibits remarkable recyclability over six consecutive catalytic cycles. Therefore, this study underscores the potential of rationally designed metal-free catalysts in advancing sustainable catalysis through carbon capture and utilization technologies.