Chinese Journal of Catalysis最新文献

Utilizing single atom sites doping into metal oxides to modulate their intrinsic active sites, achieving precise selectivity control in complex organic reactions, is a highly desirable yet challenging endeavor. Meanwhile, identifying the active site also represents a significant obstacle, primarily due to the intricate electronic environment of single atom site doped metal oxide. Herein, a single atom Cu doped TiO₂ catalyst (Cu₁-TiO₂) is prepared via a simple “colloid-acid treatment” strategy, which switches aniline oxidation selectivity of TiO₂ from azoxybenzene to nitrosobenzene, without using additives or changing solvent, while other metal or nonmetal doped TiO₂ did not possess. Comprehensive mechanistic investigations and DFT calculations unveil that Ti-O active site is responsible for triggering the aniline to form a new PhNOH intermediate, two PhNOH condense to azoxybenzene over TiO₂ catalyst. As for Cu₁-TiO₂, the charge-specific distribution between the isolated Cu and TiO₂ generates unique Cu₁-O-Ti hybridization structure with nine catalytic active sites, eight of them make PhNOH take place spontaneous dissociation to produce nitrosobenzene. This work not only unveils a new mechanistic pathway featuring the PhNOH intermediate in aniline oxidation for the first time but also presents a novel approach for constructing single-atom doped metal oxides and exploring their intricate active sites.

Precise control of the local environment and electronic state of the guest is an important method of controlling catalytic activity and reaction pathways. In this paper, guest Pd NPs were introduced into a series of host UiO-67 MOFs with different functional ligands and metal nodes, the microenvironment and local electronic structure of Pd is modulated by introducing bipyridine groups and changing metal nodes (Ce₆O₆ or Zr₆O₆). The bipyridine groups not only promoted the dispersion Pd NPs, but also facilitated electron transfer between Pd and UiO-67 MOFs through the formation of Pd-N bridges. Compared with Zr₆ clusters, the tunability and orbital hybridisation of the 4f electronic structure in the Ce₆ clusters modulate the electronic structure of Pd through the construction of the Ce-O-Pd interfaces. The optimal catalyst Pd/UiO-67(Ce)-bpy presented excellent low-temperature activity towards dicyclopentadiene hydrogenation with a conversion of > 99% and a selectivity of > 99% (50 °C, 10 bar). The results show that the synergy of Ce-O-Pd and Pd-N promotes the formation of active Pd^δ+, which not only enhances the adsorption of H₂ and electron-rich C=C bonds, but also contributes to the reduction of proton migration distance and improves proton utilization efficiency. These results provide valuable insights for investigating the regulatory role of the host MOFs, the nature of host-guest interactions, and their correlation with catalytic performance.

Designing a step-scheme (S-scheme) heterojunction photocatalyst with vacancy engineering is a reliable approach to achieve highly efficient photocatalytic H₂ production activity. Herein, a hollow ZnO/ZnS S-scheme heterojunction with O and Zn vacancies (V_{O, Zn}-ZnO/ZnS) is rationally constructed via ion-exchange and calcination treatments. In such a photocatalytic system, the hollow structure combined with the introduction of dual vacancies endows the adequate light absorption. Moreover, the O and Zn vacancies serve as the trapping sites for photo-induced electrons and holes, respectively, which are beneficial for promoting the photo-induced carrier separation. Meanwhile, the S-scheme charge transfer mechanism can not only improve the separation and transfer efficiencies of photo-induced carrier but also retain the strong redox capacity. As expected, the optimized V_{O, Zn}-ZnO/ZnS heterojunction exhibits a superior photocatalytic H₂ production rate of 160.91 mmol g^–1 h^–1, approximately 643.6 times and 214.5 times with respect to that obtained on pure ZnO and ZnS, respectively. Simultaneously, the experimental results and density functional theory calculations disclose that the photo-induced carrier transfer pathway follows the S‐scheme heterojunction mechanism and the introduction of O and Zn vacancies reduces the surface reaction barrier. This work provides an innovative strategy of vacancy engineering in S-scheme heterojunction for solar‐to‐fuel energy conversion.

Heterojunction has been widely used in vibration-driven piezocatalysis for enhanced charges separation, while the weak interfaces seriously affect the efficiency during mechanical deformations due to prepared by traditional step-by-step methods. Herein, the intimate contact interfaces with shared S atoms are ingeniously constructed in SnS₂/SnS anchored on porous carbon by effective interface engineering, which is in-situ derived from temperature-dependent self-transformation of SnS₂. Benefiting from intimate contact interfaces, the piezoelectricity is remarkably improved due to the larger interfacial dipole moment caused by uneven distribution of charges. Importantly, vibration-induced piezoelectric polarization field strengthens the interfacial electric field to further promote the separation and migration of charges. The dynamic charges then transfer in porous carbon with high conductivity and adsorption for significantly improved piezocatalytic activity. The degradation efficiency of bisphenol A (BPA) is 6.3 times higher than SnS₂ and H₂ evolution rate is increased by 3.8 times. Compared with SnS₂/SnS prepared by two-step solvothermal method, the degradation efficiency of BPA and H₂ evolution activity are increased by 3 and 2 times, respectively. It provides a theoretical guidance for developing various multiphase structural piezocatalyst with strong interface interactions to improve the piezocatalytic efficiency.

The conversion of acetone derived from biomass to isobutene has attracted extensive attentions. In comparison with Brønsted acidic catalyst, Lewis acidic catalyst could exhibit a better catalytic performance with a higher isobutene selectivity. However, the catalyst stability remains a key problem for the long-running acetone conversion and the reasons for catalyst deactivation are poorly understood up to now. Herein, the deactivation mechanism of Lewis acidic Y/Beta catalyst during the acetone to isobutene conversion was investigated by various characterization techniques, including acetone-temperature-programmed surface reaction, gas chromatography-mass spectrometry, in situ ultraviolet-visible, and¹³C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy. A successive aldol condensation and cyclization were observed as the main side-reactions during the acetone conversion at Lewis acidic Y sites. In comparison with the low reaction temperature, a rapid formation and accumulation of the larger cyclic unsaturated aldehydes/ketones and aromatics could be observed, and which could strongly adsorb on the Lewis acidic sites, and thus cause the catalyst deactivation eventually. After a simple calcination, the coke deposits could be easily removed and the catalytic activity could be well restored.

Two-dimensional covalent organic frameworks (2D COFs) feature extended π-conjugation and ordered stacking sequence, showing great promise for high-performance photocatalysis. Periodic atomic frameworks of 2D COFs facilitate the in-plane photogenerated charge transfer, but the precise ordered alignment is limited due to the non-covalent π-stacking of COF layers, accordingly hindering out-of-plane transfer kinetics. Herein, we address a chiral induction method to construct a parallelly superimposed stacking chiral COF ultrathin shell on the support of SiO₂ microsphere. Compared to the achiral COF analogues, the chiral COF shell with the parallel AA-stacking structure is more conducive to enhance the built-in electric field and accumulates photogenerated electrons for the rapid migration, thereby affording superior photocatalytic performance in hydrogen evolution from water splitting. Taking the simplest ketoenamine-linked chiral COF as a shell of SiO₂ particle, the resulting composite exhibits an impressive hydrogen evolution rate of 107.1 mmol g^–1 h^–1 along with the apparent quantum efficiency of 14.31% at 475 nm. Furthermore, the composite photocatalysts could be fabricated into a film device, displaying a remarkable photocatalytic performance of 178.0 mmol m^–2 h^–1 for hydrogen evolution. Our work underpins the surface engineering of organic photocatalysts and illustrates the significance of COF stacking structures in regulating electronic properties.

Defect engineering has become a promising approach to improve the performance of hydrogen evolution reaction (HER) catalysts. Non-noble transition metal-based catalysts (TMCs) have shown significant promise as effective alternatives to traditional platinum-group catalysts, attracting considerable attention. However, the industrial application of TMCs in electrocatalytic hydrogen production necessitates further optimization to boost both catalytic activity and stability. This review comprehensively examines the types, fabrication methods, and characterization techniques of various defects that enhance catalytic HER activity. Key advancements include optimizing defect concentration and distribution, coupling heteroatoms with vacancies, and leveraging the synergy between bond lengths and defects. In-depth discussions highlight the electronic structure and catalytic mechanisms elucidated through in-situ characterization and density functional theory calculations. Additionally, future directions are identified, exploring novel defect types, emphasizing precision synthesis methods, industrial-scale preparation techniques, and strategies to enhance structural stability and understanding the in-depth catalytic mechanism. This review aims to inspire further research and development in defect-engineered HER catalysts, providing pathways for high efficiency and cost-effectiveness in hydrogen production.

Since the D-band center theory was proposed, it has been widely used in the fields of surface chemistry by almost all researchers, due to its easy understanding, convenient operation and relative accuracy. However, with the continuous development of material systems and modification strategies, researchers have gradually found that D-band center theory is usually effective for large metal particle systems, but for small metal particle systems or semiconductors, such as single atom systems, the opposite conclusion to the D-band center theory is often obtained. To solve the issue above, here we propose a bonding and anti-bonding orbitals stable electron intensity difference (BASED) theory for surface chemistry. The newly-proposed BASED theory can not only successfully explain the abnormal phenomena of D-band center theory, but also exhibits a higher accuracy for prediction of adsorption energy and bond length of intermediates on active sites. Importantly, a new phenomenon of the spin transition state in the adsorption process is observed based on the BASED theory, where the active center atom usually yields an unstable high spin transition state to enhance its adsorption capability in the adsorption process of intermediates when their distance is about 2.5 Å. In short, the BASED theory can be considered as a general principle to understand catalytic mechanism of intermediates on surfaces.

Hematite (α-Fe₂O₃) constitutes one of the most promising photoanode materials for oxygen evolution reaction (OER). Recent research on Fe₂O₃ have found a fast OER rate dependence on surface hole density, suggesting a multisite reaction pathway. However, the effect of heteroatom in Fe₂O₃ on the multisite mechanism is still poorly understood. Herein we synthesized Fe₂O₃ on Ti substrates (Fe₂O₃/Ti) to study the oxygen intermediates of OER by light-dark electrochemical scans. We identified the Fe-OH species disappeared and Ti-OH intermediates appeared on Fe₂O₃/Ti when pH = 11−14, which significantly improved the OER performance of Fe₂O₃/Ti. Combined with the density functional theory calculations, we propose that Ti atom acts as cocatalyst site and captures proton from neighboring Fe-OH species under highly alkaline condition, thereby promoting the coupling of Fe=O and reducing the energy barrier of the non-electrochemical step. Our work provides a new insight into the role of heteroatom in OER multisite mechanism based on clarifying the reaction intermediates.

Developing Cu single-atom catalysts (SACs) with well-defined active sites is highly desirable for producing CH₄ in the electrochemical CO₂ reduction reaction and understanding the structure-property relationship. Herein, a new graphdiyne analogue with uniformly distributed N₂-bidentate (note that N₂-bidentate site = N^N-bidentate site; N₂ ≠ dinitrogen gas in this work) sites are synthesized. Due to the strong interaction between Cu and the N₂-bidentate site, a Cu SAC with isolated undercoordinated Cu-N₂ sites (Cu_1.0/N₂-GDY) is obtained, with the Cu loading of 1.0 wt%. Cu_1.0/N₂-GDY exhibits the highest Faradaic efficiency (FE) of 80.6% for CH₄ in electrocatalytic reduction of CO₂ at −0.96 V vs. RHE, and the partial current density of CH₄ is 160 mA cm⁻². The selectivity for CH₄ is maintained above 70% when the total current density is 100 to 300 mA cm⁻². More remarkably, the Cu_1.0/N₂-GDY achieves a mass activity of 53.2 A/mg_Cu toward CH₄ under −1.18 V vs. RHE. In situ electrochemical spectroscopic studies reveal that undercoordinated Cu-N₂ sites are more favorable in generating key *COOH and *CHO intermediate than Cu nanoparticle counterparts. This work provides an effective pathway to produce SACs with undercoordinated Metal-N₂ sites toward efficient electrocatalysis.