Journal of Catalysis最新文献

Herein, a green and highly efficient strategy was developed to fabricate lead-free perovskite Cs₃Bi₂Br₉ through solid-state mechanochemical process under mild conditions, wherein the effects of rotation speed, grinding duration and ball-to-powder ratio on the formation of Cs₃Bi₂Br₉ powers were investigated. The photocatalytic performance of the as-prepared Cs₃Bi₂Br₉ powers was evaluated for catalyzing oxidative coupling of various aldehydes or alcohols to anhydrides using O₂ as the sole oxidant. Furthermore, a probable reaction mechanism was proposed basing on series active species capture experiments.

Transition metal-catalyzed cycloaromatization reactions of diarylalkynes offer a swift and versatile approach to synthesizing a wide array of polycyclic aromatic compounds. However, the specific mechanism of Pd-catalyzed C–H/C–H aromative carbonylation of diarylalkynes, particularly those bearing adjacent functional groups, remains a relatively unexplored area. Herein, we present a palladium-catalyzed C–H/C–H aromative carbonylation of diarylalkynes, which proceeds through an exclusive 6-endo-dig carbocyclization pathway, followed by the incorporation of CO to yield carbonyl compounds. This methodology provides a novel and efficient route for generating complex aromatic structures, thus expanding the potential applications in organic synthesis.

Photocatalytic CO₂ reduction to fuels and chemicals is a promising pathway towards carbon resource recovery. Herein, three isomorphic Fe-porphyrinic MOFs, Zr₆O₄(OH)₄(Fe-TCPP)₃ (MOF-525, Fe-TCPP = iron 5,10,15,20-tetra(4-carboxyphenyl)-porphyrin), Zr₆O₄(OH)₄(Fe-TCPP-NO₂)₃ (MOF-525-NO₂, Fe-TCPP-NO₂ = iron 5,10,15,20-tetra(2-nitro-4-carboxyphenyl)-porphyrin), and Zr₆O₄(OH)₄(Fe-TCBPP-NO₂)₃ (MOF-526-NO₂, Fe-TCBPP-NO₂ = iron 5,10,15,20-tetra[4-(4′-carboxyphenyl)-2-nitrophenyl]-porphyrin) were synthesized and employed as photocatalysts for CO₂ reduction. Among them, MOF-525-NO₂ exhibited the highest catalytic activity with CO and H₂ yields of 10.36 and 0.46 mmol·g⁻¹ without any photosensitizer under visible light. Mechanism investigations suggested that the micro-environments of these MOFs were adjusted by introducing porphyrinic fragments with different lengths and functional groups, resulting in stronger CO₂ affinity, faster photocurrent response, and efficient photogenerated electron-hole separation and transfer, which finally promoted the efficiency for photocatalytic CO₂ reduction.

Tuning the catalyst’s activity and selectivity is usually achieved by modifying the electronic structure through strategies such as alloying, doping, strain, and ligand modification, but inevitably accompanied by geometric structure changes of catalysts. It is challenging to modify a catalyst’s electronic structure without changing its geometric structure. Recent studies found that the second-order ferromagnetic to paramagnetic (FM-PM) phase transition could promote catalytic performance without altering the geometric structures of active sites, which was also known as the magneto-catalytic effect (MCE). However, the understanding of the MCE is still incomplete. Herein, we conducted systematic density functional theory (DFT) calculations to clarify the complex reaction mechanisms for conversions of nitrogen-containing small molecules on both FM and PM Ni (1 1 1) surfaces. Our microkinetic modeling (MKM) results demonstrate that FM-PM phase transition promotes the N₂O decomposition activity of FM Ni catalyst but decreases its activity for NO decomposition while showing a negligible influence on the activity of ammonia decomposition. These results indicate the promotion, inhibition, and disappearance mechanisms of MCE on the catalytic activity, which further changes the selectivity of different products. We anticipate the MCE will work as an effective strategy for fine-tuning the activity and selectivity of ferromagnetic catalysts in heterogeneous catalysis, providing an extra basis for rational catalyst design.

The 12-connected UiO-66 MOFs with great defect regulation ability have attracted significant attention due to the easily tunable electronic structure and surface electrostatic potential distribution of metal nodes. In this density functional theory (DFT) study, we systematically explored the effect of bi-active site types as the frustrated Lewis pair (FLP) and classical Lewis pair (LP) as well as metal elements of secondary building units (SBUs) on the catalytic hydrogenation of dicyclopentadiene (DCPD) to tetrahydrodicyclopentadiene (THDCPD). These design strategies effectively modulate the frontier molecular orbital energy level that determines the binding strength between MOFs and adsorbed species *H^δ+-H^δ- and charges transfer before and after H₂ chemisorption. We also found that the heterolytic H₂ adsorption energy and charges transfer linearly correlate with the energy barrier. In order to unravel the clear-cut designing strategies and further simplify computational complexity, we firstly proposed the ADCH charges difference between the Lewis acid and the Lewis base centers (ΔQ_M-O) as an intrinsic descriptor for catalytic activity of DCPD into THDCPD, which can effectively describe the reactivity and electrostatic effects of oppositely charged bi-active sites in the system. Furthermore, the defective UiO-66(Ce) MOF with moderate ΔQ_M-O effectively balance the contradiction between the barriers of two primitive reaction: the heterolytically H₂ dissociation to *H^δ+-*H^δ- and the desorption of the active hydrogen species to hydrogenate 8,9-dihydrodicyclopentadiene (8,9-DHDCPD), resulting in the optimal catalytic performance. This work provides a deep understanding of the catalytic mechanism of MOFs with multiple active sites and might open up avenues for the rational design of novel hydrogenation catalysts.

Ti-Beta zeotypes, possessing three-dimensional 12-membered ring pore-opening channels, have shown some superior catalytic performance in the epoxidation of bulky cycloalkenes with hydrogen peroxide (H₂O₂) in comparison with other titanosilicate zeotypes. However, some further improvement on the catalytic activity and selectivity of Ti-Beta zeotypes is still demanded for the industrialization of cycloalkenes epoxidation. In the present work, the catalytic performance of Ti-Beta in cyclohexene epoxidation was significantly improved via the transformation of their closed Ti(OSi)₄ sites into the open Ti(OSi)₃OH ones by a simple NH₄F treatment. Based on the extensive characterization results, it is found that the NH₄F-treated Ti-Beta zeotypes with open Ti(OSi)₃OH sites, named OH-Ti-Beta, possess a stronger Lewis acidity that is favorable to the production of cyclohexene oxide (CHO) from the epoxidation of cyclohexene with H₂O₂, compared to the parent Ti-Beta with closed Ti(OSi)₄ sites. Moreover, OH-Ti-Beta catalysts are reusable after the calcination of the deactivated zeotypes. Hence, it is expected that the current developed NH₄F treatment can obtain efficient OH-Ti-Beta catalysts industrially applied in cyclohexene epoxidation.

The design and modification of heterojunction photocatalysts to enhance efficient interfacial charge transfer and superior photocatalytic performance are fundamental objectives in the field of solar-light-driven energy conversion and production. This study presents a novel S-scheme heterojunction which features lattice-matched morphological hetero-nanostructures, composing of two-dimensional (2D) graphitic carbon nitride (CN) loaded with uniformly distributed and size-consistent 2D nano-rhombohedral α-Fe₂O₃ (Fe₂O₃ NR/CN). The directional charge transfer in the lattice-matched S-scheme heterojunction was confirmed using a combination of in situ irradiated X-ray photoelectron spectroscopy, metal deposition experiments, electron paramagnetic resonance, and density functional theory calculations. The optimized heterojunction demonstrates exceptional photocatalytic activity, achieving a hydrogen generation rate that surpasses those of g-C₃N₄ and α-Fe₂O₃ alone by factors of 2.1 and 7, respectively. Additionally, this heterojunction exhibits an excellent styrene conversion rate of 94.1 % and a styrene epoxidation selectivity of 95.3 % under light irradiation at 80 °C using tert-butyl hydroperoxide (TBHP) as the oxidant. The incorporation of uniformly distributed nano-rhombohedral α-Fe₂O₃ particles with g-C₃N₄ successfully constructs an unobstructed interfacial pathway to form the lattice-matched S-scheme heterojunction, enabling efficient separation of photogenerated carriers. This unique structure provides a valuable reference for dual-functional photocatalytic reactions.

The local environment of active sites is a key focus in the field of redox chemistry research. Here, the manipulation of lattice oxygen in La_0.8Sr_0.2Fe_0.8M_0.2O₃ facilitates the chemical looping redox oxidative cracking (CL-ROC) process. Among the samples, La_0.8Sr_0.2Fe_0.8Cu_0.2O₃ exhibits exceptional olefin yield (61.74 %) in the cyclohexane CL-ROC reaction. The integration of experiments and density theory calculations shows that the introduction of foreign redox-inert cations into the B-sites of the matrix can effectively alter the configuration of FeO₆, improve the activation of lattice oxygen, and enhance the activity of surface oxygen and the mobility of bulk lattice oxygen. Furthermore, the improvement in olefin selectivity is closely linked to the suppression of peroxide products formation, a result of increased oxygen vacancy and decreased bulk lattice oxygen. These findings exemplify the feasibility to manipulate the activity of lattice oxygen in perovskite oxides by adjusting the distortion of the BO₆ in ABO₃ perovskite structures.