Catalysis Science & Technology最新文献

Tuning the chemoselectivity of a supported metal heterogeneous catalyst during hydrogenation reactions is extremely important and challenging, often achieved by changing the metal or adding homogeneous additives to the reaction. Tuning of the chemoselectivity for a given reaction over a supported metal catalyst, with a better understanding of the nature of the active site, is highly valuable to both academia and industry. Here, we report a support induced chemoselectivity (SIC) switch between Pt/TiO₂ and Pt/Nb₂O₅ during the hydrogenation of 3-nitrostyrene with high chemoselectivity. Specifically, 0.2%Pt/TiO₂ selectively reduces the -NO₂ group to form 3-vinyl aniline, whereas 0.2%Pt/Nb₂O₅ selectively reduces the C[double bond, length as m-dash]C bond to form 3-ethylnitrobenzene. Advanced characterisation and ab initio calculations indicate that the observed differences in selectivity could be because of support-dependent interactions at Pt-support interfacial sites, which modify the local electronic environment and adsorption behaviour of the substrate. These results suggest that the support-metal interfacial sites could potentially play a key role in controlling and switching chemoselectivity during 3-nitrostyrene hydrogenation. These results demonstrate that, in addition to modifying the metallic sites, the chemoselectivity of supported Pt nanoparticles can also be tuned by changing the support, offering an additional approach for designing new chemoselective supported metal catalysts for 3-nitrostyrene hydrogenation.

Efficient heterogeneous catalysts have been developed owing to their advantages in reusability and sustainability. However, conventional catalysts composed of fine or nanosized particles suffered from a high pressure drop and catalyst loss in fixed-bed or batch reactors, limiting their practical applications. In this work, macro-mesoporous hierarchical silica monoliths were fabricated via an emulsion-templating method with easily available silica colloids as building blocks. Post-grafting of -SH groups and subsequent oxidation with H₂O₂ generated hierarchically porous silica monoliths with sulfonic acid sites. The resulting H-(0.9) SO₃-75%-silica exhibited an interconnected macroporous morphology with a pore volume of 2.67 cm³ g^-1 and a surface area of 232.7 m² g^-1. NH₃ temperature programmed desorption analysis confirmed the presence of acidic sites, while the sulfonic acid site density was estimated from the sulphur content determined by elemental analysis. The H-(0.9) SO₃-75%-silica catalyst demonstrated high performance in both oleic acid-rich fatty acid feedstock esterification and glycerol acetalization. The free fatty acid conversion reached 95% at 90 °C in 6 h with a turnover frequency (TOF) of 32.1 h^-1, while glycerol acetalization achieved 98.6% conversion and 98% solketal selectivity at 20 °C within 30 min (TOF = 1155 h^-1). Moreover, the catalyst maintained high activity over five consecutive cycles, and its monolithic form allowed easy separation from the reaction system, indicating its potential suitability for practical continuous or fixed-bed applications.

Fixed-bed reactors are widely employed in heterogeneous catalysis, providing controlled gas flow, efficient gas-solid contact, homogeneous heating and quantitative analysis of catalytic performance. Here, we present a modular platform for operando scanning electron microscopy (OSEM) inspired by these key design principles of fixed-bed reactors, while remaining compatible with the constraints of SEM operation. We demonstrate the system's capabilities using copper oxide reduction and the technologically relevant CO₂ hydrogenation over a zincian malachite catalyst as benchmark reactions. We further explore how pressure influences product distribution during CO₂ hydrogenation over a spinel catalyst. By combining the imaging ability of electron microscopy with quantitative performance analysis in the proposed configuration, the platform unlocks catalytic insights during activation, reaction and deactivation that were previously inaccessible to conventional SEM approaches.

The dry reforming of methane (DRM) converts two major greenhouse gases, CH₄ and CO₂, into a synthesis gas (H₂ and CO). Bimetallic DRM catalysts, such as CoPt catalysts, offer structural and electronic tunability and, in turn, potentially a higher product formation rate than monometallic systems. Bimetallic systems can occur as random or ordered alloys (intermetallics), yet it is currently unclear to what extent atomic ordering can affect the intrinsic DRM kinetics. Here, we investigate the structural dynamics of CoPt nanoparticles for DRM using operando X-ray diffraction coupled with X-ray absorption spectroscopy (XRD-XAS), and correlate our structural findings with the observed kinetics. Under DRM conditions, the intermetallic L1₀-CoPt phase is stable at 700 °C, whereas a random alloy phase dominates at 800 °C. Kinetic analysis of CH₄ activation reveals a change in the apparent activation energy around this structural transition, i.e., a higher apparent activation energy for the disordered structure, and a lower apparent activation energy for the ordered intermetallic phase. These results provide evidence that the DRM activity of the bimetallic CoPt system is structure-sensitive; a high degree of atomic ordering enhances CH₄ activation.

Photocatalysis remains a crucial field to investigate. It is seen as a powerful tool which allows more efficient, relatively greener and economical chemical reactions. Nevertheless, catalysts usually include rare and pricy metals, with supplies being highly dependent on geopolitics. Thus, chemists turned their attention to alternatives such as natural products or organic molecules, conciliating performances, polyvalence and easy access. Among the promising candidates, polyaromatics rise as robust species and precursors of stable radicals which could be used as photocatalysts. Triangulenes are polycyclic hydrocarbons which are expected to shine in multiple fields such as spintronics, energy and data storage or semiconductors. This work reports the studies of photocatalytic reactions including the trioxotriangulene (TOT). Through the studies of three reactions ranging from sulfoxidation to dehalogenation of 4-bromoacetophenone, including the reduction of nitroaromatics, we discuss the performances, the polyvalence and the mechanism of the systems including this triangulene. As a proof of concept, we conclude this work with a description of "a sequential RBG photoredox catalytic system" where the three reactions are successively and selectively performed in a "one-pot" fashion.

The dry reforming of methane (DRM) converts two greenhouse gases, CH₄ and CO₂, into a synthesis gas, providing a route for CO₂ valorization. Bimetallic nanoparticles offer a versatile strategy to improve the performance of monometallic catalyst systems by altering the electronic and local structures of the active metal sites. Here, we investigate SiO₂-supported, Co _x Pt_1-x nanoalloys with varying composition (x = 0.1-0.9) for DRM. Structural characterization using pair distribution function analysis and electron microscopy revealed that the bimetallic nanoparticles feature fcc-type alloy structures with diameters of 1-2 nm, highly dispersed on SiO₂. Catalytic evaluation under DRM conditions shows that Pt-rich catalysts exhibit the highest initial CH₄ conversion rates, while increasing the Co content lowers the DRM activity and the H₂ : CO ratio due to an enhanced reverse water-gas shift activity. When normalized per Pt loading, the initial (20 min) CH₄ consumption rates remain largely unchanged, confirming Pt as the primary active site for CH₄ activation. Pt-rich catalysts deactivate rapidly with time on stream via coking (graphite), whereas alloying with Co improves their stability by suppressing carbon deposition. However, Co oxidation induces dealloying and contributes to deactivation, in particular at low temperatures (750 °C). Intermediate Co : Pt ratios, i.e., Co_0.5Pt_0.5-Co_0.7Pt_0.3, yield the best performing catalyst as they strike a balance between activity, H₂ : CO ratio, and stability, enabling an effective utilization of expensive Pt.