Catalysis Science & Technology最新文献

A useful strategy for the co-polymerization of ethylene and functional olefins relies on palladium catalysts, as palladium typically shows in contrast to many other metals a high tolerance to a variety of functional groups. Here we have prepared a set of palladium complexes containing a N,N-bidentate coordinating bis(pyridinium amidate) (bisPYA) ligand. Ligand variation included either para- or an ortho-pyridinium amidate arrangement, with the pyridinium site either sterically flexible or locked through a dimethyl substitution ortho to the amidate. Activation of these complexes with NaBArF in the presence of ethylene indicated that sterically locked ligand structures promoted ethylene conversion and produced polymeric materials. In particular, complex 4d with an ortho-pyridinium amidate bisPYA ligand was active with a production of 10.8 kg polyethylene per mol palladium at room temperature and 1 bar ethylene. Synthesis of the complexes in the presence of K₂CO₃ or Ag₂CO₃ afforded adducts in which the K⁺ or Ag⁺ ion is bound by the two oxygens of the bisamidate core, thus leading to trimetallic Pd⋯K⋯Pd complexes. Such adduct formation indicates a dual role of NaBArF in halide abstraction and metal sequestration, thus rationalizing the need for 2.5 equivalent of NaBArF per palladium complex for effective polymerization.

The interaction between Cu and Zr is crucial for the performance of Cu-based catalysts in CO₂ hydrogenation. This study compares a series of Cu–Zr catalysts with different Cu–Zr ratios prepared at two flow rates in a microreactor. The structural evolution of the catalysts was investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (CO₂-TPD). It is found that the enhanced mixing in the microreactor improves component dispersion in the Cu–Zr precipitates, leading to smaller CuO crystallite sizes in the calcined oxides and more Cu–Zr interfaces in the reduced catalysts, which thereby exhibit superior catalytic performance. Additionally, superior mixing in the coprecipitation enables the catalyst to achieve abundant Cu–Zr interfaces even at lower Zr content, whereas catalysts prepared under inferior mixing require higher Zr content to establish adequate Cu–Zr interfaces.

Industrial ammonia (NH₃) production is predominantly achieved by the Haber–Bosch process, which consumes substantial energy and emits significant CO₂. The electrochemical nitrate reduction reaction (NO₃RR) presents a promising alternative to the Haber–Bosch process due to its environmentally benign nature. Developing highly active, selective, and stable electrocatalysts for the NO₃RR remains a focal point of contemporary research. In this work, the d-band center of the Cu₁Ni₁@GO catalyst was strategically modulated via an alloying approach, endowing it with balanced adsorption and desorption capabilities for reaction intermediates. This optimization resulted in exceptional performance, achieving an ammonia yield of 3.47 mg h⁻¹ cm⁻² and a Faraday efficiency (FE) of 85.2% at an overpotential of −0.5 V vs. RHE. Theoretical calculations confirmed the d-band center shift in Cu₁Ni₁@GO and its profound influence on intermediate adsorption dynamics and NO₃RR activity, offering crucial insights for the rational design of advanced alloy catalysts. By elucidating the synergistic effect in CuNi @GO composites, this study offers insights for designing efficient catalysts for nitrate reduction to ammonia, with promising applications in sustainable energy and environmental protection.

Bifunctional Zn-modified HZSM-5 catalysts demonstrate excellent catalytic performance in ethylene aromatization. However, they often undergo rapid deactivation owing to the loss of zinc species. Here, we show that the activity of surface zinc species in Zn/ZSM-5 for ethylene aromatization can be enhanced by fine-tuning the synthesis parameters during the preparation of Zn-modified HZSM-5. Specifically, the Zn/ZSM-5 catalyst prepared under weakly acidic conditions exhibited superior anti-carbon deposition and anti-Zn loss properties compared to that prepared under alkaline conditions. We suggest that the reactivity of surface zinc species for ethylene aromatization was enhanced because of the formation of a hexacoordinated ZnOH⁺ species structure, which serves as the catalytic active center to facilitate dehydrogenation, thereby exhibiting a positive correlation with the catalyst's aromatization performance.

The extreme toxicity of nerve agents highlights the urgent need for catalytic materials that can operate under realistic, dry conditions. Zirconium-based MOF-808 is effective for the aqueous-phase hydrolysis of these agents, but its performance drops sharply in solid-phase environments due to poisoning by tightly bound bidentate products. Here, we introduce a manganese (Mn) single-atom modified version of MOF-808 that overcomes this limitation. Unlike the native framework, Mn@MOF-808 achieves catalytic turnover (turnover number or TON > 1) for nerve agent and simulant degradation under ambient, unbuffered, and solvent-free conditions. The Mn sites help avoid product inhibition by favoring monodentate interactions over bidentate coordination. Experimental results show sustained reactivity during degradation of sarin and its simulants, and DFT calculations support reduced desorption energies of bound products. This work marks the first example of a MOF-based catalyst demonstrating turnover in solid-phase nerve agent degradation and moves a step closer to practical chemical threat mitigation.

Chemical recycling can convert polymers into useful chemicals. Polyolefins can be chemically recycled into their monomers and other hydrocarbons via catalytic pyrolysis or mechano-chemistry. While pyrolysis catalysts are highly active but not selective, mechano-chemistry is more selective but lacks quantitative yields. To address these issues and unlock potential synergies, we herein investigate the effect of zeolite-based pyrolysis catalysts on the conversion of polypropylene during ball milling at room temperature and elevated temperatures, as well as during catalytic kneading. Initially, zeolite catalysts are highly active in the ball mill and their activity is dependent on acid site density. However, they deactivate quickly under the harsh collisions in the ball mill due to the collapse of their crystalline framework. To circumvent deactivation, we used the concept of direct mechano-catalysis and immobilized the zeolite material on surface-roughened grinding spheres. This effectively protects active sites against contact with the container wall or other grinding spheres while allowing contact with polypropylene, leading to sustained catalytic activity and requiring much lower amounts of zeolite. In addition, catalytic kneading of molten polypropylene was investigated as an alternative where energy input is more uniformly distributed in the volume and time compared to highly localized and forceful impacts within the ball mill. Although a synergy of thermo- and mechano-chemical effects was observed initially, the energy intake was limited by a fast decline of melt viscosity due to polymer backbone cleavage. Mechano-chemical conversion and catalytic pyrolysis of polyolefins are two promising platforms for chemical recycling. Our study illustrates the difficulties in combining both and possible pathways to overcome these challenges.

Hydrogen transfer via water splitting with an iron catalyst presents challenging opportunities. In this note, we have introduced a novel approach for the transfer hydrogenation of internal acetylenes, yielding highly chemo- and stereo-selective E-stilbenes using an earth-abundant iron-catalyst and water as a green hydrogen source. The established protocol showed a broad applicability towards various directing acetylenes, while maintaining high tolerance for functional groups. The method avoids the common issue of isomerization and over-reduction to alkanes. Interestingly, the method is cost-effective for the synthesis of deuterated substrates too. The iron-hydride formed as an intermediate is responsible for the semi-hydrogenation of alkynes, and it is validated through DFT calculations.

Anthraquinone (AQ) hydrogenation, a critical industrial step for hydrogen peroxide production, is catalyzed by γ-Al₂O₃-supported Pd catalysts. However, the reaction mechanism remains poorly understood due to unresolved structural evolution of the active Pd phase under hydrogenation conditions. Thus, hydrogenated Pd surface/cluster structures and their catalytic impact on AQ hydrogenation are elucidated by particle swarm optimization (PSO) and density functional theory (DFT) in this study. Under industrial conditions, β-PdH_0.5 and Pd₉H₄ are identified as thermodynamically stable phases for Pd(111) surfaces and γ-Al₂O₃-supported clusters, respectively. Hydrogenation induces subsurface H penetration and lattice distortion at high coverage. Electronic structure analysis reveals d-band center downshifting on hydrogenated Pd(111) weakens adsorbate bonding, while supported Pd₉H₄ enhances AQ adsorption. Reaction pathway studies demonstrate that clean Pd(111) favors aromatic ring hydrogenation, yielding dihydroanthraquinone (H₂AQ). In contrast, hydrogenated Pd(111) achieves a lower energy barrier at the rate-determining step and higher selectivity for target anthrahydroquinone (AH₂Q) via carbonyl oxygen hydrogenation. This high selectivity is attributed to steric effects that suppress side reactions. Pd₉H₄ clusters promote undesired OAN formation due to restricted H diffusion. Large particles (>2 nm), represented by hydrogenated Pd(111), enable efficient AH₂Q production but exhibit low atom utilization, while small clusters (<1 nm), represented by the Pd₉H₄ cluster, suffer from low activity and poor selectivity. Particle size and hydrogenated surface structure are identified as critical factors for optimizing Pd-based catalysts, enhancing activity and selectivity in industrial anthraquinone hydrogenation processes.

Photocatalytic alcohol dehydrogenation is a promising technique for the simultaneous production of hydrogen (H₂) and carbonyl compounds. In this study, titanium(IV) oxide (TiO₂) photocatalysts co-loaded with rhodium oxide (RhO_x) and platinum (Pt) particles were successfully prepared via a multi-step process involving the equilibrium adsorption of Rh ions, post-calcination, and Pt colloid impregnation. In the resulting system, RhO_x acts as a visible-light sensitizer, while Pt serves as the hydrogen evolution co-catalyst. A series of RhO_x/TiO₂–Pt samples were synthesized by systematically varying the calcination temperature of the RhO_x/TiO₂ precursor prior to Pt loading. These materials were then evaluated for photocatalytic alcohol dehydrogenation under visible light irradiation. The effects of calcination temperature on the electronic states and light absorption characteristics of the Rh species were investigated, along with their influence on photocatalytic activity. The RhO_x/TiO₂–Pt photocatalysts exhibited efficient dehydrogenation of various alcohols. In particular, benzyl alcohol was selectively converted to benzaldehyde and H₂ in a stoichiometric ratio, with no over-oxidation observed. This work demonstrates a novel strategy for coupling oxidative organic synthesis with hydrogen production under visible light, offering new insights into photocatalyst design for sustainable energy and chemical synthesis.

Extensive research in heterogeneous catalysis has highlighted the potential of non-noble metal catalysts for efficient alkane dehydrogenation. Although Ni species are widely employed for activating C–H bonds, their utilization as active catalysts for alkane dehydrogenation is limited by thermal sintering, coke deposition, and undesired side reactions that compromise the stability and selectivity of the catalyst. This work reports the synthesis of a C₆₀-modified nickel-based catalyst (C₆₀–Ni/SiO₂), which was employed for the direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). Owing to its tailored electronic structure, the C₆₀–Ni/SiO₂ catalyst reached an ST formation rate of 2.7 mmol g⁻¹ h⁻¹ while maintaining a selectivity exceeding 99.0%. XRD, Raman, TEM, and XPS characterization revealed that the C₆₀ served as an electronic promoter, which decreased the electron density of Ni species without disturbing its crystalline structure. Such modulation of the electronic structure of Ni centers effectively suppresses the cracking side reactions and coke formation, thereby improving both selectivity and stability of the catalyst during EB DDH. The present work introduces a promising Ni-based catalyst for EB dehydrogenation, potentially offering prospects for developing advanced non-noble metal catalysts for alkene production via the DDH process.