Catalysis Science & Technology最新文献

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.

Understanding how substrate structure alters an enzyme's conformational landscape is central to catalyst design. Using single-molecule electronic sensors, we reveal how substitutions on an HDAC8 substrate modulate the enzyme's underlying catalytic dynamics. We demonstrate that a trifluoroacetyl group accelerates catalysis, while a Boc cap and an allosteric activator synergistically simplify the kinetic pathway by stabilizing productive conformations. These findings provide direct, real-time insight into how substrate-induced conformational dynamics control enzyme catalysis.

Adipic acid plays a crucial role as a key constituent of polymers. The electrocatalytic strategy of KA oil (cyclohexanol and cyclohexanone) electrooxidation has been recognized as an effective way to produce adipic acid compared to the commercial thermocatalytic oxidation method using corrosive nitric acid and producing nitrous oxide. Herein, we report a ligand covalent modification strategy to enhance the current density of KA oil electrooxidation by NiMn-LDH modified with dodecyl triethoxysilane (NiMn-LDH-DTES) via a silanization reaction. For example, NiMn-LDH-DTES exhibits 1.7-fold current density for cyclohexanol electrooxidation compared to pure NiMn-LDH. The cyclohexanol conversion rate and H₂ production rate reach 0.044 mmol cm⁻² h⁻¹ and 43.2 mL cm⁻² h⁻¹ at 1.52 V vs. RHE, which are 1.7- and 1.5-fold higher than those of NiMn-LDH, respectively. And at high cyclohexanol conversion of 96.2%, the yield of adipic acid reaches 79.4% with FE of 83.4% and selectivity of 94.4%. NiMn-LDH-DTES demonstrated its efficiency for cyclohexanone oxidation with enhanced performance. We confirmed that the modification of NiMn-LDH by DTES can promote the generation and exposure of more reactive sites, and also facilitates the adsorption of KA oil, thus enabling the high reaction rate.

In this work, activation oxidants like H₂O₂ and peroxydisulfate (S₂O₈²⁻) were investigated in the presence of a recycled magnetite (rMG) obtained from Hymag'in company (France) both in the dark and under UVA light. The rMG is a micro-powder (0.5–1 μm particle size) predominantly composed of magnetite, but it also contains cubic γ-Fe₂O₃. Picloram (PIC) was employed as a model pollutant to investigate the performance of rMG. The effects of oxidants (type and concentration), light and water matrix were assessed. Better efficiencies were observed in systems containing peroxydisulfate (PDS) due to the better stability of sulfate radicals compared to hydroxyl radicals. In addition, iron leaching was observed in PDS-based systems, thus suggesting that homogeneous Fenton reactions increased the catalytic efficiency. The effect of light boosted the efficiency due to regeneration of Fe(II) by Fe(III) photolysis. The 0.2 g L⁻¹ rMG can completely degrade PIC under UVA light in the presence of PDS after only 2 h of reaction. In wastewater effluents, rMG exhibited promising results with the removal of about 60% of PIC after 4 h, and rMG was significantly better than commercial magnetite. The present work highlights the feasibility of using wastes from the iron industry to treat wastewater, which is an added value for the circular economy of water.