Search Results (7,160)

Steric effects refer to the effect of the size and spatial arrangement of atoms or groups on the reactions, interactions, and catalytic activities of molecules. The incorporation of Cl (chlorine) and Br (bromine) atoms as substituents into phthalocyanine (Pc) structures can have important catalytic effects. These effects arise mainly from their electronic and steric properties, which influence the behavior of the central metal ion and the overall catalyst performance. In this work, Co(II)PcQBr₂ was synthesized and characterized by spectral techniques. The catalytical activity of Co(II)PcQBr₂ was then evaluated for the oxidation of benzyl alcohol. The effects of the substrate/catalyst ratio, oxidant/catalyst ratio, oxidant type and temperature on the oxidation reaction of benzyl alcohol were investigated. Both catalysts exhibited high TON, TOF and total conversion yields in the presence of H₂O₂ as the oxidant at 50 °C. (substrate/oxidant/catalyst:1000/500/1). When the total product conversions were calculated for both catalysts, Co(II)PcQBr₂ was found to have a lower product conversion (88.7%, with a TON of 914 and a TOF of 457 ) than Co(II)PcQCl₂. Moreover, Co(II)PcQCl₂ was determined to have higher selectivity of benzyl benzoate (94.0%, with a TON of 940 and a TOF of 470 ). The larger size of the Br atom compared to that of the Cl atom was observed to reduce catalytic activity. Considering the size of the Cl atom, it was concluded that steric effects favor the formation of benzyl benzoate by inhibiting possible side reactions, thus increasing the catalytic activity. Full article

The global dissemination of carbapenem resistance is predominantly facilitated by plasmid-mediated carbapenemase genes, notably blaOXA-48-like genes. A comprehensive understanding of their evolutionary relationships and structural conservation is essential for monitoring their spread and informing therapeutic strategies. This study aimed to investigate the phylogenetic relationships and structural conservation of blaOXA-48-like carbapenemase genes in multiple Gram-negative bacterial species. We analysed blaOXA-48-like carbapenemase sequences obtained from a hospital in Pakistan and compared them with globally reported variants retrieved from GenBank. Carbapenemase gene sequences (blaOXA-48-like, blaNDM, and blaVIM) were analyzed using maximum-likelihood phylogenetics (MEGA11, Tamura–Nei model, 1000 bootstrap replicates). Comparative global sequences were retrieved from GenBank. Structural modeling of blaOXA-48-like genes was performed using SWISS-MODEL Workspace with the template PDB 3HBR, followed by validation using GMQE, QMEANDisCo, and Ramachandran plot analyses. Phylogenetic analysis revealed a tight clustering of blaOXA-48-like genes across A. baumannii, K. pneumoniae, and E. meningoseptica, showing high similarity to globally distributed plasmid-associated sequences. Structural modeling demonstrated strong conservation of the enzyme, with preserved catalytic residues (Ser70, Lys73, Ser118, Trp157, and Tyr211) and minimal structural deviation (RMSD < 0.3 Å). blaOXA-48-like carbapenemases exhibit strong phylogenetic conservation and structural stability across species and regions, consistent with the horizontal dissemination of blaOXA-48-like genes across bacterial hosts. These findings indicate that blaOXA-48-like carbapenemases have high evolutionary stability. Full article

The development of efficient catalysts for the glycerol oxidation reaction (GOR) is crucial for advancing direct glycerol fuel cells. This study provides mechanistic insights into the glycerol electro-oxidation reaction (GOR) on Co@Pt/C, Ni@Pt/C, and Sn@Pt/C catalysts using in situ FTIR spectroscopy. While the structural and electrochemical properties of these materials have been previously reported, their reaction pathways and product selectivity under alkaline conditions remain unclear. Electrochemical performance was evaluated through cyclic voltammetry (CV) and chronoamperometry (1.0 M KOH + 1.0 M glycerol), revealing that the bimetallic catalysts exhibited superior catalytic activity compared to Pt/C. Co@Pt/C demonstrated the highest performance, with a 7.5-fold increase in current density relative to Pt/C, followed by Sn@Pt/C (3.4-fold) and Ni@Pt/C (2.8-fold). In situ FTIR analysis identified key oxidation products, including C3, C2, and C1 species, with evidence of both partial and complete oxidation. These findings demonstrate that the core metal plays a key role in governing reaction pathways and C–C bond cleavage, providing important insights for the rational design of anode materials in direct glycerol fuel cells. Full article

The development of highly efficient, stable, and cost-effective non-precious metal electrocatalysts to replace conventional platinum-based materials holds profound significance for accelerating the commercialization of advanced energy conversion devices, such as zinc–air batteries (ZABs). Herein, we propose a facile and highly efficient strategy to prepare a defect-rich, highly active nitrogen-doped porous carbon-based electrocatalyst (denoted U-Fe-N-C, urea-assisted iron–nitrogen–carbon material), via high-temperature co-pyrolysis of heme with urea. Our results demonstrate that urea not only serves as an excellent nitrogen source during pyrolysis, introducing abundant topological defects and heteroatom doping sites, but also induces the carbon substrate to form a hierarchical sponge-like porous structure with a high specific surface area. This unique microenvironment effectively prevents the agglomeration of iron species at high temperatures, achieving enhanced dispersion of iron species stabilized within the nitrogen-rich carbon matrix. Electrochemical evaluations reveal that under the optimal synthesis conditions (a precursor mass ratio of 1:3, calcination at 900 °C), U-Fe-N-C exhibits excellent oxygen reduction reaction (ORR) catalytic performance, delivering a half-wave potential of 0.731 V vs. RHE, and shows long-term operational durability that significantly surpasses that of commercial Pt/C. Furthermore, liquid rechargeable zinc–air batteries assembled with U-Fe-N-C as the air cathode deliver remarkable cycling stability, operating for up to 270 h of charge–discharge cycling without noticeable performance degradation. This study not only provides useful insights into the mechanisms of pore formation and assistance but also offers a practical perspective for the rational design and scalable synthesis of high-performance metal–nitrogen–carbon (M-N-C) electrocatalysts. Full article

Monometallic nanoparticles tend to aggregate and exhibit limited catalytic performance, rendering them inadequate for high-efficiency electrocatalytic applications. In this study, a green and mild liquid-phase reduction method was employed, using sodium borohydride to simultaneously reduce graphene oxide (GO) and metal precursors. This approach enabled the uniform and highly dispersed loading of silver–copper bimetallic alloy nanoparticles (Ag_1−xCu_x NPs) onto the surface of reduced graphene oxide (RGO). By tuning the Ag/Cu molar ratio, the size, composition, and morphology of the nanoparticles were precisely controlled. Characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed that GO was efficiently reduced to RGO, and the bimetallic nanoparticles were uniformly distributed on the RGO surface in an alloy state with small particle size and no obvious agglomeration. A strong interfacial interaction between the metal nanoparticles and the support was also observed. Electrochemical tests demonstrated that the composite exhibits excellent electrocatalytic activity toward the reduction of H₂O₂. Notably, the reduction peak current at the Ag_0.5Cu_0.5NPs/RGO modified electrode was 1.8 and 2.3 times higher than those at the monometallic Ag/RGO and Cu/RGO electrodes, respectively. These results provide a reliable theoretical basis and a viable research route for the controllable synthesis of low-cost, high-performance electrocatalytic nanocomposites and their application in electrochemical H₂O₂ sensing. Full article

4-Ethylguaiacol (4-EG) is a volatile phenolic compound associated with smoky, woody, and spicy aroma notes in fermented foods and beverages, including Baijiu. In this study, a 4-EG-producing strain, designated JN11, was obtained by screening isolates from Baijiu pit mud and identified as Bacillus coagulans based on morphological, physiological, biochemical, and 16S rRNA analyses. In sorghum juice medium, strain JN11 produced 271.6 ± 2.7 μg/L 4-EG. To investigate the upstream decarboxylation step involved in volatile phenol formation, the phenolic acid decarboxylase gene, BcPAD, was cloned and heterologously expressed in Escherichia coli BL21(DE3). The BcPAD gene comprises 504 bp and encodes a 167-amino-acid protein. Recombinant BcPAD exhibited maximal activity at pH 6.0 and 50 °C and retained more than 60% residual activity after 5 h at 30–40 °C. Fe³⁺ increased enzyme activity to 115.36% of the control, whereas Zn²⁺ markedly inhibited enzyme activity and SDS completely inactivated the enzyme. BcPAD showed the highest activity toward p-coumaric acid, with a specific activity of 460.6 ± 18.3 U/mg and a catalytic efficiency (Kcat/Km) of 12.1 ± 1.4 mM⁻¹·s⁻¹, while lower activities were observed toward caffeic acid and ferulic acid, and no activity was detected toward sinapic acid. Homology modeling and molecular docking suggested that the superior catalytic performance toward p-coumaric acid may be related to favorable hydrogen-bonding interactions and substrate orientation within the active site. Although 4-EG production was observed during fermentation by strain JN11, BcPAD was biochemically characterized as a phenolic acid decarboxylase likely responsible for the upstream formation of vinyl derivatives in the proposed pathway. These findings improve our understanding of phenolic acid decarboxylases from B. coagulans and provide a basis for further investigation of the roles of strain JN11 and BcPAD in volatile phenol formation during Baijiu production. Full article

In recent years, synergistic effects between inorganic clay minerals (e.g., montmorillonite, sepiolite, kaolinite) and bio-based flame retardants (e.g., chitosan-based, lignin-based, phytate-based) have achieved certain progress in the area of polymer flame retardancy. The effects of bio-based flame retardants are exerted through mechanisms such as catalytic char generation and vapour-phase hindrance. However, they have limitations when used alone, including insufficient thermal stability and the need for a high dosage. Inorganic clays form physical barriers through their layered or tubular structures. The high thermal stability of these structures suppresses heat and mass transfer, thereby offsetting the shortcomings of bio-based flame retardants. This synergistic combination greatly improves the flame retardancy of polymer composites, often strengthening their mechanical performance in the process. It therefore offers great potential for the design of multifunctional, eco-friendly flame-retardant polymer composites. Nevertheless, a systematic review of the synergistic mechanisms, fabrication approaches and application progress of different inorganic clay minerals when combined with various bio-based flame retardants is still lacking. Therefore, this article offers a comprehensive review of the current developments of synergistic systems that incorporate various primary clays, such as sepiolite and montmorillonite, with bio-based flame retardants for usage in polymers. Before this, the synergistic flame-retardant mechanism and the key preparation techniques of the composite system were explained in detail. Finally, this article puts forward solutions to the current challenges and sets out prospects for innovation in the designing of flame-retardant materials and the optimisation of processes. The aim is to promote the sustainable growth of efficient, eco-friendly flame-retardant materials. Full article

In the Arabian Gulf region, saltwater desalination is considered to be a significant process in producing clean water. This paper presents a sustainable, combined process for upgrading a Doha reverse osmosis (RO) plant in Kuwait. A pilot-scale microbial desalination cell (MDC) stack is proposed as a pre-treatment unit prior to the RO process in order to improve plant performance. A cost–benefit analysis is conducted for the combined system to emphasize the significance of the MDC–RO process. In RO, the expected energy consumption is 2.6–13 kWh per m³ of desalinated water, whereas using MDC can reduce this to about 0.52–5.3 kWh/m³. Moreover, this new technology using catalytic MDCs can help in improving electric current production and reducing the amount of rejected brine and membrane fouling in the RO process. The electric current is improved by reducing MDCs’ internal resistance using a reduced graphene oxide/polyaniline composite-coated stainless steel mesh cathode electrode. Layer-by-layer electro-deposition can be applied to achieve these coatings. An intermediate zeolite filter is proposed to mitigate RO membrane fouling. The combined system’s natural zeolite-membrane filter improves water purification. In this study, we assessed the combined MDC–RO process for upgrading the Doha plant’s performance in terms of quality, cost, and time. The suggested catalytic MDC, using efficient, low-cost materials as cathode electrodes with an equivalent daily cost of 0.01 USD/m³ and a desalination efficiency of about 40%, acts as an alternative to high-cost platinum metal electrodes. The results also indicate that the equivalent daily cost of energy consumption using the MDC process is about 0.03 USD/m³, whereas the investment cost is about 0.4 USD/m³ daily for one year of cell operation. Full article

Driven by the growing demand for sustainable polymers, polylactic acid (PLA) has attracted increasing attention due to its renewable origin and biodegradability. Lactide, the key cyclic monomer for PLA production via ring-opening polymerization (ROP), plays a decisive role in determining the molecular weight, stereoregularity, and final performance of PLA materials. However, current lactide synthesis processes still face significant challenges, including competing side reactions under high-temperature and high-vacuum conditions, difficulties in controlling stereochemical purity, and relatively high energy consumption. In this review, recent advances in lactide synthesis are systematically analyzed by examining the two principal industrial routes: the one-step process based on the direct dehydration–cyclization of lactic acid (LA), and the two-step process involving prepolymerization of LA followed by depolymerization/cyclization of oligomeric intermediates. The reaction mechanisms, key intermediates, and major side reactions—including racemization, transesterification, and deep polycondensation—are discussed, together with the regulatory roles of catalytic systems and reaction–separation coupling strategies. Comparative analysis reveals that the one-step route offers advantages in process integration and potential energy efficiency, whereas the two-step route provides superior control over stereochemical purity and process stability. Future research directions focusing on green catalysts, process intensification, and sustainable lactide production are also highlighted. Full article

Polymeric materials face serious fire-safety challenges in construction, electrical and electronic devices, and aerospace because of their high heat release, melt-dripping tendency, and severe smoke and toxic emissions during burning. This review systematically summarizes the roles of nanofillers in the fire safety of polymer nanocomposites across three interconnected levels: functional mechanisms, regulatory factors, and macroscopic fire behavior. It focuses on four main mechanisms, namely physical barriers, catalytic charring, free-radical scavenging, and rheological network reconstruction, and further discusses how filler geometry, loading level, interfacial compatibility, dispersion state, and spatial orientation regulate fire-safety performance. By linking these factors to time to ignition, thermal stability, heat release, flame spread, and smoke emission and toxicity, the review clarifies the intrinsic structure–mechanism–property relationships. Current studies indicate that the fire-safety improvements provided by nanofillers do not arise from any single effect, but from their coupled regulation of heat transfer, mass transfer, radical reactions, and high-temperature rheology throughout thermal degradation, ignition, heat release, flame spread, and smoke and toxic-gas emission. Remaining challenges include the lack of unified evaluation criteria, limited in situ mechanistic evidence, and insufficient application-oriented rational design. Future work should establish verifiable, comparable, and predictive structure–mechanism–property relationships for polymer nanocomposites. Full article

Methane combustion over palladium-based catalysts is a critical process for reducing greenhouse gas emissions from lean-burn engines and natural gas installations, yet the role of oxide support in controlling both the population and the intrinsic reactivity of Pd active centres remains incompletely understood. In this work, Pd catalysts at two series of higher and lower loading were prepared on five oxide supports—Al₂O₃, CeO₂, SiO₂, TiO₂, and ZrO₂—and characterised by a complementary suite of techniques including SEM-EDX, XRD, BET, AAS, in situ CO-FTIR, DRIFTS with methanol as a probe molecule, and Raman spectroscopy. Catalytic activity testing revealed the order Pd/CeO₂ > Pd/ZrO₂ > Pd/Al₂O₃ > Pd/TiO₂ > Pd/SiO₂. In situ CO-FTIR site quantification showed that active site density spans nearly an order of magnitude across the series, with Pd/CeO₂ reaching 105.44 µmol g⁻¹ and Pd/Al₂O₃ only 11.63 µmol g⁻¹. Turnover frequency analysis revealed a striking inversion: Pd/Al₂O₃ exhibited the highest TOF (0.1327 s⁻¹), approximately six times greater than Pd/CeO₂ (0.0226 s⁻¹). DRIFTS/methanol profiling demonstrated that CeO₂ and ZrO₂ expose cooperative redox and basic centres that promote methane activation, while SiO₂ supports only weakly bound methoxy species, consistent with its lowest activity. These results establish that the oxide support simultaneously governs Pd dispersion—and hence site density—and the electronic environment of each Pd centre, thereby modulating intrinsic reactivity. High specific surface area alone does not guarantee catalytic performance, and rational support selection is therefore the decisive lever for optimising methane combustion catalysts at ultra-low Pd loadings. In all, our findings provide a quantitative, molecular-level framework that disentangles support-controlled site density from intrinsic site reactivity under identical reaction conditions. By combining in situ CO-FTIR, DRIFTS, and Raman spectroscopy with kinetic analysis on well-defined, high-purity oxide supports, this work transforms previously qualitative “support effects” in Pd-catalysed methane combustion into predictive structure–activity relationships. Full article

Background: Doramectin (CHC-B1) is an excellent antiparasitic drug produced by feeding cyclohexanecarboxylic acid (CHC) to Streptomycesavermitilis bkd⁻ mutants. AveC, a bifunctional enzyme encoded by aveC (sav_0940), catalyzes the stereospecific spiroketalization and selective dehydration of dihydroxy ketone polyketide intermediates and modulates both the yield and the proportion of avermectin/doramectin in Streptomyces avermitilis. In our previous work, we constructed a strain harboring a synthetic aveC* gene encoding ten amino acid mutations, which produced nearly pure doramectin. However, the doramectin yield achieved only approximately 60% of the total doramectin and CHC-B2 output observed in the parental strain. Methods: To investigate the roles of Ser138 and Ala139 of AveC in the biosynthesis of doramectin and avermectin, site-directed mutagenesis was performed at both sites. The production and proportion of avermectin and doramectin were determined using high-performance liquid chromatography (HPLC). AlphaFold2-based molecular docking simulations were used to interpret the results. Results: Among the tested mutants, S138G, S138T, and A139H exhibited the highest doramectin production, achieving 143.87%, 151.22%, and 153.36% of the control level, respectively. Unfortunately, almost none of the tested mutants showed a positive effect on avermectin production. Molecular docking simulations revealed distinct affinities of these mutants for the dihydroxy ketone polyketide intermediate, both with and without a cyclohexyl group. Notably, all three mutants displayed larger substrate-binding cavity volumes compared with the wild-type enzyme, which likely facilitates doramectin synthesis by effectively accommodating the cyclohexyl moiety. Docking results further indicated that Ser138 and Ala139 are positioned within the binding cavity but probably do not directly participate in the dehydration activity. Conclusions: These findings suggest that optimizing cavity size through residue substitutions can enhance substrate specificity for doramectin production while preserving catalytic functionality. Full article

An efficient catalyst for the reaction of ethanol–acetaldehyde into 1,3-butadiene (EATB) is prepared through the grafting of zirconia into a zeolite Beta lattice. The grafting is achieved through the dealumination of a zeolite framework by acid treatment followed by zirconia impregnation, leading to the substitution of aluminum in the zeolite framework by zirconia. The catalyst with zirconia grafted into the zeolite framework promotes desirable catalyst properties like high zirconium dispersion, stability, and the close proximity of Lewis acid, Bronsted acid, and medium basic sites. The phase, the coordination of zirconia, the location of the active center and the cooperative synergism were elucidated through various characterization techniques, including X-ray diffraction, Raman spectroscopy, N₂ adsorption, UV–vis spectroscopy, XPS, ²⁹Si MAS NMR, NH₃-TPD, Py-IR, CO-IR and CO₂-TPD. The catalytic results show that a suitable phase and content of zirconia were needed to improve the ethanol–acetaldehyde conversion, butadiene selectivity and catalyst stability. Among the catalysts, m+t-ZrO_x-Beta-H₂O-9020 (m = monoclinic, t = tetragonal ZrO₂ phase) achieved the best butadiene selectivity of 82–73% at the conversion of 100–66%, run over 200 h. The results allow us to propose a Lewis acid–medium basic pairing for the Si–O–Zr–O–Si group, where the adjacent Si-OH is the active center for reactions. Full article

In this work, the catalytic effect of a mechanochemically synthesized Co–Fe metal–organic framework (Co–Fe-MOF) on the thermal decomposition behavior of composite ammonium perchlorate–aluminum (AP-Al) systems was studied. The structural and morphological properties of the synthesized catalyst were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results confirmed the formation of a highly dispersed Co–Fe-MOF structure with a heterogeneous surface morphology and uniformly distributed active regions, as observed by SEM. The thermal decomposition behavior of the composites based on AP was studied using differential scanning calorimetry (DSC) at different heating rates. The addition of Co–Fe-MOF significantly affected the thermal decomposition process, moving the main exothermic decomposition step towards lower temperatures. At 5 wt.% of catalyst, the decomposition temperature decreased from 438–467 °C to 358–398 °C. The kinetic parameters were evaluated using the Kissinger and Ozawa–Flynn–Wall methods. The activation energy decreased from around 191–200 kJ·mol⁻¹ for pure AP and 184–194 kJ·mol⁻¹ for the AP-Al system to 95–109 kJ·mol⁻¹ after the introduction of 5 wt.% of Co-Fe-MOF. The observed catalytic activity is associated with accelerated electron transfer processes involving the redox couples Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺, which favor the decomposition of AP and the oxidation of aluminum. The results demonstrate that the mechanochemically synthesized Co–Fe-MOF is an effective catalyst to improve the thermokinetic performance of AP-based energetic systems. Full article

The selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) is of great importance for the production of dyes, pesticides, and pharmaceuticals, but it is often plagued by the undesired hydrodechlorination side reaction. In this work, we report a PtNi bimetallic catalyst supported on nano-sized LTL zeolite (PtNi/Nano-HL) for the selective hydrogenation of p-chloronitrobenzene under mild conditions. The catalyst was systematically characterized by X-ray diffraction (XRD), nitrogen sorption (N₂ sorption), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and ammonia temperature-programmed desorption (NH₃-TPD). The results reveal abundant oxygen vacancies (RIR = 0.73) and an optimized distribution of medium–strong acid sites on the catalyst surface, as well as electronic interaction between Pt and Ni, which collectively enhance the catalytic performance. Remarkably, the PtNi/Nano-HL catalyst achieves 100% conversion and over 99% selectivity for p-chloroaniline under ambient conditions (30 °C, 0.1 MPa H₂) using ethanol as a solvent. Even after 24 recycling runs, it retains 100% conversion and >93% selectivity, demonstrating excellent stability. Moreover, the catalyst requires an extremely low Pt loading (only 0.11 wt%) and exhibits good substrate universality for various substituted nitroarenes. This work provides a promising strategy for designing high-performance bimetallic catalysts on nano-zeolite supports for the selective hydrogenation of halonitrobenzenes. Full article