Catalysis Science & Technology最新文献

In this work, we study the reducibility of a PdO precursor placed by strong electrostatic adsorption on either NiO or SiO₂ of NiO/SiO₂ obtained by incipient wetness impregnation. The catalysts were characterized by HAADF-STEM, quasi-in situ XPS, CO IR spectroscopy and H₂ chemisorption as a function of the reduction temperature and evaluated for their performance in cinnamaldehyde hydrogenation. PdO on SiO₂ requires reduction at higher temperatures to achieve appreciable rates of cinnamaldehyde hydrogenation. Pd placed on NiO particles dispersed on the SiO₂ support can already be reduced at room temperature and show a higher activity in cinnamaldehyde hydrogenation, which is argued to be due to the higher Pd dispersion obtained at low reduction temperatures.

A commercially available Ni–Mo/Al₂O₃ catalyst was evaluated for its effectiveness in the partial CH₄ oxidation to methanol by using various oxidants, including O₂, H₂O, and N₂O. The main products from the reactions were methanol, formaldehyde, hydrogen and carbon oxide gases. The study revealed that the one-step activation of CH₄ into oxygenates on the Ni–Mo/Al₂O₃ catalyst depended on the type of oxidant utilized. The research examined how the mobility and storage of lattice oxygen within the catalyst influenced its performance in methane conversion. High oxygen storage and release improved catalytic activity but reduced selectivity. Methane conversion without oxygenated products occurred when H₂O or N₂O was used, while O₂ promoted the formation of CO_x. The highest methanol yield was obtained at a 2 : 1 molar ratio of oxidant to methane, at reaction temperatures of 250 °C and 350 °C. When H₂O was used, significant quantities of H₂ and CO were produced, likely due to a simultaneous reforming reaction. Partial oxidation of nickel and molybdenum was observed under H₂O and N₂O conditions. Temperature-programmed reduction (TPR) indicated the transformation of higher-valence oxides into different sub-oxides. In temperature-programmed reduction–oxidation (TPRO), three peaks were detected, corresponding to oxygen surface sites and two framework locations. These peaks shifted to lower temperatures with N₂O, suggesting improved oxygen migration from the bulk to the surface. X-ray diffraction (XRD) analysis identified an active α-NiMoO₄ phase, which facilitated oxygen termination on molybdenum atoms. Under O₂ conditions, nickel also underwent oxidation. Overall, the Ni–Mo/Al₂O₃ catalyst showed notable methanol productivity, reaching up to 9.85 g of methanol per gram of catalyst per hour with N₂O as the oxidant, surpassing other catalysts reported in the literature.

Single-atom catalysts (SACs) have shown great potential in catalyzing the oxygen reduction reaction (ORR) in fuel cell batteries. In carbon-based SACs, besides the most representative TM-N₄-C, other 2D carbon nitrides are used as substrates to fabricate SACs, such as C₂N, which receives less attention than TM-N₄-C. In addition, the significant effects of spin multiplicity and spin evolution in TM-N₄-C have been proposed, underlining the necessity to include spin evolution in mechanistic studies. To understand the influence of spin and coordination of TM-C₂N SACs in ORR catalysis, we employed first-principles density functional theory (DFT) calculations with a constant-potential model (CPM) to systematically investigate the ORR mechanism with various TM centers (Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). A spin-dependent ORR pathway was found to dominate the reaction rate, depending on electrode potential. The *OH adsorption energy on the TM site is the key factor to determine the valence, spin state and coordination number of active sites. By fully exploring the constant-potential free energy diagram of all ORR pathways, the potential-dependent switchable ORR path was found in Fe-, Co-, and Ni-based TM–C₂N, accompanied with spin-state transition in active centers. However, the most excellent ORR activity was found in Cu–C₂N with a predicted onset potential of 0.9 V vs. SHE and subtle spin variation on the Cu center during the ORR process. Decomposed polarization current indicates that overall ORR kinetics is jointly determined by the partition and activity of active moieties, which are both correlated with G_*OH and magnetic moment on the TM center. Our work reveals the voltage-driven evolution of the spin state and coordination on TM–C₂N in the ORR process, which could provide significant insights into the development of spin-related catalytic mechanism and SACs.

This study has explored a novel and sustainable solution for detecting lead after designing a highly selective and efficient sensor from Parthenium hysterophorus. Two nanocomposites were developed after the functionalization of biomass-derived carbon with nitrogen and sulfur-rich organic molecule 1-methyl-1,3,4-thiadiazole-2-thiol and carboxylic acid functionalized carbon nanotubes, respectively, through a facile refluxing method. The layered morphology and partially crystalline structure of MTT-NC were observed through HR-TEM, FE-SEM, Raman, and XRD studies. At the same time, CNT-NC has a hybrid layered and tube-like structure with high crystallinity. The high efficiency, excellent sensitivity and selectivity of CNT-NC toward lead can be due to the pyridine groups, unique hybrid morphology, high crystallinity and conductivity of the nanocomposite. The detection limit of CNT-NC was 100 nM, while MTT-NC demonstrated a detection limit of up to 800 nM. Both the sensors MTT-NC and CNT-NC are also compared with pure nanocarbon, which indicates that functionalization and hybridization enhance the performance and improve the crystallinity and sensitivity of the nanomaterial. The study supports exploring simple and sustainable methods for developing cost-effective and safe nanosensors to monitor the most common and toxic heavy metal ion lead.

Herein, we described the synthesis and characterization of various pyridine appended ImNHC supported chelating Co-complexes (Co1–Co5) of compositions [(ImNHC)Co(acac)₂]⁺/[(ImNHC)Co(Cp*)I]⁺ with differing auxiliary ligands (acac, acetylacetonate or Cp*, pentamethyl cyclopentadienyl). These complexes were next applied as catalysts in alkyne functionalization and interestingly, this reaction can be directed either towards cyclotrimerization or hydroboration, by aptly selecting the auxiliary ligands (acac or Cp*) under solvent and base-free conditions. The presence of a rigid Cp* auxiliary ligand in Co4–Co5 facilitates the hydroboration reaction with β-selective trans-product formation, while the use of a labile acac ligand in Co1–Co3, that offers a flexible coordination environment around the Co-center, promotes cyclotrimerization under ambient conditions providing primarily the 1,2,4-substituted benzene derivatives (with selectivity of ∼90%) in good yields of 70–80% within 12 h. The present protocols are also compatible with various alkynes offering excellent functional group tolerance. Furthermore, detailed mechanistic probes via active-intermediate-capture, steric mapping, and various control experiments including deuterium labelling helped us to understand the underlying reaction mechanism leading to selective transformation.

Bidentate N,N-ligand moieties were covalently tethered on a RAFT agent by Hüisgen cycloaddition, and poly(N-isopropylacrylamide) (PNIPAAm) bearing the ligand moiety was obtained by living-radical polymerization using these RAFT agents. The polymer formed a palladium complex covalently immobilized at the terminus of each polymer chain. Palladium-catalysed Mizoroki–Heck and Suzuki–Miyaura cross coupling reactions proceeded in water with these polymer-immobilized Pd catalysts. The products were obtained in good yields and the aqueous layer containing the polymer catalysts could be reused. Electron microscopic analysis suggested that palladium nanoparticles formed during the reaction were responsible for the catalytic activity. Using an NNC-pincer Pd complex tethered on the polymer, the catalytic reaction was completed with 0.01 mol% of Pd loading. The aqueous solution could be reused 8 times, and a turnover number (TON) of up to 82 800 was achieved.

Correction for ‘Integrated adsorption and photocatalytic degradation of VOCs using a TiO₂/diatomite composite: effects of relative humidity and reaction atmosphere’ by Guangxin Zhang et al., Catal. Sci. Technol., 2020, 10, 2378–2388, https://doi.org/10.1039/D0CY00168F.