Hollow and Yolk–Shell Co-N-C@SiO₂ Nanoreactors: Controllable Synthesis with High Selectivity and Activity for Nitroarene Hydrogenation

The use of hollow and yolk–shell nanocomposites is an effective route to enhance catalytic performance. A strategy that allows precise control of the nanocomposites was developed to synthesize novel hollow and yolk–shell SiO2 nanoreactors of Co-N-C@SiO2, which used ZIF-67 as the hard template and also as the source for active sites. A size dependence of the nanoreactor structure was observed. Large size of ZIF-67 gave yolk–shell Y-Co-N-C@SiO2 while small size of crystals gave hollow H-Co-N-C@SiO2. The hydrogenation reaction results showed that the Co-N-C@SiO2 catalyst exhibited a high selectivity (>99%) to aniline and gave an activity (35.3 h–1) ∼3.3 times higher than that of Co/SiO2 (11.8 h–1). The excellent performance was attributed to that Co nanoparticles were doped in the N-C framework where they formed Co-Nx species and that the HSN had a void structure that had a reduced diffusion limitation

Enhanced Selectivity in the Hydrogenation of Acetylene due to the Addition of a Liquid Phase as a Selective Solvent

The selective hydrogenation of acetylene is usually a gas-phase reaction. In this work, a liquid phase was introduced as a selective solvent to improve the selectivity to ethylene by coupling absorption to the reaction. The catalyst was 0.01% Pd supported on a low surface area silica. <i>N</i>-methyl-2-pyrrolidone (NMP) was used as a selective solvent, and decane was used as a nonselective solvent for comparison. The liquid-phase hydrogenation was carried out in a stirred flat bottom flask operated in gas continuous and liquid batch mode, and the gas-phase hydrogenation was carried out in a fixed bed reactor. The selectivity to ethylene in the gas-phase hydrogenation was 50–70%. In contrast, the highest selectivity to ethylene in the NMP liquid-phase hydrogenation was increased to 96%, while in decane it had the same value as in the gas phase. In NMP, a low reaction temperature below 80 °C did not give a high selectivity to ethylene because the relatively high ethylene solubility in NMP led to deep hydrogenation and the high acetylene solubility caused more oligomerization. Good catalyst stability was obtained under the optimized conditions of a relatively low space velocity, H₂:C₂H₂ ratio above 10, and reaction temperature above 80 °C. Significant deactivation also occurred in NMP under other conditions due to oligomerization

Supported Ultrafine NiCo Bimetallic Alloy Nanoparticles Derived from Bimetal–Organic Frameworks: A Highly Active Catalyst for Furfuryl Alcohol Hydrogenation

Highly dispersed NiCo bimetallic alloy nanoparticles have been successfully immobilized on the SiO₂ frameworks by using heteronuclear metal–organic frameworks (MOFs) as metal alloy precursors. Catalyst characterizations revealed that the average size of NiCo alloy particles was less than 1 nm, with a total metal loading of about 20 wt %. As compared to individual Ni or Co MOF-derived catalysts and the catalysts prepared by the conventional impregnation method, the ultrafine NiCo/SiO₂-MOF catalyst showed a much better catalytic performance in the catalytic hydrogenation of furfuryl alcohol (FA) to tetrahydrofurfuryl alcohol (THFA) under mild conditions, giving 99.8% conversion of FA and 99.1% selectivity to THFA. It was found that a significant synergistic effect existed between Co and Ni within the subnanometer NiCo/SiO₂-MOF catalyst, which was 2 and 20 times more active than Ni/SiO₂-MOF and Co/SiO₂-MOF, respectively

Insights into the Activity Screening and Hydroformylation Kinetics of Rh-Based Bimetallic Phosphides

Heterogeneous hydroformylation is of great industrial and economic interest. Here, we proposed a screening strategy to search highly active Rh-based bimetallic phosphide catalysts and successfully predicted Rh7Pd1P4 as a new active site, which was more active than other phosphide catalysts. Experimental verifications confirmed the synthesis of bimetallic phosphides and the activity enhancement for styrene hydroformylation. The kinetics of styrene hydroformylation was studied based on the rate-determining step (RDS) achieved from density functional theory (DFT) calculations. The proposed two-parameter kinetics was more consistent with the experimental data than previously used first-order or zero-order models. By changing the reaction pressure, the RDS could be identified by experiments with the help of the kinetic model. The RDS identified from the experiments and the kinetic model agreed well with the DFT calculations, which further proved the accuracy of the kinetic model

Highly Selective Hydrogenation of Furfural to Cyclopentanone over a NiFe Bimetallic Catalyst in a Methanol/Water Solution with a Solvent Effect

The aqueous phase hydrogenation of furfural to cyclopentanone over a NiFe bimetallic catalyst was investigated for the efficient utilization of biomass-derived compounds. Catalyst characterization by XRD, EDS mapping, and TPR revealed significant synergetic effects in the NiFe/SBA-15 catalyst. With NiFe/SBA-15, cyclopentanone selectivity was increased to 78.4% from 46.1% with Ni/SBA-15. The use of different supports showed that weak acidity favors cyclopentanone formation. The solvent played an important role: methanol/water solutions with different compositional ratios gave significantly changed product distributions. With pure methanol, and methanol-dominated and water-dominated solutions, respectively, the main product was furfuryl alcohol, tetrahydrofurfuryl alcohol, and cyclopentanone. Furfural in the water inhibited THFA formation, which led furfural to preferentially produce cyclopentanone. At the optimized reaction temperature, NiFe/SBA-15 in water gave 99.8% furfural conversion and 90% cyclopentanone yield at 300 min, which was much better than most reported nonprecious metal catalysts

High-Performance Ni₃P Catalyst for CO Hydrogenation of Ethyl Levulinate: Ni^δ+ as Outstanding Adsorption Sites

It is important but challenging to develop non-noble metal catalysts with high activity and selectivity for biomass conversion. The activation of CO bond is a crucial step in biomass upgradation. Herein, a series of Ni-xP/Al2O3 catalysts with different P/Ni molar ratios were prepared for the conversion of ethyl levulinate to γ-valerolactone. The developed Ni-0.38P/Al2O3 catalyst was 5.4 times more active than conventional Ni/Al2O3 based on turnover frequency and significantly outperformed the state-of-the-art non-noble metal catalysts. The unique catalytic performance was ascribed to the formation of Ni3P phase, which was identified by several characterizations. The results of DFT calculation and characterization by XPS and CO-FTIR revealed that electron was transferred from Ni to P with the formation of Niδ+ sites. In situ FTIR for the surface reaction indicated that Niδ+ acted as a new active site to activate the CO bond, which rendered the high intrinsic activity of Ni3P for the CO hydrogenation of EL

Nano-H-ZSM‑5 with Short <i>b</i>‑Axis Channels as a Highly Efficient Catalyst for the Synthesis of Ethyl Levulinate from Furfuryl Alcohol

For the ethanolysis of biomass-derived furfuryl alcohol (FA) to value-added ethyl levulinate (EL), the development of an efficient solid acid catalyst is very important for industrial application with high FA concentration. Herein, a H-ZSM-5 catalyst with nano b-axis channels (NB-H-ZSM-5) was synthesized and used for the conversion of FA. Detailed catalyst characterization proved that the NB-H-ZSM-5 catalysts (Si/Al = 25∼125) with ∼70 nm b-axis channels were successfully prepared. The NB-H-ZSM-5 catalyst with Si/Al = 75 showed the highest activity. Its structural characteristics allowed for fast diffusion of reactants and products and full utilization of active sites, which endowed it with higher activity compared to commercial H-ZSM-5 (C-H-ZSM-5). Its moderate acidity effectively inhibited the polymerization of FA even at a high FA concentration of 20 wt %. The spent catalyst was easily regenerated by coke burn-off to give a good recyclability. Furthermore, based on the proposed reaction network, a method of physically mixing the NB-H-ZSM-5 (75) catalyst with a small amount of Amberlyst-15 was proposed to further increase the EL yield from 64.7 to 82.1% at an FA concentration of 6 wt %

Highly Effective Removal of Pharmaceutical Compounds from Aqueous Solution by Magnetic Zr-Based MOFs Composites

In this research, the magnetic UiO-66-NH2 composites were prepared and applied as adsorbents for the effective removal of salicylic acid (SA) and acetylsalicylic acid (ASA) from aqueous media. The as-prepared adsorbent inherits both the excellent properties of metal organic frameworks and the magnetic separation property of magnetic material, which makes the magnetic UiO-66-NH2 composite exhibit a rapid separation rate and high capacity. The adsorption kinetics were well fitted with the pseudo-second-order model, and the adsorption isotherm could be well explained using the Langmuir isotherm. The dominant mechanism for adsorption of SA and ASA was hydrogen-bonding, the affinity of carboxyl groups with Zr–O clusters, and electrostatic interactions. The high adsorption capacities, easy separation process, fast adsorption kinetics, and satisfactory reusability of the magnetic UiO-66-NH2 give it fantastic potential as adsorbents for adsorptive separation of pharmaceutical contaminants from aqueous media

Interaction between Single Metal Atoms and UiO-66 Framework Revealed by Low-Dose Imaging

Atomically dispersed metals encapsulated in metal–organic frameworks (MOFs) have attracted extensive attention in catalysis and energy fields. Amino groups were considered conducive to the formation of single atom catalysts (SACs) due to the strong metal–linker interactions. Here, atomic details of Pt1@UiO-66 and Pd1@UiO-66-NH2 are revealed using low-dose integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). Single Pt atoms locate on the benzene ring of p-benzene­dicarboxylic acid (BDC) linkers in Pt@UiO-66, while single Pd atoms are adsorbed by the amino groups in Pd@UiO-66-NH2. However, Pt@UiO-66-NH2 and Pd@UiO-66 show obvious clusters. Therefore, amino groups do not always favor the formation of SACs, and density functional theory (DFT) calculations indicate that a moderate binding strength between metals and MOFs is preferred. These results directly reveal the adsorption sites of single metal atoms in UiO-66 family, paving the way for understanding the interaction between single metal atoms and the MOFs