High Catalytic Performance of a CeO2-Supported Ni Catalyst for Hydrogenation of Nitroarenes, Fabricated via Coordination-Assisted Strategy

Highly Efficient Iron-Based Catalyst for Light-Driven Selective Hydrogenation of Nitroarenes

Light-driven hydrogenation of nitro compounds to functionalized amines is of great importance yet a challenge for practical applications, which calls for the development of high-performance, nonprecious photocatalysts and efficient catalytic systems. Herein, we report a high-efficiency Fe3O4@TiO2 photocatalyst via a sol-gel and subsequent pyrolysis strategy, which exhibits desirable photothermal hydrogenation performance of nitro compounds to functionalized amines with the excellent selectivity of >90% exceeding those of the state-of-the-art heterogeneous photocatalysts. Our experimental results and theoretical calculations for the first time reveal that Fe3O4 is the major active phase, and the strong metal-support interaction between Fe3O4 and reducible TiO2 further leads to performance improvement, taking advantage of the enhanced photothermal effect and the improved adsorption for the reactant and hydrazine hydrate. Notably, a variety of halonitrobenzenes and pharmaceutical intermediates can be completely converted to functionalized amines with high selectivities, even in gram-scale reactions. This work provides a new insight into the rational design of nonprecious photo/thermo-catalysts for other catalytic reactions.

Structure engineering of CeO2 for boosting the Au/CeO2 nanocatalyst in the green and selective hydrogenation of nitrobenzene

Exploring eco-friendly and cost-effective strategies for structure engineering at the nanoscale is important for boosting heterogeneous catalysis but still under a long-standing challenge. Herein, multifunctional polyphenol tannic acid, a low-cost natural biomass containing catechol and galloyl species, was employed as a green reducing agent, chelating agent, and stabilizer to prepare Au nanoparticles, which were dispersed on different-shaped CeO₂ supports (e.g., rod, flower, cube, and octahedral). Systematic characterizations revealed that Au/CeO₂-rod had the highest oxygen vacancy density and Ce(III) proportion, favoring the dispersion and stabilization of the metal active sites. Using isopropanol as a hydrogen-transfer reagent, deep insights into the structure-activity relationship of the Au/CeO₂ catalysts with various morphologies of CeO₂ in the catalytic nitrobenzene transfer hydrogenation reaction were gained. Notably, the catalytic performance followed the order: Au/CeO₂-rod (110), (100), (111) > Au/CeO₂-flower (100), (111) > Au/CeO₂-cube (100) > Au/CeO₂-octa (111). Au/CeO₂-rod displayed the highest conversion of 100% nitrobenzene and excellent stability under optimal conditions. Moreover, DFT calculations indicated that nitrobenzene molecules had a suitable adsorption energy and better isopropanol dehydrogenation capacity on the Au/CeO₂ (110) surface. A reaction pathway and the synergistic catalytic mechanism for catalytic nitrobenzene transfer hydrogenation are proposed based on the results. This work demonstrates that CeO₂ structure engineering is an efficient strategy for fabricating advanced and environmentally benign materials for nitrobenzene hydrogenation.

Synthesis of Mesoporous Silica-Supported NiCo Bimetallic Nanocatalysts and Their Enhanced Catalytic Hydrogenation Performance

In this work, mesoporous silica SBA-16-supported NiCo bimetallic nanocatalysts were synthesized by coimpregnation of Ni and Co precursors followed by calcination and reduction, and various characterization techniques confirm the formation of NiCo bimetallic nanostructures in the catalysts. The synthesized NiCo/SBA-16 shows enhanced catalytic performance for hydrogenation of a series of nitroaromatics. Under the reaction conditions of 80 °C and 1.0 MPa of H₂, the yields of aniline for nitrobenzene hydrogenation over NiCo_0.3/SBA-16 can reach more than 99% at 2.0 h. The enhanced catalytic performance can be ascribed to the formation of NiCo bimetallic nanostructures, where the synergistic effect between Ni and Co improves their catalytic activities for hydrogenation of nitroaromatics.

Carbon dots capped cerium oxide nanoparticles for highly efficient removal and sensitive detection of fluoride

Since the excess exposure to F^- may induce serious issues to human health, the effective adsorption and sensitive detection of F^- is essential. Therefore, carbon dots (CDs) capped CeO₂ (CeO₂@CDs) was synthesized via hydrothermal treatment of tannic acid and CeCl₃. Due to abundant phenolic hydroxyl are reserved and excellent hydrophilicity, CeO₂@CDs possess high F^- adsorption capacity. The partition coefficient parameters (PC) are determined to be 2.65 L/g, which is comparable with previous work. The kinetics results and adsorption isotherm are consistent with pseudo-second-order model and Freundlich model, respectively, indicating the chemisorption dominate the adsorption, mainly via the ion exchange between hydroxyl and F^-. Since phenolic hydroxyl existed on the CeO₂@CDs, synergetic effect of CDs and CeO₂ contribute to superior ROS eliminating capacity, even at acidic conditions. Moreover, due to the ROS scavenging of CeO₂ @CDs abilities can be potentiated by F^-, colorimetric detection of F^- can be realized via horseradish peroxidase as an indicator. The linear range is 0.3-2.1 mM with limit of detection is 0.13 mg/L. The current results imply that CeO₂@CDs possess potential in both efficient removal and sensitive detection of F^- related contamination issues and elucidation of development to address other anions related issues.

Nonoxidative Coupling of Methane over Ceria-Supported Single-Atom Pt Catalysts in DBD Plasma

Plasma-catalytic direct nonoxidative coupling of methane (NCM) into C₂ hydrocarbons was investigated over ceria-supported atomically dispersed Pt (Pt/CeO₂-SAC) and nanoparticle Pt (Pt/CeO₂-NP) catalysts in dielectric barrier discharge (DBD) plasma. Nonthermal plasma facilitated C-H bond dissociation in CH₄ at low temperatures (<150 °C) and atmospheric pressure. The presence of Pt/CeO₂ catalysts in plasma further enhanced CH₄ conversion and C₂ hydrocarbon selectivity by enabling the conversion of vibrationally excited methane species with high internal energy on active Pt sites. Noticeably, the Pt/CeO₂-SAC catalyst displayed a more remarkable performance, with a CH₄ conversion of 39% and a C₂ selectivity of 54% at 54 W. The enhanced CH₄ conversion was attributed to abundant coordinatively unsaturated Pt sites in Pt/CeO₂-SAC, which were more active for C-H bond scission. Meanwhile, isolated Pt atoms in Pt/CeO₂-SAC promoted C₂ hydrocarbon formation by hindering the unselective formation of coke from deep dehydrogenation of CH_x^• intermediates and higher hydrocarbons from oligomerization reactions.

A highly efficient LaOCl supported Fe–Fe3C-based catalyst for hydrogenation of nitroarenes fabricated by coordination-assisted pyrolysis

A highly efficient LaOCl supported Fe–Fe₃C-based catalyst derived from bi-MOFs prepared by coordination-assisted pyrolysis for hydrogenation of nitroarenes to arylamines.

Insights into the Pt (111) Surface Aid in Predicting the Selective Hydrogenation Catalyst

The d-band center position of the metal catalyst is one of the most important factors for catalytic selective hydrogenation, e.g., the conversion of nitrostyrene to aminostyrene. In this work, we modulate the d-band center position of the Pt surface via H coverage manipulation in order to assess the highly efficient selective hydrogenation catalyst using density functional theory (DFT) calculation, which is validated experimentally. The optimal transition metal catalysts are first screened by comparing the adsorption energy values of two ideal models, nitrobenzene and styrene, and by correlating the adsorption energy with the d-band center positions. Among the ten transition metals, Pt nanoparticles have a good balance between selectivity and the conversion rate. Then, the surface hydrogen covering strategy is applied to modulate the d-band center position on the Pt (111) surface, with the increase of H coverage leading to a decline of the d-band center position, which can selectively enhance the adsorption of nitro groups. However, excessively high H coverage (e.g., 75% or 100%) with an insufficiently low d-band center position can switch the chemisorption of nitro groups to physisorption, significantly reducing the catalytic activity. Therefore, a moderate d-band center shift (ca. −2.14 eV) resulted in both high selectivity and catalytic conversion. In addition, the PtSn experimental results met the theoretical expectations. This work provides a new strategy for the design of highly efficient metal catalysts for selective hydrogenation via the modulation of the d-band center position.

Co3O4-Impregnated NiO-YSZ: An Efficient Catalyst for Direct Methane Electrooxidation

Co₃O₄-impregnated NiO-YSZ (yttria-stabilized zirconia) is a possible electrocatalyst for direct methane electrooxidation with both high catalytic activity and the ability to mitigate coking. The physical and electrochemical properties of Co₃O₄-impregnated NiO-YSZ anodes are investigated and benchmarked against NiO-YSZ and CeO₂-impregnated NiO-YSZ anodes. The following methane electrooxidation activity trend: Co₃O₄-impregnated NiO-YSZ > CeO₂-impregnated NiO-YSZ > NiO-YSZ with i_o (exchange current density) values of 88, 83, and 2 mA cm^-2, respectively, is obtained in the high overpotential region. The high activity of Co₃O₄-impregnated NiO-YSZ is attributed to the changes in the electronic structure and microstructure with the incorporation of nickel into the lattice of Co₃O₄ as observed using X-ray photoelectron spectroscopy, temperature-programmed reduction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. Co₃O₄-impregnated NiO-YSZ also demonstrated the least coking during operation, confirming its utility as a methane electrooxidation catalyst.

Effect of Pd/Ce loading on the performance of Pd-Ce/γ-Al2O3 catalysts for toluene abatement

A single metal Pd/γ-Al₂O₃ catalyst and a bimetallic Pd-Ce/γ-Al₂O₃ catalyst were prepared by the equal-volume impregnation method to investigate the effect of CeO₂ loading on the catalytic oxidation of toluene. The specific surface area, surface morphology, and redox performance of the catalyst were characterized by N₂ desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), H₂-TPR, O₂-TPD, and electron paramagnetic resonance (EPR). The results showed that bimetal catalysts loaded CeO₂ had smaller nano-PdO particles than those of the Pd/γ-Al₂O₃ catalyst. Compared with the catalyst of 0.2Pd/γ-Al₂O₃ (percentage of mass, the same as below), the catalyst doped with 0.3CeO₂ had a stronger reduction peak, which was shifted to the low-temperature zone by more than 80 °C. The results of XPS and O₂-TPD showed that the introduction of CeO₂ provided more surface oxygen vacancy for the catalyst and enhanced its catalytic oxidation ability, and the amount of desorbed O₂ increased from 3.55 μmol/g to 8.54 μmol/g. The results of EPR were that the addition of CeO₂ increased the content of active oxygen species and oxygen vacancies on the surface of the catalysts, which might be due to the supply of electrons to the O₂ and PdO during the Ce³⁺toCe⁴⁺ conversion process. That could have accelerated the catalytic reaction process. Compared with the single precious metal catalyst, the T₁₀ and T₉₀ of the Pd-Ce/γ-Al₂O₃ catalyst were decreased by 22 °C and 40 °C, respectively.

Pt nanoparticles anchored on rare metal oxide coated on SBA-15: a highly active catalyst for synergistic catalytic hydrogenation of benzaldehyde

We report a novel hybrid nano-structure Pt catalyst, by coating rare metal oxide (CeO₂ or La₂O₃) on the surface of SBA-15, then anchoring Pt nanoparticles on the CeO₂/SBA-15 or La₂O₃/SBA-15 via a photochemical route. For the hydrogenation of benzaldehyde, the Pt/@-CeO₂/SBA-15 and Pt/@-La₂O₃/SBA-15 catalysts demonstrated outstanding activity and excellent selectivity, much higher than that of Pt/CeO₂, Pt/La₂O₃ and Pt/SBA-15. In particular, the TOF of Pt/@-La₂O₃/SBA-15 reached 2324 h^-1, 2.3-fold higher than the atomically dispersed catalyst (Pd₁/TiO₂, 1002 h^-1) in the literature. The superior catalytic performance was attributed to the special structure and the synergistic effect between the Pt nanoparticles and CeO₂/SBA-15(La₂O₃/SBA-15). The content of metal oxide played an important role in the reaction, as only a suitable content of metal oxide could ensure that this hybrid structure would show the best performance.

General and selective synthesis of primary amines using Ni-based homogeneous catalysts

The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H₂ metathesis as the rate-determining step.

A Ni-triphos based homogeneous catalyst enabled the synthesis of all kinds of primary amines by reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes.

Catalytic Oxidation of Chlorobenzene over Pd-TiO2 /Pd-Ce/TiO2 Catalysts

A series of Pd-TiO2/Pd-Ce/TiO2 catalysts were prepared by an equal volume impregnation method. The effects of different Pd loadings on the catalytic activity of chlorobenzene (CB) were investigated, and the results showed that the activity of the 0.2%-0.3% Pd/TiO2 catalyst was optimal. The effect of Ce doping enhanced the catalytic activity of the 0.2% Pd-0.5% Ce/TiO2 catalyst. The characterization of the catalysts using BET, TEM, H2-TPR, and O2-TPD showed that the oxidation capacity was enhanced, and the catalytic oxidation efficiency was improved due to the addition of Ce. Ion chromatography and Gas Chromatography-Mass Spectrometer results showed that small amounts of dichlorobenzene (DCB) and trichlorobenzene (TCB) were formed during the decomposition of CB. The results also indicated that the calcination temperature greatly influenced the catalyst activity and a calcination temperature of 550 °C was the best. The concentration of CB affected its decomposition, but gas hourly space velocity had little effect. H2-TPR indicated strong metal–support interactions and increased dispersion of PdO in the presence of Ce. HRTEM data showed PdO with a characteristic spacing of 0.26 nm in both 0.2% Pd /TiO2 and 0.2% Pd-0.5% Ce/TiO2 catalysts. The average sizes of PdO nanoparticles in the 0.2% Pd/TiO2 and 0.2% Pd-0.5% Ce/TiO2 samples were 5.8 and 4.7 nm, respectively. The PdO particles were also deposited on the support and they were separated from each other in both catalysts.

Effect of Fe, Co and Ni promoters on MoS2 based catalysts for chemoselective hydrogenation of nitroarenes

The effect of Fe, Co and Ni promoters on supported MoS₂ catalysts for hydrogenation of nitroarenes were systematically investigated via experiment, characterization and DFT calculation. It was found that the addition of promoters remarkably improved the reaction activity in a sequence of Ni > Co > Fe > Mo. Meanwhile Ni promoted catalyst with the best performance showed good recyclability and chemoselectivity for a wide substrate scope. The characterization results revealed that the addition of promoters decreased the interaction between Mo and support and facilitated the reductive sulfidation of Mo species to produce more coordinated unsaturated sites (CUS). DFT calculations showed that the addition of promoters increased the formation of CUS, and enhanced the adsorption of hydrogen. The influence degree of promoters followed the sequence Ni > Co > Fe > Mo, which was consistent with those of the activities. Nitrobenzene hydrogenation and hydrogen activation occurred at the S and Mo edge, respectively. The adsorbed hydrogen diffused from the Mo edge to the S edge to participate in the hydrogenation reaction. Mechanism investigation showed that the main reason for increased activity by the addition of promoters was the increase of amounts of CUS and the secondary reason was the augmentation of intrinsic activity of CUS. The present studies give a new understanding for promoter modified MoS₂ catalysts applied for hydrogenation of nitroarenes.

The addition of promoters remarkably improved the activity for hydrogenation of nitroarenes in a sequence of Ni > Co > Fe > Mo and the amount of CUS active center was supposed to be the main reason to influence the reaction activity.

Mild and selective hydrogenation of nitriles into primary amines over a supported Ni catalyst

The mesoporous Al₂O₃ supported Ni catalyst demonstrated a high activity and selectivity for the hydrogenation of nitriles into primary amines under the mild conditions (60–80 °C and 2.5 bar H₂) with ammonia as the additive.

Integrating Catalysis of Methane Decomposition and Electrocatalytic Hydrogen Evolution with Ni/CeO2 for Improved Hydrogen Production Efficiency

Ni/CeO₂ enables either methane decomposition or water electrolysis for pure hydrogen production. Ni/CeO₂ , prepared by a sol-gel method with only one heat treatment step, was used to catalyze methane decomposition for the generation of H₂ . The solid byproduct, Ni/CeO₂ /carbon nanotube (CNT), was further employed as an electrocatalyst in the hydrogen evolution reaction (HER) for H₂ production. The Ni/CeO₂ catalyst exhibits excellent activity for methane decomposition because CeO₂ prevents carbon encapsulation of Ni nanoparticles during the preparation process and forms a special metal-support interface with Ni. The derived CNTs act as antenna to improve conductivity and promote the dispersion of agglomerated Ni/CeO₂ . In addition, they provide H₂ diffusion paths and prevent Ni/CeO₂ from peeling off the HER electrode. Although long-term methane decomposition reduces the HER activity of Ni/CeO₂ /CNTs (owing to degradation of the delicate Ni/CeO₂ interface), the tunable nature of the synthesis makes this an attractive sustainable approach to synthesize future high-performance materials.

Ni@PC as a stabilized catalyst toward the efficient hydrogenation of quinoline at ambient temperature

A novel and efficient strategy, namely as starch-assistant-confine, was used to design and rationally construct a series of porous carbons featuring uniform dispersal of Ni@PC-T-h with highly-efficient catalytic hydrogenation of quinoline.

Ultrafine NiMoOx nanoparticles confined in mesoporous carbon for the reduction of nitroarenes: effect of the composition and accessibility of the active sites

The design of ultrafine NiMoO_x nanoparticles (NPs) confined in hierarchically porous carbon remains a great challenge due to its high calcination temperature. In addition, the composition of active sites of NiMoO_x NPs for the hydrogenation reaction is still ambiguous. Herein, we report a general approach for the synthesis of ultrafine NiMoO_x NPs confined in mesoporous carbon with different morphologies and compositions using the replication method with SBA-15 as a hard template. The pore structure of mesoporous carbon and the Ni/Mo composition valence-state were discovered to be the main factors in the reduction of nitroarenes. The NiMoO_x/mesoporous carbon-platelet (NiMoO_x/MC-PL) with short mesochannels (∼350 nm) and high surface area (∼995 m² g⁻¹) possessed excellent catalytic activity towards the reduction of 4-nitrophenol, whereas NiMoO_x/mesoporous carbon-hexagonal-prism (NiMoO_x/MC-HP), NiMoO_x/mesoporous carbon-long-rod (NiMoO_x/MC-LR), and NiMoO_x/mesoporous carbon-spherical (NiMoO_x/MC-SP) with long mesochannels and relatively less surface area exhibited poor catalytic performance. The bifunctional mechanism or electronic synergistic effects of Ni and Mo species enhanced their catalytic performance. A good balance between MoO_x and metallic Ni (NiMoO_x/MC-PL-450) was found to be suitable for the reduction of 4-NP.

Ultrafine NiMoO_x NPs were confined in the framework of mesoporous carbon by using the replication method for the reduction of nitroarenes.

Amorphous Flowerlike Goethite FeOOH Hierarchical Supraparticles: Superior Capability for Catalytic Hydrogenation of Nitroaromatics in Water

Fabrication of anilines from the corresponding nitroaromatics is a hot topic both for academia and for industry; however, conducting this protocol in water over a noble-metal-free catalytic system is still a great challenge. Continuous efforts are being made on exploiting novel catalysts for this transformation. In this work, we developed a scalable method for synthesizing the uniform flowerlike amorphous α-FeOOH hierarchical supraparticles. The well-defined amorphous α-FeOOH was prepared through an environmentally benign method, which is hydrolysis of the self-assembled iron glycolate at room temperature. Compared with other iron-only catalysts, this flowerlike amorphous α-FeOOH hierarchical supraparticle catalyst exhibits the best performance in the catalytic reduction of nitroaromatics to corresponding anilines by using water as the reaction solvent (turn over frequency is 106 h^-1 for 4-nitrophenol in water). The further results indicated that the amorphous structure, special nanostructures, and adsorption-desorption synergy offered excellent activity. The kinetics study shows that the reduction of 4-nitrophenol is first order for α-FeOOH, and the apparent active energy E_a is 75.9 kJ mol^-1. Furthermore, this catalyst can be used for eight times without obvious catalytic activity loss. We believe that this novel flowerlike amorphous α-FeOOH hierarchical supraparticle catalyst is a milestone in the reduction of nitro compounds.