Performance In Selective Hydrogenation Research Articles

Effect of preparation conditions of nanocrystalline Pd/MgO catalysts on their performance in selective hydrogenation of acetylene

In the present work, an alkoxide sol-gel method was applied to prepare Pd/MgO catalysts. The sol-gel procedure was followed by supercritical drying (aerogels) or conventional drying (xerogels) in a furnace. These materials were compared with the impregnated samples. The Pd loading was 1 wt% in all the cases. The as-prepared catalysts were characterized by a set of physicochemical methods. Both the type of the Pd precursor and the preparation route were found to affect the porous structure of the materials as well as the dispersion of the palladium particles and their localization over the MgO support. Both the xerogel and incipient wetness impregnation methods lead to a narrower pore size distribution in comparison to the aerogel technique. The most dispersed particles with an average size of ∼ 2.0–2.2 nm were observed for the samples prepared by xerogel and impregnation methods. In the case of aerogel-prepared samples, metallic palladium particles possess bimodal distribution with average diameters of 4.3 and 8.4 nm. The best catalytic performance in acetylene hydrogenation to ethylene (50 % acetylene conversion at 37 °C with selectivity ∼60 %) was observed for the Pd/MgO catalyst prepared via the aerogel route using [Pd(NH3)4](NO3)2. Compared to other samples, this material is characterized by relatively weak metal-support interactions and the availability of active sites for reactants, which ensures the kinetic mode of the hydrogenation reaction (Ea = 74.9 kJ/mol).

Visible-Light-Driven Selective Hydrogenation of Nitrostyrene over Layered Ternary Sulfide Nanostructures.

Selective hydrogenation of nitrostyrenes is a great challenge due to the competitive activation of the nitro groups (─NO2 ) and carbon-carbon (C═C) double bonds. Photocatalysis has emerged as an alternative to thermocatalysis for the selective hydrogenation reaction, bypassing the precious metal costs and harsh conditions. Herein, two crystalline phases of layered ternary sulfide Cu2 WS4 , that is, body-centered tetragonal I-Cu2 WS4 nanosheets and primitive tetragonal P-Cu2 WS4 nanoflowers, are controlled synthesized by adjusting the capping agents. Remarkably, these nanostructures show visible-light-driven photocatalytic performance for selective hydrogenation of 3-nitrostyrene under mild conditions. In detail, the I-Cu2 WS4 nanosheets show excellent conversion of 3-nitrostyrene (99.9%) and high selectivity for 3-vinylaniline (98.7%) with the assistance of Na2 S as a hole scavenger. They also can achieve good hydrogenation selectivity to 3-ethylnitrobenzene (88.5%) with conversion as high as 96.3% by using N2 H4 as a proton source. Mechanism studies reveal that the photogenerated electrons and in situ generated protons from water participate in the former hydrogenation pathway, while the latter requires the photogenerated holes and in situ generated reactive oxygen species to activate the N2 H4 to form cis-N2 H2 for further reduction. The present work expands the rational synthesis of ternary sulfide nanostructures and their potential application for solar-energy-driven organic transformations.

Improving catalytic performance and reusability of flower-like Co-B-P amorphous alloy nanobelts for the selective hydrogenation of furfural in water

Herein, active, low-cost, stable, and sustainable amorphous alloy Co-B-P nanobelts (NBs) are synthesized for the selective hydrogenation of furfural (FFR) to furfuryl alcohol (FFA) in H2O. The Co-B-P NBs are flower-like bundles of ultrathin nanosheets obtained by reducing Co ions in a layered liquid crystal using double-reducing agents at room temperature. The specific surface area, hydrogen adsorption capacity, surface states, and FFR selective hydrogenation performance of the Co-B-P NB catalyst can be modified via low-temperature plasma treatment. The treatment does not change the amorphous structure of Co-B-P NBs. In H2O, Co-B-P NBs treated with plasma at an appropriate power and time exhibit 100% FFR conversion and 95.8% FFA selectivity within 80 min at 80 °C and 1.2 MPa H2 pressure. Moreover, plasma treatment can be used to regenerate Co-B-P NB catalysts. The catalytic activity of Co-B-P NB catalysts can be restored using plasma treatment when it decreases because of their oxidation after several hydrogenation cycles.

Novel Reaction-Adsorption Method for Preparation of Ru–Zn–La/ZrO2 Catalysts with High Catalytic Performance for Selective Hydrogenation of Benzene

A novel wet-chemistry reaction-adsorption strategy via the facile acid–base interaction under mild conditions is demonstrated to fabricate the state-of-the-art Ru–Zn–La/ZrO2 catalysts for selective hydrogenation of benzene to cyclohexene. The catalyst preparation process is systematically investigated and verified with the combination of various characterization techniques. Preloading of lanthanide salts and alkali treatment after calcination not only favor the introduction of ruthenium and zinc species in the later stages but also help enhance the dispersion of the catalysts. The reaction rate constants (k1 and k2) decrease with the increment of the Zn/Ru molar ratio, and the selectivity at 40% conversion (S40) is positively correlated with the k1/k2 ratio, demonstrating the role of Zn species in retarding the hydrogenation activity of Ru and improvement of the selectivity to cyclohexene. In general, the catalytic behavior is dependent on the particle size of Ru, the La-to-Ru electron transfer effect, the content of Zn species, and the surface hydrophilicity of catalyst. These factors are generated by using different precursors and various predesigned La/Ru molar ratios in the preparation recipe. Moreover, a passivation treatment before the hydrogenation reaction can promote the cyclohexene selectivity of the catalyst Ru–Zn–La/ZrO2 (1.6 La/Ru) to 80.6% at a benzene conversion of 43.7%, which meets the industrial requirement. Notably, the specific activity of the catalyst is as high as 1224 gBZ·gRu–1·h–1, over 10 times higher than the industrial criterion. This work provides new insights into the design of Ru-based catalysts for benzene hydrogenation and other hydrogenation reactions as well.

Structure-controlled graphene-encapsulated nickel nanoparticle with tailored work function to steer chemoselective hydrogenation of nitroarenes

In recent years, novel carbon-layer encapsulation strategies have been emerging for the construction of heterogeneous catalysts. However, the mechanism action of thermos-catalytic systems is still unclear. The synergistic effect of metal particle size and carbon layer quantity on catalytic performance has not been reported. The strategy to control the carbon layer quantity and metal particle size is still a big challenge. Here, we proposed a novel idea to design catalysts connecting the performance and the structure via work function. The direct pyrolysis of organometallic coordination polymer is induced to control the carbon layer quantity and metal particle size of the carbon-encapsulated catalyst. The results show that the reduction in the nickel nanoparticle size and the carbon layer quantity were favorable for pumping electrons from the nickel core. There was a corresponding relationship between the work function of the catalyst and its selective hydrogenation performance of halogenated aromatic nitro compounds. With low carbon-halogen bond dissociation energy, a high work function decreased catalytic selectivity. Therefore, the work function can be served as a bridge connecting to the configurational relationship of catalysts.

N,S-Co-doping Significantly Improves the Co–Nx Content of the Co-NSPC Catalyst and Enhances the Catalytic Performance for Selective Hydrogenation of Halogenated Nitrobenzenes

Non-noble metals have attracted worldwide attention for the catalytic hydrogenation of halonitrobenzene due to their high activity, low price, and abundance on Earth. However, the construction of effective and stable non-noble-metal catalysts for the selective hydrogenation of halonitrobenzene to haloaniline by a simple method remains challenging. Herein, we report a facile one-pot method for the synthesis of N,S-co-doped mesoporous carbon-supported non-noble-metal catalysts through carbonization of a mixture of metallic precursors and 2-aminothiazole in molten ZnCl2. The prepared Co-NSPC catalyst showed excellent activity and selectivity with a turnover frequency of 84.4 h–1 in the hydrogenation of p-chloronitrobenzene to p-chloroaniline. Furthermore, Co–Nx was found to be the main active site for this reaction on the basis of characterization and experimental data, and the introduction of S promoted the formation of Co–Nx sites. Moreover, the Co-NSPC-800 catalyst can be reused at least four times and applied to the hydrogenation of 10 kinds of halogenated nitrobenzenes with excellent selectivity.

Regulation of the selective hydrogenation performance of sulfur-doped carbon-supported palladium on chloronitrobenzene

The overall performance of metal catalysts can be efficiently adjusted by modifying carbon carriers with different valence sulfur precursors. The wet impregnation technique successfully prepared carbon material carriers doped with varying sources of sulfur (Na2SO4, NaHSO3, Na2S·9H2O). Palladium carbon catalysts doped with different sulfur precursors had been prepared with the aid of the liquid-phase reduction method of the selective hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN). The catalyst prepared for Na2S·9H2O as a precursor has excellent performance, and the selectivity for o-CAN is more than 99.9% at 100% conversion. In addition, the characterization results show that with the decrease of S valence, the electronic effect between S and Pd increases, and the outer electron shift of Pd increases, which reduces the adsorption and dissociation ability of Pd to hydrogen, resulting in excellent selectivity. The effects provided a good idea for the hydrogenation of o-CNB and a different point of view on sulfur doping in a variety of hydrogenation reactions.

Enhanced selective hydrogenation of glycolaldehyde to ethylene glycol over Cu0-Cu+ sites

Selective hydrogenation of hydroxyaldehydes to polyalcohols is challenging due to the competitive hydrogenation of CO and CO. This study develops heterogeneous Cu catalysts for the selective synthesis of ethylene glycol via batch liquid-phase hydrogenation of glycolaldehyde. SiO2 supported Cu, fabricated by ammonia evaporation, enables to catalyze the CO bond hydrogenation with retaining the CO bond intact, yielding higher selective hydrogenation activity with ethylene glycol selectivity up to 99.8 % relative to MgO, Al2O3, CeO2, and TiO2 supports and Cu/SiO2 synthesized by deposition–precipitation and impregnation. Characterizations confirm that highly efficient 20Cu/SiO2-AE-623 K catalyst fabricated by ammonia evaporation is featured with larger Cu0 and Cu+ surface areas, of which the Cu+ species created from reducing copper phyllosilicate exhibit higher reactivity. A synergistic effect between Cu+ and Cu0 facilitates the selective adsorption/activation of glycolaldehyde on Cu+ sites and the dissociation of H2 on Cu0 sites, bringing a remarkable improvement in the selective hydrogenation performance.

Unveiling the mechanism of controllable CO2 hydrogenation by group VIB metal single atom anchored on N-doped graphite: A density functional theory study

CO2 hydrogenation has raised considerable interest due to concerns about climate change. Realizing low-temperature reverse water gas shift (rWGS) reaction remains a significant challenge in the context of coupling it with the C–C growth reactions to convert CO2 to C2+ fuels. We carried out systematic DFT simulations to unveil the underlying low-temperature mechanism for the selective hydrogenation of CO2 to produce CO, over a variety of metal-based single atom catalysts (SACs) supported on the nitrogen-doped graphite. Group VIB metal-based SACs outperformed other 15 metal candidates in terms of versatile capacities in both selective activation of CO2 molecule and facilitating escaping of CO and H2O. Mo1/N3-Gt was especially outstanding by giving rise to spontaneous production of CO and O∗ through an effective electron injection into the CO2 molecule. Water formation has been identified as the potential rate-controlling step in such a catalytic reaction over Mo1/N3-Gt with an energy barrier of 1.10 eV. Herein, the H migration played a pivotal role and had tight affinity to the charge of H∗ on the active site of catalyst. The dynamic coordination environment of Moδ+ was revealed to be the dominant factor affecting the surface H∗ charge, leading to a variety of hydrogenation behaviors. The electron-deficient ligands of CO2 and O∗ on Mo1/N3-Gt, as well as additional adsorbed H2, were effective in adjusting the 4d and 5s electronic structure of central Mo and consequently resulted in nearly electric neutral surface H∗s, thus most benefiting the hydrogenation process. The optimal charge of the coordinated Mo for an outstanding selective hydrogenation performance in this scenario was found to be no less than +1.7e.

Controlling nanostructures of PtNiCo/C trimetallic nanocatalysts and relationship of structure-catalytic performance for selective hydrogenation of nitroarenes

Herein, we report a simple synthesis of PtNiCo trimetallic nanoparticles (NPs) loaded on carbon black (PtNiCo/C) via ambient-temperature chemical reduction and galvanic replacement reaction. The influence of thermal treatment temperature in 10 %H2/N2 on PtNiCo NPs in PtNiCo/C-X nanostructures is revealed, where, X = 200 °C, 500 °C. XRD, XPS, TEM, HAADF-STEM, HRTEM, STEM-EDX elemental line-scanning (mapping), HS-LEIS, H2-TPR, atomic resolution aberration-corrected STEM (AC-STEM), XANES and EXAFS have been employed to characterize various nanostructures of PtNiCo NPs in PtNiCo/C-X. We established the relationship of nanostructure-reducing temperature thus catalytic behavior of PtNiCo/C-X: PtNiCo/C-200 ∼ Pt island (single atom and cluster)-on-NiCo alloy NP, PtNiCo/C-500 ∼ PtNiCo alloy NPs. PtNiCo/C-200 provides much improved catalytic activity and selectivity to target products (NO2 group hydrogenation) as compared to PtNiCo/C-500 for nitroarenes selective hydrogenation under mild reaction conditions (1.0 MPa-H2 pressure, 18 °C or 40 °C-reaction temperature). That is considered to be closely correlated with the synergy effect of Pt islands and NiCo alloy nanoparticles in PtNiCo/C-200.

Breaking the Activity-Selectivity Trade-Off of Pt Nanoparticles Encapsulated in UiO-66 for Hydrogenation by Constructing Suitable Hierarchical Structure

The simultaneous enhancement of activity and selectivity during hydrogenation is a great challenge. Herein, by encapsulating Pt nanoparticles (NPs) into the hierarchical defective metal–organic framework (MOF) of UiO-66, the steric screening effect of the pores, Lewis acid sites of the nodes, and metal-MOF synergy have been finely tuned and effectively utilized for selective hydrogenation. Benefiting from optimal meso/micropores, favorable Lewis acid sites and strengthened metal–support interaction, Pt NPs encapsulated in hierarchical UiO-66 exhibited superior performance in selective hydrogenation. With the proper loading of Pt NPs into suitable meso/microporous UiO-66, the conversion of cinnamaldehyde is increased from 18.2% to 85% along with the selectivity for cinnamyl alcohol being improved from 15.8% to 76% under 70 °C and 2 MPa. The conventional trade-off relationship between increasing selectivity and promoting activity for encapsulated metal catalysts has been broken with the as-developed catalyst. This study provides a promising strategy to optimize transformation efficiency by the design of a tailored MOF-based framework for encapsulating metal NPs with the needed steric effect and synergistic effect.

A zirconium(IV)-based metal–organic framework modified with ruthenium and palladium nanoparticles: synthesis and catalytic performance for selective hydrogenation of furfural to furfuryl alcohol

A zirconium(IV)-based metal–organic framework modified with ruthenium and palladium nanoparticles: synthesis and catalytic performance for selective hydrogenation of furfural to furfuryl alcohol

Synergistic effects of PtFe/CeO2 catalysts afford high catalytic performance in selective hydrogenation of cinnamaldehyde

Selective hydrogenation of unsaturated aldehydes remains a grand challenge in controlling chemoselectivity up to now. We synthesized a series of PtFex/CeO2 catalysts, which were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) as well as temperature-programmed-reduction by hydrogen (H2-TPR). The catalytic performance of PtFex/CeO2, including cinnamaldehyde (CAL) conversion and selectivity toward cinnamyl alcohol (COL), is improved remarkably by introduction of Fe species in the Pt particles in the selective CAL hydrogenation under mild conditions. XPS results indicate that the electron transfer from Fe to Pt promotes CAL adsorption, resulting in the enhanced CAL conversion. And the COL selectivity is improved by CAL adsorption via an interaction of CO group with surface oxygen defect sites because of interaction between PtFe and CeO2 support. In all, this study may provide some hints to design efficient nano Pt particles for the selective hydrogenation.

Polyphenylene sulfide as an efficient solid-phase ligand for improved selective alkyne hydrogenation

Liquid phase catalytic selective hydrogenation of alkynes to alkenes is a widely used reaction in the industry. Pairing nanocatalysts with soluble ligands or developing advanced catalytic nanostructures are two general protocols to realize preferable hydrogenation performance. However, both protocols are not cost-effective, and it is still challenging to achieve high selectivity and high activity with conventional hydrogenation nanocatalysts. In this work, commercial available, low-cost, and reactant-inert polyphenylene sulfide (PPS) is used as a new solid-phase ligand for palladium nanocatalysts in selective alkyne hydrogenation. Hydrogenation experiments have been carried out on different terminal and internal alkyne substrates, to investigate the universal effects of PPS on hydrogenation. As a result, over-hydrogenation and/or isomerization could be effectively suppressed upon the addition of solid PPS powders. The beneficial effects can be easily tuned by varying the PPS dosage. Importantly, both solid supported nanocatalysts and PPS can be simply separated via sedimentation and washing for subsequent experiments. A recycling experiment with PPS/Pd@CaCO3 has demonstrated the good cyclability (ten times of usage without much changes in effectiveness) of the catalyst system. X-ray photoelectron spectroscopy results indicate that the weak binding of PPS as a solid-phase ligand to nanocatalysts may contribute to the improved selective hydrogenation performance.

Preparation of Pd/γ-Al2O3/nickel foam monolithic catalyst and its performance for selective hydrogenation in a rotating packed bed reactor

Selective hydrogenation plays an important role in chemical industries, yet its selectivity is usually limited by the mass transfer. In this work, the enhanced hydrogenation selectivity was achieved in a rotating packed bed (RPB) reactor with excellent mass transfer efficiency. Aiming to be used under the centrifugal filed, a monolithic catalyst Pd/γ-Al 2 O 3 /nickel foam suiting for the shape and size of the rotor of RPB reactor was prepared by the electrophoretic deposition method. The mechanical strength of the catalyst can meet the requirement of high centrifugal force in the RPB. The hydrogenation selectivity in the RPB reactor using the 3-methyl-1-pentyn-3-ol hydrogenation system was 3–8 times higher than that in a stirred tank reactor under similar conditions. This work proves the feasibility of intensifying the selectivity of hydrogenation process in the RPB reactor.

Synthesis of methyl glycolate by hydrogenation of dimethyl oxalate with a P modified Co/SiO2 catalyst

A P-modified Co/SiO2 catalyst exhibited excellent performance in selective hydrogenation of dimethyl oxalate to methyl glycolate.

An efficient NiCu@C/Al2O3 catalyst for selective hydrogenation of acetylene.

The development of non-noble metal catalysts for selective hydrogenation still remains a challenge. Herein, NiCu@carbon core-shell nanoparticles supported on Al2O3 (NiCu@C/Al2O3) were prepared, which showed enhanced catalytic performance of acetylene-selective hydrogenation in comparison with NiCu/Al2O3 without carbon encapsulation. In detail, NiCu@C/Al2O3 displayed high ethylene selectivity (>86%) even at an acetylene conversion of 100% and excellent stability (>90 h). Thus, NiCu@C/Al2O3 exhibited great potential as an alternative to Pd-based catalysts for acetylene-selective hydrogenation.

Controlling Nanostructures of Ptnico/C Trimetallic Nanocatalysts and Relationship of Structure-Catalytic Performance for Selective Hydrogenation of Nitroarenes

Controlling Nanostructures of Ptnico/C Trimetallic Nanocatalysts and Relationship of Structure-Catalytic Performance for Selective Hydrogenation of Nitroarenes

In‐Situ Incorporation of Pt Nanoparticles on Layered Double Hydroxides for Selective Conversion of Cinnamaldehyde to Cinnamyl Alcohol

AbstractDesigning efficient and low‐cost catalysts for generation of cinnamyl alcohol (CMO) from cinnamaldehyde (CMA) hydrogenation is of practical value. Herein, layered double hydroxide supported Pt nanoparticles (Pt‐s/LDH) were prepared by in‐situ reduction of PtCl62− in PtCl62−‐LDH with ethylene glycol, and the PtCl62− was intercalated in LDH by ion‐exchange method. The characterization results verify that small Pt nanoparticles are uniformly distributed on LDH with average diameter of 1.9 nm and narrow size distribution. The prepared Pt‐s/LDH catalyst exhibits excellent catalytic performance for selective hydrogenation of CMA under relatively mild reaction conditions (80 °C, 2 MPa H2) with high turnover frequency (TOF) (0.574 s−1) and CMA conversion (92.6 %). Furthermore, the CMA conversion rate and CMO selectivity remain almost unchanged after the fourth run compared with the results of the first run. This study provides an effective route for synthesis of efficient and stable LDH‐supported metal catalysts.

Recent Progress in Pd-Based Nanocatalysts for Selective Hydrogenation.

Selective hydrogenation plays an important role in the chemical industry and has a wide range of applications, including the production of fine chemicals and petrochemicals, pharmaceutical synthesis, healthcare product development, and the synthesis of agrochemicals. Pd-based catalysts have been widely applied for selective hydrogenation due to their unique electronic structure and ability to adsorb and activate hydrogen and unsaturated substrates. However, the exclusive and comprehensive summarization of the size, composition, and surface and interface effect of metal Pd on the performance for selective hydrogenation is still lacking. In this perspective, the research progress on selective hydrogenation using Pd-based catalysts is summarized. The strategies for improving the catalytic hydrogenation performance over Pd-based catalysts are investigated. Specifically, the effects of the size, composition, and surface and interfacial structure of Pd-based catalysts, which could influence the dissociation mode of hydrogen, the adsorption, and the reaction mode of the catalytic substrate, on the performance have been systemically reviewed. Then, the progress on Pd-based catalysts for selective hydrogenation of unsaturated alkynes, aldehydes, ketones, and nitroaromatic hydrocarbons is revealed based on the fundamental principles of selective hydrogenation. Finally, perspectives on the further development of strategies for chemical selective hydrogenation are provided. It is hoped that this perspective would provide an instructive guideline for constructing efficient heterogeneous Pd-based catalysts for various selective hydrogenation reactions.