Hydrogenation Of P-chloronitrobenzene Research Articles

Tailoring Catalysis of Encapsulated Pt Nanoparticles by Pore Wall Engineering of Covalent Organic Frameworks.

While supported metal nanoparticles (NPs) have shown significant promise in heterogeneous catalysis, precise control over their interaction with the support, which profoundly impacts their catalytic performance, remains a significant challenge. In this study, Pt NPs are incorporated into thioether-functionalized covalent organic frameworks (denoted COF-Sx), enabling precise control over the size and electronic state of Pt NPs by adjusting the thioether density dangling on the COF pore walls. Notably, the resulting Pt@COF-Sx demonstrate exceptional selectivity (>99%) in catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline, in sharp contrast to the poor selectivity of Pt NPs embedded in thioether-free COFs. Furthermore, the conversion over Pt@COF-Sx exhibits a volcano-type curve as the thioether density increases, due to the corresponding change of accessible Pt sites. This work provides an effective approach to regulating the catalysis of metal NPs via their microenvironment modulation, with the aid of rational design and precise tailoring of support structure.

Photo-thermal Catalytic Hydrogenation of Halogenated Nitrobenzenes over Ni/P25 Catalyst.

As haloanilines (HANs) are important organic intermediates and fine chemicals, their preparation over non-noble-metal-based catalysts by catalytic hydrogenation has attracted wide attention. However, the reaction suffers from relatively harsh conditions. Herein, we found that a 3.5%Ni/P25 catalyst exhibited superior photo-thermal catalytic activity with a TOFs of 5207 h-1 for hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline under a 300 W full spectrum, which was much higher than that of photo- and thermal catalysis alone. Moreover, the 3.5%Ni/P25 catalyst could be recycled 4 times and was effective for the hydrogenation of various halonitrobenzenes (HNBs) with superior selectivity. Furthermore, the kinetic research showed that the excellent catalytic performance could be attributed to the better activation and dissociation of H2 by photo-thermal catalysis and the hydrogenation of p-CNB obeyed the condensation routine by ionic hydrogenation over 3.5%Ni/P25.

Metal-Sulfur Interfaces as the Primary Active Sites for Catalytic Hydrogenationsf.

The determination of catalytically active sites is crucial for understanding the catalytic mechanism and providing guidelines for the design of more efficient catalysts. However, the complex structure of supported metal nanocatalysts (e.g., support, metal surface, and metal-support interface) still presents a big challenge. In particular, many studies have demonstrated that metal-support interfaces could also act as the primary active sites in catalytic reactions, which is well elucidated in oxide-supported metal nanocatalysts but is rarely reported in carbon-supported metal nanocatalysts. Here, we fill the above gap and demonstrate that metal-sulfur interfaces in sulfur-doped carbon-supported metal nanocatalysts are the primary active sites for several catalytic hydrogenation reactions. A series of metal nanocatalysts with similar sizes but different amounts of metal-sulfur interfaces were first constructed and characterized. Taking Ir for quinoline hydrogenation as an example, it was found that their catalytic activities were proportional to the amount of the Ir-S interface. Further experiments and density functional theory (DFT) calculations suggested that the adsorption and activation of quinoline occurred on the Ir atoms at the Ir-S interface. Similar phenomena were found in p-chloronitrobenzene hydrogenation over the Pt-S interface and benzoic acid hydrogenation over the Ru-S interface. All of these findings verify the predominant activity of metal-sulfur interfaces for catalytic hydrogenation reactions and contribute to the comprehensive understanding of metal-support interfaces in supported nanocatalysts.

Cu@SiO2 catalyst with high copper dispersion for chemoselective hydrogenation of p-chloronitrobenzene

Selective hydrogenation of p-chloronitrobenzene (p-CNB) is not only of significant industrial importance, but also an important model reaction for selectivity investigation. Despite non-precious metal Cu has been proven to be an effective promoter in bimetallic catalysts, Cu as a single active metal achieving both high conversion and high selectivity are rare reported. In this work, Cu@SiO2 catalysts with high specific surface area (509.8–694.3 m2/g), high Cu dispersion (58.4–69.6 %), and small particle size (2.0–3.0 nm) has been prepared by a simple sol–gel method. The catalysts completely suppress the dechlorination reaction, achieving complete conversion of p-CNB with 99.9 % selectivity for p-chloroaniline (p-CAN). Its microstructure, composition, chemical state, adsorption and reaction behavior have been identified by various conventional ex-situ characterizations of catalysts and in-situ DRIFTs of hydrogenation of p-CNB. Interestingly, even at high loadings, Cu in the catalyst could be highly dispersed, thus exhibiting good catalytic activity. In addition, the Cu catalyst exhibits unique adsorption performance towards p-CNB, which perhaps one of the factors for its good performance. This work not only provides a selective hydrogenation catalyst with high Cu dispersion even at high loading amount by a simple method and but also reveals the importance of the adsorption mode of p-CNB, providing guidance for the development of more efficient catalysts in the future.

Graphene Chainmail Shelled Dilute Ni─Cu Alloy for Selective and Robust Aqueous Phase Catalytic Hydrogenation.

Cost-effective non-noble metal-based catalysts for selective hydrogenation with excellent activity, selectivity, and durability are still the holy grail. Herein, an oxygen-doped carbon (OC) chainmail encapsulated dilute Cu-Ni alloy is developed by simple pyrolysis of Cu/Ni-metal-organic framework. The CuNi0.05@OC catalyst displays superior performance for atmospheric pressure transfer hydrogenation of p-chloronitrobenzene and p-nitrophenol, and for hydrogenation of furfural, all in water and with exceptional durability. Comprehensive characterizations confirm the close interactions between the diluted Ni sites, the base Cu, and optimized three-layered graphene chainmail. Theoretical calculations demonstrate that the properly tuned lattice strain and Schottky junction can adjust electron density to facilitate specific adsorption on the active centers, thus enhancing the catalytic activity and selectivity, while the OC shell also offers robust protection. This work provides a simple and environmentally friendly strategy for developing practical heterogeneous catalysts that bring the synergistic effect into play between dilute alloy and functional carbon wrapping.

Bimetallic and trimetallic Pt-based catalysts for selective hydrogenation of p-chloronitrobenzene to p-chloroaniline

The selective hydrogenation of p-chloronitrobenzene (p-CNB) is a crucial step in the preparation of p-chloroaniline (p-CAN). However, the competitive reactions of NO2 hydrogenation and C-Cl hydrogenolysis make it challenging to inhibit the undesired dechlorination side reaction during this process. Herein, we developed a series of bimetallic PtM/γ-Al2O3 (M = Co, Cu, Ni, Fe, Zn, Ga, and Sn) and trimetallic PtCuCox/γ-Al2O3 catalysts to enhance the selectivity of p-CAN and suppress the formation of aniline (AN). Among the bimetallic catalysts, PtCo/γ-Al2O3 showed the highest hydrogenation activity due to its high electron-rich degree of Pt. Conversely, PtCu/γ-Al2O3 displayed the highest p-CAN selectivity and the lowest AN selectivity, primarily owing to the presence of electron-deficient Pt. Remarkably, the trimetallic PtCuCo/γ-Al2O3 catalyst exhibited superior hydrogenation performance, achieving 97.3 % p-CAN selectivity and 0.4 % AN selectivity at complete conversion of p-CNB, while maintaining good stability over five cycles. This enhancement was attributed to the synergistic effect among Pt, Cu and Co. To further investigate the effect of support, we prepared bimetallic PtM3 (M = Co, Cu, Ni and Zn) catalysts supported on reducible CeO2. Interestingly, the use of CeO2 as a support facilitated the condensation path from p-CNB to p-CAN via azobenzene compounds, distinct from the direct path observed with γ-Al2O3 support. Furthermore, the AN selectivity on all PtM3/CeO2 was less than 1 %, indicating effective inhibition of dechlorination reactions. This study highlights the importance of a multi-metal synergistic strategy and the effect of the support to achieve superior performance in chloronitrobenzene hydrogenation.

Promoting effect of trace amount of Pd for p-CNB hydrogenation in Pd-Au/TiO2 bimetallic catalyst

Pd-Au bimetallic catalysts supported on TiO2 with traces of Pd for p-chloronitrobenzene (p-CNB) hydrogenation were prepared by the deposition-precipitation method. It is found that the ultra-low loading of Pd can improve significantly the catalytic activities of Pd-Au/TiO2 bimetallic catalyst compared with Au/TiO2. The minimal loading of Pd favors the Au dispersion and leads the Au NPs with small size. The existence of a large number of Au/Pd interfaces and the interaction between Au and Pd make Au NPs surface electron-enriched (Auδ-) and the Pd positively charged (Pdn+). The synergetic effect of Auδ-, Pdn+, and Pd0 improves the catalytic performance of 0.01 %Pd-0.5 %Au/TiO2. For 0.01 %Pd-0.5 %Au/TiO2, the p-CNB conversion is 99.9 %, with p-CAN selectivity of 98.6 %. After eight circles of reuse, the conversion of p-CNB and the selectivity of p-CAN is still as high as 98.18 and 99.97 %, respectively, indicating the good stability of 0.01 %Pd-0.5 %Au/TiO2. Through twenty times scale-up preparation or after sixty days of storage, our catalysts still maintain excellent catalytic performance in p-CNB reduction, demonstrating the promising prospects of 0.01 %Pd-0.5 %Au/TiO2 for industrial applications. This work offers a facile method to design bimetallic noble metal catalysts with excellent catalytic activities and good reusability, and clarifies their potential applications in industry.

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.

Role of hydroxyl on metal surface in hydrogenation reactions

The important role of surface hydroxyl in metal catalysis is attracting more attentions but rarely studied for liquid-phase hydrogenation reactions. Here we report such deliberate research with two model substrates, p-chloronitrobenzene and cinnamaldehyde. Graphene-supported iridium nanoparticles with hydroxyl on the metal surface were prepared by hydrothermal synthesis, and the surface hydroxyl can be removed by a mild pre-reduction. The catalyst with surface hydroxyl exhibited around three times higher rate for the hydrogenation of p-chloronitrobenzene than the catalyst without hydroxyl, and an opposite trend was found for the hydrogenation of cinnamaldehyde. Kinetic study revealed that although the surface hydroxyl halved the coverage of H on iridium, it increased the rate constant by a factor of eight through reducing the reaction barrier for the hydrogenation of p-chloronitrobenzene. Theoretical calculation confirmed that the surface hydroxyl can polarize the nitro group via a weak hydrogen-bond interaction and thus facilitate its hydrogenation.

Boosting Catalytic Selectivity through a Precise Spatial Control of Catalysts at Pickering Droplet Interfaces.

Exploration of new methodologies to tune catalytic selectivity is a long-sought goal in catalytic community. In this work, oil-water interfaces of Pickering emulsions are developed to effectively regulate catalytic selectivity of hydrogenation reactions, which was achieved via a precise control of the spatial distribution of metal nanoparticles at the droplet interfaces. It was found that Pd nanoparticles located in the inner interfacial layer of Pickering droplets exhibited a significantly enhanced selectivity for p-chloroaniline (up to 99.6%) in the hydrogenation of p-chloronitrobenzene in comparison to those in the outer interfacial layer (63.6%) in pure water (68.5%) or in pure organic solvents (46.8%). Experimental and theoretical investigations indicated that such a remarkable interfacial microregion-dependent catalytic selectivity was attributed to the microenvironments of the coexistence of water and organic solvent at the droplet interfaces, which could provide unique interfacial hydrogen-bonding interactions and solvation effects so as to alter the adsorption patterns of p-chloronitrobenzene and p-chloroaniline on the Pd nanoparticles, thereby avoiding the unwanted contact of C-Cl bonds with the metal surfaces. Our strategy of precise spatial control of catalysts at liquid-liquid interfaces and the unprecedented interfacial effect reported here not only provide new insights into the liquid-liquid interfacial reactions but also open an avenue to boost catalytic selectivity.

Coupled Co-Doped MoS2 and CoS2 as the Dual-Active Site Catalyst for Chemoselective Hydrogenation

Catalytic hydrogenation plays an important role in the industrial production of fine chemicals. Herein, we report a Co-doped MoS2 and CoS2 composite with a coupling interface and successfully apply it for the chemoselective hydrogenation of p-chloronitrobenzene to p-chloroaniline. The target catalyst 0.5CoMoS has ∼100% conversion and ∼100% selectivity. Experiments and theoretical calculations reveal that CoS2 is more favorable for adsorbing and activating H2 and provides active hydrogen (Ha) to Co-doped MoS2 by the coupling interface. By matching the production and consumption rates of Ha, the maximization of the reaction yield was achieved. This work may promote the study of MoS2-based catalysts for chemoselective hydrogenation.

Nano porous PtRu alloy catalyst with enhanced synergic effect for selective hydrogenation of chloronitrobenzene

Selective hydrogenation of chloronitrobenzene (CNB) to chloroaniline (CAN) is a critical reaction for producing multiple valuable fine chemicals. Inhibiting the dechlorination is extremely vital for this reaction. In this work, we synthesize supported nano porous PtRu alloy catalyst for this catalytic reaction. The special structure of alloy catalyst, mutual-accessible Ru enriched surface and Pt enriched core, strengthens the synergic effect between Ru and Pt, thus improves the catalytic performance. As a result, 100% of o-chloronitrobenzene (o-CNB) conversion and 99.9% of o-chloroaniline (o-CAN) selectivity are achieved by the most optimal catalyst. Besides, the catalyst shows superior selectivity of o-CAN (98%) even under harsh reaction conditions such as high temperature of 150 °C and high pressure of 6 MPa. The excellent catalytic performance is also observed in selective hydrogenation of m-chloronitrobenzene (m-CNB) and p-chloronitrobenzene (p-CNB) as well.

NiOx-promoted Cu-based catalysts supported on AlSBA-15 for chemoselective hydrogenation of nitroarenes

Chemoselective hydrogenation of aromatic nitro compounds to the corresponding anilines is an environmentally benign technology for the production of key intermediates in manufacturing of pharmaceuticals, agrochemicals, dyes and fine chemicals. Non-noble metal Cu-based catalysts have been reported as a low-cost alternative but suffer from poor activity. Herein, by fabricating nickel oxide promoted Cu catalysts, a promoted activity was obtained in supported Cu-Ni bimetal catalyst system. Characterizations such as H2-TPR and XPS indicate a strong interaction between Cu and Ni, which contributes to its high activity and selectivity in hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). Control experiments suggest that either monometallic copper or pure nickel oxide is less active for the reaction but the interaction of NiOx with Cu generates much more active species, resulting in significantly improved catalytic reactivity and selectivity. The activity was found to be highly dependent on the contents of Cu0 & Cu+ in Cu-Ni bimetal catalyst, as the specific reaction rates for hydrogenation of p-CNB grew linearly with the increment of Cu0 & Cu+ loadings. Kinetic studies and in-situ DRIFTS of p-CNB imply the 10Cu-5Ni/AlSBA-R catalyst possesses good capacity for the activation of hydrogen and nitro group, leading to high p-CNB conversion and p-CAN production. The present work provides a good example for understanding the interaction between Cu and nickel oxides, and helps to develop highly efficient non-noble metal catalysts for selective hydrogenation of aromatic nitro compounds to corresponding anilines.

One-step hydrothermal synthesis of hierarchically structured MoS2 nanorods via reaction intermediates as self-templates for chemoselective hydrogenation

Two-dimensional (2D) materials have unique planar structures and ultrathin thicknesses, but are prone to restacking and agglomerate due to the high surface energy. Building hierarchical structures is one of the effective ways to exploit their inherent properties and unique structural advantages. We unexpectedly found that the introduction of saturated NaCl solution to the hydrothermal synthesis of MoS2 could significantly change its structure, resulting in the hierarchically structured nanosheet-assembled MoS2 nanorods (R-MoS2) with intercalated alkali ions. The formation process and synthesis mechanism of R-MoS2 via NaNH4Mo3O10·H2O reaction intermediate are systematically revealed by morphology and spectroscopy. Benefiting from this interesting hierarchical structure, the catalytic conversion of R-MoS2 for p-chloronitrobenzene hydrogenation is significantly improved. Density functional theory calculation also demonstrates the intercalation of Na in MoS2 can downshift the d-band center of Mo and favors the key final desorption process.

Facet Engineering of a Metal-Organic Framework Support Modulates the Microenvironment of Palladium Nanoparticles for Selective Hydrogenation.

The exposed facets of supported catalysts play a crucial role in catalysis; however, they are usually ignored and related studies remain rare. Herein, we have fabricated a series of sandwich-structured metal-organic framework composites, denoted ZIF-8X @Pd@ZIF-8 (x represents the morphology of ZIF-8 core, i.e., ZIF-8C exposing (100) facet, ZIF-8RD exposing (110) facet, and ZIF-8TRD exposing mixed (100) and (110) facets), featuring Pd nanoparticles deposited on the specific crystal facets of ZIF-8 core, for hydrogenation of p-chloronitrobenzene. The Pd electronic state is tailored by the ZIF-8 core, where more electron-deficient Pd is found in ZIF-8C @Pd@ZIF-8 than that in ZIF-8RD @Pd@ZIF-8, leading to discriminative adsorption of the -NO2 and -Cl groups of p-chloronitrobenzene. Consequently, ZIF-8C @Pd@ZIF-8 exhibits excellent activity (97.6 %) and selectivity (98.1 %) to p-chloroaniline. This work highlights crystal facet engineering of supports to modulate the microenvironment and electronic state of supported metal nanoparticles, offering a promising avenue to enhanced catalysis.

Oxygen vacancy-rich WO3-x/rGO composite supported Pd catalyst for efficient selective hydrogenation of nitroaromatics

The development of efficient catalysts for selective hydrogenation of nitroaromatics to corresponding aromatic amines has significant application requirement. In this study, a novel and effective catalyst was prepared by anchoring Pd nanoparticles on oxygen vacancy-rich tungsten oxide (WO3−x) and reduced graphene oxide (rGO) composite support (Pd-WO3−x/rGO). Owing to the strong metal support interaction (SMSI), which can significantly regulate the d-electronic structure of Pd, the Pd-WO3−x/rGO catalyst showed remarkable catalytic activity and selectivity for the hydrogenation of nitroaromatics. Under the reaction conditions of 100 °C and 1 MPa H2, a 100 % yield was achieved for the selective hydrogenation of p-chloronitrobenzene to p-chloroaniline. The catalyst also delivered excellent reusability, which can be readily recycled for at least 10 times without significant loss of activity. This work provide a feasible avenue for the construction of high-performance catalysts for the selective hydrogenation of nitroaromatics and beyond.

Supported Ni0@C[sbnd]N catalyst with dual-reaction surfaces: Structure-performance relation in the selective hydrogenation of p-chloronitrobenzene

How to break the activity-selectivity dependence in halonitrobenzene hydrogenation remains a challenge. In this work, Ni@CN/SiO2 were synthesized and examined in the hydrogenation of p-chloronitrobenzene. It showed that the electron transferred from nitrogen doped carbon shell to Ni0 core (core–shell synergistic effect) dominated the intrinsic activities of Ni@CN/SiO2 with dual-reaction surfaces (H2 dissociated on Ni0 core, while p-chloronitrobenzene was hydrogenated on carbon shell) in the thiophene-free hydrogenation, leading to their higher turnover frequencies than Raney Ni catalyst. During the thiophene-involved hydrogenation, the adsorption of thiophene on Ni0 changed its electron density and blocked the active sites. These enhanced the selectivity, but significantly reduced the activity for Raney Ni catalyst. Comparatively, the carbon shell protected Ni0 core from thiophene adsorption so that the hydrogen dissociated on Ni0 as usual. However, the adsorption of thiophene on the carbon shell reduced the available sites for p-chloronitrobenzene adsorption. Although Ni@CN/SiO2 had lower activities in the thiophene-involved reactions than those of thiophene-free reactions, they achieved ∼100 % p-chloroaniline selectivities and 8-fold higher turnover frequencies than Raney Ni, breaking the activity-selectivity dependence. This reveals that the available sites on the carbon shell and the core–shell synergistic effect determine the thiophene-involved hydrogenation activities of Ni@CN/SiO2 catalysts.

Surface engineering improving selective hydrogenation of p-chloronitrobenzene over AuPt alloy/SnNb2O6 ultrathin nanosheets under visible light

AuPt alloy/SnNb2O6 ultrathin nanosheet (AuPt/SN) as a photocatalyst is constructed for selective hydrogenation of p-chloronitrobenzene (p-CNB) under visible light irradiation. A typical catalyst (Au0.5Pt0.5/SN) exhibits a high conversion of halonitrobenzenes (99.8%) and selectivity of haloaniline (99.1%). The results of in situ ATR-IR, XPS and Raman indicate a preferential chemoselective adsorption of –NO2 that Lewis base sites (Sn2+) on the catalyst could selectively coordinate with –NO2 whereas C-Cl bond is not be bonded, improving the catalytic selectivity. Atom Pt in alloy is responsible for the formation of ·H, while Au inhabits the dissociation of C-Cl via repressing the generation of Pt-H. The photogenerated electrons can accelerate the ·H formation. ·H could be transferred to Sn2+ sites for the hydrogenation of –NO2 by hydrogen spillover. Therefore, the high performance of the catalyst can be attributed to a surface synergetic effect among Lewis base sites (Sn2+), AuPt alloy and photogenerated electrons.

Decoupling the electronic and geometric effects of Pt catalysts in selective hydrogenation reaction

Decoupling the electronic and geometric effects has been a long cherished goal for heterogeneous catalysis due to their tangled relationship. Here, a novel orthogonal decomposition method is firstly proposed to settle this issue in p-chloronitrobenzene hydrogenation reaction on size- and shape-controlled Pt nanoparticles (NPs) carried on various supports. Results suggest Fermi levels of catalysts can be modulated by supports with varied work function (Wf). And the selectivity on Pt NPs of similar size and shape is linearly related with the Wf of support. Optimized Fermi levels of the catalysts with large Wf weaken the ability of Pt NPs to fill valence electrons into the antibonding orbital of C–Cl bond, finally suppressing the hydrodehalogenation side reaction. Foremost, the geometric effect is firstly spun off through orthogonal relation based on series of linear relationships over various sizes of Pt NPs reflecting the electronic effect. Moreover, separable nested double coordinate system is established to quantitatively evaluate the two effects.

In Situ Transformation of ZIF-8 into Porous Overlayer on Ru/ZnO for Enhanced Hydrogenation Catalysis.

Supported metal catalysts play a significant role in heterogeneous catalysis in liquid phase reaction systems, but they usually suffer from a stability problem. Encapsulation of active metal species without the compromise of catalytic performance has been considered as an effective strategy. Here, we report an ultrastable Ru-based catalyst with particle size of around 1.1 nm for selective hydrogenation reaction. The highly dispersed Ru species are covered by the in situ formed porous N-C-ZnO overlayer, which is induced through the transforming of ZIF-8 shell that derives from a ZnO substrate. The resulting Ru/ZnO@N-C-ZnO catalyst can exhibit good stability in the hydrogenation of p-chloronitrobenzene after 20 cyclic runs with 100% selectivity toward p-chloroaniline. Comparatively, the naked Ru/ZnO catalyst with larger Ru particles shows serious metal leaching issue with inferior stability and poor selectivity. It is revealed that the excellent performance of Ru/ZnO@N-C-ZnO is attributed to the porous overlayer, which strengthens the bonding of Ru nanoparticles on ZnO.