Selective hydrogenation of nitrobenzene to aniline is an environmentally relevant transformation for converting hazardous nitroaromatic compounds into value-added chemical intermediates under mild conditions. However, nitrobenzene hydrogenation over single-atom catalysts is often limited by the kinetic mismatch between H₂ activation at isolated metal sites and the sustained supply of reactive hydrogen to adsorbed nitro groups. Herein, we report a defect-rich boron nitride-supported Pd single-atom catalyst, Pd₁/u-d-BN, prepared via a urea-assisted ball-milling strategy. Isolated Pd atoms are stabilized in a well-defined Pd₁–N₄ coordination environment, enabling efficient nitrobenzene hydrogenation to aniline under ambient conditions with a turnover frequency of 3672 molNB·molPd−1·h⁻¹ , an aniline selectivity of 99.5%, and an apparent activation energy of 36.2 kJ mol−1. The catalyst also shows broad applicability toward substituted nitroarenes, affording the corresponding aminoarenes with high selectivity. Kinetic analysis, in situ spectroscopic characterization, and theoretical calculations reveal that Pd₁–N₄ sites promote H₂ dissociation and nitro-group activation, while adjacent vacancy defects act as transient reservoirs for spillover H species and mediate their local delivery to adsorbed nitro intermediates. This activation–spillover–buffering mechanism addresses the coupled limitations of H₂ activation and reactive hydrogen utilization in single-atom hydrogenation catalysis.

Catalytic hydrogenation of aromatic carboxylic esters (ACE) makes them intrinsic safe and environmentally friendly, meanwhile endowing with tailored functionalities (e.g., flexibility or weatherability). In this work, a Ru catalyst supported on porous boron nitride (Ru/p-BN) were prepared and applied in the hydrogenation of dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD). The p-BN with rich B/N vacancies and boron-oxygen defects promoted the dispersion of Ru. The 2Ru/p-BN catalyst harbored Ru clusters with an average particle size of 1.86 nm, featured abundant Ru edge sites and a high proportion of Ru0. With this unique structure, its catalytic performance and stability were significantly enhanced, with a DMT conversion over 99 %, and a DMCD selectivity of 99.7 %, under 50 degrees C and 5 MPa. The initial reaction rate was 252 molDMT center dot molRu-1 center dot h-1 with a low activation energy of 21.2 kJ/mol. The edge sites Ru clusters were identified as the dominant active sites for the DMT hydrogenation based on further study. Besides, the catalyst showed wide applicability, providing guidance regarding future catalyst design to the hydrogenation of a range of ACE.

The efficient hydrogenation of nitroaromatics under mild conditions remains a significant challenge, particularly while retaining sensitive functional groups. Herein, we report a cobalt-based catalyst supported on nitrogen-doped carbon (10% Co@NC), which achieved 100% conversion and >99% selectivity in the hydrogenation of nitrobenzene at mild temperature (30 °C) and pressure (10 bar). The catalyst exhibited an exceptional space-time yield of up to 1.89 g·gcat-1·h-1, surpassing most reported cobalt-based catalysts. The catalyst demonstrated remarkable stability for over 400 h. The outstanding performance originated from the synergistic effect between the nitrogen-doped carbon support and the metallic cobalt particles. Such efficient hydrogenation under ambient temperatures is exceedingly rare among non-noble metal-based catalysts. In situ DRIFTS experiments and Density Functional Theory (DFT) calculations revealed that the nitrogen vacancy (Nv) in the carbon matrix played a pivotal role by giving rise to the spontaneous hydrogenation of the nitro group, thereby enabling the high-performance catalysis under mild conditions.

Bio-based pentamethylene dicarbamate (PDC) serves as a crucial intermediate in the synthesis of bio-based pentamethylene diisocyanate (PDI) via a non-phosgene route, and its carbonylation synthesis holds significant scientific and industrial importance. In this study, niobium-doped ceria (NbxCe) catalysts were designed and synthesized for the carbonylation reaction between pentanediamine (PDA) and methyl carbamate (MC). The catalytic performance of CeO2 on the carbonylation of PDA was promoted by the surface modulation by Nb doping. Nb0.06Ce achieved a space-time yield of PDC up to 32.4 gPDC·gcat.-1·h-1, which was 1.4 times higher than that of CeO2. The catalysts were characterized by XRD, BET, TEM, XPS, EPR, NH3/CO2-TPD, and Py-IR. Catalyst characterization results suggested that the superior catalytic performance of Nb0.06Ce may be attributed to the synergistic combination of high oxygen vacancy concentration, abundant surface-adsorbed oxygen species, plentiful acid-base sites, and a large specific surface area. In-situ FTIR analysis confirmed that the alcoholysis of polyurea intermediates was a key step in the synthesis of PDC, and this process was notably accelerated in the presence of the catalyst. In-situ DRIFTS further indicated the Nb0.06Ce facilitated the adsorption and activation of reactants. In the catalytic reaction, the polyurea intermediate was activated by the acid-base sites on the surface of NbxCe, generating the final product PDC. The Nb0.06Ce catalyst demonstrated excellent stability, maintaining its catalytic activity after multiple reaction cycles. Furthermore, it was successfully applied to the efficient carbonylation synthesis of various aliphatic carbamates, highlighting its broad applicability.

Non-noble metal-based catalysts are highly desired for the catalytic hydrogenation of nitroaromatics. Here we reported a catalyst of Co-1/Co-n@NCNS prepared with raw materials for efficient hydrogenation of nitrobenzene (NB), in which the Co nanoparticle (Co-NP) was tightly coated in a nitrogen-doped graphite carbon shell, and the Co single atom (Co-SA) was uniformly anchored on graphite support. The catalyst achieved a conversion of NB for over 99 % under mild conditions at 50 degrees C and 10 bar. The catalyst was able to consistently maintain over 90 % conversion and 99 % selectivity for 100 h, and exhibited outstanding catalytic activity and selectivity (>99 %) towards the reduction of various nitroaromatics, even though for halogen-containing substrates. The superior catalytic performance resulted from the synergy between the internal Co (NP) and the surface Co-SA on the nitrogen-doped carbon shells. Both Co-NP and Co-SA synergistically facilitated electron transfer to nitrogen atoms in the carbon framework, and rendered them catalytic activity during the hydrogenation.

Cyclic carbonates are valuable green chemicals with wide-ranging applications, but their conventional synthesis often involves toxic reagents or inefficient catalytic systems. In this work, zirconia catalysts with different crystalline phases (getragonal, monoclinic, and mixed-phase) were developed and evaluated for the trans-esterification of 1,2 butanediol with dimethyl carbonate. The tetragonal ZrO2 (t-ZrO2) exhibited superior cata-lytic activity (space-time yield of 41.76 g1,2-sc goat h(1)) due to favorable surface properties and exposed active (101) facet. This study establishes a green, efficient route for 1,2-butylene carbonate synthesis, providing key insights into catalyst structure-activity relationships.

Green production of dicycloalicyclic amine is of great importance and faces significant challenges. At the same time, the addition of liquid alkali to prevent deamination and condensation is environmentally hazardous, and the hydrogenation of aromatic amines requires high temperature and pressure. In this study, a urea-assisted ball milling process was developed to prepare defect-rich boron nitride (d-BN) as a support for Ru/d-BN catalysts, enabling environmentally friendly and efficient hydrogenation of 4,4′-diaminodiphenylmethane (MDA) to produce alicyclic amines. As a result, exceptional activity was achieved with only 3.0 wt% Ru loadings on d-BN nanosheets at 130 °C and 3 MPa, reaching 100% MDA conversion and 99.6% selectivity of 4,4-diaminodicyclohexylmethane (PACM). Based on the correlation between the catalytic activities of defective sites, amino groups and active metal Ru clusters, combined with the results of defective site quenching experiments, electron paramagnetic resonance (EPR), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and density functional theory (DFT) calculations, a synergistic interaction between the defects, amino groups and the metal Ru was proposed. The Ru/d-BN catalysts modulated the metal Ru at the Fermi energy level through the Ru–N and Ru–B bonds, which promoted the adsorption of MDA and desorption of the product PACM. Moreover, the d-BN support played a crucial role in metal particle dispersion and promoting hydrogen spillover. Stability evaluations and substrate experiments demonstrated the outstanding hydrogenation activity and robust stability of Ru/d-BN catalysts. Kinetic analysis revealed a reduced activation energy of 75.08 kJ/mol for the reaction, 50 kJ/mol lower than that of Ru/h-BN.

The selective hydrogenation of nitroaromatics to aromatic amines is of great significance in green chemistry and chemical engineering, but mild and efficient hydrogenation remains a challenge. Here we reported a novel catalyst consisting of palladium single atoms (PdSA) and palladium clusters (PdC) supported on defective TiO2 (TiO2-OV) for highly efficient nitrobenzene hydrogenation to aniline. The 0.20% PdSA+C/TiO2-OV achieved a turnover frequency (TOF) of 21154 h-1 under 25 degrees C and 0.15 MPa, which outperformed most of the reported noble metal-based catalysts. In situ DRIFTS showed that Pd enhanced & horbar;NO2 adsorption but the excessive Pd would lead to unnecessary adsorption of the aromatic ring. This work proposed a strategy of developing highly efficient synergistic Pd-based catalysts for the hydrogenation of a variety of nitroaromatics.

Green production of alicyclic amines is highly desirable but of great challenges. Herein, an efficient one-pot synthesis of alicyclic amines from nitroaromatics was realized with a Pt-Ru bimetallic catalyst. 0.5 %Pt-2.5 % Ru supported on an air-exfoliated C3N4 nanosheet achieved 100.0 % conversion of nitrobenzene (NB) with 98.9 % selectivity of cyclohexylamine (CHA) under mild conditions of 80 degrees C and 1 MPa, attaining a yield rate for alicyclic amine of 357.9 mmol/gmetal & sdot;h. Our study has shown hydrogenation of nitro group and aromatic ring took place in sequence over Pt and Ru in a tandem manner due to the highly selective adsorption. During the hydrogenation, the homolytic dissociation of H2 occurred on the bimetal sites and the inter-site hydrogen spillover between the bimetal played a crucial role. C3N4 nanosheet as the support not only gave rise to the uniform dispersion of metal nanoparticles, but was crucial in curbing the unnecessary adsorption of intermediate aromatic amines. Our study has also demonstrated the good stability and wide applicability of the Pt-Ru/C3N4-air catalyst for the hydrogenation of various nitroaromatic derivatives.

Dimethyl hexane-1,6-dicarbamate (HDC), the vital intermediate for nonphosgene production of hexamethylene-diisocyanate (HDI), was effectively synthesized via carbonylation of 1,6-hexanediamine (HDA) using methyl carbamate (MC) as a carbonyl source over a silanol-rich MCM-41 catalyst. The effects of reaction conditions, including the reaction temperature, molar ratio of raw materials, methanol dosage, catalyst dosage, and reaction time, on the HDC yield were evaluated. Under the reaction conditions with a reaction temperature of 190 °C, a molar ratio of HDA, MC, and methanol of 1:6:50, a catalyst dosage of 10 wt %, and a reaction time of 3 h, the yield of HDC can reach as high as 92.6% with 100% HDA converted. Characterizations based on N2 physical adsorption/desorption, scanning electron microscopy (SEM), X-ray diffractometry (XRD), NH3-temperature-programmed desorption (TPD), Fourier transform infrared spectroscopy (FTIR), and 1H magic-angle spinning (MAS) NMR indicated that the abundance of silanol groups on the surface of MCM-41 probably resulted in the good performance of MCM-41. After five cycles of MCM-41, the HDC yield decreased from 92.6 to 67.9%, probably due to the loss of surface silanol groups and the carbon deposition on the catalyst as well as the particle agglomeration. The study on the substrate scope suggested that MCM-41 shows good-to-excellent catalytic performance in the synthesis of a variety of aliphatic and alicyclic dicarbamates.

Bio-based pentamethylene dicarbamate (PDC) belongs to N-substituted carbamates, which are important fine chemicals and organic intermediates. In this work, well-defined CeO2 rods, cubes, and octahedrons were successfully prepared to catalyze the synthesis of PDC by carbonylation of 1,5-pentanediamine (PDA) with methyl carbamate (MC). Among them, CeO2 rods with higher amounts of acid-base sites and abundant oxygen vacancies showed superior intrinsic activity in the PDA carbonylation reaction. In situ FTIR results showed that intermediate polyureas were readily formed in the reaction, and then, CeO2 rods promoted the alcoholysis of polyureas to PDC. In situ DRIFTS results indicated that the surface of CeO2 rods is more favorable for the adsorption and activation of the reactants. CeO2 rods can also be used for the efficient synthesis of a series of N-substituted carbamates. We believe that this work will contribute to the efficient, green, and sustainable production of N-substituted carbamates.

Developing efficient and green catalytic systems is highly desired in the syntheses of alicyclic amines via hydrogenation of nitroaromatics. Herein, we developed Ru-Pd dual active site catalysts in which Ru and Pd species were anchored and highly dispersed on air-exfoliated carbon nitride (Ru-Pd/C3N4-air). As-prepared catalysts were employed in the hydrogenation of nitrobenzene (NB) to cyclohexylamine (CHA). Compared with single Ru or Pd based catalysts, Ru-Pd dual active site catalysts obtained a higher CHA production rate of 26.7 mol CHA mol-1 Ru·Pd h-1 at 80 °C and 3 MPa H2. The activation energy for the hydrogenation of the nitro group and benzene ring was calculated as 26.26 kJ mol-1 and 66.30 kJ mol-1, respectively. Intrinsic kinetic studies demonstrated that Pd was the dominant metal for hydrogenation of nitro group, while Ru was dominant for benzene ring. Thereinto, the corresponding non-dominant metals enhanced activation and dissociation of H2, thereby improving catalytic activity significantly. This excellent performance of Ru-Pd catalysts could be attributed to highly dispersed Ru-N x and Pd-N x at a nanoscale distance, which was conducive to metal-assisted hydrogenation. Stability investigation showed that the performance of Ru-Pd catalysts could be essentially maintained at a high level. Additionally, the substrate scope could be successfully extended to hydrogenation of other nitroaromatics with different substituents.

Saturated hydrogenation of aromatic amines is a crucialmethodologyfor synthesizing alicyclic amines. The dispersion of Ru atoms occurredafter chemical reduction treatment, which was constrained to B andN coordination, further promoting the Ru species' uniform distributionthrough interaction with the B-N bond of boron nitride. Moreover,the Ru coordinated with h-BN and further formed the stable catalyticactive center. By virtue of its excellent stability, the hydrogenationof MDA executed in the fixed-bed reactor could run for more than 200h. However, the density functional theory showed that the hydrogenationrate of the second benzene ring was comparatively slower because ofthe strong intermediate adsorption during the conversion from 4,4 & PRIME;-diaminodiphenylmethaneto 4,4 & PRIME;-diaminodicyclohexylmethane. Furthermore, Ru/h-BN exhibitedexcellent performance in the hydrogenation of other aromatic amines,resulting in corresponding alicyclic amines. Therefore, this researchoffers a stable and effective catalyst for the green hydrogenationof aromatic amines leading to the production of alicyclic amines.

Diethyl pentane-1,5-diyldicarbamate (PDC), a bio-based intermediate used for isocyanate and polyurethanes, was synthesized by the direct carbonylation of CO2 and pentanediamine (PDA) with 2-cyanopyridine (2-CP) over Zr-doped CeO2. In this study, Zr-doped CeO2 catalysts with different contents of Zr are successfully synthesized to produce PDC from PDA, CO2, and ethanol. Among them, Zr0.05Ce exhibits enhanced reaction activity and the productivity reached 6.0 mmol center dot g (-1)center dot h (-1). Characterizations based on X-ray photoelectron spectroscopy, Raman, and CO2/NH3-temperature-programmed desorption prove that the doping of Zr atoms into CeO2 regulates the acid-base sites and promotes oxygen vacancy formation, which is primarily responsible for the formation of monoethyl carbonate, an intermediate for diethyl carbonate (DEC). In-situ diffuse reflectance Fourier-transform spectrometry and Fourier-transform infrared spectroscopy reveal that PDA reacts with 2-CP to form N, N'(pentane-1,5-diyl)dipicolinamide, which are transformed into PDC. Finally, the catalytic activity could be regenerated after calcination. This study presents a green route for producing bio-based carbamate by constructing C-N bond using CO2 as a carbonyl source, which can replace carbamates derived from petrochemical resources in the future.

In this work, the isomer mixture of 4,4'-diphenylmethane diisocyanate (MDI) and 2,4'-MDI was separated and purified by dynamic falling film melt crystallization, and 99.3% purity and 50.8% yield of 4,4'-MDI could be obtained under optimized conditions. The separation mechanism was simulated by density functional theory (DFT) and molecular dynamics (MD) simulation. Results showed that compared with 2,4'-MDI, 4,4'-MDI molecules could form a more stable and symmetrical crystal structure due to their stronger charge density symmetry and electrostatic potential energy. Furthermore, the separation phenomenon and the formation of the crystal structure were observed according to the radial distribution function (RDF) and orientation correlation function obtained from MD simulation. Finally, the attachment energy (AE) model was used to observe and compare different crystal surfaces; it was proposed that the aggregation of 4,4'-MDI was attributed to the polar attraction between isocyanate groups according to the results of the orientation correlation function. It was also observed that compared with 2,4'-MDI, 4,4'-MDI molecules on the (110) crystal surface were easier to form crystal structures.

Pentamethylene dicarbamate (PDC), a bio-based intermediate used for isocyanate and polyurethanes, was synthesized by the direct carbonylation of CO2 and PDA over Zr-doped CeO2 in the presence of 2-cyanopyridine. As this route adopts renewable, cheap, and available starting materials, i.e., PDA and CO2, the renewable carbon in pentamethylene diisocyanate (PDI) based on PDC reaches 100%. In this study, Zr-doped CeO2 catalysts with different contents of Zr were synthesized successfully for the production of PDC from PDA, CO2, and ethanol. Among them, Zr0.05Ce exhibits better reaction activity and the productivity reached 6.0 mmol·g-1·h-1. Characterizations based on XPS, Raman, and CO2/NH3-TPD prove that doping of Zr atoms into CeO2 not only regulates the acid-base sites but also promotes oxygen vacancy formation, which is primarily responsible for better performance. In situ DRIFTS and FTIR spectra revealed that PDA is prone to react with 2-CP forming intermediate, then transformed to PDC. Finally, it is observed that the catalytic activity was regenerated when the used catalyst was calcinated. This study presents a green route for the production of bio-based carbamate using CO2 as carbonyl source, which is poised to replace carbamates derived from petrochemical resources in the future.

The core strategy for one-top synthesis of alicyclic amine is to develop alkali-free catalytic system with high efficiency . Herein, we devised the strategy that catalyzing multiple hydrogenation processes via dual metals anchored on support rich in alkaline nitrogen sites and developed dual metal cascade catalyst that highly dispersed Ru and Pd species were anchored on air-exfoliated carbon nitride (Ru-Pd/ C 3 N 4 -air). As-prepared catalysts were employed in hydrogenation of nitrobenzene (NB) to cyclohexylamine (CHA). Compared with single Ru and Pd based catalysts, Ru-Pd cascade catalyst obtained higher CHA production rate of 26.7 mol CHA/mol Ru·Pd/h under 80 ℃ and 3MPa H 2 . The activation energy for hydrogenation of nitro group and benzene ring was calculated as 26.26 kJ/mol and 66.30 kJ/mol, respectively. Intrinsic kinetics demonstrated that Pd was dominant metal for hydrogenation of nitro group, while Ru was dominant for benzene ring. Accordingly , for tandem hydrogenation of nitro group and benzene ring, the assisted hydrogenation of non-dominant metal enhanced activation and dissociation of H 2 , thereby improving the catalytic activity significantly. XPS showed that the formed Ru-N x and Pd-N x strong coordination as dual metal active sites facilitated high dispersion of Ru and Pd species at a nanoscale distance, which was conducive to metal-assisted hydrogenation and H 2 spillover. The recyclability investigation showed NB conversion maintained at 100% and CHA selectivity was higher than 90% after 5-cycle using. Additionally, Ru-Pd cascade catalyst was adaptive for tandem hydrogenation of other nitroaromatics with different substituents, suggesting excellent universality for substrate scope.

以碳酸二乙酯(DEC)、1,6-己二胺(HDA)为原料、无水醋酸锰为催化剂,合成了 1,6-六亚甲基二氨基甲酸乙酯(HDEC).通过红外光谱、核磁共振氢谱、气相色谱确定HDEC标样的结构和纯度,并建立了定量分析方法.进一步采用气质联用对反应的主副产物进行定性分析,推测反应路径.同时,对合成工艺进行反应参数优化,并推测反应机理.结果表明,该反应通过两步实现,首先HDA与DEC反应生成单取代的1-(6-氨基)-六亚甲基单氨基甲酸乙酯(HMEC)中间体,HMEC进一步与DEC羰化反应生成HDEC目标产物,同时反应过程中DEC与HDA以及HMEC反应生成脲类副产物.在最佳反应条件原料DEC与HDA摩尔比为3.5∶1、反应温度120℃、无水醋酸锰催化剂用量为HAD初始用量的15％、反应时间5h、转速400r/min下,HDA转化率为100％,HDEC收率达89.6％.本研究为非光气法合成六亚甲基二异氰酸酯(HDI)重要中间体HDEC提供理论借鉴.

An efficient catalyst for chemoselective hydrogenation of nitroaromatics to produce aromatic amines under mild conditions is highly desirable. In this work, a series of N-doped carbon (NC-x) with high nitrogen contents were firstly synthesized by pyrolysis of 1-butyl-3-vinylimidazolium bromide-co-acrylonitrile with a template of g-C3N4. Furthermore, Ru/NC-x catalysts were successfully prepared by ultrasonic-assisted impregnation method. The catalysts were characterized by various methods in detail, e.g.X-ray diffraction, N-2 physical adsorption-desorption, Transmission electron microscopy, Raman spectra, Scanning electron microscopy and H-2 temperature programmed reduction. Characterization results revealed that N-doping on carbon contributed to the high dispersion of Ru nanoparticles and resulted in the forming of the electron-deficient of Ru species. Nanosheet Ru/NC-2 with high N-doping content of 28 wt% exhibited superior performance under room temperature, i.e., nitrobenzene conversion > 99.0% and aniline selectivity 98.4%. Kinetic study indicated that the hydrogenation of nitrobenzene over Ru/NC-2 was the first-order kinetics with an intrinsic activation energy of 43.7 kJ/mol. Density functional theory calculation results suggested that Ru-N-x species, especially, Ru-pyrrolic-N facilitated nitrobenzene adsorption and H-2 dissociation, resulting in enhanced catalytic performance. In addition, the excellent stability of Ru/NC-2 made it essentially reserved for 410 h in the fixed-bed reactor. Moreover, Ru/NC-2 exhibited superior performance for the hydrogenation of various nitroaromatics to corresponding aromatic amines. This work could provide meaningful guidance on designing effective and stable catalyst for chemo-selective hydrogenation of nitroaromatics to aromatic amines under mild conditions.

In this study, nanosheet g-C3N4-H2 was prepared by thermal exfoliation of bulk g-C3N4 under hydrogen. A series of Ru/g-C3N4-H2 catalysts with Ru species supported on the nanosheet g-C3N4-H2 were synthesized via ultrasonic assisted impregnation-deposition method. Ultrafine Ru nanoparticles (<2 nm) were highly dispersed on nanosheet g-C3N4-H2. Strong interaction due to Ru-Nx coordination facilitated the uniform distribution of Ru species. Meanwhile, the involvement of surface basicity derived from abundant nitrogen sites was favourable for enhancing the selective hydrogenation performance of bi-benzene ring, i.e., almost complete 4,4′-diaminodiphenylmethane (MDA) conversion and >99% 4,4′-diaminodicyclohexylmethane selectivity, corresponding to a reaction activity of 35.7 molMDA molRu−1 h−1. Moreover, the reaction activity of catalyst in the fifth run was 36.5 molMDA molRu−1 h−1, which was comparable with that of the fresh one. The computational results showed that g-C3N4 as support was favorable for adsorption and dissociation of H2 molecules. Moreover, the substrate scope can be successfully expanded to a variety of other aromatic diamines. Therefore, this work provides an efficient and green catalyst system for selective hydrogenation of aromatic diamines.