Hean Luo

Palladium Supported Catalysts for Nitrocyclohexane Hydrogenation to Cyclohexanone Oxime with High Selectivity

Different kinds of activated carbon‐ and carbon nanotube‐supported palladium catalysts were investigated in the selective hydrogenation of nitrocyclohexane to cyclohexanone oxime under mild conditions. Carbon nanotube‐supported palladium catalysts demonstrate better catalytic performance than activated carbon‐supported palladium catalysts in general because of their mesoporous structures, which are favorable supports for the accessibility of the reactants to the active sites and the product desorption from the catalyst. Hydrogen chemisorption, transmission electron microscopy and X‐ray photoelectron spectroscopy indicate that higher composition of Pd+ on the catalyst surface, larger palladium surface area, and better palladium dispersion contribute to an increase in the activity and selectivity toward cyclohexanone oxime. In addition, single‐wall carbon nanotube‐supported palladium catalysts give the best result of 97.7 % conversion of nitrocyclohexane and 97.4 % selectivity toward cyclohexanone oxime. On the basis of the results of GC–MS and the designed experiments, a possible reaction scheme was proposed.

One-Step Cyclohexane Nitrosation to ε-Caprolactam over Metal Substituted AlPO-5

Abstract Crystalline AlPO-5, SAPO-5, and metal substituted AlPO-5 (MeAlPOs) were prepared by the hydrothermal method and characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, particle size distribution, inductively coupled plasma (ICP) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, NH3 temperature-programmed desorption (TPD), H2 temperature-programmed reduction, and thermogravimetric-differential thermogravimetric (TG-DTG) analysis. All the samples crystallized with the AFI structure. TPD profiles showed that stronger Bronsted acid sites appeared and the number of Lewis acid sites increased when Si or a metal was introduced into the framework of AlPO-5. ICP, FT-IR spectra, and TG-DTG curves confirmed that Si or the metals were incorporated into the framework of the AlPO-5. The catalytic properties of the samples in cyclohexane nitrosation to e-caprolactam were studied. SAPO-5 with a larger BET surface area, more Lewis acid sites, and stronger Bronsted acid sites gave better activity and selectivity than AlPO-5. Among the MeAlPOs, CrAPO-5 with the larger BET surface area, more Lewis acid sites, and stronger Bronsted acid sites gave the better result with a conversion of 8.16% and e-caprolactam selectivity of 68.17%.

Catalytic properties of nickel/sepiolite promoted with potassium and lanthanum in adiponitrile hydrogenation under mild conditions

Ni/sepiolite, potassium and (or) lanthanum doped Ni/sepiolite catalysts were prepared by the incipient impregnation method and characterized by N2 adsorption–desorption, temperature programmed reduction (TPR), hydrogen chemisorption, powder X-ray diffraction (XRD), ammonia temperature programmed desorption (NH3-TPD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was revealed that the potassium could inhibit the formation of the ACH by-product by neutralizing some acid sites on the catalyst, and the lanthanum could efficiently reduce the diameter and improve the dispersion of the active nickel particles. These catalysts were tested in liquid phase hydrogenation of adiponitrile (ADN). The products include 6-aminocapronitrile (ACN), hexamethylenediamine (HMDA), 1-azacycloheptane (ACH) and C12 compounds. It shows that the catalyst doped with potassium and lanthanum gives the best catalytic performance, the selectivity to ACN and HMDA reaches to 91.32% at 92.56% conversion of adiponitrile under 393 K and 2.0 MPa.

The influences of preparation methods on the structure and catalytic performance of single-wall carbon nanotubes supported palladium catalysts in nitrocyclohexane hydrogenation

Single-wall carbon nanotubes (CNTs) supported palladium catalysts were prepared by different methods. The influences of different preparation methods on the structure and catalytic performance in nitrocyclohexane hydrogenation were investigated. The catalysts were characterized by nitrogen adsorption–desorption, XRD, TEM, hydrogen chemisorption and X-ray photoelectron spectroscopy. The results show that Pd/SWCNTs prepared by a water impregnation method provide a smaller particle size of palladium. The reduction conditions have great influence on the valence state of palladium on the support. A catalyst with smaller particle size, better dispersion and higher content of monovalent palladium exhibits better catalytic performance in nitrocyclohexane hydrogenation to cyclohexanone oxime. Pd/SWCNTs-2 prepared by a water impregnation method and reduced at 723 K has 96.4% selectivity when synthesizing cyclohexanone oxime with a 96.0% conversion from nitrocyclohexane under mild conditions of 0.3 MPa and 323 K.

Catalytic oxidation of cyclohexane by substituted metalloporphyrins: experimental and molecular simulation

A series of meso-substituted metal tetraphenylporphyrins were synthesized and characterized by UV-vis, FT-IR and elemental analysis. The experimental results show that cobalt tetra(4-nitrophonyl)porphyrin (Co–TNPP) gives better catalytic performance in cyclohexane oxidation. The KA oil (cyclohexanol and cyclohexanone) selectivity is 79.54% at the cyclohexane conversion of 10.43%, and the turnover number reaches to 0.93 × 104. Cyclohexane oxidation catalyzed by meso-substituted metalloporphyrins was studied by molecular simulation and experiment. The results of molecular simulation performed by Materials Studio show that the substituted electron-withdrawing groups in the same central metal porphyrins reduce the HOMO and LUMO energies. The metalloporphyrins with lower energy gap have stronger ability to activate the oxygen, the metalloporphyrin intermediates with lower energy gap have stronger ability to activate the cyclohexane.

Influence of preparation conditions on the structure of MCM-41 and catalytic performance of Ru/MCM-41 in benzene hydrogenation

The influence of the preparation conditions on the structures of mesoporous molecular sieve MCM-41 were studied. The prepared MCM-41 samples were characterised by nitrogen physical adsorption–desorption, powder X-ray diffraction, transmission electron microscopy, FT-IR spectroscopy, thermo gravimetric analysis, differential scanning calorimetry and water/benzene static adsorption technologies. Ru/MCM-41 catalysts were then prepared by double solvent impregnation method and tested for benzene hydrogenation to cyclohexene. The structure characteristics of MCM-41 have a great effect on cyclohexene selectivity in benzene hydrogenation process. Ruthenium supported on MCM-41 with moderate surface area, larger pore size and pore volume, better long-range-order of hexagonal mesoporous shows better catalytic performance for benzene hydrogenation to cyclohexene.

One-step synthesis of ɛ-caprolactam via the liquid phase catalytic nitrosation of cyclohexane in the presence of concentrated sulfuric acid

A simple and efficient approach for the synthesis of ɛ-caprolactam via the liquid phase nitrosation of cyclohexane and nitrosyl sulfuric acid in the presence of concentrated sulfuric acid has been developed. A series of novel AlVPO composites were prepared by an impregnation method and the composites were then employed to catalyze the nitrosation reaction of cyclohexane and nitrosyl sulfuric acid. Compared to the reaction using fuming sulfuric acid, the selectivity for the desired product was significantly improved using this one-step catalytic process. This method affords a shortcut to prepare ɛ-caprolactam and its analogs from cyclohexane.