X.-H. Lu

Highly active electron-deficient Pd clusters on N-doped active carbon for aromatic ring hydrogenation

N-doped active carbon (N-AC) has been synthesized via heat treatment of a mixture consisting of dicyandiamide as the nitrogen source and commercial active carbon as the precursor. This material is especially adapted for anchoring ultrafine Pd nanoparticles by a very clean strategy using H2 as the reductant. The physicochemical properties of materials were investigated by powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results reveal that the variation of the treatment temperature can assist the tuning of the content of N and the dispersion of Pd on xN-AC, by which Pd nanoparticles with a narrow size distribution centered at around 1.8 nm can be obtained. These robust catalysts show very high catalytic activity for the aromatic ring hydrogenation of acidic substrates, such as electron-deficient benzoic acid or electron-rich phenol, under mild conditions in aqueous media. Excellent catalytic results (9.2 times higher activity in comparison to non-doped catalyst for benzoic acid hydrogenation), high stability and easy recyclability of the catalyst were achieved. The strong interaction between the pyridinic nitrogen group and Pd species will lower the reducibility of the Pd species and result in the formation of relatively electron-deficient and ultra-small sized Pd clusters, thus leading to high hydrogenation activity.

Mild-temperature hydrodeoxygenation of vanillin over porous nitrogen-doped carbon black supported nickel nanoparticles

Porous nitrogen-doped carbon black (NCB) was synthesized by facile carbonization of carbon black (CB) coated with polypyrrole (CB@polypyrrole) and used as a support for Ni nanoparticles (NPs). The microstructure, reducibility and crystallinity of the as-synthesized materials were investigated by transmission electron microscopy (TEM), H2-TPR/TPD, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that surface nitrogen species on NCB significantly promote the decomposition of the nickel precursor and the reduction of nickel oxide, and improve the stability of metallic Ni in ambient atmosphere. In the selective hydrodeoxygenation (HDO) of vanillin in the aqueous phase at low hydrogen pressure (0.5 MPa) and mild temperature (<150 °C), Ni/NCB shows much higher activity than N-free catalysts. This is ascribed to the higher reducibility, the lower oxidation state of Ni NPs and the enhanced hydrogen spillover of Ni to the support. Moreover, the Ni/NCB catalyst is relatively cheap and easy to scale-up the production of, thus achieving a low-cost transformation of biomass to bio-oils.

Transfer hydrogenation of bio-fuel with formic acid over biomass-derived N-doped carbon supported acid-resistant Pd catalyst

Nitrogen-enriched highly mesoporous carbons (NMCs) are synthesized via the one-pot carbonization of biomass-derived glucose and harmless melamine with ZnCl2 as the porogen agent and catalyst. NMC contains an N content of 15.4 wt% and specific surface area of 1017 m2 g−1 with the mesopore volume proportion of 92.1%. Owing to its rich N species and high mesoporosity, NMC can be adapted as a proper support for the fabrication of well-dispersed Pd catalysts for the transfer hydrogenation of vanillin in the water phase with formic acid (FA) as the hydrogen donor. For example, Pd/NMC exhibits 2.9 times higher activity in comparison to nitrogen-free catalysts, and affords 100% vanillin conversion with 2-methoxy-4-methylphenol (MMP) as the sole product. The Pd/NMC catalyst demonstrates enhanced acid-resistance in acid media and adsorption of substrates. It is found that the electron-deficient Pd (Pdδ+) percentage is affected by the N species, and the strong Pd–N interaction generates the co-existence of Pdδ+ and metallic Pd (Pd0), which results in Pd/NMC as a novel bifunctional nanocatalyst for both FA dehydrogenation and vanillin hydrogenation.

Efficient aqueous hydrodeoxygenation of vanillin over a mesoporous carbon nitride-modified Pd nanocatalyst

Highly mesoporous carbon nitrides (CN) are synthesized through a simple polymerization reaction, including ethylenediamine (EDA), organic chlorides, with nano SiO2 as a hard-template. The degree of polymerization of the as-synthesized CN can easily be controlled by varying the organic chlorides. The CN derived from chloroform exhibits a low degree of polymerization, along with a high specific surface area of 315.9 m2 g−1 and pore volume of 0.87 cm3 g−1, in which the mesopore volume proportion reaches as high as 90.9%. Owing to the rich N groups (15.6 wt%), this basic network with open channels renders homogeneously dispersed Pd coordinated in the mesoporous carbonaceous framework and creates a highly active and stable Pd/CN catalyst for the selective hydrodeoxygenation of vanillin at low pressure (<1 MPa) and temperature (<70 °C). The best TOF reaches 295.4 h−1, and the Pd/CN catalyst can be used at least 6 times without obvious loss of its catalytic performance.

Co embedded within biomass-derived mesoporous N-doped carbon as an acid-resistant and chemoselective catalyst for transfer hydrodeoxygenation of biomass with formic acid

An N-doped Co@C catalyst (Co@NC) is synthesized by a one-pot carbonization of biomass-derived glucose and harmless melamine with CoCl2 as the catalyst, where C and N resources could be transformed into highly graphitic N-doped carbon, while the coordinated Co2+ ions are reduced to uniform Co nanoparticles (NPs), which are embedded in N-doped graphitic structures. Under base-free conditions with formic acid (FA) as a hydrogen donor, the optimized Co@NC-700 (pyrolyzed at 700 °C) shows a highly efficient H2 generation from FA and the best activity for vanillin hydrodeoxygenation (HDO) with FA. For example, Co@NC-700 exhibits 15.4 times higher activity in comparison with uncovered Co on AC (Co/AC), and affords >95% vanillin conversion with 2-methoxy-4-methylphenol (MMP) as the sole product at 180 °C for 4 h. Compared with molecular hydrogen, Co@NC-700 gives a much higher activity and MMP selectivity for vanillin HDO with FA. The Co@NC-700 demonstrates enhanced acid resistance in acidic medium and adsorption of vanillin, and is recyclable and versatile for hydrogenating various unsaturated compounds. The superior performance of Co@NC-700 could be ascribed to N-derived defective sites on Co@NC, which could play multiple roles as base additives in FA dehydrogenation and as a metal-like active center in vanillin HDO.

Highly selective one-step hydrogenation of nitrobenzene to cyclohexylamine over the supported 10% Ni/carbon catalysts doped with 3‰ Rh

The carbon supported 10% Ni catalysts doped with 3‰ Rh have been prepared by an impregnation method. These catalysts have been used to catalyze the one-step hydrogenation of nitrobenzene to cyclohexylamine. The results show that the 3‰ Rh–10% Ni/CSC (biocarbon) catalyst exhibits an excellent performance to achieve 100 mol% conversion of nitrobenzene and 91.6% selectivity of cyclohexylamine under reaction conditions of 3.5 MPa and 140 °C. The recycling tests reveal recyclable stability of 3‰ Rh–10% Ni/CSC. This catalyst is active for the hydrogenation of a series of electron-deficient nitrobenzenes. Some factors such as the type of carriers, the content of Ni and Rh, the type of metals and additives play important roles in controlling the selective hydrogenation.

Microwave-activated Ni/carbon catalysts for highly selective hydrogenation of nitrobenzene to cyclohexylamine

Biocarbon supported Ni catalysts have been prepared by facile impregnation of Ni species by microwave-heating and used for selective hydrogenation of nitrobenzene to cyclohexylamine. These catalysts were characterized by X-ray diffraction, Raman spectra, N2 sorption measurement, X-ray photoelectron spectroscopy, temperature programmed reduction of H2 and H2 temperature-programmed desorption. The morphology and particle size of catalysts were imaged by scanning electron microscope and transmission electron microscope. For the hydrogenation of nitrobenzene to cyclohexylamine, 10%Ni/CSC-II(b) exhibits the best catalytic activity to achieve 100 mol% conversion of nitrobenzene and 96.7% selectivity of cyclohexylamine under reaction conditions of 2.0 MPa H2 and 200 °C, ascribed to high dispersion of Ni species and formation of nanosized Ni particles on the support aided by microwave-heating. Thus-prepared Ni/CSC catalyst is greatly activated, in which the addition of precious metal like Rh is totally avoided.

Oxidative desulfurization of thiophene derivatives with H2O2 in the presence of catalysts based on MoO3/Al2O3 under mild conditions

The catalysts based on MoO3/Al2O3 were synthesized and tested using aqueous hydrogen peroxide as the oxidant in the oxidative desulfurization of thiophene, benzothiophene (BT) and dibenzothiophene (DBT) into the corresponding sulfones. Among catalysts tested, 15%(MoO3–WO3)/Al2O3 prepared by a conventional impregnation method was considerably active for the oxidation of thiophene, BT and DBT, which could achieve higher than 99.2% conversions at lower reaction temperature (≤338 K). The use of hexadecyltrimethyl ammonium bromide as the phase-transfer reagent in small amounts could promote the reaction efficiently.

High-Rota Synthesis of Single-/Double-/Multi-Unit-Cell Ti-HSZ Nanosheets To Catalyze Epoxidation of Large Cycloalkenes Efficiently

This work first reports high-efficiency epoxidation of large cycloalkenes (carbon number ≥ 7) with tert-butyl hydroperoxide (TBHP) over single-/double-/multi-unit-cell nanosheet-constructed hierarchical zeolite, which is synthesized by one-step hydrothermal crystallization using piperidine as the structure-directing agent of the microporous structure. The excellent catalytic property of the material is ascribed to its unique structural characteristic. Plenty of surface titanols or silanols on the surface of MWW nanosheets are beneficial for the formation of transition-state intermediates; a large number of intercrystalline mesopores in the shell of the material not only facilitate the formation of the intermediate for TBHP but also have nearly no hindrance for the diffusion and mass transfer of bulky cycloalkene to the above intermediates; the 12-MR side cups penetrating into the crystals from the external surface are exposed as much as possible to the reaction system because of the single-/double-/multi-unit-cell MWW nanosheet, serving as the primary reaction space for the epoxidation of bulky cyclic alkene and oxidants and providing enough space for the transition state of Ti-OOtBu and bulky cycloalkane. Moreover, an efficient calcination-free catalytic reaction-regeneration method is developed to overcome the challenge for the recyclability of microporous Ti-zeolite in the catalytic epoxidation of bulky cycloalkenes.