Qunfeng Zhang

Aqueous system for the improved hydrogenation of phenol and its derivatives

The hydrogenation of phenol to cyclohexanol under mild conditions (∼340 K) was achieved over Raney Ni catalyst in the aqueous phase. The adsorption–desorption properties of the reactants (phenol and H2) and the products (cyclohexanone and cyclohexanol) on the Raney Ni catalyst are different in the aqueous phase and the organic phase. The hydrogenation rate of phenol is improved because the Raney Ni catalyst adsorbs more H2 and phenol in water than in methanol. Meanwhile, the higher uptakes of H2 and the lower desorption rates for cyclohexanone on the Raney Ni catalyst in the aqueous system result in the further hydrogenation of cyclohexanone to cyclohexanol.

Tailoring supported palladium sulfide catalysts through H2-assisted sulfidation with H2S

Supported palladium sulfide catalysts are of great interest in selective hydrogenation reactions. In this work, “Pd4S”, “Pd3S”, “Pd16S7” and “PdS” supported on activated carbon were selectively synthesized by tailoring the H2-assisted sulfidation of Pd/C with H2S at 150–750 °C, and were characterized by means of XRD, XPS, TEM, HRTEM, EDS, BET and H2-TPR techniques. The results indicated that the sulfidation atmosphere, the sulfidation temperature and the metal–support interaction all played important roles in determining the crystal structure and composition of the PdxSy/C catalysts, which in turn gave different catalytic performances in the synthesis of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) by the reductive N-alkylation of aromatic amines. PdS/C showed the highest selectivity (>97%) and stability among all the PdxSy/C catalysts.

The effect of Si/Al ratio on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

Ethylbenzene is the major side product in benzene alkylation with methanol and it is difficult to be suppressed over hierarchical porous ZSM-5. Moreover, the separation of ethylbenzene from xylene still remains a great challenge. Our research indicated that ethylbenzene formation could be highly suppressed by changing the Si/Al ratio of the catalyst. Hierarchical porous ZSM-5 catalysts with different Si/Al ratios were prepared via reducing the amount of Al in the solvent evaporation assisted dry gel conversion method. In this method, tetra-n-propylammonium hydroxide was used as the direct agent to create micropores, and hexadecyltrimethoxysilane was added to create additional porosities by forming organic assemblies which occupied a certain space between zeolitic walls. The catalyst with a Si/Al ratio of 1800 could achieve high benzene conversion (59.5%) and high xylene selectivity (39.0%) as well as excellent suppression of ethylbenzene formation (<0.1%).

Catalytic Activity of Pt Modified Hierarchical ZSM-5 Catalysts in Benzene Alkylation with Methanol

Hierarchical ZSM-5 zeolite showed an improved performance as compared to conventional ZSM-5 catalysts in the alkylation of benzene with methanol. However, ethylbenzene yet remains as a major problem. In this study, we modified hierarchical ZSM-5 with Pt to evaluate the alkylation of benzene with methanol in a fixed-bed continuous flow reactor. It was found that Pt modified hierarchical ZSM-5 could successfully combine the catalytic advantages of hierarchical ZSM-5 and the high suppression of Pt to ethylbenzene formation. Moreover, employing direct reduction could improve the utilization of Pt by avoiding Pt particles sintering.Graphical Abstract.

Alkylation of benzene with methanol over hierarchical porous ZSM-5: synergy effects of hydrogen atmosphere and zinc modification

The competitive reaction of methanol to olefins is difficult to be suppressed in benzene alkylation with methanol over hierarchical porous ZSM-5. The influence of ZnO content and different atmospheres on the catalytic performance of hierarchical porous ZSM-5 catalyst was investigated. The results indicated that the introduction of ZnO could form the Lewis acid sites of zinc species (ZnOH+) at the expense of the Bronsted acid sites, and the reduction of strong Bronsted acid would help to suppress the side reaction of methanol to olefins. However, the presence of ZnOH+ could catalyze the dehydrogenation reaction of light hydrocarbons to olefins which would result in the formation of coke under the nitrogen atmosphere, while the hydrogen atmosphere could inhibit the dehydrogenation ability of ZnOH+.

A phosphorus–carbon framework over activated carbon supported palladium nanoparticles for the chemoselective hydrogenation of para-chloronitrobenzene

A novel Pd–P–C framework structure was fabricated by supporting Pd on a P-doped carbon layer coated with activated carbon. A P-doped carbon layer was generated via calcination of sodium hypophosphite and ethanediol under inert gas atmosphere. The catalysts were characterized by Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) and were evaluated in the selective hydrogenation of p-CNB to p-CAN. The results indicate that the carbon layer generated via calcination of ethanediol presents a higher disordered structure and then the P-doped carbon layer becomes more ordered due to the formation of a P–C framework. Some electrons were transferred from C atoms adjacent to the P atoms to P atoms, which favors the formation of stable Pd–P species such as the Pd15P2 phase. Pd in the Pd–P–C framework structure possesses electron-rich properties resulting from electron transfer from C atoms to Pd atoms via P atoms, which induces the formation of electron-rich hydrogen (H−) when hydrogen was absorbed on the Pd particles. The produced electron-rich H− might prefer the nucleophilic attack on the nitro group rather than the electrophilic attack on the C–Cl bond. We suggest that it is responsible for the superior selectivity of up to 99.9% to p-CAN for the hydrogenation of p-CNB. The catalytic performance of the Pd particles supported on the P-doped carbon layer remains unchanged after five cycles indicating excellent stability.

N-Heterocyclic carbene catalyzed direct carbonylation of dimethylamine

N-Heterocyclic carbene (NHC) catalyzed direct carbonylation of dimethylamine leading to the formation of DMF was successfully accomplished under metal-free conditions. The catalytic efficiency was investigated and the turnover numbers can reach as high as >300. The possible mechanism was also proposed.

Cu–Pd/γ-Al2O3 catalyzed the coupling of multi-step reactions: direct synthesis of benzimidazole derivatives

The coupling of multi-step reactions catalyzed by a heterogeneous catalyst is an important path to accomplish some unconventional chemical transformations. Since the starting materials generated from previous steps were adsorbed on the catalyst, the activation energy of following steps was largely decreased, and thus the reaction conditions were more mild and environmental friendly. Catalyzed by a multifunctional Cu–Pd/γ-Al2O3 catalyst, the transfer hydrogenation and successive cyclization coupling reaction from o-nitroaniline and alcohol to afford benzimidazole derivatives in high yield was realized. The catalyst could be reused several times without loss of activity. The synergies of reforming hydrogenation of Cu–Pd bimetal and support acidity of γ-Al2O3 were responsible for this catalytic transformation.

Promoting effects of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for catalyzing benzene alkylation with methanol

The effect of MgO and Pd modification on the catalytic performance of hierarchical porous ZSM-5 for benzene alkylation with methanol was investigated. The results indicated that the introduction of MgO could reduce the Bronsted acid sites which suppressed the side reaction of methanol to olefins and in turn effectively promoted the alkylation of benzene. However, the single modification of MgO could not completely suppress the formation of ethylbenzene and coke. Doping a small amount of Pd had a positive effect on inhibiting the generation of ethylbenzene and coke, which could be attributed to the hydrogenation of ethylene into ethane on Pd. The dual modified catalyst (MgO and Pd) exhibited high benzene conversion (56%) and xylene selectivity (39.1%), and the lowest ethylbenzene selectivity (0.13%) and coke content (0.4 wt%).

Preparation of supported core–shell structured Pd@PdxSy/C catalysts for use in selective reductive alkylation reaction

Supported noble-metal sulphide catalysts have attracted extensive scientific interest for their good selectivity in selective hydrogenation. However, the application of noble-metal catalysts is limited due to their lower activity, leading to harsh reaction conditions and poor conversion during hydrogenation reactions. In this study, Pd/C was sulphidized by H2S to prepare a series of core–shell structured Pd@PdxSy/C catalysts, which were characterized by BET, EDS, XPS, XRD and CO chemisorption to investigate the influences of sulphidation temperature, sulphidation time and sulphidation atmosphere on the structure of the resulting catalysts. The sulphidation of Pd/C at low temperatures resulted in a core–shell structured catalyst, Pd@PdxSy/C; with increasing sulphidation temperature, the size of Pd0 as the core decreased, and the thickness of palladium sulphides as the shell increased correspondingly. When the sulphidation temperature reached 150 °C, the resulting catalyst transformed to a complete palladium sulphide catalyst, PdxSy/C. The structure of Pd@PdxSy/C sulphidized at 30 °C was independent of sulphidation time and sulphidation atmosphere. The sulphidized catalysts were applied to the reductive alkylation of PADPA and MIBK to DBPPD. The sulphidized catalysts presented a much higher selectivity for DBPPD compared with Pd/C, and Pd@PdxSy/C showed higher activity than PdxSy/C; moreover, the greater amount of PdxSy content in the resulting catalyst led to a lower activity.