Guangxing Li

Glycerol as a promoting medium for electrophilic activation of aldehydes: catalyst-free synthesis of di(indolyl)methanes, xanthene-1,8(2H)-diones and 1-oxo-hexahydroxanthenes

Glycerol was used, for the first time, as a green and effective promoting medium for electrophilic activation of aldehydes, and with which, a catalyst-free system for some reactions that conventionally carried out using acid catalysts, such as synthesis of di(indolyl)methanes, 3,4,5,6,7,9-hexahydro-9-aryl-1H-xanthene-1,8(2H)-dione and 1-oxo-hexahydroxanthenes, was developed.

PdCl2(py)2 encaged in monodispersed zeolitic hollow spheres: a highly efficient and reusable catalyst for Suzuki–Miyaura cross-coupling reaction in aqueous media

By encaging the PdCl2(py)2 complex (py = pyridine) in the interior space of silicalite-1 hollow spheres (SHS), a novel solid palladium catalyst, PdCl2(py)2@SHS, was successfully prepared. The structure and composition of the solid catalyst was characterized by SEM, TEM, XRD, N2 sorption, FT-IR and XPS. This catalyst afforded fast conversions for the Suzuki–Miyaura cross-coupling reactions of various aryl halides and arylboronic acids even at Pd loadings of 0.0188 mol% in aqueous media. The turnover frequency (TOF) could be up to 63 210 h−1 under mild conditions in air. In particular, because of the antileaching effect of the surrounding zeolitic shell toward the entrapped Pd species, PdCl2(py)2@SHS showed outstanding stability and reusability, which could be reused at least 10 times without appreciable loss of its activity. The developed solid catalyst combined with the mild conditions represented one of the most efficient heterogeneous systems for the Suzuki–Miyaura cross-coupling reactions of aryl halides.

Preparation of hierarchical mesoporous Zn/HZSM-5 catalyst and its application in MTG reaction

Abstract The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline (MTG) was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2-20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.

One-pot synthesis of glycidol from glycerol and dimethyl carbonate over a highly efficient and easily available solid catalyst NaAlO2

The one-pot synthesis of glycidol from glycerol and dimethyl carbonate (DMC) was developed by using a solid base catalyst. A series of solid base catalysts have been investigated in this reaction. It was found that NaAlO2, a cheap and easily available raw material, was a highly efficient heterogeneous catalyst for the one-pot synthesis of glycidol, and it can be easily recovered and reused. Under the reaction conditions of a DMC–glycerol molar ratio of 2, catalyst–glycerol weight ratio of 3%, reaction time of 90 min, and temperature of 80–92 °C, the conversion of glycerol and the selectivity to glycidol reached 94.7% and 80.7%, respectively. Activity tests of the catalyst after exposure to the air showed that, to a certain extent, the NaAlO2 catalyst is tolerant to water and carbon dioxide, which makes the present system a practically interesting process for glycidol synthesis.

Facile synthesis of hierarchical nanocrystalline ZSM-5 zeolite under mild conditions and its catalytic performance

Hierarchical nanocrystalline ZSM-5 zeolite (NZ5) was synthesized at 100 °C under atmospheric pressure using methylamine as a mineralizing agent. The crystallization process of NZ5 was characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results of contrastive experiments showed that evaporation of the solvent promoted the aggregation of primary particles, and the addition of methylamine accelerated the crystallization process. The NZ5 aggregate consisted of 20 nm individual particles, as shown in scanning electron microscope (SEM). The lattice fringes in the transmission electron microscope (TEM) images and the XRD results indicated that individual particles of NZ5 were highly crystalline. N(2) adsorption-desorption isotherms showed that NZ5 had high BET surface areas with mesopores having a mean diameter of about 9 nm. NZ5 exhibited a long lifetime, a stable and high yield of liquid hydrocarbons, and a high anti-coking performance in methanol-to-hydrocarbons reaction. Catalytic testing and TGA results showed that the lifetime of NZ5 was about ten times longer than that of micro-sized ZSM-5 zeolite (MZ5), and the average coking rate with NZ5 was one fifth over that of MZ5.

Effective and recoverable homogeneous catalysts for the transesterification of dimethyl carbonate with ethanol: Lanthanide triflates

The catalytic activities of metal triflates were tested for the transesterification of dimethyl carbonate (DMC) with ethanol. It was found that yttrium triflate was the most efficient homogeneous catalyst. When the transesterification reaction was catalyzed by yttrium triflate at 76–80°C, 7 h, ethanol to DMC in 6: 1 molar ratio, 0.35 mol % of catalyst based on DMC, the conversion of DMC was 89.2%, the selectivities of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were 85.1 and 13.6%, respectively. Yttrium triflate was reused 5 times for the transesterification without loss of its catalytic activity.

Mesoporous core–shell TiO2 walnuts for photocatalysts and photodetectors with improved performances

Mesoporous core-shell TiO2 walnuts (CSTWs) were successfully prepared by a facile one-step hydrothermal method. This superior micro-nanostructure endowed the sample with hierarchical mesopores and a high surface area of 90.97 m(2) g(-1). Their particle size, diameter and morphology could be readily controlled by varying the growth parameters. The influence of the glucose amount, the urea amount and the calcination temperature on the formation of microspheres was investigated. The formation mechanism of the mesoporous CSTWs was studied. The photocatalytic activity of CSTWs had been carried out by degradation of gaseous benzene. The results indicated that, compared with commercial TiO2 (Degussa P25), CSTWs exhibited significant photocatalytic activity. Moreover, the mesoporous CSTWs were also configured as high-performance photodetectors. When illuminated by UV light with a wavelength of 365 nm, the current was found to be significantly enhanced, and an IUV/Idark of about 500, a good rise time and decay time were obtained.

Palladium supported on an amphiphilic porous organic polymer: a highly efficient catalyst for aminocarbonylation reactions in water

Exploring environmentally friendly, efficient and recyclable heterogeneous catalysts for organic reactions in aqueous media is important for the development of green and sustainable processes. In this work, an amphiphilic porous organic polymer supported palladium catalyst (Pd@UPOP) was synthesized via a facile urea-forming condensation of commercially available 3,3′-diaminobenzidine and 1,4-phenylene diisocyanate, followed by immobilizing palladium acetate at room temperature. Physico-chemical characterization suggested that the obtained material possessed a good porous structure and amphiphilic properties. Aminocarbonylation of aryl iodides with amines in water showed that Pd@UPOP is more active than previously reported heterogeneous palladium catalysts. Under balloon pressure of carbon monoxide, a palladium catalyst loading as low as 0.5 mol% was sufficient for a 98% yield of N,N-diethylbenzamide in the model reaction, corresponding to a high turnover frequency of 98 h−1. The catalyst could be used for at least five consecutive runs with the catalytic activity being recovered easily after simple manipulations.

Palladium‐Catalyzed Carbonylation of Chloroacetates to Afford Malonates: Controlling the Selectivity of the Product in a Buffer

We report an efficient process for the synthesis of diethyl malonate (DEM) and other malonates through the palladium‐catalyzed carbonylation of chloroacetates. Excellent selectivity (96 %) and yield (94 %) were obtained without the formation of Pd black. For the first time, a weakly alkaline buffer was used to control the selectivity for DEM in the reaction and we discuss the relationship between the buffer medium and selectivity in the reaction. The combination of anisole as the solvent and a Na2HPO4/NaH2PO4 buffer was beneficial for completely restraining the phase‐transfer‐catalyzed substitution of DEM with ethyl chloroacetate, as well as accommodating the proposed [(PPh3)2PdI]−[Bu4N]+ intermediate, by providing a suitable environment for its stable existence. We achieved the highest efficiency in the catalytic cycle by fine‐tuning the balance between the rates of oxidative addition and reductive elimination; moreover, we synthesized a recoverable heterogeneous polymer‐bound Pd catalyst in 85 % yield that could be reused without an appreciable loss in activity over four cycles.

Activities of Co(II) Schiff base complexes in the redox carbonylation of aniline and nitrobenzene to methyl N-phenyl carbamate

The series of cobalt(II) complexes with different Schiff base ligands was synthesized and used as catalyst for the redox carbonylation of aniline and nitrobenzene. Effects of reaction temperature, CO pressure, promoter, and catalyst additions on the conversion of substrate were studied. When Co[(OH)2saloph] — p-toluenesulfonic acid system was used as catalyst, the reaction was carried out at the next conditions: both Co[(OH)2saloph] and p-toluenesulfonic acid—0.2 mmol, aniline—20 mmol, nitrobenzene—10 mmol, methanol—30 ml, Co—5 MPa, temperature 170°C, reaction time 7 h. The highest conversion of nitrobenzene and selectivity of methyl N-phenyl carbamate were 54.5 and 92.2%, respectively.