Jingqi Guan

Immobilized Cu(II) and Co(II) salen complexes on graphene oxide and their catalytic activity for aerobic epoxidation of styrene

Novel graphene oxide (GO) tethered Cu(II) and Co(II) salen complexes [M–Salen–GO (M = Cu, Co)] were synthesized via a stepwise procedure and examined as catalysts in the epoxidation of styrene. Acetonitrile was used as a solvent and air as the oxidant in combination with a sacrificial co-reductant isobutyraldehyde. A comparison with homogeneous salen complexes of Co and Cu and graphene oxide (GO) tethered salen complexes was made. Heterogeneous copper(II) and cobalt(II) catalysts were confirmed by X-ray diffraction (XRD), FT-IR, diffusion reflection UV-visible spectroscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), TEM, TG, Raman and XPS. FT-IR, diffusion reflection UV-visible and inductively coupled plasma atomic emission spectroscopy (ICP-AES), along with TG, Raman and XPS results showed that Cu(II) and Co(II) salen complexes were successfully grafted on GO; X-ray diffraction (XRD) and TEM indicated that the sample structures were well preserved. It was found that heterogeneous catalysts were active and showed good recoverability without significant loss in activity and selectivity within successive runs.

Core–shell structured Fe3O4@SiO2 supported cobalt(II) or copper(II) acetylacetonate complexes: magnetically recoverable nanocatalysts for aerobic epoxidation of styrene

Organic–inorganic hybrid heterogeneous nanocatalysts were successfully fabricated via covalent anchoring of cobalt(II) or copper(II) acetylacetonate complexes ([Co(acac)2] or [Cu(acac)2]) onto core–shell structured Fe3O4@SiO2 previously functionalized with 3-aminopropyltriethoxysilane (APTES). Surface functionalized nanomaterials were analyzed by a series of characterization techniques such as SEM, TEM, XRD, FT-IR, XPS, ICP-AES and VSM. The catalytic performance of the prepared nanocatalysts was evaluated in the epoxidation of styrene using eco-friendly air as the oxygen source. Both of the nanocomposites Fe3O4@SiO2–NH2–Co and Fe3O4@SiO2–NH2–Cu presented excellent styrene conversion (90.8% vs. 86.7%) and good epoxide selectivity (63.7% vs. 51.4%), much higher than the corresponding homogeneous counterparts. In addition, the magnetically recoverable nanocatalysts (MRNCs) can be conveniently separated and recovered from the reaction system by applying an external magnetic field and reused for four cycles with insignificant loss of catalytic activity. These results demonstrate that the heterogeneous nanocatalysts possess potential applications for green and sustainable development.

Different transition metal (Fe2+, Co2+, Ni2+, Cu2+ or VO2+) Schiff complexes immobilized onto three-dimensional mesoporous silica KIT-6 for the epoxidation of styrene

Highly ordered three-dimensional Ia3d mesoporous silica KIT-6 was functionalized with 3-aminopropyltriethoxysilane (3-APTES), following by post-grafting of various transition metal (Fe2+, Co2+, Ni2+, Cu2+ or VO2+) Schiff complexes onto amino-functionalized KIT-6. The surface functionalized materials were analyzed by a series of characterization techniques such as XRD, X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, IR spectroscopy, inductively coupled plasma (ICP), scanning electron microscopy (SEM), and thermal gravimetric analyses (TGA), etc. The characterization results demonstrated structural intact of the mesoporous hosts throughout the grafting procedures and successfully anchoring of transition metal Schiff complexes on the modified KIT-6. The obtained organic–inorganic hybrid materials were subsequently employed as catalysts for the epoxidation of styrene under optimized reaction conditions. It was indicated that Cu-NH2-KIT-6 showed very high substrate conversion (98.6%) and excellent epoxide selectivity (97.8%) when using tert-butyl hydroperoxide (TBHP) as the oxidant at 80 °C after 6 h. It was also observed that the catalyst could be recycled three times without obvious loss in catalytic activity and selectivity.

Synthesis of Beta/MCM-41 composite molecular sieve with high hydrothermal stability in static and stirred condition.

Beta/MCM-41 micro/mesoporous composite materials have been prepared through assembly of zeolite Beta nanoclusters and their hydrolysis products in the presence of CTAB under static or stirred conditions. The resulting materials were characterized by powder XRD, TEM and nitrogen adsorption-desorption. Hydrothermal stability of the obtained Beta/MCM-41 composites was evaluated by boiling in distilled water for different periods of time under refluxing. All materials exhibit very high hydrothermal stability.

Immobilization of transition metal (Fe2+, Co2+, VO2+ or Cu2+) Schiff base complexes onto graphene oxide as efficient and recyclable catalysts for epoxidation of styrene

Transition metal (Fe2+, Co2+, VO2+ or Cu2+) Schiff base complexes were immobilized onto graphene oxide previously functionalized with 3-aminopropyltriethoxysilane (3-APTES). X-ray diffraction (XRD), IR spectroscopy, thermal gravimetric analyses (TGA) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) confirmed the successful incorporation of the metal Schiff base onto the graphene oxide. N2 adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the intact structure of the graphene oxide. Catalytic results showed that the immobilized copper(II) Schiff base complex catalyst was more active than the immobilized iron(II), cobalt(II) and oxovanadium(IV) complexes in the epooxidation of styrene. Above 94% styrene conversion and excellent ∼99% selectivity to the epoxide could be achieved over the copper(II) Schiff base heterogeneous catalyst in the epoxidation of styrene using tert-butyl hydroperoxide (TBHP) as oxidant after 7 h reaction. The recycling experiment results indicated that the catalyst could maintain very high styrene conversion (>93%) and epoxide selectivity (>99%) even after being used for four cycles.

Oxovanadium(IV) and iron(III) salen complexes immobilized on amino-functionalized graphene oxide for the aerobic epoxidation of styrene

Oxovanadium(IV) and iron(III) salen complexes grafted onto amino-modified graphene oxide (NH2–GO) have been synthesized via a stepwise procedure and the prepared materials were used as heterogeneous catalysts in the aerobic oxidation of styrene. The structures of these materials have been thoroughly investigated using different characterization techniques such as XRD, N2 adsorption–desorption, TEM, FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TEM, TG, Raman, and XPS. The results of XRD, N2 adsorption–desorption and TEM revealed that the structures of the prepared catalysts were well preserved. In addition, the results of FT-IR, diffuse reflectance UV-visible spectroscopy, ICP-AES, TG, Raman and XPS suggested that the oxovanadium(IV) and iron(III) complexes had been incorporated onto amino-modified graphene oxide (GO). It was found that the heterogeneous oxovanadium(IV) catalyst was more active than its homogeneous analogue in the epoxidation of styrene, using acetonitrile as solvent and air as the oxidant in combination with the sacrificial co-reductant isobutyraldehyde, due to site-isolation. Furthermore, the tethered vanadium catalyst was quite stable and could be recycled many times.

Synthesis, Characterization, and Catalytic Performance of Mesoporous Al-SBA-15 for Tert-butylation of Phenol

Abstract Mesoporous Al-SBA-15 was synthesized by the post-synthesis grafting of Al atoms on a parent siliceous SBA-15. Both SBA-15 and Al-SBA-15 with different Si/Al ratios were characterized by powder X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption. The hexagonal p6mm mesostructure of the parent siliceous SBA-15 was maintained very well in Al-SBA-15. NH3 temperature-programmed desorption indicated that Al-SBA-15 has both medium and strong acid sites. During the alkylation of phenol with tert-butanol, the Al-SBA-15 catalyst showed a higher conversion of phenol and selectivity for 2,4-di-tert-butyl phenol (2,4- DTBP) than the traditional Al-MCM-41 catalyst. At a reaction temperature of 145°C, a higher phenol conversion of 75.2% and a 2,4-DTBP selectivity of 31.3% over Al-SBA-15 were observed as compared to those over Al-MCM-41, which were 61.3% and 13.4%, respectively. Due to the large pore size (about 9 nm), which allows a faster diffusion of reactants and products, catalyst deactivation of Al-SBA-15 was not observed even after reaction for 5 h.

Direct synthesis of acid–base bifunctionalized hexagonal mesoporous silica and its catalytic activity in cascade reactions

A series of efficient acid-base bifunctionalized hexagonal mesoporous silica (HMS) catalysts contained aminopropyl and propanesulfonic acid have been synthesized through a simple co-condensation by protection of amino group. The results of small-angle XRD, TEM, and N(2) adsorption-desorption measurements show that the resultant materials have mesoscopic structures. X-ray photoelectron spectroscopies, elemental analysis (EA), back titration, (29)Si NMR and (13)C NMR confirm that the organosiloxanes were condensed as a part of the silica framework. The resultant catalysts exhibit excellent acid-basic properties, which make them possess high activity for one-pot deacetalization-Knoevenagel and deacetalization-nitroaldol (Henry) reactions.

Epoxidation of styrene over Fe(Cr)-MIL-101 metal- organic frameworks

Epoxidation of styrene is one of the key reactions in organic synthesis. In this paper, we investigated the effect of different metal ions in MIL-101 metal–organic framework on styrene epoxidation using various oxidants such as air, H2O2 and TBHP. For the aerobic epoxidation of styrene, Fe-MIL-101 and Cr-MIL-101 presented good styrene conversion (87.2 vs. 65.5%) and epoxide selectivity (54.4% vs. 37.7%) using air as the oxidant. The styrene epoxidation activity for the different oxidants over Fe-MIL-101 was as follows: air > TBHP > H2O2, while that over Cr-MIL-101 showed a different trend: H2O2 > air > TBHP. Moreover, the selectivity to styrene oxide for the different oxidants was similar over the two catalysts: TBHP > air > H2O2. The study of the effect of various solvents revealed that CH3CN is the optimal solvent for the aerobic epoxidation of styrene. Furthermore, the catalysts could be reused three times without any significant loss in catalytic activity.

Encapsulation of tetraazamacrocyclic complexes of cobalt(II), copper(II) and oxovanadium(IV) in zeolite-Y and their use as catalysts for the oxidation of styrene

Encapsulation of tetraazamacrocyclic complexes of Co(II), Cu(II) and V(IV) into zeolite-Y has been accomplished, and the resulting materials were used as heterogeneous catalysts for aerobic oxidation of styrene. The materials were prepared by a ship-in-a-bottle method, in which the transition metal cations were first ion-exchanged into zeolite-Y and then reacted with ethylenediamine, followed by acetylacetone. The pure tetraazamacrocyclic complexes were characterized by FTIR, solid UV–Vis and elemental analysis. The structural integrity throughout the immobilization procedure, the successful immobilization of the macrocyclic complexes, and the loadings of metal ions and macrocyclic ligands were determined by characterization techniques such as FTIR, diffuse reflection UV–Vis, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, TG/DTA and powder X-ray diffraction. Compared with their homogeneous analogues, the catalytic properties of the encapsulated macrocyclic complexes in the oxidation of styrene with air were investigated. The immobilized complexes proved to be active catalysts and could be reused without significant loss in activity.