Shujie Wu

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.

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.

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 activity of cubic Ia3d and hexagonal p6mm mesoporous aluminosilicates with enhanced acidity

Through a two-step crystallization procedure, an ordered mesoporous aluminosilicate with cubic Ia3d structure denoted as MB48 has been synthesized from the assembly of preformed zeolite beta precursors, utilizing cetyltrimethylammonium bromide (CTAB) as a template. By adjusting the alkalinity during the second crystallization step, an ordered mesoporous aluminosilicate with hexagonal p6mm structure named as MB41 has also been prepared. MB48 and MB41 were characterized with PXRD, FTIR, 27Al-MAS NMR, N2 adsorption–desorption and NH3-TPD techniques, etc. Experiments show that both MB48 and MB41 are pure mesoporous phases, containing the secondary structural units of zeolite beta. Compared with conventional mesoporous aluminosilicates, MB48 and MB41 have enhanced acidity and show higher catalytic activity in the cracking of cumene and the phenol alkylation with tert-butanol.

Correlation between the microstructures of graphite oxides and their catalytic behaviors in air oxidation of benzyl alcohol.

A series of graphite oxide (GO) materials were obtained by thermal treatment of oxidized natural graphite powder at different temperatures (from 100 to 200 °C). The microstructure evolution (i.e., layer structure and surface functional groups) of the graphite oxide during the heating process is studied by various characterization means, including XRD, N2 adsorption, TG-DTA, in situ DRIFT, XPS, Raman, TEM and Boehm titration. The characterization results show that the structures of GO materials change gradually from multilayer sheets to a transparent ultrathin 2D structure of the carbon sheets. The concentration of surface COH and HOCO groups decrease significantly upon treating temperature increasing. Benzyl alcohol oxidation with air as oxidant source was carried out to detect the catalytic behaviors of different GO materials. The activities of GO materials decrease with the increase of treating temperatures. It shows that the structure properties, including ultrathin sheets and high specific surface area, are not crucial factors affecting the catalytic activity. The type and amount of surface oxygen-containing functional groups of GO materials tightly correlates with the catalytic performance. Carboxylic groups on the surface of GO should act as oxidative sites for benzyl alcohol and the reduced form could be reoxidized by molecular oxygen.

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.

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.

Optimizing the matching between the acid and the base of cooperative catalysis to inhibit dehydration in the aldol condensation.

A series of acid-base bifunctional catalysts were prepared, and high yields and excellent selectivity in the aldol condensation were achieved through adjustment of the matching between the acid and the base. The results indicated that proper matching between the acid and the base can both efficiently activate the substrate through cooperative activation and inhibit dehydration without diminishing the yield.

Highly dispersed cobalt oxide nanoparticles on CMK-3 for selective oxidation of benzyl alcohol

Nano cobalt oxide particles supported on ordered mesoporous carbon CMK-3 (CMK: carbon material from Korea) were prepared by a hydrothermal synthesis method. The catalysts were characterized by various characterization methods such as XRD, FT-IR, TEM, FESEM, N2 adsorption and desorption, XPS, Raman and ICP-AES, which indicated that the size of the cobalt oxide nanoparticles was estimated to be ∼2 nm and that they were uniformly dispersed on CMK-3. The approach obtained smaller and narrow distributed cobalt oxide nanoparticles which was the key to complete the reaction with 82.1% conversion and 97.7% benzaldehyde selectivity within 6 h. The average TOF of Co3O4/CMK-3 can reach as high as 25.4 h−1 in the initial two hours, which was far higher than that of the unsupported nano Co3O4 (less than 1.0 h−1) and so far reported cobalt-based catalysts (e.g. 1.34 h−1 for Co3O4/RGON). In addition, the catalytic activity of Co3O4/CMK-3 was not obviously deteriorated after 4 runs.

Application of metal organic frameworks M(bdc)(ted)0.5 (M = Co, Zn, Ni, Cu) in the oxidation of benzyl alcohol

The selective oxidation of benzyl alcohol to benzaldehyde is an important process in heterogeneous catalysis and green organic chemistry. Herein, we investigated the effect of different metal ions in the metal organic framework M(bdc)(ted)0.5 (M = Co, Zn, Ni, Cu, bdc = 1,4-benzenedicarboxylate, ted = triethylenediamine) on the catalytic activity of benzyl alcohol oxidation. The catalytic results demonstrated that Co(bdc)(ted)0.5 achieved good benzyl alcohol conversion (81.8%) and benzaldehyde selectivity (>99%) by using O2 as the oxidant. The catalysts could be reused several times without significant degradation in activity.