Wenjie Xin

Production of propene from 1-butene metathesis reaction on tungsten based heterogeneous catalysts

Abstract A new propene production route from 1-butene metathesis has been developed on heterogeneous 10WO 3 /Al 2 O 3 -HY catalysts with different HY contents. It is found that the catalysts play bi-functionally first for the isomerization of 1-butene to 2-butene and then for the cross-metathesis between 1-butene and 2-butene to propene and 2-pentene. The combination of HY zeolite and Al 2 O 3 is prerequisite for the production of propene. The propene yield keeps increasing with the HY content in the range of 10–70 wt%, where 10WO 3 /Al 2 O 3 -70HY exhibits the highest propene yield. The MS-H 2 -TPR and MS-O 2 -TPO characterizations indicate that the increase of HY content in the catalysts weakens the interaction between W species and supports, whereas enhance the probability of coking on the metal species and acid sites.

Cross metathesis of butene-2 and ethene to propene over Mo/MCM-22-Al2O3 catalysts with different Al2O3 contents

Abstract A series of 3.0Mo/MCM-22-Al 2 O 3 catalysts with γ-Al 2 O 3 contents in the range of 0-100 wt% were prepared and applied in the metathesis reaction of ethene and butene-2. Addition of γ-Al 2 O 3 did not affect the structure of MCM-22 zeolite as evidenced by XRD and N 2 adsorption measurements. It was deduced from TPR experiments that γ-Al 2 O 3 phase favored the formation of polymolybdate or multilayered Mo oxide, while more Al 2 (MoO 4 ) 3 species were generated over MCM-22 zeolites. Alumina content in the support was directly related to the metathesis activity of ethene and butene-2 to propene. Mo species with higher valence (Mo 6+ or Mo 5+ ) contributed more to the excellent performance of catalyst than metallic Mo. The best catalyst activity and stability was obtained over 3.0Mo/(MCM-22-30%Al 2 O 3 ) under the reaction condition of 1.0 MPa and 125 γ C using N 2 as the pretreatment gas.

Hierarchical ZSM-11 zeolite prepared by alkaline treatment with mixed solution of NaOH and CTAB: characterization and application for alkylation of benzene with dimethyl ether

A facile alkaline treatment with the addition of surfactant cetyltrimethylammonium bromide (CTAB) to prepare hierarchical ZSM-11 zeolite (Z-xat-yCTAB) is presented. The textural and structural properties of Z-xat-yCTAB were characterized by XRD and adsorption and desorption of N2 and benzene. By virtue of CTAB addition, uniform intracrystalline mesopore distribution centered at ca. 4.2 nm was introduced accompanied by well-protected microporosity. Based on characterization results such as TEM images and BJH curves as well as 29Si and 27Al MAS NMR spectra, the composite effects of NaOH and CTAB on mesoporosity production were proposed. Acidity was characterized thoroughly by FTIR of adsorbed pyridine (Py-IR) and pivalonitrile. Accordingly, the ratio and accessibility factor of Bronsted and Lewis acid sites are discussed systematically. In the alkylation of benzene with dimethyl ether, Z-xat-yCTAB series samples exhibited better reaction stability than ZSM-11 samples treated with NaOH solution. The catalytic promotion could be attributed to the dual effects of NaOH and CTAB on the porosity and acidity regulation. Moreover, based on the correlation between the reaction stability and the ratio of Bronsted to Lewis acid concentration with weak–medium strength, measured by Py-IR, it was revealed that the regulation of acidity could play a more important role for better reaction stability. In addition, the physicochemical properties and reaction activity were compared between ZSM-11 samples derived from alkaline treatment with CTAB addition and with tetrapropylammonium bromide (TPABr) addition under the same conditions.

Differences between Zn/HZSM-5 and Zn/HZSM-11 zeolite catalysts in alkylation of benzene with dimethyl ether

Abstract HZSM-11 zeolite supported Zn catalysts with different Zn contents ( x Zn/HZSM-11A) were prepared. In the alkylation of benzene with dimethyl ether (DME) in a fixed bed reactor, the catalyst with Zn content of 6 wt% (6Zn/HZSM-11A) showed appropriate performance. Focus was put on the comparison between 6Zn/HZSM-5 and 6Zn/HZSM-11 with the same crystal size of 600–800 nm, and also with the similar BET surface area, micropore volume, Si/Al2 molar ratio, and acidity. In the alkylation of benzene with DME, the 6Zn/HZSM-11 showed better activity and stability, and especially enhanced the conversion of benzene and selectivities to xylene and trimethylbenzene, compared with the 6Zn/HZSM-5. This was mainly related to the higher adsorption capacity and adsorption-desorption rates to the three adsorbates (benzene, m -xylene and 1,3,5-trimethylbenzene) over the 6Zn/HZSM-11 in comparison with the 6Zn/HZSM-5.

CTAB modification of MCM-49 zeolite containing HMI and its acylation of anisole

A series of MCM-49 zeolite catalysts containing different amounts of the hexamethyleneimine (HMI) template were calcined at different temperatures, and then modified with cetyltrimethylammonium bromide (CTAB). Changes in structural and acidic properties were investigated by XRD, N2 adsorption, NH3-TPD, adsorbed pyridine infrared and DRIFTS measurements, and 29Si and 27Al MAS NMR. There were cleaning off of amorphous particles and extraframework Al atoms inserted into the framework of the zeolite due to the CTAB modification. These two effects resulted in more framework Al in the CTAB modified samples than the untreated samples, and a higher Bronsted acid concentration, which was confirmed by the acylation of anisole with acetic anhydride. The catalytic roles of the acid sites located in the different pore systems in the zeolite were investigated. It was verified that the active sites after CTAB modification were mainly in the HMI-free regions.

Direct synthesis of three-dimensional MWW zeolite with cyclohexylamine as an organic structure-directing agent

MCM-49 zeolite with a three-dimensional MWW framework was directly synthesized using low-toxicity and cost-effective cyclohexylamine (CHA) as an organic structure-directing agent under hydrothermal conditions. Compared with the traditional hexamethyleneimine template, the interaction between CHA with the framework was weaker and more CHA molecules occupied the surface pockets and supercages of as-synthesized MCM-49 zeolite. The obtained sample showed good catalytic performance in the liquid phase alkylation reaction of benzene with ethylene.