Sujuan Xie

The effect of acidity on olefin aromatization over potassium modified ZSM-5 catalysts

The transformation of olefin to aromatics over ZSM-5 catalysts with different K-loadings has been investigated both in a continuous flow fixed-bed reactor and in a pulse microreactor. Investigation of variation of olefin aromatization activity with K-loadings shows that strong acid sites are indispensable for the converting of olefin to aromatics. As intermediates of olefin aromatization process, butadiene and cyclopentene not only show much higher aromatization activity than mono-olefins, but also can be transformed into aromatics over relatively weak acid sites of K/ZSM-5. A proposal is put forward, stating that among all the steps experienced in olefins aromatization, the formation of diene or cycloolefin from mono-olefins through hydrogen transfer is the key step and can be catalyzed by strong acid sites.

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.

Shape selectivity in methane dehydroaromatization over Mo/MCM-22 catalysts during a lifetime experiment

Dehydroaromatization of CH4 with 2% CO2 on 6Mo/MCM-22 in a 100-h lifetime test was carried out at 993 K, atmospheric pressure and 1500 mL/gh. The duration of the lifetime test can be divided into an induction stage, stable stage and deactivation stage on the basis of the selectivities of hydrocarbons and coke. The characteristics of deposited coke with different time onstream were studied using TPO and TG techniques. There were two peaks corresponding to two kinds of coke recorded in TPO profiles, and the oxidation temperature of coke shifted to higher values with less hydrogen content with the increase of coke deposits. BET and Benzene-TPD techniques were employed to study the variation of specific surface area of the external and micropore surface versus time onstream. With the accumulation of coke deposits, although the pores became partially blocked and the internal surface decreased, methane could still enter the channel and was converted to benzene with shape selectivity until a critical value of coke deposition was reached.

Thermal and hydrothermal stabilities of the alkali-treated HZSM-5 zeolites

Abstract HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH 3 -TPD characterization techniques. Compared to the unmodified zeolite, the thermal and hydrothermal stabilities of the alkali-treated ZSM-5 zeolites were slightly deteriorated because of the introduction of mesopores caused by the desilication. Nevertheless, the alkali-treated zeolite framework could be maintained until the temperature increased to 1175 °C.

Partial oxidation of propane to syngas over nickel supported catalysts modified by alkali metal oxides and rare-earth metal oxides

Abstract The reaction performance, catalyst acidity and basicity property, and carbon-deposition of various nickel-supported catalysts for partial oxidation of propane (POP) to syngas were investigated with a flow-reactor, FTIR, TG and UVRRS analyses. The NiO/γ-Al 2 O 3 catalyst is the most suitable for the POP reaction among NiO/γ-Al 2 O 3 , NiO/MgO and NiO/SiO 2 . And the reaction performance of the NiO/γ-Al 2 O 3 shows little difference from those of the nickel-supported catalysts modified by alkali metal oxides and rare-earth metal oxides. However, modification with alkali metal oxide Li 2 O and rare-earth metal oxide La 2 O 3 can reduce the Lewis acidity intensity of the NiO/γ-Al 2 O 3 and enhance its ability to suppress carbon-deposition during the POP reaction. The carbon-deposition contains graphite-like species that were detected by UVRRS. The nickel-supported catalysts modified by alkali metal oxides and rare-earth metal oxides possess good reaction performance and carbon-deposition resistance.

Probing the porosity of cocrystallized MCM-49/ZSM-35 zeolites by hyperpolarized 129Xe NMR.

One- and two-dimensional 129Xe NMR spectroscopy has been employed to study the porosity of cocrystallized MCM-49/ZSM-35 zeolites under the continuous flow of hyperpolarized xenon gas. It is found by variable-temperature experiments that Xe atoms can be adsorbed in different domains of MCM-49/ZSM-35 cocrystallized zeolites and the mechanically mixed counterparts. The exchange of Xe atoms in different types of pores is very fast at ambient temperatures. Even at very low temperature two-dimensional exchange spectra (EXSY) show that Xe atoms still undergo much faster exchange between MCM-49 and ZSM-35 analogues in the cocrystallized zeolites than in the mechanical mixture. This demonstrates that the MCM-49 and ZSM-35 analogues in cocrystallized zeolites may be stacked much closer than in the physical mixture, and some parts of intergrowth may be formed due to the partially similar basic structure of MCM-49 and ZSM-35.

Activity enhancement of ZSM-35 in dimethyl ether carbonylation reaction through alkaline modifications

A series of ZSM-35 zeolites with different alkaline treatment degrees were prepared. The precise effects of alkaline treatment on composition, morphology, porosity, transportation and acidity of the samples were characterized by means of multiple techniques including N2 sorption, transmission electron microscopy (TEM), intelligent gravimetric analyzer (IGA) and Fourier transform infrared spectroscopy (FTIR). ZSM-35 after moderate alkaline treatment exhibited enhanced carbonylation activity compared with the parent sample. As revealed by the N2 adsorption and TEM results, alkaline treatment could induce the deaggregation of ZSM-35 clusters and remove the amorphous debris on the surface of ZSM-35 platelets. Furthermore, an improved diffusion behavior of the dimethyl ether reactant molecule was observed on the alkali-treated sample from IGA experiments which directly led to the better catalytic performance for the carbonylation of the dimethyl ether with carbon monoxide. Mesoporosity created by severe alkaline leaching does not enhance the catalytic properties of ZSM-35 in dimethyl ether carbonylation reaction. Especially, a decrease in reaction stability was observed due to the limitation effect of carbonaceous deposit formation.

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.

Effect of Reaction Temperature and Pressure on the Metathesis Reaction between Ethene and 2-Butene to Propene on the WO3/Al2O3-HY Catalyst

Abstract Effect of reaction temperature and pressure on the metathesis reaction between ethene and 2-butene to propene was studied on the WO3/γ-Al2O3-HY catalyst. The activity is found to increase with elevated temperature and reaches a plateau at 150–240 °C. After that, the activity undergoes a remarkable decrement at too high temperature. The effect of temperature is elucidated by the oxidation state of tungsten species. The evaluation results also indicate that the stability is dependent on this reaction parameter. Medium pressure (0.5–0.8 MPa) is favorable for stability, while atmospheric pressure or too high pressure (>1.0 MPa) deteriorates the stability. For explanation, UV Vis, FT-IR, O2-TPO, and TG techniques are used to characterize the spent catalysts.