Qinhua Xu

Fe-containing mesoporous molecular sieves materials : very active Friedel-Crafts alkylation catalysts

Benzylation of benzene has been conducted over Fe-containing zeolite molecular sieve materials prepared by different methods and exhibiting different pore sizes. It was shown that the mesoporous Fe-containing materials were very active benzylation catalysts with a monoalkylated product selectivity of 100%, and had better stability than the previously reported iron pillared clays (FePILCs). Temperature and pore size were two critical factors influencing the activities of the investigated catalysts. A redox mechanism can explain the observed experimental results.

Synthesis and characterization of FeSiMCM-41 and LaSiMCM-41

Mesoporous materials SiMCM-41, FeSiMCM-41, LaSiMCM-41, AlSiMCM-41, and LaAlSiMCM-41 were synthesized. The mesoporous structure of these materials was characterized by XRD, FT-IR, nitorgen and benzene adsorption methods. EPR and Mossbauer spectra suggested the incorporation of Fe(III) in the channel wall of as-synthesized FeSiMCM-41 sample. The introduction of Fe(III) and La(III) inproved the thermal and hydrothermal stabilities of SiMCM-41.

A novel method of varying the diameter of carbon nanotubes formed on an Fe-supported Y zeolite catalyst

A new method was proposed for varying the diameter of carbon nanotubes by pretreating zeolite supports loaded with active iron metal. Different diameters of carbon nanotubes were obtained by acetylene decomposition on Fe-supported Y zeolitic catalysts. Transmission electron microscopy observations show that the larger iron particles are deposited on the surface of zeolites and that the larger diameter nanotubes were growing on them. The pore diameter distribution measurement confirms that the dealuminated zeolite supports created larger secondary pores. The experimental results indicated that the larger the secondary pores generated, the larger were the diameters of nanotubes formed.

An investigation of KF modification to generate strong basic sites on NaY zeolite

Abstract Through an interaction with zeolite NaY to liberate KOH, KF modification provoked a basicity similar to that of KOH/NaY, and the resulting catalyst exhibited the same basic catalytic properties as KOH/NaY in the decomposition of isopropanol (IPA). Owing to the competitive reaction of the silicon component in NaY with the KOH liberated to form species with a low base strength, however, KF modification did not generate strong basic sites on NaY. Coating alumina onto NaY by hydrolysis of aluminum isopropoxide produced a new porous material without any significant change in the pore size of the NaY zeolite, and after modification with KF this new solid base exhibited a higher base strength (H−=17.2) than the parent NaY zeolite (H−=9.3).

Study of autoreduction and dispersion of Pt in β zeolite

TPR, TPO and FTIR were used to study the elementary processes occurred in the calcination of Pt (NH 3 ) 2 Cl 2 supported on Kβ zeolite. Using CO–FTIR, we found directly that while the Pt ammine complexes decomposed at about 300°C, autoreduction of Pt 2+ ions by NH 3 groups occurred and led to the formation of Pt° atoms prematurely. Reoxidation of the reduced sample could decrease the extent of Pt agglomeration caused by autoreduction. The unique effect of Ba 2+ ions on Pt dispersion was also studied. Aromatization of n-hexane and methylcyclopentane were used to study the effect of Pt dispersion on catalytic properties.

Comparison between β and L zeolites supported platinum for n-hexane aromatization

Abstract The performance of zeolite Kβ supported platinum as a bifunctional catalyst for the reforming of n-hexane has been examined using pulse and continuous flow microreaction methods. A comparison under the same conditions with zeolite KL supported platinum was carried out. It is found that due to the stronger acidity of zeolite β, Pt Kβ exhibits more skeletal isomerization and cracking than does Pt KL zeolite, while the latter shows superior aromatization activity. Ion exchange of β zeolite with alkali cations as Cs+ can reduce the acidity and increase benzene selectivity. Ba2+ exchange also can lead to better dispersion of platinum and so can improve the aromatization activity. In contrast to the high sensitivity to sulphur poisoning of Pt KL , Pt Kβ is relatively stable to sulphur poisoning and regains to some extent its initial activity. All these observations are explained in terms of support acidity, the electron state and the dispersion of platinum.

Novel porous material derived from hydrolysis of aluminum isopropoxide on NaY zeolite

Abstract A new porous material, with a layer of alumina coated on NaY zeolite with no significant change in the zeolite pore size, was prepared by hydrolysis of aluminum isopropoxide. After supporting with KF or KNO 3 , this new solid base exhibited a higher basic strength (H − = 17.2–18.4) than the parent zeolite (H − = 9.3).

Characterization of titanium-modified USY zeolites and their catalytic performance on n-heptane cracking

Abstract Titanium-modified USY zeolites were prepared by impregnation of USY zeolites with tetra-butoxide titanium and post-synthesis treatment with (NH4)2TiF6. The samples before and after modification were characterized by X-ray diffraction, Raman spectroscopy, UV-DRS, FTIR and NH3-TPD. The results indicate that the titanium species are highly dispersed over USY zeolites, and that the states of titanium over zeolites are dependent on the modification conditions. Extra strong Bronsted acid sites which resulted from interaction between titanium species and their neighboring hydroxyl groups of zeolites appeared on Ti-modified USY zeolites, and the catalytic activity in n-heptane cracking was enhanced after titanium modification for USY zeolites.

Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular materials

Abstract Effect of trivalent elements on the thermal and hydrothermal stability of MCM-41 mesoporous molecular sieve materials has been investigated. Al(III) decreases the thermal and hydrothermal stability of MCM-41 materials, whereas La(III) and Fe(III), especially Fe(III), can improve the thermal and hydrothermal stability. Benzene adsorption and IR spectra suggested that thick channel wall and the fewer structural defect sites in MCM-41 would enhance the thermal and hydrothermal stability of MCM-41.

Boronation and galliation of zeolites β in an alkaline medium

Abstract Zeolite β (with a Si/Al ratio of 15.20) was boronated or galliated in an alkaline solution containing boron or gallium species. The boronated or galliated samples were characterized by XRD, FTIR, MAS NMR and N 2 sorption measurement and the process for boronation/galliation was understood upon the characterization. By comparing with the alumination process, a difference between boronation/galliation and alumination was shown, i.e., boron or gallium atoms insert into the framework with more difficulty than aluminum atoms, resulting in a limited degree of introduction of the heteroatoms and a modification of the porous property of zeolite under the conditions similar to those for alumination. In combination with the deformability of beta framework, the state and the stability of boron atom in the framework were also discussed. The poor stability of boron or gallium atom in the framework and their unsuitable atomic sizes should be responsible for the low level of boronation or galliation.