Gong Yanjun

STUDY OF MESOPOROUS SILICA MATERIALS BY SMALL ANGLE X-RAY SCATTERING

Small angle X-ray scattering experiments have been performed to study the microstructure of mesoporous silica materials prepared by condensation of tetraethylorthosilicate using non-ionic alkylpolyethyleneoxide (AEO9) and ionic cetyltrimethylammonium bromide (CTAB) surfactant as templates. It is the pores within the nanometre range that produce the main scattering. The scattering of the pure silica systems obey Porods law. The scattering of the systems with templates remaining in the pores show positive deviations from Porods law. This may be because the templates produce some additional scattering background and then make the scattering of pores distorted. The results show that the full removal of templates from the pores of the materials by Soxhlet extraction is very easy for AEO9, but it is difficult for CTAB. The positive deviation correction is also performed.

Catalytic Conversion of Methanol to Propylene over (NH4)(2)SiF6-Modified Nanosized HZSM-5 Zeolite

(NH4)(2)SiF6-modified nanosized HZSM-5 zeolite was prepared and investigated as a catalyst for methanol to propylene conversion. The effects of this modification on the framework, textural properties and acidity of both the parent and the modified HZSM-5 zeolite were investigated by powder X-ray diffraction (XRD), Al-27 magic angle spinning nuclear magnetic resonance (Al-27 MAS NMR), X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), N-2 adsorption, transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (NH3-TPD), and infrared spectroscopy of adsorbed pyridine (Py-IR). The catalytic performance of these materials on the methanol to propylene (MTP) conversion process was tested under operating conditions of T=450 degrees C, p=0.1 MPa (p(MeOH)=50 kPa) and WHSV=1 h(-1). The results showed that surface aluminum on the nanosized ZSM-5 zeolite could be selectively removed by the (NH4)(2)SiF6 solution and that the number of acidic sites on the HZSM-5 zeolite gradually decreased with increasing (NH4)(2)SiF6 concentration. Moreover, after modification with an optimally concentrated (NH4)(2)SiF6 solution, an obvious increase in specific surface area as well as mesopore volume was observed for the nanosized HZSM-5 with a resulting dramatic improvement in the catalytic performance of this material for the MTP reaction. Both the propylene selectivity and propylene/ethylene (PIE) mass ratio resulting from use of the modified HZSM-5 increased significantly to 45.1% and 8.0, as compared to results of 28.8% and 2.6 obtained with the original material. In addition, the catalytic lifespan of the modified zeolite was double that of the original.

Synthesis of Vinyl-functionalized MSU-X Silicates

Vinyl-functionalized MSU-X silicates were prepared by one-pot synthesis methodology at the presence of Tx-15 and AEO(9) surfactants respectively. The solids were characterized by XRD, FT-IR, Si-29 MASNMR, HRTEM, SEM, N-2 physisorption techniques. The surface morphology and textural properties of such materials varied with the synthesis mechanism and content of vinyl groups in the channel. The effects of the organic groups on the modified MSU-2 were investigated carefully. The vinyl-modified mesopore with 10% (x) VTES templated by AEO(9) was of 3.1 nm. pore diameter, but that templated by Tx-15 displayed a bimodal mesoporous channels, in which the smaller pore size was about 3 nm, while the bigger one was in the range of 40 similar to 46 nm.

Effects of Na + in Dilution Steam and Coke Deposition on Catalytic Performance of Methanol-to-Propylene Catalysts

The effects of Na~+ in dilution steam and coke deposition on the physicochemical properties and catalytic performance of ZSM-5 catalysts for the methanol-to-propylene(MTP) reaction were investigated. The deactivated and regenerated catalysts were characterized by means of X-ray diffraction(XRD), scanning electron microscopy(SEM),X-ray fluorescence(XRF) spectrum,nitrogen adsorption/desorption, temperature-programmed desorption of ammonia(NH_3-TPD),and thermogravimetry(TG).Their catalytic performance for MTP reaction was tested in a continuous flow fixed-bed micro-reactor at 470℃,101325 Pa,and with methanol weight hourly space velocity(WHSV) in the range of 1.0-3.0 h~(-1).The results indicated that the catalyst crystal structure and morphology was not significantly altered after 970 h on stream.In the MTP reaction,Na~+ in the dilution steam can easily enter the pore channels of the catalyst, and partially replace H protons,thereby gradually decreasing the amount of acidity and acid strength of the catalyst,which eventually causes deactivation.In addition,coke deposits on the catalyst surface blocking its micropores are the main reason for deactivation of the MTP catalyst.Coke deposits are mostly eliminated through the burning charcoal regeneration process.The effect of framework dealumination from the catalyst by steam in the MTP process is slow but more serious.Through regeneration and ion exchange process,the catalytic activity of the deactivated catalyst can be fully restored.The conversion of methanol is consistently above 99%,and propylene selectivity is greater than 46%even after 470 h on stream.With increasing reaction time,the propylene selectivity gradually increases,while ethylene selectivity gradually decreases.

Synthesis and Desulfurization Performance of Nanocrystal-Assembled Zeolite L with a Hierarchical Pore Structure

Zeolite MeLTL with a micro-mesoporous composite pore structure was synthesized by using nanocrystal clusters of zeolite L prepared by the crystallization nurturing method as a precursor and [3-(trimethoxysilyl)propyl] hexadecyldimethylammonium chloride (TPHAC) as the organic mesopore directing surfactant. Several techniques including X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Al-27 magic angle spinning nuclear magnetic resonance (Al-27 MAS NMR), and Fourier transform infrared spectroscopy of pyridine adsorption (Py-FTIR) were used to characterize the samples. Results show that zeolite MeLTL is formed by the self-assembly of zeolite L nanocrystals, and it has bimodal pore distributions with a stepwise mesoporous structure and the microporous structure of zeolite L. The BET surface area and the pore volume increased significantly and were 611 m(2).g(-1) and 0.696 cm(3).g(-1), respectively. Zeolite MeLTL was composed of zeolite L units and this was responsible for the adequate surface acid amount and acid strength. As a result, the pore diffusion ability and the catalytic performance of zeolite MeLTL are enhanced by the improvement in textural properties. For diesel hydrodesulfurization, the catalyst introduced zeolite MeLTL gave better hydrodesulfurization activity compared to the catalysts introduced zeolite L or Al-MCM-41 or used bare gamma-Al2O3 as a support. The sulfur content of diesel oil after hydrotreatment was 9.3 mu g.g(-1) and the desulfurization rate was 99.3%.

Positive deviation from Debye's theory in small-angle x-ray scattering

The small-angle x-ray scattering (SAXS) resulting from a non-ideal two-phase system having sharply defined phase boundaries but with micro-fluctuations of electron density within any phase shows a positive deviation from Debyes theory. We have found a simple method suitable for fitting the slit-smeared SAXS data and correcting the positive deviation. The validity of this procedure is tested on porous ZrO2 xerogel prepared using the sol-gel process.