Guo Xinwen

Synthesis of titanium silicalites in different template systems and their catalytic performance

Abstract Titanium silicalites have been synthesized in the TPABr+ammonia, TPABr+hexanediamine, TPABr+ethylenediamine, TPABr+diethylamine, TPABr+TEAOH, TPABr+n-butylamine, TPABr+TBAOH and TBAOH+n-butylamine systems. As-synthesized titanium silicalites were characterized by XRD, IR and 13 C CP MAS NMR. Catalytic performance in epoxidation of propylene and template effect was investigated. It has been shown that both TPABr and TBAOH serve as templating agent in TPABr+TBAOH system. But in other systems, when there is enough TPABr, organic amines or ammoniums only act as the bases. TEAOH or n-butylamine can take the role of template when less TPABr is added. It indicates that the ability of organic amines or ammoniums to direct the Pentasil structure decreases as follows: TPA+>TBA+>TEA+>n-butylamine. Catalysts exhibiting good performance in epoxidation of propylene can be attained using TPABr as the template and ammonia, n-butylamine, diethylamine, hexanediamine or TBAOH as bases.

Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH3 at 773 K and then loaded with La2O3 and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH3-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH3-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C7–C9 aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.

Epoxidation of Propylene with Dilute H2O2 over Titanium Silicalite Containing Trace Aluminum

Titanium silicalite (TS-1) was successfully synthesized by using TPABr as the template and silica sol as silicon source in a 100 l stainless steel autoclave. IR, XRD, UV--vis, elemental analysis, and 27Al and 31P MAS NMR were used to characterize the synthesized products. The results show that the synthesized material has an MFI structure with high crystallinity and large crystal size and two kinds of titanium species. Trace aluminum in silica sol is also incorporated into the zeolite framework. The synthesized TS-1 exhibits high activity in the epoxidation of propylene with dilute H2O2 with high selectivity to methyl mono-ethers and low selectivity to propylene oxide (PO). The low selectivity toward PO is due to the residual acidity onto TS-1. The selectivity of PO can reach up to 90% through adjusting the pH of the reaction mixture. Extra amounts of base decrease the H2O2 utilization and the H2O2 conversion. However, in over acid-treated TS-1 in which part removal of extra-framework titanium takes place, the utilization of H2O2 is quite different: for the low Si/Ti ratio of TS-1, the H2O2 utilization increases. But the utilization of H2O2 does not change for the high Si/Ti ratio TS-1. Thermal analysis shows that the as-synthesized TS-1 exhibits high activity and thermal stability in the calcined range 540-900 °C.

Epoxidation of Propylene over Small-Crystal TS-1 Extrudate in a Fixed-Bed Reactor

A small-crystal titanium silicalite-1 (TS-1) with a size of 600 nm × 400 nm × 250 nm was synthesized using a nano-sized TS-1 mother liquor as the seed in a tetrapropyl ammonium bromide (TPABr)-ethylamine hydrothermal system,and was extruded with silica sol.The obtained TS-1 extrudate was characterized by X-ray powder diffraction (XRD),Fourier-transform infrared (FTIR) spectroscopy,ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy,and nitrogen physisorption.The reaction conditions,including temperature,pressure,molar ratio of propylene/H2O2 (n(C3H6)/n(H2O2)),the weight hourly space velocities (WHSVs) of propylene,methanol and H2O2,and the concentration of NH3·H2O,were systematically studied to identify ideal conditions for propylene epoxidation over small-crystal TS-1 extrudate.The reaction temperature had little effect on the propylene oxide (PO) yield under the conditions examined.The highest PO yield was obtained when the pressure was 2.0 MPa and the n(C3H6)/n(H2O2) was 4.The PO content in the product was maximized when the WHSVs of propylene,methanol and H2O2 were 0.93,2.5,and 0.25 h-1,respectively.A low concentration of NH3 · H2O was beneficial for a high PO yield.Under the optimized condition,we compared catalytic performances of TS-1 with different crystal sizes and performed a long-term test over the small-crystal TS-1.The tests indicated that H2O2 conversion and PO selectivity could both reach 95%,even after 1000 h on stream.

Effect of Water on Biphenyl Methylation over Modified HZSM-5

Nanosized HZSM-5 (n(SiO2 )/n(Al2O3)=26) samples were hydrothermally treated with and without subsequent HNO 3 leaching. The performance of the samples for the alkylation of biphenyl (BP) with methanol to 4-methylbiphenyl (4-MBP) under fixed-bed down-flow conditions was investigated. Characterization was conducted by the adsorption of pyridine using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analysis. The effect of water on the catalytic performance of modified HZSM-5 was investigated. Both hydrothermal and combined hydrothermal-HNO3 treatments improved catalytic stability, with the latter exhibiting better stability. Without the addition of water, BP conversion behavior resembled an open down parabolic vs reaction time over modified HZSM-5. However, this change disappeared upon the addition of water to the reaction system. Both catalytic stability and selectivity of 4-MBP were improved upon the addition of water. BP conversion after 30 h on stream was 8.6%, and the selectivity of 4-MBP was as high as about 60% . Elevating the reaction temperature to 500 ° C in the presence of water led to increased BP conversion with time on stream up to 30 h, and the selectivity was stable at ~58%. The activity and stability of HZSM-5 were improved, and para selectivity was enhanced with the addition of water.

Preparation of titanium-containing large pore molecular sieve from H-Al-Beta zeolite

Abstract Ti-Al-Beta zeolite has been synthesized by gas-solid isomorphous substitution with H-Al-Beta zeolite as precursor. X-ray diffraction pattern showed that its structure was similar to that of zeolite H-Al-Beta. The only difference between their IR spectra was an extra adsorption band appearing at 960cm−1. The study of IR and UV-Vis spectra showed that Ti was incorporated into the framework of Beta zeolite and Ti was tetrahedrally coordinated as part of the framework. After the precursor was treated with acid, the incorporation of titanium became easy. With increasing acid concentration, the content of Ti into the framework increased. In addition, increasing substitution time, the content of Ti into the framework also increased.