Young Sun Uh

Synthesis and characterization of the vanadium-incorporated molecular sieve VAPO-5

Abstract The vanadium-incorporated molecular sieve VAPO-5 was synthesized hydrothermally and characterized by X-ray diffraction, electron paramagnetic resonance, thermogravimetric analysis, diffuse reflectance spectroscopy, chemical analysis and adsorption techniques. It seems that the vanadium is incorporated mainly as V 4+ in the as-synthesized VAPO-5 framework. The vanadium in VAPO-5 exists in a well dispersed state and shows redox properties, changing its oxidation state readily between V 4+ and V 5+ .

Selective Alkylation of Aniline With Methanol Over Boronsilicate Molecular Sieve

The selective alkylation of aniline with methanol catalyzed by boronsilicates was investigated. Correlation of acidity of ZSM-5, (B)ZSM-5 and ion-exchanged (B)ZSM-5s with the selectivity towards methylated anilines suggested that strong acid sites T m 600K, medium acid sites 450T m 600K, and weak acid sites (T m 450) are active sites to produce C-alkylate and coke, N, N-dimethyl aniline (NNDMA) and N-methyltoluidine (NMT), and N-methylaniline (NMA), respectively. However, Cu exchanged (B)ZSM-5 having only weak acid sites is selective to NMT and does not deactivate during the reaction.

Skeletal isomerization of 1‐butene on synthetic clinoptilolite zeolite

A pure, highly crystalline clinoptilolite (CLI) zeolite with a Si/Al ratio of 5.8 has been synthesized using a small amount (1%) of seed crystals and tested as a catalyst for the skeletal isomerization of 1‐butene at 623–723 K at atmospheric pressure. The catalytic results are compared to those obtained from a ferrierite (FER) zeolite with a Si/Al ratio of 7.6. It is found that selectivity for isobutene is very high on CLI zeolite, but conversion was lower than for FER zeolite. The simulated distribution and calculated potential profile of 1‐butene molecules in CLI zeolite pore 10‐ring channels show that the spatial constraints imposed by the pores are very severe. The exceptional selectivity and the low conversion of CLI zeolite results from the strict restriction of adsorption to very specific sites, inhibiting dimerization, as well as from the high potential barrier which reduces mass transfer.

Preparation and characterization of vanado-, ferri-, and gallosilicate catalysts in the presence of fluoride ions

Vanado-, ferri-, and gallosilicate catalysts were prepared from the mixtures containing colloidal silica, corresponding metal source, tetrapropylammonium bromide, and NH4F by hydrothermal crystallization at 175°C for 7 days. The pH value of the reaction mixture was low (pH<8) compared to the conventional methods. The metal compounds have higher solubilites in these conditions than conventional conditions (pH>10). The size distribution and the size of final products were found to be more homogeneous and larger than those of metallosilicates prepared in strong alkaline media. The characterization of metallosilicates with IF!, X-ray diffraction, SEM, EPR, and29Si MAS NMR, indicated that corresponding metal atoms were successfully incorporated into the tetrahedral lattice sites of the ZSM-5 structure.

Thermal stability of [B]ZSM-5 molecular sieve

The thermal stability of [BJZSM-5 (boronsilicalite) has been examined by IR, XRD,11B MAS NMR and XPS techniques. [B]ZSM-5 and amorphous borosilicate were converted to α-cristobalite at high temperatures (=750C). However, Na-free amorphous borosilicate was not converted to a-cristobalite at 750C. Therefore, the presence of Na ions in [BJZSM-5 would determine whether this transition occurred or not. When the phase transition to α-cristobalite occurred, most of B atoms tetrahedrally coordinated were released from the ZSM-5 structure and migrated to the exterior surface as a boron compound having trigonal BO3 units and oxidation states of 3.

Adsorption of oxygen on the paramagnetic defect centers in aluminophosphate molecular sieves

Temperature-programmed desorption (TPD) and electron spin resonance (ESR) techniques have been employed to investigate the oxygen adsorbed on the paramagnetic defect centers in dehydroxylated AlPO4-20, AlPO4-11, AlPO4-5, and VPI-5 molecular sieves. Two different adsorption sites are observed for the small-pore AlPO4-20, where oxygen is entrapped within the intracrystalline voids generated during the calcination step, as well as within the β-cages. However, the unidimensional molecular sieves AlPO4-11, AlPO4-5, and VPI-5 have only one type of adsorption site within their inner pores. The apparent activation energies of desorption (12.0-21.7 kcal mol-1) determined from the oxygen TPD results demonstrate that, as the pore size of the AlPO4 molecular sieve is larger, the interaction between the adsorbed oxygen and the molecular sieve framework becomes weaker.