Supported transition metal compounds: Infrared studies on the acidity of Co/ZSM-5 and Fe/ZSM-5 catalysts

The acidity of Fe/ZSM-5 and Co/ZSM-5 synthesis gas conversion catalysts, prepared by extraction of Fe₃(CO)₁₂ and Co₂(CO)₈, is investigated by infrared characterization of chemisorbed pyridine. A portion of the total concentration of iron or cobalt is shown to incorporate into the channels of the ZSM-5. Such incorporation involves ion-exchange during Co₂(CO)₈ extraction onto ZSM-5 but occurs only upon H₂ reduction of Fe/ZSM-5 subsequent to Fe₃(CO)₁₂ extraction. The ion-exchange causes a redistribution of the Bronsted and Lewis acidity of the ZSM-5. As a result of this redistribution, the oxidation state of the ion-exchanged iron is calculated.     

苯并噻吩/二苯并噻吩在改性Y型分子筛上的吸附

主要研究了金属离子交换分子筛对有机硫化物苯并噻吩和二苯并噻吩的吸附.首先通过液相离子交换法对商品的Na(Ⅰ)/Y分子筛进行改性,分别制备了5种过渡金属离子的Y型分子筛Ag(Ⅰ)/Y、Ni(Ⅱ)/Y、Zn(Ⅱ)/Y、Cu(Ⅱ)/Y和Fe(Ⅲ)/Y,用静态吸附法测定了苯并噻吩和二苯并噻吩分别在6种Y型分子筛上的吸附等温线,应用软硬酸碱理论分析和讨论了其吸附能力的差异.结果表明: Na(Ⅰ)/Y对苯并噻吩有吸附,而对二苯并噻吩无吸附作用;a(Ⅰ)/Y分子筛经离子交换Ag 、Ni2 、Zn2 、Cu2 、Fe3 后,其吸附苯并噻吩和二苯并噻吩的能力得到了不同程度的提高,其中交换软酸离子的Ag(Ⅰ)/Y其吸附容量增加最多,交换交界酸的Ni(Ⅱ)/Y、Zn(Ⅱ)/Y、Cu(Ⅱ)/Y次之,而交换硬酸的Fe(Ⅲ)/Y增加最少.这表明,当Na(Ⅰ)/Y分子筛上分别离子交换以上5种软酸性大于Na 的金属离子时,所得到的改性分子筛其对苯并噻吩和二苯并噻吩的吸附容量均增强.同时,这种吸附能力的大小顺序基本上与这些离子的绝对硬度η成反比.     

Adsorption of nitrogen oxides by the moisture-saturated zeolites in gas stream

This investigation examined the instantaneous adsorption of NO(x) by moisture-saturated zeolites at ambient temperature. Among the zeolites studied, Faujasite exhibited the highest adsorption capacity owing to its relatively large pore size. Besides, the influence of cation was demonstrated by comparing the adsorption of zeolites with different cation densities (NaX vs. NaY, mesoporous silica MCM-48-like vs. Faujasite) and treatments (ion exchange of NaY with Cu(2+)). For the adsorption of NO, the effects of gas flow rates and pre-adsorbed hydrocarbons such as benzene, acetaldehyde or 1,3-butadiene were evaluated. It was proven that zeolite could efficiently capture nitrogen oxides in gas stream even it had been saturated by moisture, which will be valuable for the protection of environment and public health.     

Carbon nanotube templated growth of nano-crystalline ZSM-5 and NaY zeolites

MFI-type(ZSM-5) and FAU-type(NaY) zeolites nanocrystals have been synthesized through crystallization of gel in mesoporous system of carbon nanotubes(CNTS) with an internal diameter of 20∼30 nm. Investigation by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscope (TEM) and scanning electron microscope (SEM) shows that the nanocrystals possess the typical nanosized zeolites' structural characteristic which is different from those of microsized zeolites.     

Decolorization of KN-R catalyzed by Fe-containing Y and ZSM-5 zeolites

Decolorization of an anthraquinone dye, Reactive Brilliant Blue KN-R by hydrogen peroxide was examined using Fe-containing Y and ZSM-5 zeolites as heterogeneous catalysts. Catalysts were prepared by ion-exchange and coprecipitation methods, and calcined at different temperatures. The surface morphologies, crystalline phases, and chemical-state of the catalysts were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Influences of reaction conditions, such as dye concentration, catalyst dosage and solution pH, were evaluated and the relations between catalytic capacity and surface microstructures were discussed. The results showed that Fe-containing Y and ZSM-5 zeolites generally exhibited similar or better catalytic efficiency compared with homogeneous Fenton reagent, with Fe-containing ZSM-5 being more efficient. Synthesis method and calcination temperature affected catalytic efficiency and the stability of catalysts. Fe-containing ZSM-5, which was prepared by coprecipitation and calcined at 450 degrees C, displayed the greatest decolorization capacity. Under the conditions of initial pH 2.5, 30.0 mmol/L H(2)O(2) and 4.0 g/L catalyst, 250 mg/L KN-R could be decolorized over 90% within 20 min.     

Alkylation of benzene with methanol on zeolites: Infrared spectroscopy studies

Chemisorption of CH₃OH and CD₃OD on NaY and HY zeolites was investigated by i.r. spectroscopy. The reaction “in situ” of methoxy groups with benzene was observed. It was found that the first step of methylation of the benzene ring is the chemisorption of methanol on the acid sites of the zeolites. Then, methoxy groups react with the aromatic ring.     

Adsorption of butyl acetate in air over silver-loaded Y and ZSM-5 zeolites: experimental and modelling studies

Adsorption behaviours of butyl acetate in air have been studied over silver-loaded Y (Si/Al=40) and ZSM-5 (Si/Al=140) zeolites. The silver metal was loaded into the zeolites by ion exchange (IE) and impregnation (IM) methods. The adsorption study was mainly conducted at a gas hourly space velocity (GHSV) of 13,000 h(-1) with the organic concentration of 1000 ppm while the desorption step was carried out at a GHSV of 5000 h(-1). The impregnated silver-loaded adsorbents showed lower uptake capacity and shorter breakthrough time by about 10 min, attributed to changes in the pore characteristics and available surface for adsorption. Silver exchanged Y (AgY(IE)) with lower hydrophobicity showed higher uptake capacity of up to 35%, longer adsorbent service time and easier desorption compared to AgZSM-5(IE). The presence of water vapour in the feed suppressed the butyl acetate adsorption of AgY(IE) by 42% due to the competitive adsorption of water on the surface and the effect was more pronounced at lower GHSV. Conversely, the adsorption capacity of AgZSM-5(IE) was minimally affected, attributed to the higher hydrophobicity of the material. A mathematical model is proposed to simulate the adsorption behaviour of butyl acetate over AgY(IE) and AgZSM-5(IE). The model parameters were successfully evaluated and used to accurately predict the breakthrough curves under various process conditions with root square mean errors of between 0.05 and 0.07.     

Correlation between the crystal zize and catalytic properties of ZSM-5 zeolites

The effect of crystal size on the catalytic properties of H-ZSM-5 has been studied. Good correlation has been observed between crystal size and the catalytic properties of H-ZSM-5. In contrast to large crystallites, the aggregated H-ZSM-5 consisting of small crystallites showed long catalytic life and high selectivities for hydrocarbon, aromatics and aromatics (polymethyl aromatics) in the conversion reaction of methaol to hydrocarbons (MTG reaction). Compared with large crystallites, the aggregated H-ZSM-5 had higher adsorption ability of 2,2-dimethylbutane, largr intercrystalline void space ranging from 5 nm to 20 nm, larger pore volume, and more external surface acid sites. These results indicate that the crystal size of H-ZSM-5 significantly affects the catalytic activity in the MTG reaction and that the catalytic life could be somewhat predicted from these physicochemical properties.