Si/Al molar ratio

Mesoporous silica was prepared using sodium silicate as silica source and cetyltrimethylammoniumbromide (CTMABr) as template as elsewhere [7]. The aluminosilicates were prepared with a similar procedure by using sodium aluminate as aluminum source, which was dissolved in the surfactant solution as described before [3]. Si/Al molar ratios were of 6, 10, 30 and 80, the impregnated iron amount was 6 wt. 

Fig 6 Variation of the Si/Al molar ratio characterizing the intermediate solid... 

Sodium, potassium LSX (NaKLSX) was synthesized following the procedure reported by Kuhl [8]. On the basis of Kuhl s work, the synthesis conditions such as the ageing temperature, reactants composition etc. were optimized further so that it was easy to repeatedly prepare NaKLSX with crystallinity near 100% in our lab [9]. The product was characterize by XRD and elemental analysis. XRD pattern indicated that the synthesized NaKLSX was pure ujasite-type zeolite without detectable crystalline impurities or amorphous materials. Elemental analysis showed that the synthesized NaKLSX had Si/Al molar ratio close to 1.0. 

Fig 6 Variation of the Si/Al molar ratio characterizing the intermediate solid phases (ZSM-20 + gel isolated at various synthesis times O = EDX values O = Si NMR values). 

Method B (Vacuum-sol method) A 0.96M aluminum nitrate solution was added to 50ml water glass solution until the Si/Al molar ratio was attained. The precipitate was collected by centrifugation and washed 7 times to remove the sodium ions. After washing, the precipitate was put into 200ml of water and then added a certain quantity of 0.94M nitric acid to peptize the precipitate to obtain the sol sample. The prepared sol was dried at room temperature in a vacuum box until it began to form the gel sample. The gels were also calcined at 550 C in air for 10 hours. The sol and solid samples produced by method B were defined as VSG samples [5]. 

The XRD analysis shows that all of synthesized materials are amorphous. Table 2 reports the solid samples specific surface area and main pore texture characteristics. The solids have large specific surface area, and this value diminish as decrease of Si/Al molar ratio in both USG and VSG series. Fig. 3 displays the pore size distribution of USGl and VSGl samples, respectively. It is clear from the figure that the both samples have a narrower pore size distribution (i.e., 2- lOnm). 

Sample No. Preparation method Si/Al molar ratio MEPV (ml/g) MIPV" (ml/g) Specific surface area (m /g) Pore size distribution (nm)... 

Tvaruzkova et al. used zeolite type HLZ-132 with a Si/Al molar ratio of 33 as a catalyst for methanol transformation. This zeolite is topologically related to levynite with an effective pore size of 0.43 nm. The experiments were carried out in the range of 350 to 500 °C and with a feed containing methanol 17%, water 68% and nitrogen 15%. The total pressure was 10 kPa. At 400 C and after 1 h on stream, the product distribution was as follows C2 hydrocarbons 51 wt% (with less than 1% of ethane), propane 3.5 wt%, propylene... 

Natural mordenite has a nearly constant Si/Al molar ratio of 5 and its typical formula can be written as ... 

Kubelkova et al. carried out experiments on dealuminated zeolite Y, with a Si/Al molar ratio of 5.7, under 3 x 10 j0/h flow conditions and low-pressure (1 to 3 Pa) at 670 K. The main hydrocarbons detected were olefins and aromatics up to C. The... 

Adsorption of dibenzothiophene (DBT) over FAU zeolites exchanged with alkali cations has been studied. Cristallinity (by XRD and IR), exchange level (XRF) and basic properties (CO2 TPD) of different adsorbents used have been determined. The influence of Si/Al molar ratio and type of cation exchanged in the zeolite as well as the presence of toluene in feedstock mixture on DBT adsorption capacity and selectivity of adsorbent has been also determined. Thermogravimetric analysis showed a stronger DBT adsorption over X zeolites. 

P-12 - New Mo and NiMo hydrodesulfurization catalysts supported on Al-MCM-41. Effect of the support Si/Al molar ratio... 

Figure 6. (a) Si spearum of a TPA siUcate solution of composition 2 mol% SiOa i = 2 at 5 C. (b) Si Spectrum of a TPA aluminosilicate solution of composition 2 mol% i = 2 and Si/Al molar ratio = 4 at 5 C. In the schematic structures, a closed circle represents the Si atom corresponding to the assigned peak, an open circle represents an A1 atom, a closed square represents a Si atom resonating in another part of the spectrum, and a solid line represents a bridging oxygen atom. Si spectral frequencies are referenced to the Qo peak in the Al-free solution [19]. 

Type Si/Al molar ratio Pore size/nm Water adsorption capacity/% Theoretical Experimental Main applications... 

Zn-Al-MCM-41 and Al-MCM-41 were used as catalysts for the synthesis of DABCQ (Scheme 41) [157]. The most suitable Si/(Zn+Al) ratio of the catalyst for the cyclization of ethanolamine to highly selective synthesis of DABCQ was 75. When the Si/(Zn+Al) and Si/Al molar ratios were increased, the yield and selectivity of DABCQ decreased. The optimum reaction conditions for the highly selective synthesis of DABCQ were foxmd at 563 K with 0.5 h (weight hourly space velocity), 4h TQS (time on stream) and 1 3 volume ratio of ethanolamine and water. 

Zeolite grade Si/Al molar ratio Some of the common mineral names and their framework codes... 

Si/Al molar ratio in the activated fly ash, zeolites can be classified/graded as low silica zeolites , intermediate silica zeolites and high silica zeolites , as listed in Table 2.2. In general, for zeolites, an increase in this parameter (i.e., Si/Al from 0.5 to infinity) [5] can significantly result in the increase in various other parameters (viz., acid resistivity, thermal stability and hydrophobicity) except few parameters (viz., hydrophilicity, acid site density and cation concentration) which get decreased [5, 8, 10,40, 41]. In general, synthetic zeolites hold some key advantages over their counterparts i.e. natural zeolites. Zeolites type A, X, Y, P and Na-Pl are well known synthetic zeolites synthesized from fly ash which have a wider range of industrial applications than the natural zeolites [1, 8, 20, 22, 36, 42, 43]. 

The heavy metal cations such as Rb, Cs, Ag, Cd, Pb, Zn, Ba, Sr, Cu, Hg, Co, and Cr have affinity towards zeolites, although, their selectivity by the zeolites for exchange depends on the hydrated molecular size of the cations, their relative concentrations in the medium associated with the process and the Si/Al molar ratio of the zeolite framework [3, 25, 37, 38, 43, 50, 51],... 

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