FTIR silicalite

Fig. 23. Time-resolved FTIR spectra of ethene polymerization reaction on a l.Owt.% Cr/Silicalite sample oxidized at 923 K and CO-reduced at 623 K (ethene pressure = 2 kPa). The CH2 stretching region is reported. The last spectrum has been obtained after 10 min. (Reproduced with permission from Spoto et al. 234))...

Figure 3.3 FTIR spectra of gaseous CO and of CO adsorbed on silica-alumina, on silicalite (150K), on Au/Ce02 and on Pt-Pd alloy nanoparticles on MCM41 mesoporous silica-alumina.

Figure 3.9 FTIR and FTFIR skeletal spectra of amorphous silica (aerosil), a-quartz, silicalite-1 and kaolinite.

The sorption kinetics of n-hexane in MFI-type zeolites of different sizes have been measured by means of micro-FTIR spectroscopy. To check for an influence of the Si/Al ratio, nsj/Ai, on the sorption characteristics, a sample of silicalite was also investigated. The measured transport diffiisivities show ndther a dependence on the crystal size nor on the Si/Al ratio. The temperature dependence is shown to follow an Arrhenius-type law. The results of this study compare well with literature data obtained by different techniques. 

Figure 10. FTIR spectra of Sil (silicalite-1) samples treated with aqueous solutions of NH3. The number in parentheses indicates the molar concentration of NH3 solutions [54], ...

Fig. 13 Set of FTIR spectra of successive states of uptake of pyridine into silicalite-1 (sample No. 4)...

Vibrational spectroscopy is a molecule-specific analytical method that probes the vibrations of molecules and solids. Fourier transform infrared (FTIR) and Raman spectroscopies are widely used in situ techniques in the analysis of chemical reactions. However, in the case of silicalite-1 synthesis, they have not yet been used [35]. Attenuated total reflectance infrared (ATR-IR) spectroscopy has however been used to study soluble silicates and shown to be able to characterize various structures [25, 35-37]. It is likely only a matter of time before we see ATR-IR used under in situ conditions. 

Nanocrystalline zeolites, NaY and NaZSM-5 and silicalite, synthesized by us, were evaluated for the decontamination of the CWA simulants, DMMP (15) and 2-CEES (16,17). The increased surface area and external surface reactivity of nanocrystalline zeolites provides potential advantages for CWA decontamination that are not found in conventional zeolite materials. The adsorption capacity and the thermal oxidation of these simulants on nanociystalline zeolites was investigated using FTIR spectroscopy and solid state NMR spectroscopy and the reactivity on different materials was compared. 

The 2-CEES molecule has a chemical stracture similar to mustard gas (Figure 1) without one chlorine atom but it is significantly less toxic. Zawadski and Parsons have shown that 2-CEES and mustard gas have very similar crystal stractures (18), therefore it is expected that 2-CEES will closely mimic the reactivity of mustard gas. FTIR spectroscopy and flow reactor measurements were used to investigate the adsorption, desorption and thermal oxidation of the mustard gas simulant, 2-CEES, on nanocrystalline zeolites. Thermal oxidation reactivity of 2-CEES on nanociystalUne NaZSM-5 (15 nm) is compared to that on nanociystalline silicalite-1 (23 nm) and NaY(22 nm) (16). 

Nanocrystallline zeolites (Y, ZSM-5 and silicalite-1) with ciystal sizes of 50 nm or less were synthesized, characterized and evalnated for CWA simulant adsorption and decontamination. The nanociystalhne zeohtes have significantly increased external surface areas that account for up to 30% of the total zeohte surface area. The external sitrface sites have been characterized by FTIR spectroscopy. Specific signals in the hydroxyl region of the FTIR spectrum have been assigned to silanol groups and to hydroxyl groups near aluminrrm sites which are botli located on the external zeolite sitrface. 

The thermal decomposition of 2-CEES on nanocrystalhne zeohtes was probed by FTIR spectroscopy. Comparison of the reactivy of nanocrystaUine NaZSM-5, silicalite and NaY indicated that NaZSM-5 was most effective for 2-CEES thermal oxidation and that external surface silanol sites were important to the zeolite reactivity. The adsorption and reaction of DMMP on nanocrystalline NaY was investigated using FTIR and sohd state NMR spectroscopy. External surface silanol and EFAL sites were implicated in the thermal oxidation of DMMP on nanocrystaUine NaY. Thus, the nanocrystalline zeolites can be envisioned as new bifunctional catalyst materials with active sites on the external surface playing an important role in the intrinsic reactivity of the material. Future studies will focus on optimizing the activity of nanocrystaUine zeolites for CWA decontamination apphcations by taUoring the surface properties. 

Llabres i Xamena FX, Otero Arean C, Spera S, Merlo E, Zecchina A. Formaldehyde oligomerization on silicalite an FTIR and NMR study. Catal Lett 2004 95 51-5. 

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