Zeolite reflectance FTIR spectroscopy

The adsorption of NO on in-situ synthesized CuZSM-5/cordierite monolithic catalysts of different Si/Al ratios was studied by diffuse reflectance FTIR spectroscopy at different NO partial pressures from 500 ppm to 2000 ppm and temperatures from 298 K to 773 K. At room temperature, Cu mostly exists in oxidized Cu form. A lot of N2O species were observed on the surface even at room temperature. A band at 2133 cm is attributed to NO -Oiattice and only related to the number of lattice A1 in the zeolite. There may exist a copper-zeolite-substrate interaction on such as synthesized monolithic catalysts. 

The acid sites of iron-exchanged Y zeolite were studied using NH3-TPD and diffuse reflectance FTIR spectroscopy. The Bronsted acids of three iron-exchanged Y zeolites were correlated with the activity for dibenzothiophene HDS at 240 and 280°C and 10.1 MPa. The FTIR data on NH3 and NO adsorption showed that Fe ions on the zeolites was correlated with their activities during dibenzothiophene HDS. 

For ferromagnetic cobalt particles in zeolite X, spin-echo ferromagnetic resonance has been used to obtain unique structural information (S6). In addition, study of the catalytic signature of metal/zeolite catalysts has been used by the groups of Jacobs (87), Lunsford (88), and Sachtler (47,73,89). Brpnsted acid protons are identified by their O—H vibration (90,91) in FTIR or indirectly, by using guest molecules such as pyridine or trimethylphosphine (92,93). An ingenious method to characterize acid sites in zeolites was introduced by Kazansky et al., who showed by diffuse reflection IR spectroscopy that physisorbed H2 clearly discerns different types of acid sites (94). Also, the weak adsorption of CO on Brpnsted and Lewis acid sites has been used for their identification by FTIR (95). The characterization of the acid sites was achieved also by proton NMR (96). 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

An analogous ship-in-bottle complex, [VO(bpy)2]2+-NaY, could be designed starting from a vanadyl exchanged Y zeolite upon bpy addition.[97] Strong spectroscopic proof for the formation of such complex was evident from FT-Raman, FTIR, diffuse reflectance spectroscopy, XPS and EPR as follows ... 

Palladium nanoparticles (nm-Pd) were synthesized by ship-in-a-bottle technique in supercages of NaA zeolite. The behaviors of electrodes of thin film of nm-Pd accommodated in NaA zeolite were characterized by cyclic voltammetry. The results illustrated that the nm-Pd possess particular properties for hydrogen reaction, i.e. in contrast to hydrogen absorption on massive palladium electrode, the surface processes of hydrogen adsorption-desorption become the dominant reaction on electrodes of thin film of nm-Pd. The processes of adsorption and desorption of carbon monoxide on the electrodes were studied using in situ electrochemical FTIR reflection spectroscopy. It has been revealed that in comparison with CO adsorbed on a massive Pd electrode, the IR absorption of CO adsorbed on nm-Pd particles accommodated in NaA zeolite has been enhanced to about 36 times. 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

Nevertheless, the conflicting conclusions regarding the formation of trimethyloxonium were problematic since different forms of spectroscopy should ultimately reveal the same truth. There were several possible sources of this discrepancy. The first could be that the assignments in either the C NMR or the FTIR work were incorrect. The second possibility was that there was some subtle difference in the zeolite samples or activation procedures that might account for the difference. Finally, both studies could be correct and the apparent discrepancy could reflect differences in the experimental protocols used in the respective in situ experiments. 

This paper presents results concerning the synthesis of Pt(2,2 -bipyridine)Cl2 (K) encapsulated in Y zeolite and its activity in C2H4 selective dimerization to linear butenes. Diffuse reflectance UV-VIS spectroscopy and FTIR are used to investigate the state of the complex encapsulation. The influence of the reaction parameters on C2H4 selective dimerization to linear butenes is studied, we concluded that Pt(2,2 -bipyridine)Cl2 encapsulated in Y zeolite is a selective cateilyst for ethylene dimerization to linear butenes at low temperatures (80 - 150 C) and a reactant flow rate corresponding toWHSV 2h". ... 

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