Dehydrated samples

Interestingly, the degree of proton transfer from a bridging hydroxyl group in a zeohte to an adsorbed molecifle was found to be correlated with the line width of the Al MAS NMR signal of framework Al species [158]. This effect 

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The quantification of the extra-framework titanium species in titanium silicalites of MFI structure, TS-1, was performed using either XANES at the Ti K-edge or XPS Ti (2p) photolines. In addition, two different framework sites, [Ti(OH)(OSi)3] and [Ti(OSi)4], were characterized in dehydrated samples using Diffuse Reflectance UV-visible, multiple scattering analysis of EXAFS, H and Si NMR spectroscopies. 

Vegetables with peroxidase activity Dehydrated samples... 

In addition to the Ti, hydroxyl groups constitute a second class of surface functional groups on dehydrated samples that can be of importance in catalytic reactions. The presence of a large number of Si-OH groups on the surfaces of all the titanosilicates is apparent from the intense absorption in the 3200-3800 cm-1 region of the infrared spectra. The experimental evidence of surface... 

The red shift of this band from its position in the dehydrated sample (Section II.A.3) is attributed to the increase of the coordination sphere about Ti4+ ions and is similar to the changes observed on adsorption of H20 and of NH3 (153). The simultaneous observation of the 837 and 3400 cm-1 bands in the infrared region (attributed to peroxidic O-O, Fig. 18) and the 360 nm band in the DRUV spectra (attributed to octahedrally coordinated Ti4+ ions, Fig. 19) further confirms that the Ti4+ ions in the side-bound Ti(02H) species are indeed 6-fold coordinated. 

Embed the dehydrated samples in epoxy resin (Quetol 653), cut into thin sections, stain with 4% uranyl acetate and 0.4% lead citrate, and examine with a Jeol 1200EXS electron microscope. 

The >>Na NMR experiments were performed on static samples and on a Bruker MSL—200 spectrometer. Dehydrated samples were evacuated at 350 C under shallow bed condition, cooled under vacuum (lO torr), stored in helium atmosphere and introduced into a sample cell in a glove-bag under helium atmosphere. 

The rehydrated samples were obtained by exposing dehydrated samples to water vapor at least three days over saturated NH4GI solution at room temperature. A duraction of 0.5 s between scans were allowed for nuclear spin to recover to their equilibrium magnetization. The one—dimensional Na NMR spectra were recorded by using the spin—echo technique. The strength of the radio-frequency field for the two dimensional nutation experiments was 80 kHz and 128 ti values were used (0 250 /is). Each two- dimensional experiment took about 12 hours of spectrometer time. 

Table II lists the thermodynamic parameters for the conduction process. For the Na+ samples the activation energies are on the average 3.5 kcal lower than those for the conduction process of the corresponding dehydrated zeolites (<8). For K+-zeolites this difference averages 2.1 kcal. NaF69.8 is not included because of experimental difficulties in pellet preparation. The activation entropies are negative for the X-type zeolites and positive for the Y-type. The activation entropies are higher than those of the dehydrated samples (8) except for KF86.5. The effect of AS on E...

The AS-values increased with respect to those of the dehydrated samples (8), especially for the samples with high H20/cation ratios. This means that there is a distortion of the cationic hydration shell or a partial dehydration of the cations during migration (18). In other words, water around the migrating cations cannot be regarded water of hydration. In that respect, hydrated zeolites resemble concentrated cationic solutions (19). 

Experimental Technique. The IR spectra of dehydrated samples were recorded by UR 10 spectrometer (VEB Carl Zeiss Jena). To obtain spectra for dehydrated zeolites, samples were activated for 10 hours in air at 570°C, cooled to room temperature in the presence of P4O10, and ground with Nujol. The accuracy of the band maximum determination of the D6-ring band was 1.5 cm-1. IR characterization of the zeolites after CO adsorption was done in a cell with NaCl windows as described by Dunken and coworkers (9). The samples were heated at 550° C for 3 hours under vacuum. After cooling under vacuum to room temperature, CO was adsorbed (pco = 450 torr), and the spectra were recorded. 

H-ZSM-5 quadrupolar effects are always dominant. The same applies to both the hydrated and the dehydrated samples of zeolite H-Y (not shown). 

Figure 37 shows the spectra of Na-ZSM-5 as a function of time of hydration. In dehydrated samples quadrupole interactions are so strong that the tetrahedral A1 line disappears, to reappear on rehydration. Dehydration has no effect on octahedrally bound Al. 

West (231) observed no 23Na resonance in dehydrated synthetic faujasites, suggesting that the EFG at the cationic site is larger than in hydrated samples because of the displacement of the cations away from their high-symmetry positions. The signal appeared when seven H20 molecules per cage were present. Fully hydrated Na-X and Na-Y had Tf of 100 and 140 fj.sec, respectively, while in dehydrated samples much faster transverse relaxation was observed. 

This protocol begins with the extraction of a dehydrated sample. It continues with a saponification scheme to initiate the isolation of the carotenoid mixture. During saponification, the esters are hydrolyzed and the free pigments released. Then, to continue the isolation, column chromatography is suggested as a simple and fast means of separating the three main groups of carotenoids based on their different polarities. 

Thermal activation of the clay up to 600°C results in a simultaneous loss of ammonia and structural hydroxyl groups. During decomposition, the ammonium ions release protons to the clay framework. Infrared spectra of dehydrated SMM samples exposed to ammonia vapor showed small amounts of ammonium ions and Lewis-bound ammonia. The ammonium ion was thought to result from interaction with silanol groups at crystal edges. Partially dehydrated samples adsorbed larger amounts of ammonia, and a greater proportion was present as ammonium ion, probably because of the lesser extent of dehydroxylation. 

Figure 5.11 Plot of fractional population of geminal sites measured for dehydrated samples vs. temperature.

The results of Maciel and Sindorf show that, for dehydrated samples, the relative apparent population of the surface geminal sites decreases from the initial value of about 15% at room temperature to a value of about 12% at 673 K. Above this temperature, there is a sharp increase in the relative population of geminal sites, which reaches a maximum of approximately 24% at 923 K and then decreases again at higher dehydration temperatures. 

VPI-5 is a crystalline mesoporous AIPO4 with VFI topology and monotubular 18-MR rings with an inner diameter of 1.27 nm.[71] Partially dehydrated samples were filled with ferrocene molecules and subsequently exposed to DCB.[72,73]... 

IR spectra of CO adsorbed on polycrystalline MgO were first reported in the 1970s (89-91). Pioneering studies were performed with samples activated at moderate temperatures and still covered by a relatively high density of OH groups (89,90). Under these conditions, CO is adsorbed as a carbonatelike species only if O2 is present. Investigations of fully dehydrated samples (85-88, 91, 92) in the absence of O2 showed that CO chemisorption leads to the formation of peculiar, highly colored, anionic polymeric species. 

Ammonia TPD Measurement. The acidic properties of the catalysts were characterized using temperature programmed desorption (TPD) of ammonia. The experiments were carried out on a flow-type apparatus equipped with a fixed-bed and a thermal conductivity detector. The samples were activated in a helium flow of 5 L/h at 773 K for 1 hour. 300 mg of the H+-form of each dehydrated sample were used to perform the ammonia TPD. Pure ammonia, with a flow rate of 3 L/h, was then passed through the sample at 423 K for 30 min. The sample was subsequently purged with helium at the same temperature for 1.5 hours in order to remove the physisorbed ammonia. The TPD was performed under a helium flow of 6 L/h from 423 K to 873 K with a heating rate of 10 K/min and subsequently at the final temperature for 30 min. 

In Figure 4.22, the FTIR spectra of dehydrated samples of the acid zeolites, H-SSZ-24 and H-ZSM-11, in the range from 3000 to 4000 cm-1 are shown [65], The measurement of the FTIR spectra was carried out in a Bio-Rad FTS 40A FTIR spectrometer with aresolution of 8cm-1 controlled by the Bio-Rad WIN IR software in an Advanced Scan Menu-Kinetics mode [65,66], To obtain the spectra, 30 scans were made. 

The magnitude of AfH° for the as-synthesized DIPA[Si]-MFI and TRIPA [Si]-MFI samples is larger than for the TPi siJ-MFI sample this observation is unexpected. In fact AfH° takes into account the enthalpy of formation of the water occluded in the DIPA[s ]-MFI and TRIP A [Si]-MFI samples. The AfH° of both dehydrated samples are slightly different, and the order of increasing magnitude of AfH° is then as expected ... 

At this time, the locations of cations in zeolites have been determined primarily by X-ray diffraction (XRD) techniques. Unfortunately, this method has the drawback of being able to locate only the most stationary cations in zeolites. In some studies of hydrated zeolites, less than 50% of the total cation population can be accounted for. A higher percentage of the cations can be located in dehydrated samples, but the effect of the dehydration step on the location of the cations is generally not well known. NMR measurements, on the other hand, are most sensitive to mobile cations and cations in high symmetry sites. 

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