Samples prepared by various

In this paper we report (i) the catalytic activity for SCR of VOx/Zr02 samples prepared by various methods (adsorption from aqueous metavanadate solutions at different pH values, dry impregnation, and adsorption from VO(acetylacetonate)2 in toluene), (ii) sample characterization (nuclearity, dispersion and oxidation state) by means of XPS, ESR and FTIR and (iii) the nature and reactivity of the surface species observed in the presence of the reactant mixture. Catalytic results are here reported in full. Characterization data relevant to the discussion of the catalytic activity will be given, whereas details on the catalysts preparation and... 

Fig. 3. Experimental and deconvoluted DRUV-visible spectra of TS-1 (Si/Ti = 33) and TS-2 (Si/Ti = 30) samples prepared by various methods/treatments. Deconvoluted bands are representated by 1-5 [from Shetti et al. (93)].

Structure of ZrOa-SO/ samples prepared by various methods and their catalytic properties in n-butane isomerization... 

In order to elucidate the reasons for the dependence of the catalytic properties of these samples on their preparation method, we studied the acid surface properties of cobalt- and chromium-modified Zr02 catalysts by ammonia thermoprogrammed desorption and IR-spectroscopy. Our results again indicated that the activity of these catalysts in the SCR of NOx by hydrocarbons is a function both of the surface acidity and content of the active metal. The acid site concentration of the starting Zr02 samples prepared by various methods is significant (0.13 and 0.23 mmol/g) but these samples are inactive, while 10% CriOilZtOi prepared by the sol-gel method displays considerable activity in the reaction studied with lower surface acidity. The acid site concentration of the sample with the same composition prepared by the precipitation method is reduced by a factor of 2.5 and, thus, this catalyst has much lower activity in the selective catalytic reduction. 

The general characteristics of the samples prepared by various preparation routes were characterised as follows ... 

Oxidation of nitrogen compounds. The manganese dioxide oxidation of organic nitrogen compounds has been reviewed in depth by Meth-Cohn and Suschitzky.7 These authors state that samples prepared by various methods seem to have about the same activity. 

Boylan and Tripp [76] determined hydrocarbons in seawater extracts of crude oil and crude oil fractions. Samples of polluted seawater and the aqueous phases of simulated samples (prepared by agitation of oil-kerosene mixtures and unpolluted seawater to various degrees) were extracted with pentane. Each extract was subjected to gas chromatography on a column (8 ft x 0.06 in) packed with 0.2% of Apiezon L on glass beads (80-100 mesh) and temperatures programmed from 60 °C to 220 °C at 4°C per minute. The components were identified by means of ultraviolet and mass spectra. Polar aromatic compounds in the samples were extracted with methanol-dichlorome-thane (1 3). 

Fig. 54. EPR spectra showing the differences in the types of superoxo species generated on various TS-1 samples prepared by different methods after contacting with aqueous H202 [from Shetti etal. (93)].

We compared our results in Pt catalysts with that of Pt-carbonyl molecules (12), which are often used as models of the Pt catalytic surface. The data for [Pt3g(C0)44]2 was obtained from a sample prepared by Dahl and Murphy at the University of Wisconsin. The data for the remaining three molecules was obtained from Brown et al. (12). As can be seen in Table I, we found that the position of the surface Pt resonance in our catalysts is very close to those in various Pt carbonyls. (The variations among the positions shown in Table I are small compared to typical variations among Pt compounds. See Figure 6.) Thus,... 

The properties of PCTA-type structures where the modifying acid is 1,4-cyclohexanedicarboxylic acid (CHDA) have also been studied [53], The incorporation of this diacid (95 % trans) as a polyester modifier maintains the toughness, but is accompanied with significant lowering of the Tg. This is contrasted to NDA modification where the Tg is enhanced but toughness is decreased. A comparison of the properties of various PCTAs versus an amorphous PCT sample, prepared by quenching, are shown in Table 7.5. 

Recently, the influence of the preparation method of various MgO samples on their catalytic activity in the MPV reaction of cyclohexanone with 2-propanol has been reported 202). The oxides were prepared by various synthetic procedures including calcination of commercially available magnesium hydroxide and magnesium carbonate calcination of magnesium hydroxides obtained from magnesium nitrate and magnesium sulfate sol-gel synthesis and precipitation by decomposition of urea. It was concluded that the efficiency of the catalytic hydrogen transfer process was directly related to the number of basic sites in the solid. Thus, the MgO (MgO-2 sample in Table IV) prepared by hydration and subsequent calcination of a MgO sample that had been obtained from commercially available Mg(OH)2 was the most basic and the most active for the MPV process, and the MgO samples with similar populations of basic sites exhibited similar activities (Table IV). 

Sample surfaces prepared by various macroscopic techniques are not well characterized on an atomic scale over the extended area of the macroscopic surfaces. It is now well known that even the most carefully processed surfaces contain only domains of well defined atomic structures of sizes of the order of 100 to 1000 A. 

The unsymmetrical nature of / -mercaptoethylamine should lead to geometric isomerism among its metal complexes, cis and trans isomers might be expected with the square planar nickel (II) and palladium (II) derivatives and facial and peripheral isomers with cobalt (III). However, during the course of the preparation of various samples in which the procedure and experimental conditions were varied, no evidence of such isomerism was apparent (6, 15). This is particularly evident in the case of the cobalt (III) complex, CoL3. Samples prepared by the addition of cobalt (II) chloride 6-hydrate to strongly basic aqueous solution of the ligand and by displacement of ammonia and (ethylenedinitrilo)-... 

F-BDAF Tg for various blend compositions, see Fig. 14. The microphase-separated morphology further manifests itself in the self-adhesion behavior of polyimide films derived from such mixtures. For mixture containing at least 25 wt% of the flexible component, peel tests of polyimide bilayer samples prepared by solution casting, bulk failure of the test specimens was observed. Since the flexible component contained fluorine, the samples could be examined by X-ray photoelectron spectroscopy to determine the surface composition. At only 10% loading, the flexible component comprised 100% of the top 75 A of the sample. The surface segregation of the flexible component is believed to be responsible for the adhesion improvements. 

Pd on ceria catalysts prepared by various methods were shown to exhibit varying characteristics depending on the preparation methods.625 Specifically, Pd on ceria samples prepared by the deposition-precipitation method are highly active in comparison with the catalyst prepared by the conventional impregnation method. Cationic palladium species are present in the former samples after reduction with hydrogen at 300°C, suggesting that the active species are produced by strong... 

The apparent melting temperature obtained for various acylated wood prepared by both the TFAA and the Chloride methods by using the thermomechanical analyzer under a pressure of 3 Kg/cm are shown in Table IV. The acylated wood samples prepared by the TFAA method show somewhat lower apparent melting temperatures compared with those prepared by the Chloride method. 

Figure 4. Inhomogeneity of silica-aluminas prepared by various methods. A series of 17 commercial samples of silica-aluminas from seven different producers was submitted to microanalysis. All of them showed considerable fluctuations of composition at the scale of several tens of nanometers to several micrometers. These samples were prepared by coprecipitation or by the sol-gel method. It is not known whether some of these samples were prepared from alkoxides. Smaller but significant fluctuations at the micrometer scale were also observed for two laboratory samples prepared from alkoxides. The samples were dispersed in water with an ultrasonic vibrator. A drop of the resulting suspension was deposited on a thin carbon film supported on a standard copper grid. After drying, the samples were observed and analyzed by transmission electron microscopy (TEM) on a JEOL-JEM 100C TEMSCAN equiped with a KEVEX energy dispersive spectrometer for electron probe microanalysis (EPM A). The accelerating potential used was 100 kV.

On-probe purification using derivatized MALDI probe surfaces has been described to simplify the sample preparation process. Various developments in this field have allowed the introduction of new techniques such as the surface-enhanced laser desorption ionization (SELDI) [42], The surface of the probe plays an active role in binding the analyte by hydrophobic or electrostatic interactions, while contaminants are rinsed away. In the same way, this technique uses targets with covalently coupled antibodies directed against a protein, allowing its purification from biological samples as urine or plasma. Subsequent addition of a droplet of matrix solution allows MALDI analysis. 

The NO adsorption and decomposition features observed for the tested samples displayed significant differences. The deviations or the dissimilarities are explained by the differences in redox character of the ions. The differences observed between the samples prepared in various ways were probably due to the concentration and the positions of the ions. 

Wurtzite (wBN) can be prepared by various static and dynamic compression methods , depending on the relative amounts of hBN and rBN in the initial sample, and the T-P conditions of the consolidation. Phase stability data for wBN is available . hBN can be converted to cBN and wBN at pressures from 12 to 40 GPa and temperatures between 300 and 1200 K , also with the use of Mg as a catalyst. A mixture of hBN, H2O, and an alkaline solution (e.g., NaOH) may be subjected to a shock wave at or above 10 GPa to prepare high quality wBN . wBN is transformed to zBN by shock compression at pressure above 100 GPa , while static high pressure transforms zBN to wBN . However, the reverse transformations are also possible". Additional references on wBN are given in physics abstracts. ... 

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