Temperature pretreatment

Table 5 shows HDS product distributions over several catalysts prepared by using the molybdenum-nickel cluster 2. Sulfur content in decane was adjusted to 5.0 wt% in these experiments. MoNi/NaY was found to be more active than MoNi/Al203. It is to be noted that during the high temperature pretreatment the original cluster structure would have been changed. However, the high activity of the MoNi/NaY catalyst for benzothiophene HDS is probably due to the formation of active sites derived from this particular mixed metal cluster. 

Formation and stabilization of M+ cation radicals of N,N-dimethyl-aniline must give rise to the appearance of the well known double absorption band at 430-470 nm (23). Actually, the absorption band is present in the curves in Figure 1 in those cases where the zeolite sample underwent high temperature pretreatment. Interaction of N,A-dimethylaniline molecules with A10 /2 sites was not clearly observed in the spectra. It would be most probably accompanied by the appearance of a band 260 nm resulting from formation of a bond by the 2pz electron pair of the nitrogen atom (18) according to ... 

The final product specification can influence the process with regard to processing conditions (pressure, temperature, pretreatment of feed material), and may require fractionated separation or further treatment such as concentration, purification or... 

In some cases, the reaction of silicon and methanol has been optimized for formation of (MeO)4Si. As discussed above, thiophene addition favored formation of (MeO SiH. Both thiophene and propyl chloride poison copper copper poisoning seems to favor formation of the trialkoxysilane. High-temperature pretreatment disfavors trialkoxysilane formation copper is formed on the surface of the silicon during pretreatment at 450 °C98. Metallic Cu catalyzes dehydrogenation of alcohols and favors formation of (RO)4Si. Workers from Tonen Corporation reported 50% conversion of silicon to make (MeO Si with 92% selectivity if silicon, methanol and Cu(OMe)2 were pretreated (lower conversion and selectivity without pretreatment) and then reacted at 180 °C and 1 atmosphere99. 

The valence of both the anion of an acid and the cation of a base have a substantial influence on the character of the surface charge and on the value of PZC and IP59 . PZC and IP of a mineral are further affected by the mineral s genesis, by a preparative pretreatment of its surface with chemical agents, the presence of impurities (other minerals), isomorphism, temperature pretreatment, and age of the surface58 60 61 . 

The different reaction parameters to be used for this series of substrates, compared to the low pretreatment temperature range, indicate a difference in deuteration process. For the high temperature pretreated samples, only isolated and geminal hydroxyls are present on the silica surface. These types of silanols have a low water physisorption ability. Therefore, instead of the formation of a hydration layer prior to H/D exchange, direct exchange from vapour phase has to occur. This is favoured at higher temperatures. 

The above considerations are applicable to the titanium dioxide samples prepared and pretreated following the standard procedures. The presence of significant amounts of impurities or, for example, the high-temperature pretreatment of the Ti02 samples lead usually to a more or less important decrease of the extent of hydroxylation. 

Pretreatment requirements. Pretreatment requirements include (a) contaminant concentration (b) ionic size of the contaminants (c) membrane type (d) presence of competing ions (e) suspended solid concentration and (f) water temperature. Pretreatment is commonly used to prevent fouling of the membrane. Typical pretreatment for NF and RO includes particle removal by filtration, sequestering hardness ions by precipitates, and pH control to prevent clogging. 

PR By solid state reaction between W and amorphous B powder pressed in compacts at elevated temperature pretreatment at 500 °C in hydrogen for 1 horn followed by 800-1200 °C in argon for 2 hours. The formation of the individual boride depends on the W/B ratio. 

Influence of oxides structure and their temperature pretreatment on chemisorption kinetics of organosilicon compounds... 

The rate of the oxygen evolution reaction (OER) on pyrolytic graphite is higher than that for glassy carbon. For both the carbon electrodes, the temperature pretreatment has no influence on the current measured at constant potential. 

Praseodymium is one of the possible "new" additives, which today attracts more and more attention. In fact, it was demonstrated that the oxygen exchange occurs at lower temperature on cerium-praseodymium mixed oxides than on ceria [7]. Furthermore, high temperature pretreatment does not affect the oxygen exchange capacity (OSC) of the mixed oxides. Moreover, high surface area PrOy-Zr02 materials with a fluorite-type structure were also prepared by the sol-gel way [7, 8]. 

Despite a decrease in the dispersion of the active phase after the high temperature pretreatment in the reaction mixture, there was an increase in activity with the DA catalyst showily a higher degree of activation (DA-900/DA-SR=42). Examination of the values of initial and final activity of the AA catalyst also indicates unstable behavior for tlm AA-SR and AA 500 that could be called an extensive induction period. These results indicate that the support has a strong influence on the catalyst stability (Figs. 1 and 2). 

Mcrogr q>hs show the ze and morphology evolution of the DA and AA series of catalysts (Fig. S and 6 ). The morphology changes in these catalysts with the high temperature pretreatment is evident initid spherical particles change to irregular ones decorated by small ones. Perforated particles are also observed (Fig. 7). 

The DA-SR presents BE values of336.0 and 337.9 eV close to those reported by Otto et al. (16) assigned to two species of PdO the first one, normal, and the second one, with BE of 338.3 eV possibly belonging to small clusters of Pd in strong interaction with the support or Pd02. The AA-SR presents a nuxture of oxidized and reduced palladium, dififo fix>m the species obtained after the reactive high temperature pretreatment. 

Structural description of the iron sites in the FER, BEA, and MFI zeolites was provided using EPR (ESR-220), FTIR (Nexus 670, ThennoNicolet), and Mossbauer (ABSORPTION 57Fe MS velocity 12 mm/s, calibration on a-Fe) spectroscopies. The experimental setup for all three spectroscopies provided for high temperature pretreatment of the samples before measurements, while the spectra were measured at RT. Before experiments all samples were oxidized by oxygen at 450°C for 1 hour and further evacuated (10 Pa) at the same temperature for 2 hours. 

As for the W added materials, W1-650/850 and W5-650/850 showed a behaviour similar to that of SN-650/850 ones. However, within the same temperature pretreatment, SN appeared as the most sensitive material. The comparison is illustrated in Fig. 3b for the materials pretreated at 650 °C. Taking the integrated intensity of the broad eleetronic absorption as a measure of the response to CO, the sensitivity is markedly and progressively lowered by... 

Olivine activity, or more specifically olivine activation, depends on its iron oxide content [76, 77]. Iron can be present either in the olivine crystalline structure or free at different oxidation states depending on levels of high-temperature pretreatment and exposure to the reducing/oxidizing conditions in the gasifier. How this is able to account for catalytic activity in biomass gasification has been well documented [78]. 

The variation of both the temperature pretreatment and the ceramic carrier of platinum - tin(rV)oxide catalysts allowed the preparation of catalysts with nearly identical platinum content and dispersion, but broadly differing oxygen sorption capeicity. 

It must be mentioned that the discussion of temperature effects is complicated by the fact that CAM is modified both by direct temperatures and to a great extent by temperature pretreatment. In general, it is well known that low night temperatures favor nocturnal acid accumulation (for example DeVries, 1884 Richards, 1915). Below 5° and above 30° C, nocturnal malic acid synthesis is inhibited. 

The catalysts are prepared from hydroxides or carbonates by thermal decomposition. Equilibrium pressures for decomposition of carbonates and peroxides are shown in Fig. 3.4. lb obtain oxides from hydroxides or carbonates, high temperature pretreatment is required. During pretreatment, evolution of H2O, CO2, and O2 occurs. Evolution of H2O begins at about 673 K as Mg(OH)2, Ca(OH)2, and commercially available BaO are heat-treated in vacuo Carbon dioxide starts to evolve at a temperature slightly higher than that for H2O evolution. From commercially available... 

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