Impregnation and activation

Another information on the oxidised form of the surface eompounds can be derived from the photoluminescence, which is observed in the cases of vanadium, chromium, and molybdenum. Considering the best investigated case, surface chromium(VI), we find a drastic increase of luminescence intensity at an activation temperature around 600 °C (Fig. 18.1). The emission shows now a well-resolved fine structure while an unstructured background decreases in intensity [50]. 

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A number of disinfectants apparentiy owe their activity to formaldehyde, although there is argument on whether some of them function by other mechanisms. In this category, the dmg with the longest history is hexamethylenetetramine (hexamine, urotropin) [100-97-0] which is a condensation product of formaldehyde and ammonia that breaks down by acid hydrolysis to produce formaldehyde. Hexamine was first used for urinary tract antisepsis. Other antimicrobials that are adducts of formaldehyde and amines have been made others are based on methylolate derivations of nitroalkanes. The apphcations of these compounds are widespread, including inactivation of bacterial endotoxin preservation of cosmetics, metal working fluids, and latex paint and use in spin finishes, textile impregnation, and secondary oil recovery (117). 

Iron impregnated on activated carbon was used as catalyst for the direct synthesis of phenol from benzene. The effect of Sn addition to the catalyst was studied. The prepared catalysts were characterized by BET, SEM and XRD analysis. The catalyst 5.0Fe/AC showed good activity in the conversion of benzene and addition of Sn seemed to improve the selectivity of phenol in the reaction. 

As can be seen in table 1, with different preparation methods and active metals, the average size of the copper particle for the catalysts A and D were 20.3 nm and 50.0 nm. While those of the catalysts B and C were 51.3 nm and 45.4 run, respectively. CuO, non-supported metal oxide, made by impregnation is sintered and cluster whose particle size was 30 pm. The water-alcohol method provided more dispersed catalysts than the impregnation method. 

Fe/MgO catalysts with 5 to 30 mol % Fe have been prepared by impregnation and coprecipitation. Their reducibility has been measured and a comparison made of their Fe° surface areas. Catalysts prepared via coprecipitation yielded larger iron areas than those via impregnation. The activity and selectivity of the reduced catalysts for the hydrogenation of propanenitrile at 20-30 bar and 473 K and of ethanenitrile at 1 bar and 508 K have been determined. The most active catalysts are those prepared by coprecipitation and they show high selectivity for primary amines. The activity for ethanenitrile hydrogenation correlates with the iron surface area. 

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... 

The Pd-ZSM-5 catalysts are prepared by impregnation and by solid exchange methods on the carrier of HZSM-5 and NaZSM-5 (Si/Al = 26) with variable palladium loading and different pre-treatment gas (He and O2). N2-physisorption, DRX and CH4-TPR are the main techniques used to characterise these catalysts. Furthermore, total methane oxidation is used to test their catalytic activity. Among the preparative variables, the solid exchange method, the NaZSM-5 support and the increase of the palladium loading improve considerably the activity of the Pd-ZSM-5 catalysts in methane oxidation. 

The preparation of catalysts usually involves the impregnation of a support with a solution of active metal salts. The impregnated support is then dried, calcined to decompose the metal salt and then reduced (activated) to produce the catalyst in its active form. Microwaves have been employed at all stages of catalyst preparation. Beneficial effects of microwave heating, compared with conventional methods, have been observed especially in the drying, calcination, and activation steps. 

Chau Y-P, Lu K-S. ZIO impregnation and cytochemical localization of thiamine pyrophosphatase and acid phosphatase activities in small granule-containing (SGC) cells of rat superior cervical ganglia. Histol Histopathol 1994 9 649-656. 

To summarize, TPR is a highly useful technique, which provides a quick characterization of metallic catalysts. It gives information on the phases present after impregnation and on the eventual degree of reduction. For bimetallic catalysts, TPR patterns often indicate whether or not the two components are mixed. In favorable cases, where the catalyst particles are uniform, TPR yields activation energies for the reduction as well as information on the mechanism of reduction. 

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