Alumina acidity

The titration of silica-alumina acid sites with neodymium oxide is clearly seen in Figure 4. The relative acid strength, as estimated by the 2,3DMB2/4MP2 ratio during 2MP2... 

Aluminum oxide 60 G neutral Aluminum oxide 60 GF254 neutral Aluminum oxide G Aluminum oxide G/UV254 Aluminum oxide N Alumina Neutral Alumina Basic Alumina Acid Alumina Basic for TLC Alumina Neutral for TLC Alumina Acid for TLC Alumina with Gypsum for TLC MP Alumina B-TLC MP Alumina N-TLC MP Alumina A-TLC MP Alumina G-TLC... 

The activity of parent H-mordenite is essentially Bronsted activity, and aluminum sites are effective proton counters (2). In parent H-mor-denite (11.2 wt % alumina), acid centers are present at a density of 100 times those in aluminum-deficient H-mordenite (0.1 wt % alumina). 

Preparation of oxidative system Finely ground potassium permanganate (50 g) dissolved in water (100 mL) was added to alumina (acidic or neutral, Merck activity I, 63-200 nm 200 g). After shaking for 15 min, the majority of the water was removed by evaporation under reduced pressure and the obtained powder was dried under microwave irradiation for 5 min. 

Alumina acidity can also be promoted by addition of other anions as well as by combination of alumina with other metal oxides (2). Recent work in this area of research is reviewed below. 

A recent infrared study of the interrelationship of silica-alumina acidity and activity for olefin polymerization was carried out by Mizuno et al. (134). They showed that Lewis acid sites on silica-alumina could be selectively poisoned with pyridine in an infrared cell by a three-step... 

The other studies of silica-alumina acidity reviewed in this section fulfill a twofold purpose the characterization of surface acidity, and an advance in the method of measuring acidity. References to these studies are also collected in Table V, which contains a general compilation of recently reported methods for acidity measurements. 

The relationship between the two catalytic components is quite complex. Interactions between the support and the hydrogenation component can alter this relationship. For example, Larson et- al. (6) showed that, with platinum on silica-alumina, a selective adsorption of platinum by acid sites causes a reduction in catalyst acidity. Similarly, nickel reacts with the acid sites on silica-alumina forming nickel salts of the silica-alumina acid sites. It has been suggested (J) that one of the effects of sulfiding a nickel on... 

GPC, acid-base, silica gel (on derivatized phenols) Alumina, florisil, GPC Alumina, acid-base... 

Both Cr111 and Cr concentrations in natural water samples were measured by flame AAS after pre-concentrations of the chromium species on microcolumns packed with activated alumina (acidic form) (Sperling et al., 1992). An FI manifold was used in this work to obtain conditions for species-selective sorption and subsequent elution of the chromium species directly to the nebuliser of the spectrometer. In this procedure, water samples were maintained at a safe pH of 4 prior to analysis. Analytical conditions of pH 2 and 7 were attained by adding buffers on-line only fractions of a second before the corresponding chromium species was sorbed into the column. In this manner, any risk of losses of analytes and/or shifts in equilibria between the species at pH 2 and 7 were minimised. The detection limits were 1.0 and O.Smgdm 3 for Cr111 and Cr, respectively. 

Alumina, acidic Al203-A — Adsorption, Similar in characteristics and application to silica a classic Lewis acid, lacking two electrons in... 

To conclude this section, it is necessary to state that besides their application in catalytic cracking, amorphous silica-alumina acid catalysts have been applied in other hydrocarbon transformations, such as isomerization of olefins, paraffins, and alkyl aromatics, the alkylation of aromatics with alcohols and olefins, and in olefin oligomerization [55],... 

Alumina, acidic AG4, Bio Rad Laboratories (catalogue 132-1240) or equivalent. Soxhlet extract with methylene chloride for 21 hours and activate by heating in a foil-covered glass container for 24 hours at 190°C. 

The total surface concentration and intensity distribution of acidic and basic active sites are presented in Fig. 7.10. The total height of the stacked bars represents the total surface concentration of the acidic and basic active sites in millimoles per gram. The individual parts of the stacked bar correspond to the intensity distribution. As shown in Fig. 7.10, these data indicate that magnesium silicate has a total acidic and basic site concentration of 1.8 and 2.3 mM/g, respectively [17]. In comparison with other types of adsorbents used in frying oil (activated carbon, alumna [basic], alumina [neutral], alumina [acidic], bleaching earth, dia-tomaceous earth, and silica), magnesium silicate shows the highest values of total acidic and basic sites. 

FIGURE 7.10 Surface concentrations and their intensity distributions for (A) the acidic and (B) the basic sites of adsorbents used in frying oil. A, activated carbon B, alumina (basic) C, alumina (neutral) D, alumina (acidic) E, bleaching earth F, diatomaceous earth G, silica and H, magnesium silicate. 

Knotnerus and Schilling (22) have recently reinvestigated these reactions at 260-280° in the presence of the silicophosphoric and silica-alumina acid catalysts. Typical yields in the isomerization of 9 (silicophosphoric acid catalyst, HLSV = 0.25 hr-i) are shown in the tabulation. These figures are based on the hydrocarbon injected (40%... 

Over Pt-Re/Al203 n-heptane is first converted to heptenes on the metal surface [8] the resultant olefin is then protonated over the alumina acid sites to generate a CyHis" carbenium ion according to ... 

In general, basic compounds are retained more strongly on mildly acidic surfaces, such as silica or acidic alumina. Acidic compounds are retained on basic surfaces, such as basic alumina. Because both silica and alumina are hydroscopic, they adsorb water to their surface. This water greatly reduces the retention of organic solutes because it deactivates the hydrogen-bonding sites. Thus, it is important to keep the SPE sorbents dry and free from water. They may be stored in a dessicator prior to use. Very polar compounds, such as carbohydrates or amino compounds, are tightly bound to nonbonded normal-phase sorbents, such as silica and alumina. However, the use of cyanopropyl or aminopropyl phases often permit the recovery of these compounds when silica does not work. 

Alumina (neutral) (Varian) Alumina (acid) (Varian) Alumina (base) (Varian) Alumina (neutral) (Waters) Alumina (acidic) (Waters) Alumina (basic) (Waters)... 

In general, basic compounds are retained more strongly on mildly acidic surfaces, such as silica or acidic alumina. Acidic compounds are retained on basic surfaces, such as basic alumina. Because both silica and alumina are hydroscopic, they adsorb water to their surface. This water greatly reduces the retention of organic solutes because it sorbs to active sorption sites and... 

Alumina-acidic, alumina-neutral alumina-basic, Florisil... 

However, due to the amphoteric character of alumina, acid catalysis due to OH surface groups or to A1 atoms can take place in a bifunctional catalysis mechanism [Eq. (13)] [24]. 

Its basic form has been used successfully for the collection of Cr(lII) [36], and cadmium [37] fnrni urine. In a detailed study on the behavior of various oxyanions on activated alumina (acidic) Cook et al.[35] have shown that while arsenate, chromate, molybdate, phosphate, selenate, and vanadate were all well retained on the sorbent, only chromate and molybdate could be reasonably well eluted using IM NH4OH, or stronger alkali solutions. About 80% of phosphate and selenate could be eluted using IM KOH, whereas arsenate and vanadates may be de-sorbed only by using stronger eluents such as 5M KOH. 

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