Protonic add sites

When H-EDTA-MOR was exposed to 0.3 kPa of NH3 at 473 K and evacuated at 473 K (Figure 6E), only protonated ammonia (NH4 ) was observed. The NH4" deformation band builds up at 1443 cm- together with a small amount of coordinated NH3 bonds (deformation) that attached to Lewis add sites at 1624 cm L... 

The recovery of the Lewis add sites and the decrease in the protonic acid sites to the original values by outgassing gas phase hydrogen are rather slow and require a high temperature. The addition of Pt/Si02 did not affect much the restoration of Ae Lewis add sites of H-ZSM-5 by outgassing gas phase hydrogen. 

Sulfate-doped zirconia was found to have both Lewis and Brdnsted add sites on the surface, where the sulfate groups were the carrier of the protonic site. The ratio of Lewis to Br0nsted sites was found to vary depending on heat treatment, but the percentage of sulfate groups associated with a proton was found to be constant at 12-17%. 

A very convenient method to quantitatively determined the number of Bronsted add sites in the often used photochemical nano-vessels, zeolites X and Y, is available.28 This method take advantage of indicator/probe molecules which undergo an intense color change upon protonation within the zeolite pore network. The amount of a base necessary to quench the color change gives a direct measure of the concentration of acidic sites. The base used to titrate the Bronsted sites must be more basic than the probe molecule and sufficiently basic to be completely protonated. 

The proton adds to the aromatic ir electron complex of o-ethyl-toluene to form a charged structure that is the same for isomerization and dealkylation. The next step depends on whether the positive charge is stabilized on the ethyl group by nearby alumina sites in the micropore or if it is dispersed over the entire molecule. Stabilization of the ethyl car-bonium ion by a negative charge from a nearby alumina tetrahedron results in a stabilized transition state that favors dealkylation. 

When K[PtX(acac)2] (X = Cl, Br) is treated with a strong proton add the uncoordinated 0,0 site is protonated and complex (170) is formed.1606,1607 If the alkyl groups on the 0,0 -bonded acac ligand are non-equivalent, exchange can be observed. Although the mechanism has not been definitively proven, a dissociative mechanism is favored.160 This proposal correlates with the observations that the 0,0 -bonded chelate complex Pt(acac)2 will react with tertiary phosphines and nitrogen bases with substitution of one of the oxygen-bonded chelate arms.1609,1610 A variety of products are formed as outlined in Scheme 17. 

On the zeolite surface the Bronsted add sites are responsible for the generation of (i) carbonium ions from paraffins, (ii) alkyl carbeniiun ions from olefins, and (iii) alkenyl carbeniiun ions from dienes by protonation, while on Lewis acid sites (i) alkyl carbeniiun ions from paraffins and (ii) alkenyl carbeniiun ions from olefins are formed by hydride ion abstraction. 

There are various acidic and basic sites on surfaces. Coordinatively unsaturated cations act as electron pair acceptors and are called Lewis acid sites. The Bronsted add sites on catalyst surfaces are hydroxyl groups able to donate protons. The basic sites are, in most cases, oxygen anions, including oxygen from hydroxyl groups. 

Mechanism ofCatafyas. H-mordenite is believed to be rich in adjacent Lewis and Bronsted add sites. Accordingly, a proton transfer from the Brensted add dtes to the monomer occurs to give carbonium ions, followed by polymerization ... 

Fundamentally, these reactions are base catalyzed via proton elimination. First, the primary and secondary hydroxyl groups of glycerol gravitate toward the base sites, then the more reactive primary alcohol group electrophilically attacks the carbon of the carbonyl. When Lewis add sites coexist on the catalyst, it is able... 

Tm = 50 ms F. 2.12(c3)), a new correlation peak arising from P resonance of TMPO (68 ppm) and bridging hydroxyl protons (Si-OH-Al at ca. 7 ppm) was also observed. Accordingly, various adsorption states and interactions of the TMPO probe molecule and add sites may be readily resolved using multinuclear NMR techniques [41]. 

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