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Modification of the saponite surface with 7 wt.% of magnetite leads to the decrease in the number of Bronsted base sites (pK = 7.6) and to the increase in the number of Bronsted acid sites (pK = 5.25), which explains the decrease in [pH.sub.iip] compared to saponite, as well as the higher adsorption affinity for anionic dye compared to saponite.
Coverage encompasses all acid-catalyzed Friedel-Crafts-like acylation reactions, including classic Lewis and Bronsted acid types, as well as innovative multicomponent super-acid catalysts.
This might be due to the increase in the pore size as a resultant of the reduced number of bronsted acid sites with dealumination (Choudhary et al., 2000) favouring the formation of ortho-isomer, which requires more space.
The structure of the strongest Bronsted acid H([CHB.sub.11][C1.sub.11]).
A band at the frequency of 1540 cm-1 represents the Bronsted acid sites.
prepared a sulfonated poly(phenylene sulfide) (SPPS) catalyst with strong Bronsted acid sites and a sulfonation degree of 21.8 mol%; when it was used for the direct conversion of cellulose to 5-HMF in IL 1-methyl-3-ethyl imidazolium bromide ([EMIM]Br) solvent, the yield of 5-HMF with 68.2% was obtained at 180[degrees]C for 4 h (Table 5, entry 1) [333].
FTIR bands associated with -OH groups (the hydroxyl region) [13] were also observed, suggesting the existence of Bronsted acid sites (the FTIR band at 3747 [cm.sup.-1] is associated with isolated Si-OH groups) in the sample prepared with acid-leached RHA.
The peaks in the HT range can be attributed to ammonia desorption from Bronsted acid sites and strong Lewis ones.
Protic ionic liquids (PILs) comprise a subset of the ionic liquids formed by the stoichiometric (equimolar) combination of a Bronsted acid with a Bronsted base and are characterized by their great ability to form H-bond and consequently show a strong interaction with polar solvents (ANOUTI et al., 2010).
The substitution of the Bronsted acidic hydroxyl groups by the [H.sub.2]P[O.sub.4] groups implies to different consequences on the strength and density of the Bronsted acid sites: (1) strong Bronsted acid sites are converted into weak Bronsted acid sites, and it is clear that the resulting terminal hydroxyl groups have a lower acid strength than the bridged hydroxyl groups.