Acid-base properties of modified aluminas

Abstract

Acid-base properties of the pure alumina and aluminas modified by addition of various ions were determined by IR spectroscopic and Benesi method. The quality and concentration of OH groups of alumina samples containing SO42-, F-, Cl-, Na+, Zn2+ and Mg2+ ions were determined by IR spectroscopy, Pyridine, benzonitrile and carbon monoxide were used to determine the concentration and strength of aprotic centres and deuteriochloroform was used to determine the concentration and strength of basic centres. The results allowed to evaluate changes in the above properties caused by changes in the concentration of ions in alumina. It was found that the total acidity of modified aluminas determined by Benesi method correlates well with the relative proportion of acidic OH groups in the total spectrum of OH groups.

Characteristics optimization of activated alumina desiccants based on product of a centrifugal thermal activation of gibbsite

“…According to the results of [16], the super-strong centers can be formed upon substitution of a proton at the end of an OH group with a sodium ion to give a bridge oxygen atom between Na + and Al 3+ ions. The concentration of superstrong basic centers grows with increasing concentration of an alkaline ion.…”

“…Measurements were made in an adsorber with diameter of 30 mm and height of 400 mm under the following conditions: (1) at low moisture content in the gas at the adsorber inlet: 0.86 g H 2 O/m 3 (dew point -18.7°C); rate of the vapor-air mixture, 3.4 L min -1 ; gas temperature 22°C; adsorbent charge 100 cm 3 ; (2) at high moisture content of the gas at the adsorber inlet: 15.6-16.6 g H 2 O/m 3 (dew point 18. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].5°C) fl ow rate of the vapor-air mixture, 4.1 L min -1 ; atmospheric pressure; gas temperature 22°C; adsorbent charge 120 cm 3 .…”

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

“…The Al site acts as aweak Lewis centre (n CO = 2204cm À1 )and the neighboringb ridgingO Hg roup is aw eak Brønsted centre( m-OH 3573cm À1 + CO = 3540 cm À1 ;T able S5). [80,83] The trends of the integrated IR bands are given in Figure 2D.E xperimental NMR data alonea re not enough to correlatet he chemicalnature of the acid sites to aspecific AlO x coordination because it was demonstrated that each 27 Al NMR resonance peak can be adistribution of aluminumcoordination. signed to silanol groups interacting with CO. [80] The hydroxyl n OH bands at 3566-3600 and around3 470 and 3320 cm À1 are assigned to CO interacting with three Brønsted acid sites (BAS) of different strength,r eferred to herein as weak, medium, and strong BAS, respectively.…”

Temperature effect on the physicochemical properties of χ-alumina interaction with CCl4

“…We propose that the introduction of chlorine decreases the number of tetrahedral vacancies occupied by aluminum atoms. It is known that the tetrahedrally coordinated Al 3+ ion is a strong Lewis acid site [41].…”