Alumina hydrogen adsorption

Maciel et al. (370,371,374) combined l3C and 15N CP/MAS NMR to study the adsorption of pyridine on silica-alumina. Hydrogen bonding was found to be the dominant interaction at high loading levels (0.5 to 1 monolayer). At lower coverages, a Lewis acid-base complex dominates and the pyridine is significantly less mobile. Bronsted complexes are found when the surface has been pretreated with HC1 gas. 

Fig. 20. Isobaric representation of spiltover hydrogen adsorption on activated aluminas, amorphous or d (and silica) (A) <5-alumina (and silica), with Pt/Al203 (B) amorphous alumina with Pt/Al203 (C) i5-alumina without Pt/Al203 (D) amorphous alumina without Pt/Al203.

In the present paper, results on the influence of reduction temperature on subsequent hydrogen adsorption are reported for platinum supported on three difficult to reduce supports (y-alumina, magnesia and sillcalite). The results indicate that the observed suppression in hydrogen uptakes, after high temperature reduction, are due to poisoning of the platinum surface by species originating from the support. This interpretation is similar to that of Wang et al. (13). 

The selectivity of metal catalysts improves in some reactions with alloying for example the alumina-supported Pd-Cu catalyst hydrogenales butadiene to 1-butene with 99% selectivity, i.e. the isomerization is less than lOli. The explanation is that hydrogen adsorption decreased on the Cu-containing catalysts . Similarly, better selectivities were observed with a polymer anchored Pd, or a Pd-Co catalyst in the gas-phase hydrogenation of butadiene and cyclopentadiene in a hollow-liber reactor 2 in the liquid-phase hydrogenation of 1,5-hexadiene with Pd-Ag catalyst. ... 

Fig. 19. Hydrogen-deuterium exchange between C2D4 and the surface of alumina (10). Adsorption temperature 24°, time 10 minutes.

In connection with ethylene hydrogenation, adsorption of hydrogen on alumina has also been studied by the TPD technique. Some of the... 

A comparative study of the structure developed by two alumina-pillared clays using the results of adsorption from nitrogen, hydrogen and carbon dioxide is reported. The samples considered come from a montmorillonite and a saponite that have been treated with solutions of hydrolysed aluminium. The solids resulting of the intercalation have been calcined at 473, 623 and 773 K for 4 h. The textural properties of the samples derived from the results of nitrogen adsorption at 77 K, show a decrease of the specific surface area and the micropore volume as the temperature of calcination increases. Results from hydrogen adsorption indicate the presence of micropores of widths smaller than the diameter of the molecule of nitrogen, while carbon dioxide adsorption reveals the presence of specific sites of chemisorption. 

M. Primet, J.M. Basset, M.V. Mathieu, M. Prettre, Infrared investigation of hydrogen adsorption on alumina-supported platinum. J. Catal. 28, 368-375 (1973)... 

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