Modified Aluminas : Relationship between activity in 1-butanol dehydration and acidity measured by NH3 TPD
1989; Elsevier BV; Volume: 5; Issue: 2 Linguagem: Inglês
10.1016/0920-5861(89)80020-3
ISSN1873-4308
Autores Tópico(s)Catalysis and Oxidation Reactions
ResumoWe have investigated the changes of the catalytic properties in 1-butanol dehydration of γ-alumina modified by introduction of small amounts (0.2–2.0 wt %) of ions : SO42−, PO43−, Cl−, F−, Mg2+ and Na+. The acidic properties of the catalysts were investigated by NH3 TPD. Ionic additives principally affected the intermediate acidity strength (NH3 desorption temperature range 473–673 K), which varied from 1.1 (Mg2+) to 3.2 (SO42−) μmol.m−2. The relative number of acid sites was increased by anions (× 4.6 for SO42−) and decreased by cations (× 2.2 for Na+). We propose a classification of the modified catalysts, according to their acidic properties, in the order : SO42− » Cl− ≥ PO43− > F− > - > Mg2+ » Na+. The catalytic activity varied in the range 0–400 μmol.h−1. m−2 and appeared to be only dependent on intermediate acidity, which is assumed to play the central role in 1-butanol dehydration. There exists an acidity optimum (2–3 μmol.m−2, observed for PO43− and Cl−. The product selectivities are dependent on intermediate acidity. Dibutylether is formed preferably to 1-butene when acidity is increased, due probably to a parallel increase of the number of acid sites.
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