Hydrothermally activated silica-alumina. II. Variations in catalytic activites for 1-butene isomerization and polymerization, and in the amount of acid with pretreatment temperature.

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The technique of hydrothermal activation was used to prepare well-mixed and fully hydroxylated silica–alumina catalysts, SA-nMHT (n=13, 25, or 50 denotes the alumina content (wt%)). Their catalytic activities and cis/trans selectivities for the 1-butene isomerization (ki and c/t), the catalytic activities for the 1-butene polymerization (kp), the amount of acid (A), and the number of the surface hydroxyl group (NOH) were measured as a function of the degassing temperature (Td) over the 25–700 °C range; the following results were obtained: (1) ki changed prominently with Td and reached its maximum around 300 °C. (2) c/t was about 0.9 below 500 °C, but exceeded 1.2 at 700 °C. (3) kp increased till 300 °C and became constant above that temperature. (4) A was almost independent of Td above 100 °C. (5) NOH decreased from 11–15 (at 100 °C) to 0.5 group nm−2 (at 700 °C). An analysis of these data led to the conclusion that the SA-nMHT sample underwent the surface structural changes three times during the thermal dehydroxylation between 25 and 700 °C. The sequence of the structural change was sketched, and the different dependencies upon Td of ki, kp, and A were explained.
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