Abstract
The catalytic activation of silica aerogel via a phenomenon called spillover was investigated. In this work, platinum supported on alumina activated a silica aerogel by indirect contact (the two materials were separated by a porous glass frit) in the presence of 1 atm of hydrogen ( ≈ 18 h at 430 °C). After activation, the Pt activator was removed and completely isolated from the system. Silica activated in this manner showed good activity at 200 °C for the hydrogenation of ethylene after an induction period (as long as 48 h observed). Total conversion occurred within 2 h. Exposure to MCP (methylcyclopropane) in H 2 poisoned the surface for ethylene hydrogenation. This new finding may be related to the strong adsorption of MCP on the active site formed by spillover activation, which blocks ethylene's access. For the first time, activity for cumene cracking in He and H 2 was investigated for a spillover material. At 400 °C, differences in product distribution were noted. The spillover-activated silica created more propene and less benzene than a nonspillover-activated silica evaluated under similar conditions. Activity in overall cracking was higher at 170°C than at 430°C. Hydrogen-spillover-activated silica shows an important change in selectivity from cracking to coking.
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