Dehydrogenation of Propane over Platinum Containing CIT-6

Abstract

The catalytic dehydrogenation of propane is carried out on platinum-impregnated CIT-6 catalysts. Prior to loading platinum, numerous postsynthesis treatments of the as-made CIT-6 are investigated, e.g., calcination, structure directing agent (SDA) extraction, ion exchange, etc., to observe the effects of catalyst preparation on the dehydrogenation of propane. The catalytic behavior depends strongly on the method of postsynthesis treatment. When the as-made CIT-6 is contacted with NH_4NO_3 to remove the SDA prior to platinum loading, an active, selective, and stable catalyst is obtained. ^(29)Si NMR studies show that, after this postsynthesis treatment, some of the zinc remains within the CIT-6 framework. Contacting as-made CIT-6 with Zn(NO_3)_2 to remove the SDA prior to platinum loading gives a solid with a higher level of extraframework zinc. This additional amount of extraframework zinc does not lead to a more stable catalyst. When as-made CIT-6 is contacted with acetic acid at 60 °C, the SDA and also the zinc are extracted to give pure-silica CIT-6. Platinum loading into this material gives a catalyst that deactivates very rapidly. Thus, framework zinc appears to be essential for the creation of a stable platinum-impregnated CIT-6 catalyst for propane dehydrogenation.

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