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Studies on the Activation of Mn-Promoted Sulfated Zirconia Catalyst for Alkane Isomerization by In-Situ UV-vis-NIR Spectroscopy

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Joshi,  Pradnya
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Citation

Joshi, P. (2005). Studies on the Activation of Mn-Promoted Sulfated Zirconia Catalyst for Alkane Isomerization by In-Situ UV-vis-NIR Spectroscopy. Master Thesis, Freie Universität Berlin, Berlin.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0011-0A2B-6
Abstract
In this thesis, Mn-promoted sulfated zirconia (0.5 wt% Mn) was investigated during activation in inert (He) and oxidizing atmosphere (O2) at 773 K and during subsequent n-butane isomerization (323 K, 1 kPa n-butane) using in-situ UV-vis-NIR diffuse reflectance spectroscopy. At first, a few experiments were carried out to test the newly installed Harrick Praying Mantis Set-up for in-situ UV-vis-NIR investigations of n-butane isomerization over the catalyst. In its initial state, i.e. after calcination and exposure to ambient conditions, the catalyst contains mainly Mn3+ and presumably small amounts of Mn2+ as well as adsorbed water. Activation in O2 only dehydrates the catalyst, while activation in He additionally leads to partial reduction of manganese (formation of new species Mn2+). Mn-SZ activated in pure O2 exhibits a maximum isomerization rate of 220 µmol g-1h-1; activation in He only yields a maximum rate of 100 µmol g-1h-1. With time on stream, the catalyst first passes through a phase of rapidly increasing conversion (induction period), then through a conversion maximum followed by partial deactivation to a steady state. Induction period was found to depend on the activation atmosphere and the n-butane concentration in the feed. During the period of maximum activity, propane and pentanes were observed as by-products. During the periods of low activity in the beginning and and at long time on stream, the high selectivity to isobutane was observed.