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Type of Document Dissertation Author Vijay, Sameer Author's Email Address blimp@iitbombay.org URN etd-03232004-001108 Title Synthesis, Characterization and Isomerization Activity Studies for Modified Sulfated Zirconia Catalysts Degree Doctor of Philosophy Department Chemical Engineering Advisory Committee
Advisor Name Title Dr. Michael M. Stanisic Committee Chair Dr. Davide A. Hill Committee Member Dr. Eduardo E. Wolf Committee Member Dr. H.-C. Chang Committee Member Dr. William C. Strieder Committee Member Keywords
- X-ray absorption
- spillover
- Pt absorption
- synthesis
- catalyst preparation
Date of Defense 2004-03-22 Availability restricted Abstract Sulfated zirconia (SZ) is an attractive alternative for use in industrial processesbecause of its good alkane activation potential as well as being a non-toxic replacement
for liquid acid catalysts currently in use. Over the past 10 years, numerous
studies have attempted to synthesize non-deactivating SZ-based catalysts by adding
modifiers and/or promoters. In this work, a synthesis method is presented that is
used to prepare a Pt-modified SZ catalyst, which shows exceptionally high and
stable activity for n-pentane isomerization at atmospheric pressure.
A 3-step method consisting of calcining a sulfated zirconium hydroxide at high
temperature prior to adding platinum, reduction of platinum followed by additional
pretreatments is presented. The activity of such an SZ catalyst remains stable for
up to 4 hours with conversion of n-pentane exceeding 70%. EXAFS studies showed
that the active catalyst contains relatively large crystallites of platinum. Presence
of Pt-S in the inactive catalyst gives evidence for the cause of deactivation of the
samples prepared in the conventional manner. XANES analysis of the data also
shows that the state of platinum in the active catalyst is that of a metallic platinum
(Pt0). Using XPS data, it is shown that the surface undergoes rearrangements
during the preparation.
Use of operando DRIFTS showed the sulfur-oxygen groups on the surface to be more complex than previously reported as species different than just sulfates, were
present. During the reaction, a particular species of OH group disappear. This
species is replenished by the atomic hydrogen provided by the metallic platinum.
The experimental results give evidence of the changes in the catalyst surface
during the preparation, pretreatment and the reaction itself. Based on the findings, a
Site-Juxtaposition hypothesis is presented. This hypothesis is based on the hydrogen
spillover occuring on the metallic crystallites, and the capability of this atomic
hydrogen to hydrogenate coke species, thus arresting deactivation. The deactivation
suppresion is brought about by juxtaposition of the metal sites and the acid sites
during the oxidation-reduction pretreatments. A simple math model is included
that attempts to corroborates this phenomenon.
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