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620477 
Journal Article 
Stability of sulfated zirconia and the nature of the catalytically active species in the transesterification of triglycerides 
Suwannakarn, K; Lotero, E; Goodwin, JG; Lu, C 
2008 
Yes 
Journal of Catalysis
ISSN: 0021-9517
EISSN: 1090-2694 
255 
2 
279-286 
WOS:000255668200016 
Abstract: Sulfated zirconia (SZ) exhibits remarkable activity for various hydrocarbon reactions under mild conditions and is of interest for biodiesel synthesis. Nevertheless, to date no detailed study has addressed its activity and stability in liquid polar media such as alcohols, although a number of papers have suggested the possibility for some sulfur leaching. This paper presents an investigation into the activity and stability of a commercial SZ catalyst for the liquid-phase transesterification of triglycerides at 120 °C. The kinetics of tricaprylin (TCP) transesterification with a series of aliphatic alcohols (methanol, ethanol, and n-butanol) were investigated at 120 °C and 6.8 atm in a Parr batch reactor. It was found that the catalytic activity for TCP conversion decreased as the number of carbons in the alkyl chain of alcohol increased, most likely as a result of increased steric hindrance. The SZ catalyst exhibited significant activity loss with subsequent reaction cycles. The characterization of used catalysts after their exposure to various alcohols at 120 °C showed that the SO2− 4 moieties in SZ were permanently removed. The SO2− 4 species were leached out, most likely as sulfuric acid, which further reacted with alcohols to form monoalkyl and dialkyl sulfate species, as demonstrated by 1H NMR studies. This was in essence the main route for catalyst deactivation. Our findings conclusively demonstrate for the first time that in alcoholic-liquid media at higher temperatures, SZ deactivates by leaching of its active sites, most likely leading to significant homogeneous rather than heterogeneous catalysis. [Copyright 2008 Elsevier] Copyright of Journal of Catalysis is the property of Academic Press Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts) 
ZIRCONIUM oxide; TRIGLYCERIDES; CATALYSTS; CATALYSIS; CHEMICAL reactions; CHEMICAL processes