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Isomerization of n ‐pentane over platinum promoted tungstated zirconia supported on mesoporous SBA ‐15 prepared by supercritical impregnation
Author(s) -
Lee Wenchao,
Yang ChiehChao,
Cheng Soofin
Publication year - 2021
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.202000473
Subject(s) - isomerization , chemistry , pentane , catalysis , supercritical fluid , dehydrogenation , hydrogenolysis , mesoporous material , inorganic chemistry , hydrogen , photochemistry , organic chemistry
Abstract Tungstated zirconia was supported on mesoporous SBA‐15 by impregnation in supercritical ethanol. The resultant catalyst promoted with 1 wt% of Pt shows 100% selectivity of iso ‐pentane and two times higher conversion in n ‐pentane isomerization than the one prepared by conventional impregnation. Supercritical impregnation exerts no destruction of the porous silica and offers better dispersion of tungstated zirconia than conventional impregnation. Optimized loading of WO 3 /ZrO 2 /SBA‐15 is 20/40/40 wt%, which infers to 2.4 W‐atoms/nm 2 and 8.9 Zr‐atoms/nm 2 dispersed on the SBA‐15 support. Moreover, introducing a proper mole fraction of hydrogen in the reactants markedly improves the catalytic activity in n ‐pentane isomerization. The role of hydrogen was not only served as the reactants, it also acted to regenerate Brønsted acid sites during n ‐pentane isomerization. However, overdose of hydrogen leaded to a leveling‐off in the rate of isomerization and enhanced hydrogenolysis reaction. The in situ IR spectroscopic studies suggested that Brønsted acid sites were the active centers for the isomerization. A reaction mechanism was, therefore, proposed that heterolytic fission of hydrogen and dehydrogenation of n ‐pentane took place over Pt. The secondary carbocation formed over Brønsted acid sites was rearranged to a tertiary carbocation by methyl migration, followed by reacting with a hydride to generate iso ‐pentane.