abstract
Trimethoxysilane pentacoordinate Schiff-base Co-(II) complexes, i.e. Co[Cl-Sal(PMeO-Si)DPTA], (3.a) and Co[F-Sal(PMeO-Si)DPTA], (3.b) and Co[FCl-Sal(PMeO-Si)DPTA], (3.c) (DPTA = bis(aminopropyl)amine, Sal = salicylaldehyde) were synthesized and anchored into SBA-15 matrix to obtain novel supported hybrid catalysts. The catalysts were characterized by FT-IR, TEM, SEM, XRD, TG and BET analysis. These supported complex catalysts were tested in the catalytic oxidation of n-hexane and n-heptane with O-2 under relatively mild and solvent free conditions. A high TON of 3320 with 19.6% yield for n-hexane oxidation and a high TON of 3180 with 17.3% yield for n-heptane oxidation were obtained with 3.b anchored over SBA-15. The oxidation product regioselectivities were obtained as C-1(1):C-2(9.2):C-3(10.7) for n-hexane and C-1(1):C-2(9.0):C-3(9.7):C-4(2.7) for n-heptane. The reaction of kinetics follows a pseudo first-order reaction for both n-alkanes. Enhanced yields (30.6% for n-hexane oxidation and 23.8% for n-heptane oxidation) were obtained with the addition of PCA (pyrazinecarboxylic acid); the catalytic results of reactions made in the presence of radical traps suggested that the catalytic oxidation of n-hexane and n-heptane proceeded via free radicals. The catalyst recycles tests showed that it could be reused up to 7th catalytic cycles. (C) 2013 Elsevier Ltd. All rights reserved.
keywords
MODIFIED SILICA-GEL; MOLECULAR-OXYGEN; CYCLOHEXANE OXIDATION; HEXANE; CATALYSTS; DIOXYGEN; HEPTANE; MCM-41; REACTIVITY; RUTHENIUM
subject category
Chemistry; Crystallography
authors
Machado, K; Tavares, PB; Freire, C; Mishra, GS
our authors
Gopal Shankar Mishra
Post-Doc FellowshipGroups
acknowledgements
This work was financially supported by the Fundacao para a Ciencia e Tecnologia (FCT), Portugal, through projects: PTDC/EQU-ERQ/110825/2009, CQVR/PEst-C/QUI/UI0616/2011 and "Indian-Portuguese cooperation program-2013". The authors also express his gratitude to CACTI, Vigo, Spain for the characterization of inorganic compounds.