Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV–Vis/ATR‐IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas‐Liquid Phase Reactions
Résumé
Operando EPR, XANES/EXAFS, UV-Vis and ATR-IR spectroscopicm ethods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobico xidation of benzyl alcoholb yaCu/TEMPO catalytic system(TEMPO = 2,2,6,6tetramethylpiperidinyloxyl).B ym ultivariate curve resolution with alternatingl east-squares fitting (MCR-ALS)o fs imultaneously recorded XAS and UV-Vis data sets, it was found that an initially formed(bpy)(NMI)Cu I-c omplex (bpy = 2,2'-bipyridine, NMI = N-methylimidazole)is converted to two different Cu II species, am ononuclear (bpy)(NMI)(CH 3 CN)Cu II-OOH species detectable by EPR and ESI-MS, and an EPR-silent dinuclear (CH 3 CN)(bpy)(NMI)Cu II (m-OH) 2 •Cu II (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)Cu II-TEMPO monomerst hat are also EPR-silentd ue to dipolar interactionw ith bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not am ajor active speciesn or ar esting state since it is irreversibly cleaved in the courseo ft he reaction while catalytic activity is maintained. Gradual formation of non-reducible Cu II leads to slight deactivation at extended reactiont imes.
Domaines
Catalyse
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