Catalysis of Organic..

Hu et al. 95ionic liquid is used in immobilizing homogeneous catalyst on SiO 2 support,homogeneous behavior predominates. XRD analysis was used to measure if anycrystalline Co(II) was formed. Background analysis on silica gel alone didn’t showcrystalline, which is commonly known in the open publications (9). Figure 3 showsthat after immobilization on SiO 2 , no crystalline Co(II) was formed. This is differentfrom conventional supported Co catalysts where crystalline Co phases can be easilydetected. Based on the XRD analysis, we believe that with Co(II)-IL/SiO 2 catalyst,the normal expected homogeneous property of Co(II) is fully retained in ionicliquid.Figure 3. XRD analysis of Co(II)-IL/SiO 2 catalyst (top spectra: reference spectra ofcrystalline of Co(OAc) 2 . 4H 2 O salt. Bottom spectra: Co(II) homogeneously dissolvedin ionic liquid on SiO 2 .Oxidation ActivityThe supported ionic liquid catalysis combines the advantages of ionic liquid mediawith solid support materials which enables the application of fixed-bed technologyand the usage of significantly reduced amounts of ionic liquid in comparing toliquid-liquid biphasic catalysis. We are able to either pack a fixed bed reactor withsolid catalyst consisting of Co(II)-IL deposited on SiO 2 beads or alternativelyimmobilize Co(II)-IL on microchannel reactor wall coated with SiO 2 . The latterconfiguration allows us to manipulate the diffusion at interfaces by varying thethickness of ionic liquids, the gap of the channel and the organic feed flow rate.Oxidation of cyclohexane was chosen as proof-of-concept demonstration reaction.Under the conditions of O 2 concentration = 5% T=150 o C, P=250 psig, LHSV=23 h -1 , we found we could obtained 2% cyclohexane conversion with 100% selectivity todesired products consisting of cyclohexanol and cyclohexanone. In thisinvestigation, we haven’t observed any CO 2 or CO by-products associated with overoxidation. Commercially, cyclohexane oxidation is catalyzed by homogeneous Cocatalyst where low single pass conversion of 4-8% is maintained to minimize CO 2