Propene epoxidation catalyst preparation

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

A. K. Sinha, S. Sedan, M. Okumura, T. Akita, S. Tsubota, M. Haruta, Three-dimensional meso-porous titanosilicates prepared by modified sol-gel method Ideal gold catalyst supports for enhanced propene epoxidation, J. Phys. Chem. B 109 (2005) 3956. 

Co-precipitation Preparation of advanced CaCC>3 supported Ag catalysts for propene epoxidation by a novel co-precipitation route... 

Catalysts prepared by impregnation were found to be completely inactive in the epoxidation reaction of propene. Figure 1.14 shows a SEM... 

The Dow Chemical Company also filed several patents [183, 184] on Au-based catalysts for hydro-oxidation (i.e., direct reaction with O2 in presence of Hj) of alkenes (propene and larger). One of them, focused on catalyst prepared starting with atomically precise Au clusters, claims stable catalyst activity over extended hfetime and improved hydrogen efficiency with selectivity of about 90% toward formation of epoxide [184]. 

In this way, the direct contact of O2 with the olefin is prevented and the radical process of addition across the double bond is avoided. Reactions (6.18) and (6.19) are slow and the selectivity towards the epoxide in reaction (6.18) strongly depends on the catalyst preparation, the nature of the metal, and the reaction temperature. Using propene, the formation of the epoxide is in concurrence with the formation of acetone and propionaldehyde. Moreover, depending on the preparation of the metal oxide, the same catalyst can push the reaction to the formation of acroleine or even to the total oxidation of propene to CO2 and water [117]. If, instead of the only olefin, a mixture of olefin and CO2 is admitted on the catalyst in its oxidized form, the carbonate is formed which can be recovered by condensation and the excess olefin recycled. 

Selectivities and Yields for Propene Epoxidation Using Titanosilicate Supported Catalysts Prepared by a Modified Sol Gel Method... 

In a subsequent paper, the authors developed another type of silica-supported dendritic chiral catalyst that was anticipated to suppress the background racemic reaction caused by the surface silanol groups, and to diminish the multiple interactions between chiral groups at the periphery of the dendrimer 91). The silica-supported chiral dendrimers were synthesized in four steps (1) grafting of an epoxide linker on a silica support, (2) immobilization of the nth generation PAMAM dendrimer, (3) introduction of a long alkyl spacer, and (4) introduction of chiral auxiliaries at the periphery of the dendrimer with (IR, 2R)-( + )-l-phenyl-propene oxide. Two families of dendritic chiral catalysts with different spacer lengths were prepared (nG-104 and nG-105). 

Precipitation vs. Impregnation by Ion-exchange Au precursors, and the effect of the method of preparation and selected support on performance in selective epoxidation of propene over Au/TiC>2 catalysts... 

In the second example we will focus on preparation methodologies for gold catalysts, and the effect on the performance of gold in selective epoxidation of propene to PO (see reaction scheme in Fig. 1.12). 

Cationic olefin complexes of dicarbonyl(> -cyclopentadienyl) iron have been of wide interest in syntheses for a number of years. These complexes, generally isolated as their tetrafluoroborate or hexafluorophosphate salts, have been prepared by the reaction of Fe(f -CsHs)(CO)2Br with simple olefins in the presence of Lewis acid catalysts, by protonation of allyl ligands in Fe(t/ -CsHjXCO)2[(allyl)KC ] complexes, or by treatment of these with cationic electrophiles, by hydride abstraction from Fe(f) -CsHjXCO)2(alkyI) complexes, through reaction of epoxides with Fe(fi -CsHjXCO)2 anion followed by protonation, or by thermally induced ligand exchange between [Fe( i -CjHsXCO)2(ij -2-methyH-propene)][BF4] " or [Fe( -C,HsXCO)2(tetrahydrofuran)][BF4] and excess olefin. 

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