MoO₂(acac)₂ immobilized on polymers as catalysts for cyclohexene epoxidation: Effect of the degree of crosslinking

Abstract

ABSTRACT:Crosslinked poly(4-vinylpyridine-co-styrene) used as support for a immobilized oxomolybdenum complex was synthesized by radical polymerization. As crosslinking agent, 1,4-divinylbenzene (DVB) was incorporated at 2, 4, and 6 mol %. Catalysts having similar MoO 2 (acac) 2 loading on different resins were obtained by refluxing a solution of the complex with the polymeric supports at 70°C. FTIR, specific surface area, and XPS techniques were used for characterization. It was found that a significant increase in the surface area occurs as the degree of crosslinking increases, presumably due to the development of branched polymers having higher porosity. XPS showed that the complex is anchored to the pyridinic nitrogen on the resin and that that Mo was present essentially as Mo(VI) species. The Mo/C atomic surface ratio exhibits a maximum for the catalyst with medium crosslinking degree. The epoxidation of cyclohexene was studied in the temperature range 40 -60°C by using tert-butyl hydroperoxide as oxidant agent. The catalysts were active and selective to the corresponding epoxide and almost no leaching of the active phase was observed. The highest catalytic activity of the studied solids was displayed by the one supported on the resin with intermedium degree of crosslinking. The results are explained in terms of the access to the active sites and surface composition.

Metal‐Doped Epoxy Resins –‐New Catalysts for the Epoxidation of Alkenes with High Long‐Term Activities

“…In the case of MoO 2 (acac) 2 supported on poly(4-vinylpyridine-co-styrene) [14] or polyaniline [15] metal leaching was not investigated in detail and data on the catalytic long-term performance of these catalysts are not available.…”

“…Highly active as well as recyclable and stable catalysts based on polybenzimidazole [12] and polyimides [13] have been reported. Recently, crosslinked poly(4-vinylpyridine-co-styrene) [14] was used as support for the immobilisation of MoO 2 (acac) 2 . Furthermore, polyaniline-supported MoO 2 (acac) 2 [15] was shown to be an active and recyclable catalyst for the oxidation of alcohols to aldehydes and ketones using molecular oxygen.…”

Aspects of Immobilisation of Catalysts on Polymeric Supports

“…[65] Reaction kinetics as well as spectroscopic results, however, indicated the presence of non-paramagnetic mononuclear and polynuclear Rh carbonyl immobilised species. Also in poly(4-vinylpyridine) cross-linked with DVB it was shown that Mo(VI) of a MoO 2 A C H T U N G T R E N N U N G (acac) 2 complex was attached on the pyridine N. [66] The most active catalyst in the epoxidation of alkenes with tert-butyl hydroperoxide was obtained at an intermediate degree (4 %) of cross-linking. Crosslinked poly(4-vinylpyridine) as such could retain mononuclear Cu species and catalysed in basic medium the low temperature water gas shift reaction as well as the hydrodechlorination of chlorobenzene into benzene and biphenyl.…”

Synthesis and characterization of a new epoxidation catalyst by grafting cis-MoO2(salpr) complex to functionalized MCM-41

“…Grafting Mo compounds to functionalized polymer supports [8,9], preparation of amorphous Mo silicates via sol-gel method [10,11] and incorporation of Mo in the framework of silicalite are examples in this regard [12]. Micelle-templated inorganic oxides of silica and alumina have emerged in the past decade as very promising support materials owing to their unique textural properties (high surface area, pore volume and narrow pore size distribution) [13][14][15][16][17].…”