J. Połtowicz

Bio: J. Połtowicz is an academic researcher from Polish Academy of Sciences. The author has contributed to research in topics: Catalysis & Cyclooctane. The author has an hindex of 17, co-authored 37 publications receiving 994 citations.

Cyclohexene oxidation by Fe-, Co-, and Mn-metalloporphyrins supported on aluminated mesoporous silica

Abstract: Water soluble cationic metalloporphyrins with different metal centres (Mn, Fe, Co) and/or different porphyrin ligands (TMPyP, TTAPP) have been supported on aluminated mesoporous silica of the MMS (HMS) type by means of cation exchange. The porphyrin species are firmly bound to the solid matrix. Their catalytic properties in the oxidation of cyclohexene with iodosobenzene depend primarily on the nature of the metal centre. Mn and Fe porphyrins are active in converting cyclohexene to allylic oxidation products, while Co porphyrin is inactive. Preferential formation of allylic compounds (100% selectivity for Mn porphyrins and 80% for Fe porphyrin) is associated with the location of porphyrin centres at the inner pore walls where steric hindrances prohibit formation of epoxide. Appearance of a small amount of epoxide in the case of supported Fe(TMPyP) is attributed to the presence of a certain amount of porphyrin attached to the external surface, possibly by means of Fe ligation to surface oxygens. The change of the porphyrin ligand when passing from Mn(TMPyP) to Mn(TTAPP) has no significant effect on the catalytic performance of supported catalysts. The use of support is beneficial for the stability of metalloporphyrins.

Oxidation of cyclohexene over Mn(TMPyP) porphyrin-exchanged Al,Si-mesoporous molecular sieves

Abstract: The mesoporous silicas of the MMS (HMS)-type, containing different amounts of Al, have been prepared using dodecylamine as a structure directing agent. Encapsulation of the +4 charge cationic chloro[meso-tetra(4-N-methylopyridinio)-porphirynato] manganese(III) tetrachloride (Mn(TMPyP)) metalloporphyrin has been carried out by means of cation exchange. In all Al-substituted materials, the porphyrin species are firmly bound to the solid matrix, in contrast to the purely siliceous support. The preparation procedure provides a simple means of controlling the amount of the supported porphyrin. The solids are active in oxidation of cyclohexene with iodosylbenzene yielding only allylic oxidation products and no epoxide. It is argued that the regioselective effect is due to the narrowness of the structural pores, which prohibits the formation of the transient complex required for the formation of the epoxide. In contrast to previous studies in which increased loading of porphyrin has been found to result in a decrease in activity, in the present case an increase in the catalytic activity with increased porphyrin loading is observed.

The effect of peripheral substituents in metalloporphyrins on their catalytic activity in Lyons system

Abstract: Manganese porphyrin catalysts with different number of halogens atoms substituted at the phenyl and pyrrole rings were investigated in the Lyons system in oxidation of cyclooctane with molecular oxygen (as air) to cyclooctanone and cyclooctanol without the use of sacrificial co-reductant. The catalytic activity of metalloporphyrins increases with the increase of the redox potential of metalloporphyrins in the investigated system and shows almost linear relationship with the number of the halogens on porphyrin macrocycle. On the basis of obtained results the new reaction mechanism is discussed and proposed.

Metallosalen complexes immobilized in zeolite NaX as catalysts of aerobic oxidation of cyclooctane

Abstract: Physicochemical properties of metallosalen complexes entrapped within NaX zeolite and their catalytic activities in the oxidation of cyclooctane with dioxygen in the absence of a reducing agent were studied, and compared with free metallocomplexes. Broadening of the zeolite structure-sensitive vibrations observed after the encapsulation gives the evidence of the zeolite framework changes due to the presence of the “ship-in-the-bottle” species. EPR spectroscopy evidences the inclusion of metallosalen complexes since it distinguishes between encapsulated metallocomplexes and those adsorbed on the zeolite external surface. UV–vis spectra confirm the immobilization and stabilization of the metallocomplexes inside the zeolite structure. The most active catalysts are free metallosalen complexes. We have found that the activity of these complexes increases in the order Ni(salen), Fe(salen), Mn(salen), Cu(salen) and Co(salen) with triple difference in the catalytic activity between the most and the least active catalyst. Upon encapsulation their activity drops about two times. Only Ni(salen) after heterogenization does not change its catalytic activity. The reduction of catalytic activity of the encapsulated catalysts is probably governed by two factors: constraints in the formation of the intermediate complex and change of the redox potential of the metal in the salen complex.

The Production of Propene Oxide: Catalytic Processes and Recent Developments

Abstract: Propene oxide, which is one of the major commodity chemicals used in chemical industry, desperately requires a new process for its production, because of the disadvantages that are encountered with the currently available processes. This paper discusses the existing processes used for the production of propene oxidethe chlorohydrin and hydroperoxide processesand their advantages and disadvantages. Furthermore, the new processes and catalysts under development for the propene oxide production are discussed, as well as the challenges that are still limiting the applications of some of those prospects. The most important new developments for the production of propene oxide discussed in this paper are: the hydrogen peroxide combination process, the ethene oxide alike silver catalysts, the molten salt systems, and the gold−titania catalyst systems.

Reaction-controlled phase-transfer catalysis for propylene epoxidation to propylene oxide

Abstract: The epoxidation of olefins with H2O2 was performed with a tungsten-containing catalyst. This insoluble catalyst forms soluble active species by the action of H2O2, and when the H2O2 is used up, the catalyst precipitates for easy recycling. Thus, the advantages of both homogeneous and heterogeneous catalysts are combined in one system through reaction-controlled phase transfer of the catalyst. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H2O2 production, O2 can be used for the epoxidation of propylene to propylene oxide with 85% yield based on 2-ethylanthrahydroquinone without any co-products. This approach avoids the problematic co-products normally associated with the industrial production of propylene oxide.