Portion Of Catalyst Research Articles

An efficient method for synthesizing monofunctionalized derivatives of 1,1,3,3-tetramethyldisiloxane in ionic liquids as recoverable solvents for rhodium catalyst

Functionalized siloxanes, as one of the most important classes of organosilicon compounds, are widely applied in industry. In our studies, we have investigated, the reaction between 1,1,3,3-tetramethyldisiloxane (TMDSO) and 1-octene, using the rhodium catalyst immobilized in six phosphonium-based ionic liquids differing in the structure of cation and anion. Studies have shown high potential for using ionic liquids to create biphasic system with reactants, where IL/catalyst phase can be separated and reused in subsequent reaction cycles allowing, in this way, for efficient and highly selective monofunctionalization of TMDSO with reuse of the same portion of catalyst up to 20 times in comparison to conventional homogenous reaction.

Comparative simulation study of gas-phase propylene polymerization in fluidized bed reactors using aspen polymers and two phase models

A comparative study describing gas-phase propylene polymerization in fluidized-bed reactors using Ziegler-Natta catalyst is presented. The reactor behavior was explained using a two-phase model (which is based on principles of fluidization) as well as simulation using the Aspen Polymers process simulator. The two-phase reactor model accounts for the emulsion and bubble phases which contain different portions of catalysts with the polymerization occurring in both phases. Both models predict production rate, molecular weight, polydispersity index (PDI) and melt flow index (MFI) of the polymer. We used both models to investigate the effect of important polymerization parameters, namely catalyst feed rate and hydrogen concentration, on the product polypropylene properties, such as production rate, molecular weight, PDI and MFI. Both the two-phase model and Aspen Polymers simulator showed good agreement in terms of production rate. However, the models differed in their predictions for weight-average molecular weight, PDI and MFI. Based on these results, we propose incorporating the missing hydrodynamic effects into Aspen Polymers to provide a more realistic understanding of the phenomena encountered in fluidized bed reactors for polyolefin production.

Efektywna synteza fluorofunkcyjnych (poli)siloksanow

Synthesis of fluorofunctional polysiloxanes based on hydrosilylation of fluoroalkyl ethers (precursors of the latter were fluoro alcohols) was studied. The most active catalyst, based on rhodium siloxide complex, was selected on the ground of a comparison of the catalytic performance of platinum and rhodium complexes. The rhodium complex was immobilized in four different ionic liquids and catalytic activities of the obtained systems were compared, while performing multiple reaction runs with the use of the same portion of catalyst.

Modeling of Freezing Phenomena Induced by Chemical Reactions

Spatial variations in the concentration of a reactive solute in solution are often encountered in a catalyst particle, and this leads to variation in the freezing point of the solution. Depending on the operating temperature, this can result in freezing of the solvent on a portion of catalyst, rendering that part of the active area ineffective. Freezing can occur by formation of a sharp front or a mush that separates the solid and fluid phases. In this paper, we model the extent of reduction in the active area due to freezing. Assuming that the freezing point decreases linearly with solute concentration, conditions for freezing to occur have been derived. At steady state, the ineffective fraction of catalyst pellet is found to be the same irrespective of the mode of freezing. Progress of freezing is determined by both the heat of reaction and the latent heat of fusion. Unlike in freezing of alloys where the latter plays a dominant role, the exothermicity of the reaction has a significant effect on freezing in the presence of chemical reactions. A dimensionless group analogous to the Stefan number could be defined to capture the combined effect of both of these.

Overall water splitting over Pt/TiO 2 catalyst with Ce 3+/Ce 4+ shuttle charge transfer system

The experiments on photocatalytic hydrogen production from aqueous solution of Ce 2(SO 4) 3 and photocatalytic oxygen production from aqueous solution of Ce(SO 4) 2 were carried out on the same catalyst platinized Degussa P25. Pure oxygen was shown to evolve from Ce(SO 4) 2 solution and pure hydrogen from Ce 2(SO 4) 3 solution with stoichiometric formation of Ce 2(SO 4) 3 and Ce(SO 4) 2, respectively. The rate of photocatalytic hydrogen production was lower than the rate of photocatalytic oxygen production on the same catalyst. The influence of initial cerium salt concentration, acidity and catalyst loading was checked for photocatalytic oxygen and hydrogen production. The dependences of the hydrogen and oxygen production rate on Ce 3+ and Ce 4+ concentration have maxima. Kinetic equation for the rate of photocatalytic oxygen production was proposed that takes into account the inner filter effect; constants of this equation were calculated. Optimal conditions for photocatalytic reactions were found and explained. The shuttle charge transfer regime was tested for consecutive O 2 and H 2 production over the same and different portions of catalyst and same Ce 3+/Ce 4+ system. It was found that separate catalyst batches are needed to avoid mixed evolution of hydrogen and oxygen.

A one-pot sequence of Stille and Heck couplings: synthesis of various 1,3,5-hexatrienes and their subsequent 6pi-electrocyclizations.

Palladium-catalyzed cross-coupling reactions of 2-bromocyclohex-1-enyl triflates 7 and 11 with a variety of alkenylstannanes occurred chemoselectively at the site of the triflate leaving group to give bromobutadienes which readily underwent Heck reactions with acrylates and styrene. Both steps could be performed in the same flask to give differentially functionalized hexatrienes in up to 88% overall yield. With simple stannanes, the same catalyst precursor could be used for both coupling steps making it possible to perform the whole sequence with only one portion of catalyst. For some of the functionally substituted stannanes, specifically adjusted catalyst systems had to be used. The 1,3,5-hexatrienes obtained were further transformed, in particular the methoxy-substituted compounds 14a-c were converted to bicyclo[4.4.0]decenones 30 (71-97%), bicyclo[4.3.0]nonenones 35 (74-93%), cyclodecynone 37a (47%), and cyclononynone 39a (15%). Thermal electrocyclizations of the other hexatrienes gave tetrahydronaphthalines 31 (60-61%), the tricyclic lactone 32 (72-75%) and decahydrophenanthrene 33 (75 %) in good yields.

Electron spin resonance study of chromium oxide catalysts for the polymerization of ethylene

IN AN investigation of the polymerization of ethylene on a chromium oxide catalyst [1], we came to the conclusion tha t the activity of the latter is produced by the action of the reacting substance ethylene. The object of the present work was to confirm this conclusion with the aid of electron paramagnetic resonance (ESR) and to at tempt to discover the nature of the active centres of the polymerization catalyst. There are a number of papers in the literature in which the ESR method has been used to establish the valency stale of chromium in chromic oxide catalysts on various supports [2-7]. Studying chromium-aluminium (CrOa/A12Oa) catalysts in the initial state and when partially reduced by hydrogen, Pecherskaya, Kazanskii, and Voyevodskii [2, 3] found two lines in the ESR spectra: a line with a width of 500-1000 oersted and a g factor of 1.97, and a narrow line with a width of 30-45 oersted and the same g factor. The authors associated the broad line with microcrystals of Cr203 [4] and assigned the narrow line to Cr +5 ions. In the work of Cossee and Van Reijen [6], the ESI~ spectra of chromium oxide catalysts which had been subjected to mild reduction were found to have one broad resonance line (ca. 600 oersted, g factor 1.97) with a narrow line (line width ca. 40 oersted, g factor 1.97) superposed on it, which the authors assigned to compounds of the ions Cr +4 and Cr +5, respectively. O'Reilly and MacIver [7] also considered the narrow line in the ESR spectra to be due to Cr +5 ions. All these investigations are of great interest; however, it would be extremely important to connect the ESR spectral data with the catalytic activity of the catalysts studied. We prepared chromium oxide catalysts by impregnating aluminosilicate with an aqueous solution of chromic anhydride, with subsequent activation. Two portions of catalyst were prepared. One was act ivated in a current of dry air at 500 ° for 4 hours, and the other in vacuum at 350 ° for the same