Laszlo T. Nemeth

Sn-zeolite beta as a heterogeneous chemoselective catalyst for Baeyer-Villiger oxidations.

The Baeyer–Villiger oxidation, first reported more than 100 years ago, has evolved into a versatile reaction widely used to convert ketones—readily available building blocks in organic chemistry—into more complex and valuable esters and lactones. Catalytic versions of the Baeyer–Villiger oxidation are particularly attractive for practical applications, because catalytic transformations simplify processing conditions while minimizing reactant use as well as waste production. Further benefits are expected from replacing peracids, the traditionally used oxidant, by cheaper and less polluting hydrogen peroxide. Dissolved platinum complexes and solid acids, such as zeolites or sulphonated resins, efficiently activate ketone oxidation by hydrogen peroxide. But these catalysts lack sufficient selectivity for the desired product if the starting material contains functional groups other than the ketone group; they perform especially poorly in the presence of carbon–carbon double bonds. Here we show that upon incorporation of 1.6 weight per cent tin into its framework, zeolite beta acts as an efficient and stable heterogeneous catalyst for the Baeyer–Villiger oxidation of saturated as well as unsaturated ketones by hydrogen peroxide, with the desired lactones forming more than 98% of the reaction products. We ascribe this high selectivity to direct activation of the ketone group, whereas other catalysts first activate hydrogen peroxide, which can then interact with the ketone group as well as other functional groups.

Selective and Shape-Selective Baeyer–Villiger Oxidations of Aromatic Aldehydes and Cyclic Ketones with Sn-Beta Zeolites and H2O2

Sn-Beta is used as a heterogeneous catalyst for the Baeyer-Villiger reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones, while unsaturated ketones are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. The catalyst is also selective for the oxidation of aromatic aldehydes with H2O2, producing the formate ester or the corresponding hydrolyzed product, that is the alcohol. Shape-selective oxidations are observed for isomeric reactants with different molecular shapes. The catalytic Sn sites have been characterized by 119Sn MAS-NMR spectroscopy, and tetrahedral incorporation into the zeolite framework has been demonstrated. In situ IR spectroscopy and 18O labeling experiments have shown that the oxidation mechanism involves an intermediate of the Criegee type.

Oxidative desulfurization of hydrocarbon fuels

A process and apparatus for the desulfurization of hydrocarbon fuels is presented. The apparatus and process use an inorganic metal peroxide and catalyst to oxidize the sulfur compounds. The oxidized sulfur compounds are then adsorbed on an adsorbent.New requirements for very low sulfur content (10 ppm) in liquid motor fuels demand novel approaches for ultra-deep desulfurization. For production of near-zero-sulfur diesel and low-sulfur fuel oil, removal of refractory sulfur compounds, like 4,6-dimethyldibenzothiophene and other alkyl-substituted thiophene derivatives, is necessary. Elimination of these compounds by hydrodesulfurization (HDS) requires high hydrogen consumption, high pressure equipment, and new catalysts. Various oxidative desulfurization processes, including recent advances in this field for diesel fuels, and the drawbacks of this technology in comparison with HDS are examined and discussed. It is shown that the oxidation of sulfur compounds to sulfones with hydrogen peroxide allows for production of diesel fuels with a sulfur content of 10 ppmw or lower at atmospheric pressure and room temperature. The gas phase oxidative desulfurization of sulfur compounds with air or oxygen is feasible at atmospheric pressure and higher temperatures: 90–300 °С and offers better economic solutions and incentives.

Synthesis and catalytic activity of UZM-12

Abstract UZM-12 is a microporous crystalline aluminosilicate with ERI topology synthesized via the Charge Density Mismatch approach. The Charge Density Mismatch approach features synthesis from clear aluminosilicate solutions with high organic template content that are subsequently treated with crystallization inducing solutions. The solution containing low amounts of alkali and a higher charge density organic “crystallization” template, yields UZM-12 with Si/Al > 5.5 and nano- to micron-sized crystallites of spherical, plate or rod morphology depending on crystallization template, K + /Al ratio and synthesis conditions. Crystallization templates include the diquat-6, diquat-4, and benzyltrimethylammonium cations. The thermal, steam stability, and acid properties of H-UZM-12 were determined using the combinatorial heptane microreactor.

Synthesis and characterization of Sn-Beta as a selective oxidation catalyst

Abstract The tin zeolite Beta (Sn-Beta = zeolite Beta structure with framework incorporated tin) is synthesized and used as a heterogeneous catalyst for the Baeyer-Villiger (BV) reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones with very high selectivity using hydrogen peroxide as a replacement of the environmentally unfriendly peracetic acid. This new oxidation system can also be used for unsaturated ketones, which are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. In some BV reactions the selectivity obtained is similar to that in the equivalent enzyme reaction. The catalytic Sn sites have been characterized using a combination of characterization techniques including TEM, FTIR, XPS and in-situ EXAFS. The most selective Sn-Beta sample, activated using a wet air calcination, shows high weak Lewis acidity and high framework tin. The data from this detailed characterization study provides a scientific basis for a deeper understanding of this fascinating catalyst system.

Sn-MCM-41—a heterogeneous selective catalyst for the Baeyer–Villiger oxidation with hydrogen peroxide

A new heterogeneous catalyst, Sn-MCM-41, is described for the Baeyer-Villiger reaction with hydrogen peroxide which selectively activates the carbonyl function for the nucleophilic attack by the oxidant, with high chemoselectivities when double bonds are present in the molecule.

Oxidative desulfurization of sulfur compounds: Oxidation of thiophene and derivatives with hydrogen peroxide using Ti-Beta catalyst

Oxidation of thiophene and its derivatives was studied using hydrogen peroxide (H2O2), t-butyl-hydroperoxide and Ti-Beta redox molecular sieve as selective oxidation catalysts. A new reaction pathway was discovered and investigated using C-13 NMR, GC, GC-MS, HPLC, ion chromatography, and XANES. The thiophene oxidized to thiophene-sesquioxide [3a,4,7,7a-tetrahydro-4,7-epithiobenzo[b]-thiophene 1,1.8-trioxide] and the sesquioxide oxidized mostly to sulfate. 2-Methyl-thiophene and 2,5 dimethylthiophene also oxidized to sulfate and sulfone products. The Benzothiophene oxidation product was sulfone. This proposed new reaction pathway is different from prior literature, which reported the formation of thiophene 1,1-dioxide (sulfone ) as a stable oxidation product

Phenol hydroxylation using Ti- and Sn-containing silicalitesElectronic supplementary information (ESI) available: XRD pattern of Ti?Sn?S-1s. See http://www.rsc.org/suppdata/cc/b3/b303455k/

New bimetallic framework and non-framework titanium and tin silicalite have been investigated for phenol hydroxylation with H2O2 in different solvents, and the optimized catalyst composition showed 26% higher initial rate than reference TS-1.