Michael Renz

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

The Baeyer–Villiger oxidation, first reported more thanu2009100 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 1.6u2009weight 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.

Sn-Beta zeolite as diastereoselective water-resistant heterogeneous Lewis-acid catalyst for carbon–carbon bond formation in the intramolecular carbonyl–ene reaction

The water-tolerant Lewis acid Sn-Beta isomerises citronellal to isopulegol with high diastereoselectivity working in batch or in fixed bed reactors with very high turnover numbers.

Coupling fatty acids by ketonic decarboxylation using solid catalysts for the direct production of diesel, lubricants, and chemicals.

There is an increasing demand in our society for sustainable development. Along this line, efforts are being made to establish processes that transform different biomass and biomass-derived products into liquid fuels and chemicals. Biodiesel, that is, fatty acid methyl esters, together with ethanol is the largest fuel product obtained from renewable resources. In many countries, it is blended with petroleum diesel and used in unmodified diesel engines. With the aim to expand the scope of application of vegetable oil derived renewables, alternative products and processes need to be developed. For instance, it is possible to transform vegetable oil into a paraffinic diesel by direct hydrotreatment. An interesting reaction to transform carboxylic acids into symmetrical ketones is their coupling or the ketonic decarboxylation. In this reaction, two carboxylic acids are condensed, and a symmetrical ketone is formed with 2n 1 carbon atoms, together with one molecule of water and one molecule of CO2 (Scheme 1). When the reaction is carried out with stearic acid (C18) to obtain stearone, the atom economy, that is, how much mass of the reactants ends up in the product, is as high as 89 %. So, this transformation can be considered to be a sustainable and green process if a simple, non-polluting catalyst and an efficient chemical process are employed. At present, the products obtained from the condensation of fatty acids, also called fatty ketones, find interesting applications in areas such as ink manufacturing, dishwashing detergents, or in personal care products. Furthermore, fatty ketones or their derivatives can also make excellent premium diesel and lubricants. In the condensation reaction, 75 % of the oxygen of carboxylic acids is eliminated and the bulk properties of the products such as hygroscopicity are considerably modified as compared to the starting acid. Nevertheless, it should be possible through a cascade-type reaction to perform hydrogenation of the ketone followed by elimination of water and further hydrogenation to remove all the oxygen from the molecule to yield an alkane that could be interesting as a diesel or biolubricant, depending on the chain length, that is, depending on the number of carbon atoms in the original acid (Scheme 1). To this end, process intensification could be achieved by designing a multifunctional catalyst that is able to promote the condensation–hydrogenation–dehydration–hydrogenation sequence in a single reactor. To design the multifunctional catalyst, we first studied the ketonic decarboxylation of carboxylic acids. Basic magnesium oxide was selected as an environmentally friendly solid catalyst to carry out this reaction in a fixed-bed continuous reactor. With lauric acid (C12H24O2), complete conversion was achieved in less than one hour of contact time at 400 8C (Table 1). At 95 % conversion, the desired ketone (C11H23COC11H23, laurone) was obtained with excellent selectivity (97 %; Table 1, entry 5). Other potential catalysts for acid condensation are manganese oxide or Fe-Al-Si-Ti mixed oxide. Scheme 1. Formation of triocsane from two molecules of lauric acid by ACHTUNGTRENNUNGketonic decarboxylation with subsequent hydrogenation of the carbonyl group, the elimination of water, and hydrogenation of the olefin.

Effect of Gas Atmosphere on Catalytic Behaviour of Zirconia, Ceria and Ceria–Zirconia Catalysts in Valeric Acid Ketonization

Ketonization of valeric acid, which can be obtained by lignocellulosic biomass conversion, was carried out in a fixed bed flow reactor over ZrO2, 5–20xa0% CeO2/ZrO2 and CeO2 both under hydrogen and nitrogen stream at 628xa0K and atmospheric pressure. Regardless gas-carrier 10xa0wt% CeO2/ZrO2 was found to show higher catalytic activity compared to zirconia per se as well as other ceria modified zirconia while ceria per se exhibited very low catalytic activity. All catalysts provided higher acid conversion in H2 than in N2 whereas selectivity to 5-nonanone was insensitive to gas atmosphere. XRD, FTIR, UV–Vis DRS, XPS, HRTEM methods were applied to characterize catalysts in reduced and unreduced states simulating corresponding reaction conditions during acid ketonization. XRD did not reveal any changes in zirconia and ceria/zirconia lattice parameters as well as crystalline phase depending on gas atmosphere while insertion of ceria in zirconia caused notable increase in lattice parameter indicating some distortion of crystalline structure. According to XPS, FTIR and UV–Vis methods, the carrier gas was found to affect catalyst surface composition leading to alteration in Lewis acid sites ratio. Appearance of Zr3+ cations was observed on the ZrO2 surface after hydrogen pretreatment whereas only Zr4+ cations were determined using nitrogen as a gas-carrier. These changes of catalyst’s surface cation composition affected corresponding activity in ketonization probably being crucial for reaction mechanism involving metal cations catalytic centers for acid adsorption and COO− stabilization at the initial step.

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.