Nicoletta Ravasio

Epoxidation on titanium-containing silicates: do structural features really affect the catalytic performance?

Five titanium-containing silicates, with different structural features, were compared: Ti–MCM-41, ordered titanium-grafted mesoporous silica, Ti–SiO2 Davison, nonordered titanium-grafted porous silica, Ti–SiO2 Aerosil, nonporous pyrogenic titanium-grafted silica, MST, nonordered in-framework mesoporous material, and TiO2–SiO2 Grace, commercial amorphous porous mixed oxide. They were tested in the liquid-phase epoxidation reaction on six unsaturated cyclic terpenes. Good performances were obtained on the commercial mixed oxide and also on the three grafted silicates. The in-framework MST showed the worst activity results. Under these conditions, the porosity features do not affect the catalytic performances noticeably and the use of an ordered mesoporous material is not strictly required. Likewise, a very high surface area is not mandatory in order to have an efficient titanium-grafted catalyst in the epoxidation of these substrates.

The use of H2O2 over titanium-grafted mesoporous silica catalysts: a step further towards sustainable epoxidation

The epoxidation of cyclohexene with aqueous hydrogen peroxide over mesostructured Ti(Cp)2Cl2-grafted silica catalysts is described for the first time. Three kinds of Ti-containing systems with different textural properties have been employed: Ti/SiO2, Ti/MCM-41 and Ti/MCM-48. A minimal local H2O2 concentration in the surroundings of Ti sites, obtained by a controlled dropwise addition of aqueous H2O2 (4.17 mmol H2O2 h−1 gcat−1), is crucial for an effective and highly selective epoxidation. Excellent selectivity (>98%) in cyclohexene epoxide is obtained at the end of the slow H2O2 addition in acetonitrile. Higher yields in epoxide are found over Ti/MCM-48 than over Ti/MCM-41 or Ti/SiO2 thanks to better isolation, dispersion and stability of Ti(IV) sites.

Heterogeneous catalytic epoxidation of fatty acid methyl esters on titanium-grafted silicas

Three different titanium-grafted silicates, with different morphological features were compared in the epoxidation, using tert-butylhydroperoxide as oxidant, of methyl oleate, methyl elaidate and of a mixture of methyl esters, obtained from high-oleic sunflower oil. Ti-MCM-41, a well-ordered mesoporous catalyst, showed very high conversions and excellent selectivity on all the substrates. The fatty acid methyl esters derived from renewable raw material were epoxidised selectively with very high yields in a reaction medium completely free from organic acidic compounds. The influence of the pore order of the catalysts on the catalytic performance was also examined. The interactions between the organic substrate and the ordered array of mesopores in Ti-MCM-41 were evidenced.

New generation biofuels: γ-valerolactone into valeric esters in one pot

Ethyl valerate and pentyl valerate, suitable as a gasoline additive and diesel component respectively, can be obtained in a one pot one step reaction from γ-valerolactone, readily available from lignocellulosic biomass. The reaction takes place in ethanol under H2 through nucleophilic addition of the alcohol to the carboxylic group giving hydroxypentanoate, dehydration to pentenoate and hydrogenation to the saturated ester. The bifunctional catalyst used consists of a non noble metal, namely copper, supported on an amorphous weakly acidic material, therefore representing an interesting alternative to Pt–zeolite catalysts. Pentyl valerate can be obtained in one pot with conversions >90% and selectivity up to 83%.

Epoxidation of methyl oleate with hydrogen peroxide. The use of Ti-containing silica solids as efficient heterogeneous catalysts

Titanium-silica catalysts, obtained by grafting titanocene dichloride onto mesoporous silica (MCM-41 and MCM-48) and onto nanosized pyrogenic silica, were tested in the epoxidation of methyl oleate using aqueous hydrogen peroxide. All titanium-containing materials, combined with the slow addition of hydrogen peroxide, showed good catalytic activity and comparable behaviour in terms of conversion, selectivity and yield of methyl epoxystearate, notwithstanding the morphology and the texture of the silica support. By optimizing the reaction conditions (especially, the catalyst to substrate ratio), high yields up to 91% in epoxide were obtained for Ti/MCM-41 with a high stereoselectivity (80%) for the cis-epoxide. The formation of the cis/trans-epoxide and the nature of the catalytic reaction pathway are also discussed.

CuO/SiO2: a simple and efficient solid acid catalyst for epoxide ring opening

A cheap, non toxic, easy to prepare and easy to use supported CuO material has shown to be a very effective catalyst for the alcoholysis of epoxides giving β-alkoxyalcohols in very good yield without generating any waste. The catalyst is heterogeneous in nature and can be reused without any reactivation treatment.

Selective hydrogenation of alternative oils: a useful tool for the production of biofuels

Selective hydrogenation over 8% Cu/SiO2catalysts has been carried out on a series of non-food oils methylesters, allowing their transformation into materials suitable for biodiesel formulation.

Highly efficient production of 2,3,5-trimethyl-1,4-benzoquinone using aqueous H2O2 and grafted Ti(iv)/SiO2 catalyst

The oxidation of 2,3,6-trimethylphenol with aqueous H2O2 over titanium(IV) grafted on commercial mesoporous silica produces 2,3,5-trimethyl-1,4-benzoquinone, with nearly quantitative yield.

Intramolecular Ene reactions promoted by mixed cogels

Abstract The activity and selectivity of SiO 2 −TiO 2 , SiO 2 −ZrO 2 and SiO 2 −Al 2 O 3 mixed cogels, both in the presence and in the absence of copper, have been investigated in the cyclization of citronellal to isopulegol. Although the nature of the catalytic sites is not clear, the very high selectivity of the reaction makes it synthetically attractive.

N-Alkylation of amines through hydrogen borrowing over a heterogeneous Cu catalyst

Substitution of alkylhalides for the synthesis of amines is a relevant target for synthetic chemists. Secondary amines can be obtained in a one pot-one step reaction from secondary and benzylic alcohols and aniline over a heterogeneous copper catalyst. The process does not require any additive, is intrinsically safe and produces no waste.