Functionalization of a layered oxide with organic moieties: towards hybrid proton conductors

The design of innovative proton conductors for intermediate-temperature fuel cells, closing the gap between PEMFC and SOFC, is a forefront research theme in materials chemistry. [1] Layered perovskites with the Dion-Jacobson structure (ALaNb2O7) have bidimensional lanthanum niobate sheets, separated by a layer of A+ cations. These can be substituted by a variety of molecules with soft chemistry, to yield inorganic-organic hybrids. In particular, the intercalation of amines, alcohols, carboxylic or phosphonic acids, and their covalent binding to the sheets has been demonstrated recently. [2-4]We present preliminary results on the intercalation and covalent bonding of different organic molecules, in order to develop hybrid proton conductors for use in intermediate temperature fuel cells. Smaller molecules (such as alcohols) are intercalated to expand the interlayer space, to form intermediates for the further binding of proton carriers such as imidazoles or sulfonates.The intercalation process is investigated by XRD (to measure the interlayer distance) and TGA (to determine the weight loss upon thermal decomposition). NMR is applied to confirm the covalent bonding between the organic and oxide parts. The intercalation behavior of different functional groups is explained in terms of van der Waals and/or hydrogen bonding between organic chains. The interplay of theory (ab initio and periodic DFT) and experiment allowed us to elucidate the 1H and 13C-NMR spectra, and to investigate the nature of interaction (i.e. ionic or covalent bond) of the organic chains with the interlayer surface

Novel prolinamide-supported polystyrene as highly stereoselective and recyclable organocatalyst for the aldol reaction

A new prolinamide derivative anchored to a polystyrene support has been straightforwardly prepared and employed as heterogeneous catalyst in the direct asymmetric aldol reaction with good results in terms of yield and stereoselectivity. The optimal reaction conditions were found when a 1:2 (v/v) water/chloroform mixture was used. This mixture was the best compromise between the good swelling properties of chloroform and the formation of a concentrated organic phase due to the presence of water. Noticeably, the enantioselectivities obtained employing acetone as ketone were, to the best of our knowledge, the highest achieved with a supported proline derivative. This catalyst can be easily recovered, regenerated and recycled, without loss of activity, at least for twelve cycles

Polystyrene-supported proline as recyclable catalyst in the Baylis-Hillman reaction of arylaldehydes and methyl or ethyl vinyl ketone

Polystyrene-supported proline has been used as co-organocatalyst (10 mol%) with imidazole (10 mol%) in the Baylis-Hillman reaction between methyl or ethyl vinyl ketone and arylaldehydes. Recycling studies showed that the proline resin can be used up to five cycles with high isolated yields. This study represents the first example of supported proline as heterogeneous catalyst in the above reaction and broaden the scope of this catalytic material

Stereoselective aldol reaction catalyzed by a highly recyclable polystyrene supported substituted prolinamide catalyst

Polystyrene supported substituted prolinamide was used as catalyst in the aldol reaction between cyclohexanone or acetone and several substituted benzaldehydes in chloroform/water. This catalyst afforded aldol products in high yields and stereoselectivities, especially in the case of reactions performed with acetone. The catalyst was easily recovered by filtration and reused, after regeneration with formic acid, up to 22 times

Toward tailorable surfaces: a combined theoretical and experimental study of lanthanum niobate layered perovskites

A comprehensive theoretical investigation of the MLaNb2O7 (M=H, Li, Na, K, Rb and Cs) series of ion-exchangeable layered perovskite is presented. These perovskites are particular interesting in view of their potential applications as inorganic supports for the design of new hybrid inorganic-organic proton conductors. In particular, their structural and electronic properties have been investigated by periodic calculations in the framework of Density Functional Theory, using different exchange-correlation functionals. A general very good agreement with the available experimental (XRD, NPD and EXAFS) data has been found. The structure of the protonated HLaNb2O7 form has also been further clarified and a new tetragonal space group is proposed for this compound, better reproducing the experimental cell parameters and yielding to a more realistic picture of the system. The electronic investigation highlighted that all the compounds considered are very similar to each other and that the interaction between interlayer cations and perovskite slabs is purely ionic, except for the proton that is, instead, covalently bound