Furfuryl alcohol polymerization in H-Y confined spaces: reaction mechanism and structure of carbocationic intermediates

The acid-catalyzed polymerization and resinification, in the 300-673 K interval, of furfuryl alcohol adsorbed in the framework of a protonic Y zeolite is studied by means of FTIR, Raman, and UV-vis spectroscopies. The idea is that restricted spaces can impose a constraint to the growth of the oligomeric chains, therefore moderating the formation of conjugated sequences responsible for the color of the products and allowing their observation by means of spectroscopic techniques. The detailed study of the evolution of UV-vis, FTIR, and Raman spectra upon dosed amount, contact time, and temperature has allowed the spectroscopic features of some of the single species, either neutral and positively charged (carbocationic intermediates), to be singled out and assigned to understand the mechanism of initiation. The vibrational assignments have been confirmed by computer simulations on model compounds and compared with the results of the mechanistic description of the reaction mechanism made in the past (Choura, et al. Macromolecules 1996, 29, 3839-3850). The spectroscopic methods have been applied in a large temperature range in order to follow also the formation of more complex products into the pores, associated with longer conjugated sequences, gradually filling the open spaces of the zeolite. For samples contacted with furfuryl alcohol at 673 K, this methodology gives information also on the incipient carbonization process, leading to the formation of a carbonaceous replica phase inside the internal porosity of the zeolite.

Direct IR observation of vibrational properties of carbonyl species formed on Pd nano-particles supported on amorphous carbon: comparison with Pd/SiO2–Al2O3

By diluting optically opaque carbon-supported Pd particles in silica Aerosil we succeeded in observing the IR bands of adsorbed carbonyls and extracting information on the particle dispersion. Comparison with literature single crystal data and with silica-alumina supported Pd allowed us to make an assignment in terms of linear and 2-fold bridged carbonyls formed on Pd(111) and Pd(100) faces. Two Pd/C samples have been investigated. The relative intensities of the two carbonyl families observed on the two samples are consistent with the Pd dispersion independently measured with CO chemisorption, TEM and EXAFS analysis.

Ferryl (Fe=O) termination of the hematite alpha-Fe2O3(0001) surface

Using scanning tunneling microscopy and infrared reflection absorption spectroscopy we have observed that the alpha-Fe2O3(0001) surface exhibits ferryl (Fe=O) groups, which may coexist with domains of the Fe-terminated surface. We therefore fully support ab initio calculations recently reported in the literature [W. Bergmeyer, H. Schweiger, and E. Wimmer, Phys. Rev. B 69, 195409 (2004)]. The close similarity to the results on the (0001) surfaces of Cr2O3 and V2O3 strongly suggests that the M=O termination under certain oxygen pressure conditions is the most stable for the close-packed surfaces of transition metal oxides with the corundum structure.