L. Dimitrov

Effect of water on the reduction of NOx with propane on Fe‐ZSM‐5. An FTIR mechanistic study

Adsorption of NO on Fe‐ZSM‐5 leads to formation of Fen+–NO (n = 2 or 3) species (1880 cm-1), Fe2+(NO)2 complexes (1920 and 1835 cm-1) and NO+ (2133 cm-1). Water strongly suppresses the formation of NO+ and Fen+(NO)2 and more slightly the formation of Fen+ –NO. Introduction of oxygen to NO converts the nitrosyls into surface nitrates (1620 and 1575 cm-1) and this process is almost unaffected by water. The nitrates are thermally stable up to ca. 300°C, but readily interact with propane at 200°C, thus forming surface C–H–N–O deposit (bands in the 1700–1300 cm-1 region). Here again, water does not hinder the process. The C–H–N–O deposit is relatively inert (it does not interact with NO or NO + O2 at ambient temperature) but, at temperatures higher than 250 °C, it is decomposed to NCO- species (bands at 2215 (Fe–NCO) and 2256 cm-1 (Al–NCO)). In the presence of water, however, the Fe–NCO species only are formed. At ambient temperature the NCO- species are inert towards NO and O2, but easily react with a NO + O2 mixture. The mechanism of the selective catalytic reduction of nitrogen oxides on Fe‐ZSM‐5 and the effect of water on the process are discussed.

FTIR study of low-temperature CO and 15N2 adsorption on a CaNaY zeolite: formation of site-specified Ca2+(CO)3 and Ca2+(15N2)3 complexes

Adsorption of CO at room temperature on a CaNaY zeolite results in formation of several species: Ca2+(CO) (2198 cm−1); Ca2+(CO)2 (2188 cm−1), Ca2+(OC) (2094 cm−1), Na+(CO) (2172 cm−1) and Na+(OC) (2119 cm−1). At 85 K no O-bonded CO is observable but, in addition to the C-bonded complexes found at room temperature, two additional species have been detected: Ca2+(CO)3 (2185 cm−1) and Na+(CO)2 (2167 cm−1). At high CO coverages (equilibrium CO pressures above ca. 100 Pa), the Ca2+(CO)3 and Na+(CO)2 species are predominant. The Ca2+(CO)3 complexes are decarbonylated stepwise and first converted into Ca2+(CO)2 and then into Ca2+(CO) species with decreasing coverage. The latter are quite stable at 85 K. The Na+(CO)2 species stepwise lose the two CO ligands. Adsorption of a 12CO–13CO mixture reveals that the CO ligands in the di- and tri-carbonyls behave as independent oscillators. Low temperature 15N2 adsorption can also be explained in terms of formation of Ca2+(15N2)n (n = 1–3) and Na+(15N2)m (m = 1–2) species. A theoretical model of the process is proposed and adsorption isotherms well describing the experimental results are derived.

FTIR study of low-temperature CO adsorption on Mn-ZSM-5 and MnY zeolites. Effect of the zeolite matrix on the formation of Mn2+(CO)x geminal species

Abstract Adsorption of CO on Mn-ZSM-5 zeolite at 85 K results in formation of physically adsorbed CO, several kinds of H-bonded CO and Mn2+(CO)x geminal species (2202 cm −1 ) . Decreasing the coverage during evacuation results in disappearance of the physically adsorbed CO and the H-bonded forms and in conversion of the dicarbonyls to linear Mn2+–CO species (2214 cm −1 ) . The latter are quite stable at 85 K. Coadsorption 12CO and 13CO reveals that the CO molecules in the geminal polycarbonyls behave as independent oscillators. In contrast, CO adsorption at 85 K on MnNaY zeolite only leads to formation of linear Mn2+–CO species ( 2210 cm −1 ) and mono- and di-carbonyls associated with residual sodium cations. The results are interpreted as evidence that site-specified geminal carbonyls are formed with cations possessing an ionic radius bigger than a critical value. This value is different for different positions in various zeolites and is bigger for cations in SII positions in Y zeolites than is the case of cations in a ZSM-5 matrix.

Electromechanical properties of polyimide composites containing titanium dioxide nanotubes

Polyimide composite films were prepared by casting solutions resulting from direct mixing of a poly(amic acid) and titanium dioxide (TiO2) nanotubes (TNTs) onto glass plates, followed by thermal imidization. TNTs with outer diameters of approximately 10–12 nm and length of several hundreds of nanometers were synthesized by the hydrothermal method. The morphology of the nanotubes was investigated by using high-resolution transmission electron microscopy. The influence of TNTs content on structural, thermal, and electromechanical properties of pure polyimide and composite films was studied. The scanning electron microscopy and atomic force microscopy showed good compatibility between TNTs filler and polyimide matrix. The value of average roughness of film surface increases with increasing the content of TNTs. The films were flexible, tough, and exhibited high thermal stability. A study of microelectromechanical properties of these films was performed. The films showed nanometric displacements in the range of 250–800 nm when an electric voltage of 500 V was applied on their surface.