Showing papers by "Luca Lietti published in 1995"

Reactivity and Physicochemical Characterization of V2O5-WO3/TiO2 De- NOx Catalysts.

Abstract: V2O5-WO3/TiO2 samples with compositions similar to those of commercial de-NOx catalysts (WO3 ∼ 9% w/w, V2O5, < 3% w/w) are characterised by XRD, surface area and pore size distribution, Fourier transform infrared, laser Raman, UV-vis diffuse reflectance, electron paramagnetic resonance spectroscopies, and catalytic tests in the reduction of NOx by NH3. The V2O5-WO3/TiO2 catalysts exhibit higher reactivity than the binary V2O5/TiO2 and WO3/TiO2 samples with the same metal loading, and the temperature window for the SCR reaction is greatly widened. The catalysts consist of anatase TiO2 and their morphological properties closely resemble that of WO3/TiO2 for (V + W) surface coverages lower than one. Monomeric vanadyls and wolframyls and polymeric WwOy groups are observed in the samples with low vanadia loadings that are apparently similar to those present on the surface of the binary oxide systems with comparable metal loadings. On increasing the vanadium loading, polyvanadate species are also formed. EPR, FTIR, FT-Raman, and UV-vis techniques indicate a strong electronic interaction between V and W oxide species at the surface of the TiO2 support. This interaction leads to a higher reducibility of the ternary sample with respect to the corresponding binary ones. A synergism between V and W oxide surface species is suggested, which accounts for the high reactivity of the ternary samples in the SCR reaction. It is suggested that the higher reducibility of the samples, due to the electronic interactions between V and W and the TiO2 support, is responsible for the higher reactivity of the ternary catalysts, particularly at low temperatures.

Selective isotopic oxygen incorporation into C5 and C6 ethers via solid acid-catalyzed reaction of methanol and ethanol with isobutanol

Abstract: Reaction of CH318OH with16O-containing isobutanol (2-methylpropan-1-ol) over strong acid Nafion-H and Amberlyst-H 35 resin catalysts gave the two distinctly labelled C5 ethers 1-methoxy(16O)-2-methylpropane (also designated as methyl isobutyl ether,16O-MIBE) and 2-methoxy(18O)-2-methylpropane (also designated as methyl tertiary-butyl ether,18O-MTBE). Reaction of CH3CH218OH with isobutanol gave the analogously labelled C6 ethers,16O-EIBE and18O-ETBE. These results show that the isobutyl and tertiary-butyl ethers are formed from the alcohols by distinctly different mechanistic pathways, i.e. the former are produced bysurface-catalyzed SN2 reactions that follow Langmuir-Hinshelwood kinetics involving competitive adsorption while the latter arise via carbenium or olefinic intermediates. There is no pathway for isomerization of the two ethers, MIBE and MTBE, under the reaction conditions employed.