Electron energy-loss spectroscopy (EELS) in combination with scanning transmission electron microscopy (STEM) reveals that the La enrichment at the surface of cerium-lanthanum solid solutions is an averaged effect and that segregation occurs in a mixed oxide phase. This separation occurs within a crystalline particle, where the dopant-rich phase is located at the surface of the dopant-deficient phase. The limiting structure appears to be a solid solution with a La fraction of x ) 0.6 in the bulk and x ) 0.75 at the surface. Up to a La fraction of 0.6, this phase will coexist with a lanthanum-type structure in different proportions depending on the dopant amount. STEM-EELS appears to be a powerful technique to clarify the existence of a multiphase system, and it shows that XRF, XPS, and XRD measure averaged results and do not show the phase complexity of the solids.

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The relative activities of a low-surface crystalline and high-surface amorphous LaOCl, further denoted as S1 and S2, have been compared for the destructive adsorption of CCl 4 . It was found that the intrinsic activity of S2 is higher than that of S1. Both samples were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N 2 -physisorption, and Raman and infrared (IR) spectroscopy. IR was used in combination with CO 2 , CO, and methanol as probe molecules. The CO 2 experiments showed that different carbonate species are formed on both materials. For S1, a high surface concentration of bidentate carbonate species and a lower concentration of monodentate carbonate were observed. In the case of S2, bulk carbonates were present together with bridged carbonates. CO adsorption shows that S2 and S1 have very similar Lewis acid sites. However, methanol adsorption experiments showed that S2 had a higher number of stronger Lewis acid sites than S1 and that twofold coordinated methoxy species were more strongly bound than threefold coordinated methoxy species. Because of the analogy between methanol dissociation and the removal of the first chlorine atom in the destructive adsorption of CCl 4 , the sites enabling twofold coordination were likely to be the same Lewis acid sites actively involved in the destructive adsorption of CCl 4 . La 2 O 3 was less active than the two LaOCl materials, and therefore, the intrinsic activity of the catalyst increases as the strength of the Lewis acid sites increases. S2 contains more chlorine at the surface than S1, which is expressed by the higher number of sites enabling twofold coordination. Moreover, this explains the difference in destructive adsorption capacity for CCl 4 that was observed for the samples S1 and S2. Since LaCl 3 , being the most acidic phase, is not active for the destructive adsorption of CCl 4 , basic oxygen atoms, however, remain needed to stabilize the reaction intermediate CCl 3 as La-O-CCl 3 .

Sulfur removal remains a challenging task for refiners. To attain high desulfurization levels for gasoline, new processes were recently patented. One of them proposed to separate sulfur compounds by distillation after being weighed down by alkylation with olefins present in the feed. In this study, the transformation mechanism of the alkylation of 3-methylthiophene with 2-methyl-2-butene was studied in a batch reactor over zeolitic catalysts at 358 K. The first step of this study was devoted to the hydrodynamic of the reactor, to ensure that the reaction proceeds under chemical control. A detailed mechanistic study, including competitive catalytic experiments, then is reported.

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