R. Carli

XPS analysis of gallium oxides

Abstract Samples of Ga 2 O, synthesized by reacting Ga 2 O 3 and metallic gallium, are analyzed by XPS measurements. These samples reveal the presence of a new photoelectron signal, assigned to Ga(I), with 3d binding energy of 19.0 eV, which is lower than the measured Ga III (3d) binding energy (20.6 eV) and higher than the measured Ga 0 (3d) binding energy (18.5 eV). A comparison between available XPS data on the Ga 2 O 3 /HZSM-5 catalytic system and the gallium binding energies measured in this work is proposed.

Low temperature reduction of gallium in a Ga2O3/HZSM-5 catalyst

Abstract Several experiments were performed to provide convincing evidence for low temperature gallium reduction in a Ga2O3/HZSM-5 catalyst. XPS measurements showed the appearance of a GaI signal after in situ hydrogen reduction at temperatures ranging between 373 and 673 K. No transfer of reduced gallium species from Ga2O3 to the zeolite particles was detected. A revision of the existing reduction mechanism is thus proposed. It is suggested here that the actual role of the HZSM-5 zeolite could be to provide a kind of activated hydrogen able to reduce Ga2O3.

Fischer—Tropsch synthesis on alumina-supported ruthenium catalysts I. Influence of K and Cl modifiers

Abstract Fischer-Tropsch synthesis (FTS) has been studied at 5 · 103 Pa, at 508 K, an H2/CO=2/1 molar ratio on Ru/γ-Al2O3 catalysts (1% Ru wt./wt.), using Ru(AcAc)3 (AcAc standing for acetylacetonate), RuCl3 and K(AcAc) as precursors; K/Ru and Cl/Ru molar ratios ranged from 0.14 to 2.18 and from 1.31 to 3.71, respectively. As Ru catalysts for FTS undergo easy alteration resulting from coke deposition, the results from kinetic runs were collected using both fresh catalysts (at 5–10 min time-on-stream) and also when steady state conditions were reached (about 150 min time-on-stream). The influence of K/Ru and Cl/Ru ratios on CO conversion and on the selectivity of the formation of different products in the reaction has been examined. Changes in activity, during the regeneration procedures of the catalysts, differ significantly when the precursor is Ru(AcAc)3 (increase in activity after regeneration cycle) or RuCl3 (significant deactivation with a decrease in Ru surface concentration, as determined by XPS).

Influence of ultrasound on the preparation of ruthenium catalysts supported on alumina

Abstract Ultrasound waves are commonly used to clean or to erode the surface of solid materials thanks to the strength of the jets of solvent, hitting the surface itself, created by the collapse of the liquid phase. In the present work, ultrasound was used to obtain highly dispersed ruthenium on alumina catalysts. The samples were characterized with different techniques to study the influence of the sonication on both the metal crystallites and the support.

Gallium containing hybrid catalysts for the aromatization of n-butane

Abstract The enhancement of the aromatization activity of the gallium containing hybrid catalysts may partly be ascribed to the formation, upon reduction, of gallium species having a lower oxidation state and their subsequent transfer/redistribution within the catalyst mass. Within the hybrid catalysts which contains the cocatalyst prepared by evaporation of a gallium salt/colloidal silica mixture, some transfer of gallium onto the external surface of the zeolite particles effectively occurs. However, the high aromatization performance of such a hybrid catalyst results mainly from the physical presence of the cocatalyst which exhibits strong hydrogen spillover effects.

Fischer-Tropsch synthesis on Co and Co(Ru-doped) ETS- 10 titanium silicate catalysts

Titanium silicate ETS-10 was found to be a suitable support for metal catalysts, having high surface area, high ion-exchange capability and no acidic functions. In this paper, the M-ETS-10 commercial form (where M stands for Na and K) was first exchanged with Co and thus tested in CO hydrogenation (Fischer-Tropsch synthesis). Moreover, the sample was also doped with small amounts of ruthenium to improve the Co reducibility. The successive catalytic tests revealed a strong increase in the CO conversion and a modification in the selectivity of the hydrocarbon fractions.

Fischer-Tropsch synthesis on alumina-supported ruthenium catalysts II. Influence of morphological factors

Abstract A Ru/γ-Al 2 O 3 (0.87% wt./wt.) catalyst has been studied for the Fischer-Tropsch synthesis (FTS) at 5 · 10 3 Pa, 508 K with a H 2 /CO ratio of 2/1. The same catalyst was also sintered at 973 K for different times in order to change the metal dispersion D M of Ru ( D M from 18 to 93%). The aim of the present work is to verify which atoms of Ru crystallites are most active in FTS. For this study a ‘model’ of truncated hexagonal bipyramid for the crystalline agglomerates has been assumed. It was verified that atoms with higher nearest neighbors i ( i ,8 and 9) on flat faces and edges are more active than those on vertexes and edges at lower i values ( i ,5 to 7). We found that larger crystallites decompose CO more easily than smaller ones, and that the turnover number for CO disappearance and for CH 4 , C2, C3, C5–C15 formation does not depend strongly on metal dispersion. However, on the contrary, we found that light olefins (C2 and C3) are easily formed on large crystallites. The above findings reveal that FTS could be considered as a structure sensitive reaction for the initial step, but are structure insensitive for the overall reaction.

Fischer-Tropsch synthesis on ruthenium supported ETS-10 titanium silicate catalysts

Titanium silicate ETS-10 was found to be a suitable metal catalyst support, having high surface area, high ion exchange capacity and no acidic functions. In this work, ETS-10 was used as a support in preparing ruthenium supported catalyst for Fischer-Tropsch synthesis. Ru/METS-10 catalytic systems (M standing for Na or K) showed some important characteristics, as good metal dispersion and shape selectivity. Moreover, no side reactions due to acidic functions were evidenced; indeed readsorption of olefins on active metal centers was found to control the activity of the catalysts.

Catalysts for the aromatization ofn-butane prepared by surface-contact transfer of gallium onto ZSM-5 zeolite particles

ZSM-5 zeolite particles into which 0.6 weight per cent or less of gallium oxide has been incorporated by surface-contact transfer, may exhibit very high activity in the aromatization ofn-butane. In some cases, the yield in aromatics is as high as that obtained with the hybrid catalyst wherein the cocatalyst is prepared by evaporation of a solution of gallium nitrate in Ludox colloidal silica.

Hydrogen sorption sites in the gallium containing hybrid catalysts used for the aromatization of light alkanes

Gallium species which were incorporated initially in the oxide form, were all in the (+3) oxidation state in the hybrid catalyst and exhibited two types of hydrogen chemisorption sites, shw and shs. The stronger sorption sites shs which predominated at higher gallium dispersion, corresponded probably to the most effective surface configuration for gallium in the aromatization ofn-butane.