Alberto Girelli

Fourier transform-infrared study of the adsorption of unsaturated and aromatic hydrocarbons on the surface of α-Fe2O3. Part III. Toluene, ethylbenzene and styrene

IR spectra of toluene, ethylbenzene and styrene adsorbed on pressed discs of hematite between room temperature and 400°C are described. Mechanisms of adsorption and transformation are discussed and compared with those reported on the basis of kinetic measurements of ethylbenzene dehydrogenation on iron oxide catalysts.AbstractПриводятся ИК спектры толуола, этилбензола и стирола, адсорбированных на прессованных дисках гематита в интервале от комнатной температуры до 400 °C. Механизм адсорбции и превращений обсуждается и сравнивается с механизмом, сообщенным, исходя из кинетических измерений дегидрирования этилбензола на катализаторе окиси железа.

Bauxite-based catalysts in heavy crude oil hydrotreating

Abstract In hydrotreating heavy crudes, shale oils and coal liquefaction products, the cost of the catalyst is expected to be a critical factor in the process economy. This is due to non-volatile metal components in the feedstocks which cause high catalyst consumption. In a systematic study of the use of natural bauxite as carrier for low cost hydrotreating catalysts, the catalytic performance of bauxite-based catalysts in hydrotreating a 60% reduced crude from the Adriatic Sea region has been determined in a trickle-bed reactor. The following systems have been considered: MoO 3 /bauxite, WO 3 /bauxite, CoO-MoO 3 /bauxite, NiO-MoO 3 bauxite, NiO-WO 3 /bauxite. Data on a commercial catalyst,containing 4 and 12 wt % of CoO and MoO 3 respectively, are included for comparison. For maximum surface dispersion of the active components, Mo(VI) and W(VI) were incorporated on bauxite by anionic exchange. The Mo(VI) and W(VI) contents of the catalysts (6.6 wt % MoO 3 and 11.6 wt % WO 3 ) correspond to the chemisorption capacity of the natural material (after thermal activation). The catalytic properties of the bauxite-based catalysts resemble those of alumina-based catalysts. The synergistic effect of cobalt and nickel on molybdenum and tungsten in hydrodesulfurization (HDS) is evident. Tungsten-based catalysts are less active than molybdenum-based systems, in accordance with literature data. The lower activity of all bauxite-based catalysts, compared with the commercial CoO-MoO 3 -a1umina system, is attributed to differences in composition and surface properties. All of the catalysts examined promoted the production of a low boiling fraction in similar amounts, i.e., all catalytic systems show similar cracking activity. However, hydrogen uptake, as measured by the increase of the H/C ratio of the product, is substantially different and suggests large differences in the hydrogen-ating activity of the catalysts. Activity in hydrodenitrogenation (HDN) is lower than in HDS. Also the nitrogen removal properties of bauxite-based catalysts are comparable with the alumina-based systems. Differences in the kinetic steps involved in the HDS and HDN processes have been proposed; the experimental data indicate that the nitrogen removal process takes place through a number of kinetically important steps and this is consistent with the reaction network proposed for the HDN of model compounds. In metal removal, bauxite-based catalysts exhibit about the same activity as the commercial catalyst; this result is attributable to the relevant role played in this reaction by the pore structure of the support. These data show that, by the use of appropriate evaluation criteria, natural minerals, such as bauxites, can be selected to prepare efficient hydrotreating catalysts and that the activity and selectivity of these systems can be, to a certain extent, adjusted by a proper choice of chemical composition.

Fourier transform-infrared study of the adsorption of unsaturated and aromatic hydrocarbons on the surface of α-Fe2O3: I. Ethylene

Benzene adsorption on α-Fe2O3 in the temperature range 300–673 K has been studied. Two different molecular adsorbed forms can be distinguished due to their spectroscopic behavior and the different equilibrium pressures needed for their formation. The more stable form, in which the benzene molecule is π-bonded on exposed metal cations, slowly transforms at room temperature into combustion products. This process is inhibited by the presence on the surface of the second form of adsorbed benzene.

The Seveso case and the safety problem in the production of 2,4,5-trichlorophenol

Abstract Extensive investigations of the “Seveso mixture” by advanced thermoanalytical techniques and engineering experiments allow an explanation of the Seveso accident and a definition of the criteria for conduction of the process for the production of 2,4,5-trichlorophenol. A critical comparison of the process in methanol and in ethylene glycol as reaction medium points to the latter as being more controllable and consequently safer.

Use of supported rhodium and cobalt carbonyls as catalysts for the CO+H2 reaction effect of the support and the metal

The use of cobalt and rhodium catalysts derived from carbonyl clusters and supported on Al2O3, Al2O3–ZnO, ZrO2 and SiO2 for the CO + H2 reaction has been investigated. Only Rh-containing catalysts were active in the formation of oxygenated compounds (essentially ethanol). In all the runs the selectivity to methane plus ethanol was > 90%. The ratios of the rates of ethanol and methane formation or the rate of ethanol formation and the CO reaction reach a maximum when equal amounts of Rh and Co are present on the catalyst surface. Cobalt alone does not form oxygenates, but when mixed with rhodium it increases the selectivity to ethanol.

Studies on the reactivity of supported rhodium and molybdenum carbonyl complexes using temperature-programmed techniques

Abstract The reactivity of zirconia-supported RH 4 (CO) 12 and Mo(CO) 6 has been studied by temperature-programmed desorption (TPD) into vacuum and temperature-programmed reaction (TPR). Thermal activation of the carbonyl precursors results in a complex reaction system including CO disproportionation, water gas shift reaction and oxidative interaction of Rh o species with hydroxyl groups on the support. The surface species formed after chemisorption of CO on the reduced samples exhibit different reactivity compared with the original metal carbonyls. K 2 O added to ZrO 2 promotes the shift reaction and selectivity to methanol but suppresses CO hydrogenation; Mo(CO) 6 co-adsorbed with Rh 4 (CO) 12 brings on formation of surface sites exhibiting weak adsorption properties towards CO and high hydrogenation activity. TPR experiments in flow of H 2 -CO mixture show that above 500 K the thermodynamically favoured products CH 4 and CO 2 rapidly become predominant; however, with RhMo/ZrO 2 , a good selectivity to oxygenated products can be obtained in a restricted temperature range by operating at high CO pressure.

FT-IR/PAS investigation of solid fuels and catalysts

Coal and catalysts are examples of substances of great technical importance, whose knowledge has advanced for many years empirically. They are considered as disordered and complex materials. FT-IR/PAS suggests models closer to the real systems as the samples can be examined “as they are”: coal with the same sampling procedure as for ASTM analysis and catalysts “during catalysis” without manipulation. Some examples are reported.

Activity Of Iron-Rich Bauxite In The Hydrotreating Of A Heavy Petroleum Residue

A sample of bauxite, containing 28% Fe 2 O 3 , was activated by hydrothermal treating and molybdenum impregnation, and tested as a catalyst in the hydro-treating of a heavy petroleum residue in a bench-scale trickle-bed reactor. The thermally treated bauxite exhibited a significant demetalation activity, attributable to iron sulfide. After addition of a small amount of molybdenum (4.7% MoO 3 ) to the activated bauxite, hydrodesulfurization was strongly promoted. At highest conversion, hydrogen consumption was less than 100 Nm 3 /m 3 of oil. NMR analysis of the products showed a limited saturation of aromatic rings. Hydrocracking, significant in the presence of activated bauxite, was somewhat reduced by molybdenum addition.

Criteria For The Evaluation Of Bauxite As Carrier For Low-Cost Hydrotreating Catalysts

The determination of the porous structure after thermal activation, the measure of the anionic exchange capacity with respect to Mo(VI) and W(VI) species and the study of the functionality of the catalytic systems in model reactions have proved to be efficient criteria for a preliminary evaluation of natural materials as carriers for low-cost hydrotreating catalysts. Experiments performed with two bauxite samples, from a USA ore and a Southern Italian ore respectively, have made it possible to ascertain the possibility of utilizing the sample with lower iron content and higher surface area as a support for catalytic systems with properties comparable to those of more expensive alumina-based catalysts.