Sergio G. Marchetti

Influence of TS-1 structural properties and operation conditions on benzene catalytic oxidation with H2O2

Abstract The preparation method described by Thangaraj et al. was used to obtain samples of titanium-silicalite (TS-1) for the catalytic hydroxylation of benzene with hydrogen peroxide. These samples were characterized by X-ray diffraction, scanning electron microscopy, skeletal infra-red spectroscopy and ultraviolet–visible diffuse reflectance spectroscopy (UV–VIS DRS). Pure TS-1 (without extra-framework titanium) with a maximum Ti/Si ratio of 0.020 was obtained. UV–VIS DRS measurements allowed us to infer the existence of different Ti 4+ sites in the TS-1 framework. Small changes in the preparation conditions lead to the presence of extra-framework titanium. The influence of extra-framework titanium, traces of sodium and the operation conditions (such as the method of H 2 O 2 addition and the presence of a solvent on TS-1 activity and selectivity to phenol) were analyzed.

Dependence of the oxide-support interaction on the size and nature of iron oxide particles on SiO2

Abstract The thermal dependence of the hyperfine fields and of the relative Mossbauer factors have been used to investigate the oxide-support interaction in the Fe-SiO 2 system. The calcination temperature (698, 898 and 1098 K in N 2 ) has an influence on the nature and particle size of the iron species, while the atmosphere (air and N 2 at 698 K) affects the oxide particle size only. α-Fe 2 O 3 particle diameters of ≅ 45 and ≅ 150 A were found for samples calcinated at 698 K in air and nitrogen, respectively. γ-Fe 2 O 3 particles of ≅ 90 A were obtained after calcination in air at 898 K and migration of iron ions into the SiO 2 matrix was verified after the 1098 K heat treatment. It is found that for α-Fe 2 O 3 , the smaller particles have a stronger oxide-support interaction and γ-Fe 2 O 3 particles have an even higher strength than α-Fe 2 O 3 .

Characterization of FeMCM-41 and FeZSM-5 catalysts to styrene production

FeMCM-41 and FeZSM-5 catalysts have been prepared and tested in the dehydrogenation of ethylbenzene to produce styrene. These new catalytic systems have high specific areas and can stabilize the trivalent state of iron. It was found that the FeZSM-5 catalysts are more active and selective than the FeMCM-41 ones and this behavior is explained in terms of the higher amount of the active oxidation state (Fe 3+ ) on the catalyst surface. These catalysts also result more active and selective than α-Fe 2 O 3 (hematite) and are less toxic than the chromium-containing commercial catalysts used for this purpose.

Preparation and characterization of iron catalysts precursors on different supports

Abstract Oxide precursors of iron catalysts to be used in the Fischer-Tropsch reaction were prepared on three different supports: MgO, SiO 2 , and Al 2 O 3 and characterized by means of X-ray diffraction (XRD), temperature programmed reduction (TPR), Mossbauer spectroscopy and diffuse reflectance spectroscopy (DRS). This technique proved to be particularly sensitive to detect the modification of the electronic structure of the cation induced by the interaction with the support. The presence of ionic Fe exchange with the support was determined in the case of the silica support. On the other supports, only the presence of α-Fe 2 O 3 was observed. The use of these techniques makes it possible to perform a comparative estimation of the size of the supported oxide crystallites on the different supports. The size of these crystallites has been found to be related to the different thermal pretreatment and to the nature of the support.

Fischer-tropsch synthesis on Pd-Co/Nb2O5 catalysts

Publisher Summary Cobalt-based catalysts have been widely used in the CO + H 2 reaction for hydrocarbons production; they are among several others to produce hydrocarbons from CO hydrogenation because of their ability to hydrogenate dissociated carbon species and promote chain growth. Cobalt is a typical metal that may adsorb CO molecules dissociatively forming carbon atoms at the surface, which may be hydrogenated, and it is an appropriate catalyst for the formation of long-chain hydrocarbons. However, the main problem of the Fischer–Tropsch synthesis (FTS) is the wide range of product distribution when conventional Fischer–Tropsch catalysts are being used. To overcome the selectivity limitations and enhance the catalyst efficiency in CO hydrogenation, several approaches have been studied such as the use of reducible supports and the addition of a second metal component. This chapter investigates the performance of the bimetallic Pd-Co/niobia systems in CO hydrogenation reaction to explain the effect of a second metal on the product selectivity of Co-based catalysts compared to the Co/Nb 2 O 5 systems.

24-P-11-Zeolite-L as support of Fe microcrystals for the Fischer-tropsch synthesis

Publisher Summary This chapter discusses zeolite-L as support of iron (Fe) microcrystals for the Fischer–Tropsch synthesis. Zeolite-L in potassic form is used as support of iron species to be used as catalyst in the Fischer–Tropsch reaction. The oxide precursor is reduced using two different programs. Thermal programmed reduction (TPR), X-Ray Diffraction (XRD), Specific Surface area (BET), In situ Mossbauer Spectroscopy (MS) between room temperature and 15K, H 2 chemisorption, and Volumetric Oxidation (VO) were used to characterize the solids. Using a slow reduction treatment, it was possible to maintain a high quantity of Fe 0 microcrystals inside the pore structure, leading to a higher activity to low molecular weight paraffin.

Mössbauer cell for low-temperature studies of catalysts under reaction conditions

Mössbauer spectroscopy is an essential tool to investigate the structure of Fe supported catalysts and their changes, when they are used in the Fischer-Tropsch synthesis. A cell, that allows keeping the samples in the same atmosphere of the reduction treatment, was designed in order to characterize the Fe species without changing the working atmosphere avoiding the oxidation. It allows to measure at low temperatures in a helium closed-cycle refrigerator. Besides, this cell is useful to perform Mössbauer measurements on the used catalysts, preserving the oxidation of its species, using an inert atmosphere. In this work, we describe the details of this new cell and, as an example of its utility, we present the results obtained with a system of 12 nm iron oxide nanoparticles supported on a mesoporous silica matrix.

Effect of the preparation method on the properties of hematite-based catalysts with lanthanum for styrene production

Abstract The influence of the preparation method on the properties of lanthanum-doped hematite prepared with potassium carbonate was studied aiming to get catalysts for styrene production from ethylbenzene dehydrogenation. The most active catalyst was obtained by adding the reactants on water. This solid has the highest intrinsic activity, the highest resistance against reduction and the lowest conversion drop. These properties were related to the presence of potassium compounds on the surface and to the presence of Fe +3 species (active phase) stabilized in lanthanum oxide lattice.

Iron Uniform-Size Nanoparticles Dispersed on MCM-41 Used as Hydrocarbon Synthesis Catalyst

We have synthesized mesoporous MCM-41 and have used it as a support for iron particles to be employed as a catalyst in the Fischer-Tropsch reaction. The solids were characterized by Mossbauer spectroscopy, X-ray diffraction, BET, TGA, CO chemisorption and volumetric oxidation. Although the catalyst showed a high CO conversion when it was used in the hydrocarbon synthesis from CO and H2 (14.3% at 1 h of reaction time) mainly methane was formed. The high methane production is likely related to the very small size of the metal particles obtained. We suggest some ways to improve the selectivity.

13-P-14-A comparative study of Ti4+ sites in titanium silicalite (TS-1) synthetized by different methods

Publisher Summary This chapter presents a comparative study of titanium (Ti) 4+ sites in titanium silicalite (TS-I) synthetized by different methods. Three TS-1 zeolites are prepared by three different methods. Infrared (IR), scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS) are used to determine that all of the zeolites are well manufactured. The joint use of probe molecules (hydrogen peroxide and benzene) and DRS helps to detect differences in the population of the named “closed” and “open” Ti 4+ sites and in their geometries in the three zeolites. These differences lead to distinct catalytic behavior when these solids are tested in the oxidation of benzene with hydrogen peroxide.