Mónica L. Casella

Hydrogenation of crotonaldehyde on Pt/SiO2 catalysts modified with tin added via surface organometallic chemistry on metals techniques

The importance of the preparation procedure and the understanding of the mechanisms that control this stage on the final properties of the catalyst are evidenced for PtSn systems obtained via surface organometallic chemistry on metals (SOMC/M) techniques. The temperature of preparation reaction also plays a fundamental role as regards the nature of the active phase finally obtained, giving rise to catalytic phases having different levels of selectivity to unsaturated alcohols (UOL) in the crotonaldehyde hydrogenation. Organobimetallic catalysts lead to very high selectivities to crotyl alcohol (80% at 5% conversion).

Hydrogenation of carbonyl compounds using tin-modified platinum-based catalysts prepared via surface organometallic chemistry on metals (SOMC/M)

Abstract The catalytic behaviour of some compounds containing Cue605O and/or Cue605C bonds has been studied over silica-supported platinum-based catalysts, modified with tin. Tin was introduced by means of surface organometallic chemistry on metals (SOMC/M) techniques. The effect of the obtention conditions upon the catalytic performance was evidenced through the study of three systems having the same Sn/Pt atomic ratio (0.4), but prepared and activated at different temperature. In the hydrogenation of butyraldehyde and butanone, the adsorption of the η1-(O) type appears as highly favourable, both from a geometric and electronic point of view. In the benzaldehyde hydrogenation, the increase in the catalytic activity for PtSn-OM and PtSn-BM systems is quite more important than in the PtSn-OM∗ system, fundamentally by electronic effects associated with the presence of ionic tin and of the phenyl group. In the case of the cyclohexene, geometric and electronic, as well as steric effects lead to a strong reduction of the hydrogenation rate of Cue605C bond. These results can be extrapolated to explain the behaviour of the unsaturated α,β-aldehydes. The hydrogenation of the Cue605O group is promoted and the adsorption modes favourable to the Cue605C hydrogenation are inhibited by tin. The combination of both effects leads to the sequence of selectivity to UOL: Pt⪡PtSn- OM ∗ PtSn -BM

Transition metal-based bimetallic catalysts for the chemoselective hydrogenation of furfuraldehyde

In this work, the liquid-phase chemoselective hydrogenation of furfural was studied, employing Pt, Rh and Ni-based catalysts. Bimetallic systems, containing different amounts of tin, were obtained by means of controlled surface reactions between a monometallic catalyst and Sn(C4H9)4. The results obtained when monometallic catalysts were employed suggest a relationship between metal properties and the activity and selectivity obtained. All systems allowed obtaining furfuryl alcohol with high selectivity (99, 97 and 76% were achieved with Pt, Rh and Ni catalysts, respectively). The addition of tin has different effects on the three systems, both in terms of conversion and selectivity. An interesting result was obtained for the Ni-based catalysts, for which the addition of tin led to a significant increase in furfuryl alcohol selectivity and, depending on the Sn/Ni ratio, also to an increase in the catalytic activity of the system.

Stability promotion of Ni/α-Al2O3 catalysts by tin added via surface organometallic chemistry on metals: Application in methane reforming processes

Abstract This paper reports the effect of selective tin addition to nickel catalysts via a controlled technique (surface organometallic chemistry on metals, SOMC/M), and the performance of the resulting systems in methane reforming processes: partial oxidation (POM), CO 2 reforming (R) and mixed (CO 2 +O 2 ) reforming (MR), with particular emphasis on their resistance to coke formation. It is demonstrated that SOMC/M techniques allow to obtain well-defined bimetallic phases in a controlled way. It is found that there is a range of tin concentrations (0.01–0.05xa0wt.%) for which the stability of the bimetallic catalysts is markedly enhanced with respect to nickel catalyst, without affecting either the activity level or the selectivity to syngas. These facts are explained in terms of a more demanding nature in size of the active sites needed for carbon formation reaction, when compared to methane activation reaction to synthesis gas.

Partial oxidation of methane to synthesis gas. Behaviour of different Ni supported catalysts

The behaviour of Ni supported catalysts, obtained using Ni(NO3)2 and Ni-acetylacetonate as precursor compounds, is analyzed. It is observed that initial activities and selectivities are similar for both systems, but the stability differs significantly. The systems show different carbon structures and sintering rates, depending on the precursor compound employed.

Characterization and performance for propane oxidative dehydrogenation of Li-modified MoO3/Al2O3 catalysts

Abstract Oxidative dehydrogenation of propane has been studied on Mo/γ-Al 2 O 3 catalysts with 13xa0wt.% of MoO 3 and promoted with Li. The changes induced on catalysts when the support is doped with different amounts of Li (from 0.3 to 1.2xa0wt.%) have been studied by BET, AAS, XRD, SEM-EDAX, TPR, DRS, XPS, Raman spectroscopy and isopropanol decomposition. The characterization of the samples showed important changes in: texture, Mo supported structure, acid–base properties and reducibility. The Li replaces Bronsted acid sites and decreases the strength of the terminal Moue605O bond. The change in the strength of the terminal Moue605O bond does not correlate with the decrease in Mo species reducibility or with the decrease in propane conversion. This behavior suggests that the terminal Moue605O bond is not the active sites for ODH of propane. The selectivity to propene increases at lower conversion whereas at higher values it leveled off around 25%.

Effect of particle size in the hydrogenation of crotonaldehyde on supported Pt and Pt-Sn catalysts

The present work reports the effect of metal particle size on the selectivity to crotyl alcohol (SUOL) in the liquid phase hydrogenation of crotonaldehyde over SiO2 and a-Al2O3-supported Pt and Pt-Sn catalysts. It was demonstrated that, for the monometallic catalysts, a higher particle size led to a higher SUOL, while for the bimetallic catalysts, this effect was not so important.

Bimetallic PtSn/C catalysts obtained via SOMC/M for glycerol steam reforming

A detailed study on the preparation of bimetallic PtSn/C catalysts using surface-controlled synthesis methods, and on their catalytic performance in the glycerol steam reforming reaction has been carried out. In order to obtain these well-defined bimetallic phases, techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) were used. The preparation process involved the reaction between an organometallic compound ((C4H9)4Sn) and a supported transition metal (Pt) in a H2 atmosphere. Catalysts with Sn/Pt atomic ratios of 0.2, 0.3, 0.5, and 0.7 were obtained, and characterized using several techniques: ICP, H2 chemisorption, TEM and XPS. These systems were tested in the glycerol steam reforming varying the reaction conditions (glycerol concentration and reaction temperature). The best performance was observed for the catalysts with the lowest tin contents (PtSn0.2/C and PtSn0.3/C). It was observed that the presence of tin increased the catalysts stability when working under more severe reaction conditions.

Hydrogenation of carbonylic compounds on Pt/SiO2 catalysts modified with SnBu4

Silica supported bimetallic and organobimetallic PtSn catalysts were prepared by Surface Organometallic Chemistry on Metals and tested in the hydrogenation of different carbonylic compounds (butanal, butanone, cyclohexanone, benzaldehyde, crotonaldehyde and cinnamaldehyde). It was studied the influence of the Sn/Pt atomic ratio on the hydrogenation of cinnamaldehyde, having been found an optimum of approximately 0.4. The selective hydrogenation of C=O group in polyfunctional molecules can be explained on the basis of the combination of geometric (specially in organobimetallic catalysts), and electronic effects due to the presence of ionic tin.

Study of different support and precursor compounds for supported nickel oxyreforming catalysts

Preparation and characterization of different nickel catalysts for the oxyreforming reaction was studied in this work. The catalysts were prepared by impregnating two different precursor compounds (nickel nitrate and nickel acetylacetonate) into α-Al2O3 and α-Al2O3 modified by a layer of aluminium oxide. This modification led to an increment in the dispersion of the active phase and to a more active catalyst.