Gerardo F. Santori

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

Aqueous phase hydrogenolysis of glycerol to bio-propylene glycol over Pt-Sn catalysts.

PtSn supported on SiO(2) obtained via surface organometallic chemistry techniques catalyzes hydrogenolysis of glycerol to obtain bio-propylene glycol (PG). Bimetallic catalysts with Sn contents between 0.1% and 1% wt were carefully prepared by selective hydrogenolysis of Sn(n-C(4)H(9))(4) on Pt. TEM, TPR, H(2) and CO chemisorptions, and XPS studies have shown that tin selective deposition on the metallic phase is obtained. At 200°C under N(2) or H(2) pressure, the presence of tin increases drastically: both the selectivity and the activity of the glycerol conversion into PG. During 2h batch runs; it could be observed that PtSn catalysts with Sn/Pt ratio=0.2 showed the best performance (PG selectivity=59% and 83% under N(2) and H(2) pressure respectively). The increase in activity and selectivity could be explained by the presence of Sn(+n) species acid Lewis sites which would facilitate the C-OH adsorption and its subsequent C-O cleavage favoring the propylene glycol production.

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.

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.

An organometallic approach for tin promotion enhancement over Pt/γ-Al2O3 alkane dehydrogenation catalysts

Pt catalysts supported on alumina and promoted by tin, were investigated. The dehydrogenation of isobutane was selected as test reaction. Tin was added using the Surface Organometallic Chemistry on Metals techniques and the atomic ratio Sn/Pt ranged from 0 to 1.6. Catalysts were characterized by FTIR of chemisorbed CO and NH 3 on reduced samples. The band of CO chemisorbed on Pt at 2074 cm − shifts to higher wavenumbers upon Sn incorporation indicating an electronic interaction Sn-Pt which weakens the Pt-CO bond. The modification introduced by the addition of tin in the distribution of Lewis and Bronsted acid sites, was put in evidence by FTIR spectra of adsorbed NH 3 , being Bronsted sites partially poisoned. The oxidation state of the metals after reduction was determined by XPS: Platinum is present as Pt 0 and tin is present both as Sn 0 and Sn n+ . The fraction of metallic tin decreases as the amount of promoter increases. The addition of Sn increases substantially the stability of the catalysts. Selectivities towards cracking and isomerization reactions diminish and dehydrogenation selectivity increases as the tin loading increases.