Guillermo J. Siri

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).

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.

Improvements in selectivity and stability of Rh catalysts modified by SnBu4. dehydrogenation of isobutane to isobutene

RhSn/SiO2 bimetallic catalysts prepared via an organometallic route have proved to be very active and selective toward several hydrogenation reactions. In this work these catalysts were studied for the dehydrogenation of isobutane to isobutene. It was found that Rh/SiO2 monometallic catalysts had a null selectivity to isobutene, and this selectivity increased up to more than 90% after the addition of tin, using SnBu4 as precursor.

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.

Sulfur Poisoning of Mo-Promoted Ni Catalysts

Summary Poisoning of Ni-based and Mo-modified Ni catalysts was studied for CH4 reforming with CO2 at 923–993 K. Two types of poisoning were carried out:in situ (1–10 ppm H2S in the feed) and presulfiding in a batch system at very low concentrations of H2S (≪ 1 ppm). The Mo-modified systems have a significantly higher thioresistance. There is also the possibility of regeneration of poisoned phases depending upon the poisoning technique. These phenomena are ascribed to the formation of surface compounds which differ in their composition depending on pretreatment and promoter.

CO Preferential Oxidation with Cu/CeO 2 -Al 2 O 3 and CuPt/CeO 2 -Al 2 O 3 Catalysts

Fil: Nunez, Natalia Elena. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico la Plata. Centro de Investigacion y Desarrollo En Ciencias Aplicadas; Argentina. Universidad Nacional de La Plata. Facultad de Ingenieria; Argentina

Use of Rh (III)-Heteropolymolybdate as Potential Catalysts for the Removal of Nitrates in Human Drinking Water: Synthesis, Characterisation and Catalytic Performance

The investigation and development of technologies to remediate water contaminated with NO3− are constantly increasing. An economically and potentially effective alternative is based on the catalytic hydrogenation of NO3− to N2. With this objective, bimetallic RhMo6 catalysts based on Anderson-type heteropolyanion (RhMo6O24H6)3− were prepared and characteri3ed in order to obtain well-defined bimetallic catalyst. The catalysts were supported on Al2O3 with different textural properties and on silica. The heteropolyanion-support interaction was analysed by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The differences obtained in activity and selectivity to the different products can be assigned to the different interaction between the RhMo6 Anderson phase and the supports. The RhMo6/G, (G: γ-Al2O3) system showed the best catalytic performance. This catalyst exhibited the lowest reduction temperature of Rh and Mo in the TPR assay and a Rh/Mo surface ratio similar to that of the original phase, as observed by XPS analysis. These studies allowed us to verify a synergic effect between Rh and Mo, through which Mo reducibility was promoted by the presence of the noble metal. The catalytic activity was favoured by the active sites generated from the Anderson phase. This fact was confirmed by comparing the activity of RhMo6/G with that corresponding to a conventional catalyst prepared through successive impregnation of both Rh (III) and Mo (VI) salts.

Pb促进的Pd/γ-Al 2 O 3 催化剂上H 2 O 2 氧化甘油反应

Abstract A series of bimetallic Pd-Pb catalysts with a constant Pd content of 1 wt% and Pb/Pd atomic ratio from 0 to 1.6 supported on Γ-Al 2 O 3 were prepared and used for glycerol oxidation with H 2 O 2 as the oxidizing agent at atmospheric pressure, 45 °C and pH = 11. The morphology and dispersion of the catalysts were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and transmission electron microscopy (TEM). The presence of an alloy phase in the bimetallic catalyst was detected by X-ray photoelectron spectroscopy (XPS). Glycerol conversion obtained with the monometallic Pd catalyst was 19%, which was increased to 100% with the addition of Pb. The four bimetallic PdPb catalysts were able to oxidize glycerol to dihydroxyacetone (DIHA) and the selectivity to DIHA reached 59%, 58%, 34% and 25% for PdPb0.25, PdPb0.50, PdPb1.00 and PdPb1.60 catalysts, respectively.

ArticleOxidation of glycerol with H2O2 on Pb-promoted Pd/Γ-Al2O3 catalysts

Abstract A series of bimetallic Pd-Pb catalysts with a constant Pd content of 1 wt% and Pb/Pd atomic ratio from 0 to 1.6 supported on Γ-Al 2 O 3 were prepared and used for glycerol oxidation with H 2 O 2 as the oxidizing agent at atmospheric pressure, 45 °C and pH = 11. The morphology and dispersion of the catalysts were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and transmission electron microscopy (TEM). The presence of an alloy phase in the bimetallic catalyst was detected by X-ray photoelectron spectroscopy (XPS). Glycerol conversion obtained with the monometallic Pd catalyst was 19%, which was increased to 100% with the addition of Pb. The four bimetallic PdPb catalysts were able to oxidize glycerol to dihydroxyacetone (DIHA) and the selectivity to DIHA reached 59%, 58%, 34% and 25% for PdPb0.25, PdPb0.50, PdPb1.00 and PdPb1.60 catalysts, respectively.