Daniel E. Damiani

Preparation and characterization of γ-Al2O3-supported PdMo catalysts

Abstract The preparation of PdMo catalysts supported on γ-Al2O3 by co-impregnation of cationic Pd complexes and anionic Mo species using the incipient wetness method was investigated. The bimetallic catalysts as well as the corresponding monometallic ones were characterized by means of conventional techniques like H2 chemisorption, Temperature programmed reduction (TPR), X-ray diffraction combined with tests of metal precursors elimination and activity in CH4 combustion. The results indicate that Pd Mo interaction is obtained as reflected by chemisorption and TPR. Although low loading of Mo are used, some loss of Mo occurs in preparation. A promotional effect of Mo and of the exposure of the catalyst to the reaction mixture was observed while the presence of Pd and PdO was detected in spent catalysts as reported by others.

Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene

Abstract This paper studies MgCl 2 /internal donor/TiCl 4 //external donor/AlEt 3 catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl 2 /internal Donor/TiCl 4 //external donor/AlEt 3 when TMPiP is the external and internal donor. In this case the insoluble fraction in n -heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts.

Theoretical and Spectroscopic UV Study of the EtInd2ZrCl2/MAO, EtInd2ZrCl2/MAO-AlCl3 and EtInd2ZrCl2/MAO-Ethyl Benzoate Interaction

This work presents a theoretical and experimental study of the active sites formation in the system EtInd 2 ZrCl 2 /MAO. Results about the effect of additives as a Lewis acid (AlCl 3 ) or a Lewis base (EB) are also analyzed. The theoretical study takes into account all the known steps in the active site formation: alkylation of zirconocene, formation of a polarized complex metallocene: MAO, formation of a contact ion pair and finally a solvent separated ion pair. Other reactions of the zirconocene with other aluminium alyls (AlCl 3 and AlMe 3 ) are also presented and studied. UV-vis experimental results of the additive effects are reported and explained taking into account the theoretical results. A short review of our results and others is presented to complete and discuss the ideas. The most probable sites are loosened contact ion pairs, not the solvent separated ion pairs.

Addition of Lewis bases and acids. Effect on α-olefins polymerization with soluble metallocenes, 1. Ethylene

In this paper the soluble system rac-Etnd 2 -ZrCl 2 /methylaluminoxane (MAO) was studied in propylene polymerization with additives. Lewis acid and base such as AlCl 3 and ethyl benzoate (EB) were used to evaluate their effects on polymerization kinetics, catalyst activities and polymer properties. The results obtained show a trend to improve the performance when AlCl 3 is added. The activity is decreased with EB, but the effect it not as strong a for ethylene (see Part 1). To further elucidate some of the different aspects of metallocene activation and reactivation in the reaction media, several reactions were carried out using different preactivation steps, with and without AlCl 3 . The preactivations were carried out taking account of the different results obtained with both additives (AlCl 3 and EB). The pretreatment with EB was not considered because the activity is decreased in the polymerization. AlCl 3 improves the activity when it is present during the preactivation step, but the presence of EB in the reactor during the polymerization step has a poisoning effect. These results show the importance of the preactivation step carried out without olefin. The molecular weight of polypropylene obtained remains almost unchanged in all the evaluated conditions. A complete discussion of ethylene and propylene results is included, taking account of Part 1 and 2.

Silica-supported metallocene for ethylene polymerization

Abstract We analyzed the effect of the addition of a Lewis acid (AlCl3) or a Lewis base (EB-ethyl benzoate) to the supported system rac-EtInd2ZrCl2/MAO/SiO2. We studied the additive effect in two different ways: as external and internal component. The results indicate that the additives are acting in different manners depending on the method of addition and the type of additive. An important result was obtained when the Lewis acid was added as an internal component. The molar ratio [MAO]:[AlCl3] of the co-impregnation step would be the most important factor to obtain an active supported catalyst.

A theoretical and experimental study about the effect of different organosilanes on immobilization of (nBuCp)2ZrCl2 on pre-treated SiO2

Abstract This work presents the results of theoretical and experimental characterization of supported ( n BuCp) 2 ZrCl 2 on organosilanes pre-treated SiO 2 . Several possibilities are analyzed and considered as an attempt to explain the observed zirconocene loadings, catalyst performance in ethylene polymerization and resulting polymer properties of these supported zirconocenes. The effect of silica pre-treatment with Ph 3 SiCl, Me 3 SiCl and Me 2 HSiCl on the immobilization of ( n BuCp) 2 ZrCl 2 was modeled. The main considered aspects were the role of the surface concentration of the organosilanes, the presence or absence of residual chlorine and the possibility of interactions between the organosilanes and the zirconocene. All these facts might afford different surface species at the impregnation step prior to the MAO activation during the polymerization reaction.

A combined theoretical and experimental study of the effects of residual chlorine on the behavior of Pd/γ-Al2O3 catalysts for methane oxidation

Abstract Studies of the methane oxidation on Pd/γ-Al 2 O 3 catalysts with and without chloride were made. The reaction was investigated at temperatures in the range 20–500°C using stoichiometric reactant mixture. Dissociation of methane and oxygen and desorption of carbon dioxide and water on Pd catalysts have been investigated using a Molecular Orbital approach of the Extended Huckel type, including repulsion terms.

Alumina-supported Ru-Mo Catalysts for the syngas reaction

Abstract Despite numerous reports on the activity and selectivity of modified Ru Catalysts for the synthesis of oxygenates from syngas, not many papers have appeared on their characterization. Several characterization techniques as well as activity and selectivity tests were used to evaluate an alumina-supported Ru-Mo Catalyst. The results are interpreted in terms of the existence of Ru-Mo contacts that are responsible for alcohols production and Cl − containing sites which affect the methanation activity. A molecular orbital method was applied to models of the surface with adsorbed modifiers on it. The results were compatible with the experimental data here reported.

NO decomposition on PdMo/γ-Al2O3 catalysts

Abstract Studies of the NO decomposition reaction on Pd/γ-Al2O3, Mo/γ-Al2O3 and PdMo/γ-Al2O3 catalysts were made. The catalytic tests revealed that the binary catalyst has different behavior for the NO decomposition, being the principal differences a longer steady state activity and an increase of oxygen evolution at elevated temperatures. Characterization by TPR, hydrogen chemisorption and FT–IR of CO indicated that palladium physicochemical properties are altered by an effective interaction with molybdenum. The results would suggest a decoration effect of Mo over Pd particle. This interaction appears to be responsible for the observed modification in NO activity and selectivity.

Effect of Co‐ and Non‐Copolymerizable Lewis Bases in Propylene Polymerization with EtInd2ZrCl2/MAO

This paper reports the effect of co- and non-copolymerizable Lewis bases in propylene polymerization with the soluble system EtInd 2 ZrCl 2 /MAO. With non-copolymerizable Lewis bases, the activity and the molar mass of poly(propylene) are diminished. This result is unusual because there is agreement about the cationic nature of the active site in Zirconocene/MAO systems and the effect of a Lewis base must be to decrease the termination constant versus the propagation constant, considering the diminished electrophilicity of Zr. In the case of copolymerizable Lewis bases, the negative effect on activity is higher. An explanation of the data is given, with a new model of Lewis bases/cationic. Zr interaction, taking account of recent reports about the structure of active sites.