S. Göbölös

New approaches to prepare supported Sn-Pt bimetallic catalysts

General principles of modification of supported Pt catalysts with tin tetraalkyls are summarized and a new approach to prepare supported Sn−Pt catalysts is described. The new approach leads to the formation of Multilayered Organometallic Complexes (MLOC) anchored onto supported platinum. The formed MLOC can be decomposed either in reductive or oxidative atmosphere with the formation of new type of supported Sn−Pt catalysts with high Sn/Pts ratios. The decomposition in a reductive atmosphere leads to the formation of alloy-type bimetallic phases, while the decomposition in the presence of oxygen provides Lewis-acid type surface species anchored to supported platinum.

Hydrogenation of benzonitrile on Sn-Pt/SiO2 Catalysts prepared by introducing SnEt4 to Pt/SiO2: Role of TIN

Liquid phase hydrogenation of benzonitrile was studied over Sn-Pt/SiO2 catalysts prepared by introducing tetraethyl tin onto the 3 wt.% Pt/SiO2 catalyst. Tin content of the catalysts ranged from 0.05 to 0.63 wt.%, whereas Sn/Pt surface atomic ratios determined by chemisorption measurements were between 0.1 to 3.5. Dibenzylamine selectivity influenced to a small extent by the level of conversion and the Sn/Pt ratio wasca. 75 %. The addition of tin to Pt in the range of (Sn/Pt)surface = 0.50–1.25 led to an increase in the turnover frequency (TOF) by a factor of 2. TOF showed a maximum at a surface atomic ratio of Sn/Pt = 1. The enhancement of catalyst activity upon the addition of tin is explained by the formation of Snδ+-Pt ensemble sites on the surface of bimetallic nanoclusters. It is suggested that highly dispersed positively charged tin species, by polarizing the triple bond, enhance the reactivity of the -CN group. Calcination at 300°C followed by re-reduction of the catalysts resulted in a monotonic decrease of specific activity with increasing Sn/Pt ratio.

Correlation between the amount of ionic copper and the activity of Cu–ZnO–Al2O3 catalyst in the alkylation of n-butylamine with methanol

Abstract The alkylation of n -butylamine with methanol was investigated over Cu–ZnO–Al 2 O 3 catalyst. Correlation has been found between the activity of the catalyst and the content of ionic copper in the catalyst. Based on this correlation, it has been suggested that in this reaction ionic copper species are involved in the rate-determining step, i.e. in the dehydrogenation of methanol into an aldehyde intermediate.

Modification of NI/Al2O3 Hydrogenation Catalysts with Lead by Using controlled surface reactions

Abstract In the present work alumina supported nickel catalysts modified by lead were used for the selective hydrogenation of acrylonitrile to propionitrile. The unmodified nickel catalyst was not selective in this reaction. The modification of the Ni/Al 2 O 3 catalyst, i.e. the preparation of Pb-Ni/A1 2 O 3 catalysts was carried out by using Controlled Surface Reactions (CSRs). CSRs applied in this work are based on the reactivity of hydrogen adsorbed on the nickel. This hydrogen reacts selectively with tetraethyl lead resulting in bimetallic surface entities. Experimental results obtained both in the surface reactions Involved in the modification of the catalyst and in the study of selective hydrogenation of acrylonitrile strongly indicate that catalyst modification via CSRs is a powerful tool to design selective hydrogenation catalysts.

Controlled Surface Reactions for the Preparation of Different Types of Alumina Supported Sn-Pt Catalysts

Different types of SnPt/Al 2 O 3 catalysts were prepared in wich the oxidation state (ionic or metallic) and the environment (platinum or support) of the corresponding forms of tin were controlled by using different types of Controlled Surface Reactions (CSRs). These catalysts were studied in n-hexane conversion. By using these catalysts additional new evidences were obtained with respect to (i) the mode and ways of control the selectivity of Pt/Al 2 O 3 catalysts, (ii) the alterations of the reaction routes in hydrocarbon conversions and (iii) the role of tin in reforming catalysts.

Long Term and Short Term Deactivation on Pt/Al2O3 and Sn-Pt/Al2O3 Catalysts in n-Hexane Conversion

Abstract Deactivation of Pt/Al 2 O 3 and different types of Sn-Pt/Al 2 O 3 catalysts in n-hexane conversion was studied at atmospheric pressure and low conversion. Two terms of deactivation, i. e. short term and long term, were distinguished. Both types of deactivation were very pronounced on catalysts, in which the acidic sites were not blocked by ionic forms of tin or lithium. It was demonstrated that the extent of deactivation in both terms can be different for different reaction products. On monofunctional Sn-Pt/Al 2 O 3 catalysts the selectivity of the benzene formation increased upon aging. Results obtained in this study are discussed in terms of a generalized reaction scheme, in which poisoning metallic and acidic sites and formation of a carbonaceous surface overlayer have their distinct contribution.

Preparation of new type of supported Sn-Pt bimetallic catalysts containing Lewis acid sites anchored to the platinum

Abstract Methods of Surface Organometallic Chemistry (SOC) were used to prepare new type of supported Sn-Pt catalysts. In the new approach the focus was laid on the stabilization of tin in the form of SnOxanchored directly to the platinum. The new surface species have been characterized by different methods. The results indicate the platinum nano-clusters are decorated by SnOx surface entities with Lewis-acid character. The new Sn-Pt/A12O3 catalysts were tested in hydrocarbon reactions above 500 °C. Due to the presence of new acid sites in the atomic closeness to the platinum the new Sn-Pt catalysts showed decreased aromatization and increased isomerization selectivities.

Bimetallic Supported Catalysts Prepared Via Metal Adsorption. Preparation And Catalytic Activity Of Pd-Pt/Al2O3 Catalysts

Alumina supported Pd-Pt bimetallic catalysts prepared by electrochemical metal adsorption via ionization of adsorbed hydrogen. The palladium content of the catalysts can be controlled by thermal treatment processes of the parent catalysts, as well as by applying subsequent adsorption steps. The Pd-Pt catalysts were tested in n-hexane dehydrocyclization. Their catalytic properties depend strongly on the thermal treatment processes applied before the reaction. Omission of oxygen treatment results in lower activities and lower selectivities for benzene formation.

Reductive transamination of methoxyacetone with benzylamine over Pd/SiO2 catalyst modified with anchored chiral compounds

Methoxyacetone was transaminated with benzylamine to methoxyisopropylamine over a Pd/SiO2 catalyst modified with L‐alaninol or L‐phenylalaninol covalently anchored to the surface of the support via an organo‐silicon spacer group. In the first step of transamination a Schiff base was formed from the ketone and benzylamine, and then it was hydrogenated in the second step on the chirally modified Pd/SiO2 catalysts to an asymmetric secondary amine (N‐benzyl‐methoxyisopropylamine). In the third step the hydrogenolysis of the asymmetric secondary amine resulting in methoxyisopropylamine and toluene was carried out over a 10 wt% Pd/C catalyst. The highest enantiomeric excess of (S)‐methoxyisopropylamine was observed in cyclohexane (ee = −20–21%) using anchored L‐alaninol as a chiral modifier.

Condensation of allyl alcohol with ammonia over phosphoric acid catalyst supported on controlled pore glass

Abstract The condensation of allyl alcohol with ammonia was studied over phosphoric acid catalyst supported on controlled pore glass (CPG). The above catalyst was compared with silica supported phosphoric acid. The CPG supported catalyst showed higher selectivity and lower rate of deactivation than the corresponding silica supported one. The above difference can be attributed to both the boron content and the large pore size of the CPG support.