Mihály Hegedűs

Preparation of new type of Sn-Pt/SiO2 catalysts for carbonyl activation

Abstract The paper is aimed to demonstrate how the activity and selectivity of a Pt/SiO2 catalyst can be tailored by introduction of tin either to hydrogenate the aldehyde group in α,β-unsaturated aldehydes (UA) or oxidize carbon monoxide at room temperature. In this paper general aspects of catalyst design based on the use of tin tetraalkyls are described in detail. Results summarized in this work show that upon using new approaches for anchoring tin into platinum high Snanch/Pts can be achieved. The experimental evidences indicate also that the hydrogenation of the aldehyde group in α,β-unsaturated aldehydes and oxidation of CO requires in situ formed “Sn4+–Pt ensemble” sites to activate either the carbonyl group or the CO molecule.

Low temperature oxidation of CO over tin-modified Pt/SiO2 catalysts

Abstract Low temperature oxidation of CO over alloy type Sn–Pt/SiO 2 catalysts with different Sn/Pt ratios has been investigated at different CO partial pressure using thermal programmed oxidation (TPO) technique and time on stream (TOS) experiments. The introduction of tin into platinum strongly increased the activity of the catalyst. The activity had a maximum, which depended on both the Sn/Pt (at./at.) ratio and the CO partial pressure. TOS experiments revealed the aging of the Sn–Pt/SiO 2 catalysts. FTIR and Mossbauer spectroscopy has been used to follow compositional and structural changes of Sn–Pt/SiO 2 catalysts during the catalytic run. The results show that the in situ formed, highly mobile “Sn n + –Pt” ensemble sites are responsible for high activity, while formation of relatively stable SnO x type surface species are involved in the catalyst deactivation.

Zeolite supported Sn-Pt catalysts prepared by surface reactions

Abstract A Pt/H–mordenite (Pt/H–MOR) catalyst has been modified with tin using the controlled surface reaction between tin tetraalklyls and hydrogen adsorbed on platinum. Experimental evidences show that upon modification of Pt/H-MOR catalyst with tin tetraalkyls, the surface chemistry established for Pt/SiO 2 and Pt/Al 2 O 3 cannot be maintained, i.e., the formation of multilayered organometallic complexes (MLOC) is hindered. Consequently, the results indicate that the introduction of tin into platinum is possible if the Sn/Pt s ratio is below 0.5. In this case, zeolite supported alloy type Sn–Pt nanoparticles are formed. At higher Sn/Pt s ratios, in addition to the formation of alloy type Sn–Pt nanoparticles, ionic forms of tin anchored onto the zeolite are also formed. The reaction between tin tetraalkyls and surface OH groups of the zeolite is involved in the formation of ionic forms of tin stabilized on the zeolite surface. Upon applying Mossbauer spectroscopy, different tin containing surface species were identified including two SnPt alloy phases. Tin introduced in this way slightly decreases the H/Pt and CO/Pt ratios measured by chemisorption and changes the activity and selectivity of these catalysts in n -hexane isomerization at 275°C.

Investigation of toluene formation on Pt/Al2O3 catalyst in n-hexane dehydrocyclization

Formation of toluene, a chain lengthening product, has been observed on Pt/Al2O3 catalyst in n-hexane dehydrocyclization. Toluene formation is influenced by the catalyst pretreatment processes and the reaction temperature. A correlation has been found between the ageing phenomena and toluene formation.AbstractВ реакции дегидроциклизации н-гексана на катадизаторе Pt/Al2O3 наблюдалось образование толуола — продукта с удлиненной цепью. На образование толуола влияет предварительная обработка катализатора и температура реакции. Была найдена корреляция между явлением старения и образованием толуола.

Investigation of n-hexane dehydrocyclization over supported Pt catalyst modified by adsorbed rhenium

A γ-Al2O3 supported Pd−Pt bimetallic catalyst prepared by electrochemical metal adsorption has been tested in n-hexane dehydrocyclization. The Pd−Pt/Al2O3 catalyst, after calcination in oxygen followed by hydrogen treatment, showed higher activities and better selectivities for benzene and iso-hexane formation. The Pd−Pt/Al2O3 catalyst appeared to be less sensitive to the changes in the temperature of hydrogen treatment than the base Pt/Al2O3 catalyst.AbstractБиметаллический катализатор Re−Pt, нанесенный на γ-Al2O3, был приготовлен электрохнмической адсорбцией. С помощью импульного метода было нсследовано его поведение в реакции дегидроциклизации н-гексана. Активность катализатора, Re−Pt/Al2O3, обработанного только в водороде, была низкой, но значитедьно повышается, применяя ступень обжига перед обработкой водородом. Модифицированный катализаиор обладает более высокой активностью и повышенной селективностью к бензолу и изогексанам, чем основной катализатор Pt/Al2O3.

TPD studies of hydrogen sorption on platinum powder catalysts modified with adsorbed gold

It has been shown that hydrogen determined from the TPD curves of platinum saturated with hydrogen sorbed above room temperature is chiefly absorbed and not adsorbed hydrogen; this absorbed hydrogen has no effect on the charging curve.AbstractНа основании измерений кривых термодесорбции сорбированного на платине водорода показано, что водород, главным образом, абсорбируется, а не адсорбируется; этот абсорбированный водород не оказывает влияния на ход кривых заряжения.

Control of the Particle Size of Gold on Tin Modified Silica Support

In this study we describe a two-step synthesis method for the preparation of gold nanoparticles supported on tin modified silica. The key step of the preparation procedure is the formation of surface grafted organotin complexes. The reduction of these surface species in a hydrogen atmosphere resulted in both metallic (Sno) and ionic (Sn2+) forms of tin. These forms of tin are capable to reduce gold from chloroauric acid solution forming gold nanoparticles with high dispersion on the surface of silica. It has been found that the particle size of gold strongly depends on the pH value of the gold solution and the presence or absence of ammonia.