S. Gőbölös

Preparation of alumina supported tin-platinum catalysts by reaction of tin tetraethyl with hydrogen adsorbed on platinum. Study of the formation and decomposition of the primary surface complex

In this work surface reactions involved in the preparation of alumina supported tin-platinum catalysts with metal-metal interaction were studied. The preparation of these catalysts is based on surface reaction between tin tetra-alkyls and hydrogen adsorbed on platinum. In the above reaction a Primary Surface Complex (PSC (I)) is formed, which has a twodimensional layer of -SnR3 moieties at the platinum surface. PSC (I) can be decomposed in hydrogen atmosphere with formation of bimetallic surface entities. The fate of the PSC (I) strongly depended on (i) the presence or absence of gas phase hydrogen, (ii) the dispersion of platinum, (iii) the time interval between its formation and decomposition. In addition to the main reactions involved in this preparation side reactions with partial dehydrogenation of the alkyl groups of the -SnR3 moieties were also evidenced. Upon using this approach to prepare tailor made supported bimetallic catalysts these side reactions should be avoided as they are responsible for the formation of surface carbon on the platinum sites.

Ruthenium molybdenum sulphide catalysts : physicochemical characterization and catalytic properties in HDS, hydrogenation and HDN reactions

Alumina supported RuMo sulphide catalysts having different weights of metal content and atomic composition ratios r=Ru/(Ru+Mo) were prepared by using ammonium heptamolybdate dissolved in water or a 10% (NH4)2S-H2O solution and RuCl3.3H2O as precursor compounds. Their activities were studied in the hydrodesulphurization (HDS) of thiophene and in the hydrogenation (HYD) of biphenyl, and optimized in terms of the preparation method and the sulphidation process. Some hydrodenitrogenation (HDN) tests were also performed on these catalysts. Electron microscopy and XPS measurements were performed, and the nature of the active phase was discussed.

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.

Role of rhenium in bimetallic reforming catalysts

The influence of rhenium on the behavior of a Pt/Al2O3 catalyst was studied in n-hexane reaction by means of dilution of the catalyst bed with Re/Al2O3. Parallel to activity, selectivity and ageing data obtained in slug pulse and continuous flow reactors, the amount of the surface carbon formed during the reaction was determined and its reactivity in hydrogen atmosphere was also studied. It is suggested that in the presence of rhenium due to the increase in the amount of hydrogen available for hydrogen consuming reactions including hydrodepolymerization of the carbonaceous surface overlayer, the routes of ageing processes are changed, resulting in lower carbon content on the catalyst and less pronounced catalyst deactivation.AbstractВлияние рения на поведение катализатора Pt/Al2O3 было исследовано в реакции н-гексана, с помощью разбавления катализаторной подложки Re/Al2O3. Параллельно с данными активности, селективности и старения в импульсном реакторе и в реакторе с проточной струей, было определено количество поверхностного углерода, образующегося в реакции, атакже его реактивность в атмосфере водорода. Полагается, гто в присутствии рения, вследствие увеличения количества водорода, доступного для реакций, потредляющих водород, включая реакцию гидродеполимерцзации углистой поверхности верхнего слоя, изменяются пути процессов старения, приводящих к пониженному содерзанию углерода на катализаторе и менее выраженной дезактивации катализатора.

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.

Qualitative determination of the efficiency of re-reduction in supported platinum catalysts. Development of a new method

Abstract A simple test reaction has been developed for the qualitative determination of the efficiency of platinum re-reduction or to show the presence of adsorbed oxygen on supported Pt catalysts. The method is based on the surface reaction taking place between tin tetraethyl and unreduced platinum or adsorbed oxygen. The formation of ethylene in the above reaction indicates that supported platinum catalyst contains either unreduced platinum or adsorbed oxygen.

Comparison of the catalytic properties of Pt/Al2O3 and bimetallic Pd-Pt/Al2O3 catalysts in n-hexane dehydrocyclization in a continuous-flow reactor

Activity and selectivity data obtained in n-hexane dehydrocyclization over Pt/Al2O3 and Pd−Pt/Al2O3 catalysts exposed to different thermal treatment processes are compared. The ageing phenomena were most pronounced on catalysts treated in hydrogen at higher temperatures. The Pd−Pt/Al2O3 catalyst possessed lower cracking activity with a parallel increase of the selectivity for benzene and iso-hexanes.AbstractСравниваются данные активности и селективности, полученные при исследовании реакции дигидроцклизации н-гексана на катализаторах Pt/Al2O3 и Pd−Pt/Al2O3, подвергнутых различной термической обработке. Явления старения наиболее явно проявлялись на катализаторах, обработанных водородом при высокой температуре. Катализатор Pd−Pt/Al2O3 обладает пониженной активностью крекинга с параллельным повьпцением селективности к бензолу и изогексанам.

n-Pentane isomerization in a continuous-flow reactor on Pt/Al2O3 catalysts modified by adsorbed bismuth and palladium

Isomerization of n-pentane has been studied in a continuous-flow reactor at atmospheric pressure on Pt/Al2O3 catalysts modified by adsorbed bismuth and palladium. Lower activity and higher selectivity have been obtained on a catalyst modified by bismuth. Both activity and selectivity have decreased on a catalyst modified by palladium. After oxygen treatment the Pd−Pt/Al2O3 catalyst showed the most pronounced change in catalytic properties and its stability was lower than that of the unmodified Pt/Al2O3 catalyst.AbstractИзомеризация н-пентана была исследована в реакторе непрерывного потока, при атмосферном давлении и на катализаторе Pt/Al2O3, модифицированном адсорбированным висмутом и палладием. Пониженная активность и повышенная селективность наблюдались для катализатора, модифицированного висмутом. Как активность, так и селективность уменьшались в случае катализатора, модифицированного палладием. После обработки кислородом самые значительные изменения в каталических свойствах наблюдались для катализатора Pd−Pt/Al2O3 и его стабильность была меньше, чем для немодифицированного катализатора Pt/Al2O3.

Reforming type Pt/Al2O3 catalyst prepared from [(CH3)3PtX]4 complexes by thermal decomposition

Pt/Al2O3 catalysts with good reforming activity were prepared from [(CH3)3PtX]4 (X=Cl, Br, I) complexes and tested in pulse and continuous-flow reactors in n-hexane dehydrocyclization. It has been demonstrated that [(CH3)3PtX]4 complexes are excellent precursors of supported platinum catalysts.AbstractКатализаторы Pt/Al2O3 с хорошей активностью в риформинге были приготовлены из комплексов [(CH3)3 PtX]4 (X=Cl, Br, I) и испытаны в импульсных и проточных реакторах на примере дегидроциклизации н-гексана. Было продемонстрировано, что комплексы [(CH3)3PtX]4 являются превосходными предшественниками платиновых катализаторов на носителях.