Heterogeneous Catalysis with Zeolites, Sulphides and Metals

Zeolitic materials with sufficiently narrow pores for shape-selective reactions are developed which do not suffer from the diffusional side effects of narrow pores, such as a high Thiele modulus, a low effectiveness factor, and pore blocking by side reactions. The diffusional limitations are remedied by the creation of mesopores through dealumination and desilylation of the zeolites by acids and complexing agents. The removal of nitrogen from N-containing aromatics takes place via a complex network of hydrogenation, hydrogenolysis and N-elimination reaction steps. To investigate the catalytic sites at which these steps take place, the kinetics of the hydrodenitrogenation of model compounds such as pyridine, piperidine, quinoline, decahydroquinoline and aniline is studied at elevated temperature and pressure in plug flow reactors. The mechanism of the formation of methanol from carbon monoxide and hydrogen at medium high pressure is studied in a plug flow reactor, as well as in a combination of a medium high pressure reactor with a surface science apparatus comprising X-ray photoelectron spectroscopy and secondary ion mass spectrometry. Experiments in plug flow equipment have shown that the methanol formation is only formed over Pd and Rh catalysts when the catalyst is doped with earth alkali metals

Diastereoselective Hydrogenation in the Preparation of Fine Chemicals

Heterogeneous catalytic diastereoselective hydrogenation is reviewed with a special emphasis on its application in the preparation of fine chemical

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

The hydrodenitrogenation of 2-methylpiperidine and 2-methylpyrrolidine was studied over sulfided NiMo/γ-Al2O3 in the presence of dialkylamines, alkylamines, and alkenes to determine why N-pentylpiperidine is formed in the hydrodenitrogenation of pyridine. N-alkylated 2-methylpiperidine and 2-methylpyrrolidine were only formed as primary products by reaction with alkylamines and not by reaction with 2-methylpiperidine and 2-methylpyrrolidine, or by reaction with an alkene. This indicates that, in the hydrodenitrogenation of pyridine, N-pentylpiperidine is formed by the reaction of the secondary intermediate pentylamine with the primary intermediate piperidine, and not by reaction of two primary piperidine intermediates or by reaction of pentene, one of the final products, with piperidin

Promotion Effect of 2-Methylpiperidine on the Direct Desulfurization of Dibenzothiophene over NiMo/γ-Al2O3

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) was studied at 300 °C, 4.8 MPa H2 and 35 kPa H2S in the presence of 0 to 6 kPa 2-methylpyridine and 2-methylpiperidine. 2-Methylpyridine suppressed the hydrogenation pathway by a factor of 6 to 30, depending on its partial pressure, and moderately inhibited the direct desulfurization pathway of the HDS of DBT (by a factor of 2 or less). 2-Methylpiperidine suppressed the hydrogenation by a factor of 10 to 50 but promoted the direct desulfurization of DBT at low partial pressures of 2-methylpiperidine. Both pathways were inhibited at high concentrations of 2-methylpiperidine. Structural and electronic factors may account for the promoting effect of 2-methylpiperidin

Promotion Effect of 2-Methylpiperidine on the Direct Desulfurization of Dibenzothiophene over NiMo/γ-Al2O3

ISSN:1011-372XISSN:1572-879

Influence of nitrogen-containing components on the hydrodesulfurization of 4,6-dimethyldibenzothiophene over Pt, Pd, and Pt-Pd on alumina catalysts

Pyridine and piperidine inhibited the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DM-DBT) over alumina-supported Pt, Pd, and Pt-Pd catalysts. The Pd catalyst was least sensitive and the Pt-Pd catalysts were most sensitive to the nitrogen-containing compounds. Pyridine was a stronger inhibitor than piperidine at low initial pressure, but the reverse was true at high initial pressure. Hydrogenation of the tetrahydro to the hexahydro and on to the perhydro sulfur-containing intermediate as well as the removal of sulfur from these intermediates was slowed down by piperidine and pyridine. The hydrogenation pathway in the hydrodesulfurization of 4,6-DM-DBT was inhibited much more than the direct desulfurization pathway. The hydrogenation of the desulfurized products 3,3′-dimethylcyclohexylbenzene and 3,3′-dimethylbiphenyl over the Pt-Pd catalysts was suppressed by piperidine and pyridine. Piperidine and pyridine substantially decrease the ability of noble metal particles to convert refractory molecules like 4,6-DM-DBT and diminish the advantage of bimetallic Pt-Pd over monometallic Pt or Pd catalyst

Characterization of highly dispersed Ni/Al2O3 catalysts by EXAFS analysis of higher shells

The size and morphology of Ni/Al2O3 catalysts in the oxidic, reduced, and passivated state were determined by EXAFS analysis of the higher shells around the Ni atoms. In the oxidic state, the Ni cations were present in small NiOx particles with predominant (111) plane. Below 4.5 wt% Ni loading, the NiOx particles consisted of one Ni layer, and of two or three Ni layers above 4.5 wt% Ni. A Ni-Al contribution was observed in samples with low Ni loading. The layer which is in contact with the Al2O3 surface is affected by the support surface and its structure is highly distorted, while the other layers were not distorted and have a structure similar to that in bulk NiO. In the reduced state, the number of Ni metal atoms in the reduced Ni particles was smaller than 100 with a narrow distribution below a loading of 15.6 wt% Ni. Above this loading, the particle size suddenly increased and the distribution became wider. The distances and Debye-Waller factors were similar to those of bulk nickel which suggested a weak interaction between the particles and the support. In the passivated state, Ni kernels with 20-40 metal atoms were covered by a one layer thick NiO ski

Sulfides, Zeolites, and Nanotowers

Three new classes of materials, which we developed and use in our catalytic research, are described. Layered and intercalated sulfides are studied for their use as model compounds for hydrodesulfurization catalysis. Dealuminated zeolites and other mesoporous materials contain mesopores which enhance diffusion and, thus, the effectiveness of zeolitic materials in liquid-phase reactions. Using lithographic techniques, nanotowers are manufactured from layers of metals and insulators placed on silicon wafers. The nanotowers are studied as model catalysts, especially for investigating size effects in heterogeneous catalysis

Nanotechnology and Model Catalysis: The Use of Photolithography for Creating Active Surfaces

New and very stable model catalysts have been developed. Two types of samples on oxidized 4-inch wafers were produced using processes that are generally employed in semiconductor device technology. A single wafer exhibits 109 to 1010 active sites on an otherwise flat silicon oxide surface. Sputter etching of a number of bilayers (Pd/SiO2), stacked on an oxidized Si wafer surface resulted in billions of isolated towers, consisting of disks of active metal layers, separated by inert substrate material. A second system was produced by etching pits into a heavily oxidized 4-inch Si wafer. Active material was deposited into the pits by e-beam evaporation or spin-coating of precursor solutions. The topography and chemical composition, and the changes induced by the reaction conditions applied, including stability and chemical behavior of the nanostructured systems, were investigated by means of AFM, SEM, temperature-programmed methods and XPS

Вероятностно-детерминированная модель расчета безопасного расстояния при разливе топлива

В статье рассматриваются основные опасные факторы при эксплуатации автозаправочных станций, опасные факторы топливных жидкостей, их физические и физико-химические свойства. Основная задача в статье - проанализировать все возможные риски, возникающие при эксплуатации АЗС, выявить наиболее вероятные неблагоприятные события, способные привести к повреждениям и разрушениям АЗС. Проанализировать возможные сценарии развития аварии для выявления наиболее опасного. Данные исследования позволят в дальнейшем использовать математическую модель для определения радиуса поражения зданий, сооружений и населения, и определения безопасного расстояния для опасных объектов - АЗС.The article deals with the main hazards during the operation of gasoline stations, the dangerous factors of fuel fluids, their physical and physicochemical properties. The main task in the article is to analyze all possible risks arising from the operation of the filling station, to identify the most likely adverse events that can lead to damage and destruction of the filling stations. Analyze possible scenarios for the development of an accident to identify the most dangerous. The given researches will allow to use in the further mathematical model for definition of radius of destruction of buildings, constructions and the population, and definition of a safe distance for dangerous objects - the gas station