Ahmad Kalantar Neyestanaki

Liquid-phase hydrogenation of citral over an immobile silica fibre catalyst

A new knitted silica fibre catalyst was introduced into liquid-phase hydrogenation of organic compounds. The fibre catalyst combines the advantages of catalyst slurries and large catalyst particles: diffusional limitations are suppressed and the catalyst is immobile. Nickel-impregnated silica fibres were used in the hydrogenation of citral to citronellal and citronellol in a tubular glass reactor where the catalyst was packed in two layers. The liquid phase was recirculated while the gas phase was flowing concurrently through the reactor to the vent. The highest selectivities to the desired product, citronellol, exceeded 90%. The catalyst performance was competitive with a conventional crushed nickel catalyst.

Gas-phase hydrogenation of o-xylene over Pt/alumina catalyst, activity, and stereoselectivity

Abstract The kinetics of the gas-phase hydrogenation of o -xylene over Pt/alumina catalysts was studied at 430–520 K, a hydrogen partial pressure of 0.19–0.36, and an o -xylene partial pressure of 0.04–0.10. The catalysts were characterized by H 2 / o -xylene TPD, H 2 chemisorption, energy-dispersive X-ray analysis, and XPS. The stereoisomers, cis- and trans -1,2-dimethylcyclohexane, were the only reaction products. A reversible maximum in the o -xylene hydrogenation activity vs temperature was observed; it was explained by a decrease in the surface concentration of o -xylene at higher temperatures. The hydrogenation rate was independent of the o -xylene concentration, whereas the reaction orders with respect to hydrogen varied from 0.9 to 3 in the temperature range investigated. The stereoselectivity of the products was found to depend on temperature, reactant concentrations, and platinum precursor. The catalyst prepared from a chlorine-containing precursor exhibited a lower hydrogenation activity and selectivity toward the trans isomer. Chlorine remained on the catalyst surface, even after reduction at 673 K. Dehydrogenation and configurational isomerization of cis - to trans -1,2-dimethylcyclohexane took place at the same time as hydrogenation. Dehydrogenation and configurational isomerization reactions are enhanced by the presence of residual chlorine on the catalyst surface. The reaction pathway is proposed.

Batchwise and continuous enantioselective hydrogenation of 1-phenyl-1,2-propanedione catalyzed by new Pt/SiO2 fibers

Abstract A new knitted silica fiber was investigated as a support material in enantioselective hydrogenation of 1-phenyl-1,2-propanedione in a pressurized batch reactor. The active metal was platinum and the catalyst was modified in situ with (−)-cinchonidine. The catalysts were prepared by impregnation method using hexachloroplatinic acid as metal precursor. The main experimental parameters were the support calcination temperature and the metal loading of the catalyst. The optimum catalyst dispersion, BET specific surface area and mean Pt particle size for enantio-differentiation were measured. A comparison of alumina and silica supports revealed that the main parameters in the enantio-differentiation were the mean metal particle size and the metal dispersion. Optimal metal particle size and dispersion were detected which optimize the enantioselection. Experiments with continuously operated fixed bed reactor demonstrated that continuous hydrogenation, over the new knitted silica fiber catalyst, gives equally high enantiomeric excesses compared to the batch operation. Continuous operation can be used as tool to study catalyst deactivation and reaction mechanisms in enantioselective hydrogenation.

Catalytic combustion of propane over Pt and Cu modified ZSM-5 zeolite catalysts

Abstract ZSM-5 zeolites were modified with copper and platinum by ion exchange and during the process of hydrothermal zeolite synthesis. The catalytic activity of the prepared Pt and Cu ZSM-5 zeolite catalysts was tested for complete oxidation of propane. It was observed that the mode of introduction of metals into the zeolite and the metal content influenced the catalytic activity. Copper introduced into the zeolite by ion exchange under basic conditions exhibited a high catalytic activity. Combustion efficiencies of 98.9 and 97.6% were achieved with the Cu ZSM-5 and Pt ZSM-5 catalysts containing 5.2 wt% Cu and 0.27 wt% Pt, respectively. The light-off temperature of the platinum containing catalyst was about 30 K lower than that of the 5.2 Cu ZSM-5 catalyst. The Cu ZSM-5 prepared during the process of hydrothermal synthesis exhibited a lower catalytic activity as compared to the ion exchanged Cu ZSM-5 catalysts. Temperature programmed desorption (TPD) measurements of CO and O2 were used to interpret the catalytic activity. The results indicated the important role of the extra lattice oxygen on these catalysts.

Modelling of catalyst deactivation in liquid phase reactions: citral hydrogenation on Ru/Al2O3

Selective hydrogenation of citral was investigated at 70 °C over Ru/Al2O3. Activity changes in a series of consecutive experiments were described by a mathematical model, which included reaction kinetics and deactivation.

Hydrothermally Stable Catalysts for the Removal of Emissions from Small-Scale Biofuel Combustion Systems

Catalytic oxidation of model pollutants, simulating the emissions from small-scale biofuel combustion systems, was studied over different fresh, aged and sulfur poisoned Pd-MeO/γ-alumina (Me = Ni, Ce and La) catalysts. Release of chlorine and restructuring of PdO particles was believed to cause activation of the Pd-MeO supported catalysts.