Isik Onal

High-Throughput Testing of Heterogeneous Catalyst Libraries Using Array Microreactors and Mass Spectrometry.

Eighty isolated channels are present in the array microreactor system that was coupled to a quadrupole mass spectrometer for high-throughput testing of heterogeneous catalyst libraries. The system was used to monitor the activities, selectivities, and reaction kinetics of 66 ternary Pt/Pd/In catalysts for the dehydrogenation of cyclohexane to benzene over 24 h. It was possible to screen the entire 80-channel library in less than 10 minutes (see picture).

Ethylene Epoxidation Catalyzed by Silver Oxide

Silver-catalyzed ethylene epoxidation to produce ethylene oxide (EO) is an industrially applied important heterogeneous catalytic process. Extensive research has led to significant insights into the epoxidation mechanism. Nevertheless, despite all the efforts, the reaction is still not fully understood at the molecular level. Scheme 1 shows the competing parallel (k1 and k2) and consecutive (k4) reactions which are catalyzed by silver supported on alumina. Formation of acetaldehyde (AA) acts as an intermediate for total combustion. While the parallel reactions are uniquely catalyzed by silver, EO isomerization (k3) predominantly occurs on the alumina support.

Hochdurchsatz‐Screening von Heterogenkatalysator‐Bibliotheken unter Verwendung eines Mehrkammerreaktorsystems und der Massenspektrometrie

80 isolierte Kanale enthalt das Mehrkammerreaktorsystem, das nach Kopplung mit einem Quadrupolmassenspektrometer als Testapparatur mit hohem Durchsatz fur Heterogenkatalysatoren verwendet wurde. Die Anlage ermoglichte die Verfolgung von Aktivitaten, Selektivitaten und der Reaktionskinetik von 66 Katalysatoren des ternaren Systems Pt/Pd/In bei der Dehydrierung von Cyclohexan zu Benzol uber 24 h. Alle 80 Kanale der Bibliothek konnen in weniger als 10 min untersucht werden (siehe Diagramm).

Ethylene epoxidation catalyzed by chlorine-promoted silver oxide

It is demonstrated that, on a silver oxide surface, direct formation of ethylene oxide (EO) through the reaction between gas phase ethylene and surface oxygen is possible. The direct reaction channel produces EO selectively without competing with acetaldehyde (AA) formation. The oxometallacycle (OMC) forms on an oxygen vacant surface and reduces EO selectivity. Cl adsorption removes these surface vacant sites and hence prevents the formation of the OMC intermediate.

Chlorine and caesium promotion of silver ethylene epoxidation catalysts

The effect of co‐adsorbed Cs and Cl on the selectivity of ethylene epoxidation was studied computationally on an Ag2O(0 0 1) surface model. Cl blocks the oxygen vacant sites and prevents oxometallacycle (OMC) formation, which is responsible for aldehyde formation on the oxide surface. Cl also prevents unfavorable surface reconstruction induced by co‐adsorption of ethylene. It also has a positive effect on the stability of selective oxygen species when Cs co‐exists. Introduction of Cs on the Ag2O(0 0 1) surface results in the formation of CsOx‐type of complexes in the absence of Cl. Whereas oxygen atom adsorption energies are increased, Cs also introduces surface oxygen vacancies that reduce catalyst selectivity. Cs and Cl co‐exist on the surface in the form of CsClxOy complexes. Under reaction conditions, these complexes stabilize the oxide surface and reduce oxygen surface vacancy formation, which results in higher ethylene oxide (EO) selectivity.

High-throughput synthesis and screening of new catalytic materials for the direct epoxidation of propylene.

Nanoparticles of 35 individual metals as well as their binary combinations were synthesized using High Throughput pulsed laser ablation (PLA), and collected on Al(2)O(3), CeO(2), SiO(2), TiO(2), and ZrO(2) pellets. These materials were then screened for their catalytic activities and selectivities for the partial oxidation of propylene, in particular for propylene oxide (PO), using array channel microreactors. Reaction conditions were the following: 1 atm pressure, gas hourly space velocity (GHSV) of 20,000 h-1, temperature 300 degrees C, 333 degrees C, and 367 degrees C, and feed gas composition 20 vol% O(2), 20 vol% C(3)H(6) and balance He. Initial screening experiments resulted in the discovery of SiO(2) supported Cr, Mn, Cu, Ru, Pd, Ag, Sn, and Ir as the most promising leads for PO synthesis. Subsequent experiments pointed to bimetallic Cu-on-Mn/SiO(2), for which the PO yields increased several fold over single metal catalysts. For multimetallic materials, the sequence of deposition of the active metals was shown to have a significant effect on the resulting catalytic activity and selectivity.

Photoionization detection (PID) as a high throughput screening tool in catalysis

A versatile photoionization detection (PID) system has been developed to rapidly screen libraries of catalytic materials. The PID approach involves the use of an appropriately selected dc discharge lamp to obtain monoenergetic photons, which are then used to photoionize gaseous molecules whose ionization potentials are lower than the photon energy. The suitability of the PID as a rapid screening tool has been demonstrated using oxidative dehydrogenation of ethane and propane as example reactions. Two 66 member ternary libraries of V-Mo-Li and V-Mo-Rb on-Al2O3 were tested for ethylene and propylene formation using the 10.6 eV photons from a Kr discharge lamp. The PID screening allowed the determination of 6% V, 3% Mo and 1% Li as the optimal catalyst formulation with regard to maximum alkene production for both reactions in a matter of hours.

Testing of a mathematical model for the combustion of lignites in an AFBC

A mathematical model, previously developed and tested for the modelling of continuous fluidized-bed combustors burning good-quality coal, has been modified to incorporate combustion of lignites having much higher VCMFC ratios and ash contents. Modifications of the model for volatiles combustion and the incorporation of overflow ash into mass and energy balances are described. Concentration and temperature profiles and combustion efficiencies predicted for 0,19 and 48% excess air levels are compared with experimental data from a pilot-scale fluidized-bed combustor. It is shown that oxygen consumption in the freeboard is mainly due to the oxidation of volatile matter released by lignite particles splashed into the freeboard. The predictions show reasonable agreement with the experimental data.

Oxidative coupling of methane over NbO (p-type) and Nb2O5 (n-type) semiconductor materials

Oxidative coupling of methane to higher hydrocarbons was investigated using two types of semiconductor catalysts, NbO (p-type) and Nb2O5 (n-type) at 1 atm pressure. The ratio of methane partial pressure to oxygen partial pressure was changed from 2 to 112 and the temperature was kept at 1023 K in the experiments conducted in a cofeed mode. The results indicated a strong correlation between C2+ selectivity performance and the electronic properties of the catalyst in terms of p-vs. n-type conductivity. The p-type semiconductor catalyst, NbO, had a larger selectivity (e.g. 95.92%) over the n-type Nb2O5 catalyst (23.08%) both at the same methane conversion of 0.64%. Catalyst characterization via X-ray diffraction, TGA and reaction studies indicated that NbO was transformed to Nb2O5 during the course of the reaction which limits catalyst life.

SYNTHESIS OF ZSM-5 FROM MODIFIED CLINOPTILOLITE AND ITS CATALYTIC ACTIVITY IN ALKYLATION OF BENZENE TO ETHYLBENZENE

ZSM-5 catalysts were prepared by utilizing clinoptilolite found in Western Anatolia in abundant amounts as a type of natural zeolite. Hydrothermal reaction was conducted with HCl-treated clinoptilolite at 180°C. After characterizing the solid products obtained by this reaction as ZSM-5 by means of XRD, IR, TGA, surface area analyzer, and chemical analysis they were tested as catalysts in benzene alkylation reaction with ethylene leading to ethylbenzene. Catalytic performance of samples prepared in this study was investigated for benzene conversion, ethylbenzene yield, and selectivity. It was found that ZSM-5(A) sample showed performance similar to that of the reference sample (ZSM-5(C)) synthesized by using patented literature information in terms of benzene conversion. When the reaction temperature was increased from 400° to 425°C ethylbenzene yield and selectivity results of ZSM-5(A) sample were improved but coke formation increased. Catalyst test results indicated the possibility of using clinoptilolite as a raw material in the synthesis of ZSM-5 catalyst for alkylation of benzene with ethylene reaction.