Volkan Degirmenci

Phosphotungstic Acid Encapsulated in Metal–Organic Framework as Catalysts for Carbohydrate Dehydration to 5‐Hydroxymethylfurfural

MIL-101, a chromium-based metal-organic framework, is known for its very large pore size, large surface area and good stability. However, applications of this material in catalysis are still limited. 5-Hydroxymethylfurfural (HMF) has been considered a renewable chemical platform for the production of liquid fuels and fine chemicals. Phosphotungstic acid, H₃PW₁₂O₄₀ (PTA), encapsulated in MIL-101 is evaluated as a potential catalyst for the selective dehydration of fructose and glucose to 5-hydroxymethylfurfural. The results demonstrate that PTA/MIL-101 is effective for HMF production from fructose in DMSO and can be reused. This is the first example of the application of a metal-organic framework in carbohydrate dehydration.

Glucose Activation by Transient Cr2+ Dimers

By combining in situ X-ray absorption spectroscopy, DFT calculations and kinetic measurements we demonstrate that the unique ability of CrCl2 in ionic liquid media to catalyze glucose dehydration to 5-hydroxymethylfurfural relates to the transient self-organization of Cr2+ dimers, which promotes the isomerization of glucose to fructose. The molecular details of the active site environment during the rate controlling step resemble those in hexose isomerase enzymes.

Dual template synthesis of a highly mesoporous SSZ-13 zeolite with improved stability in the methanol-to-olefins reaction

The dual template synthesis of zeolite SSZ-13 by use of trimethyl-adamantanammonium hydroxide and a diquaternary-ammonium mesoporogen induces considerable mesoporosity without impeding zeolite microporosity. The strongly improved accessibility of Brønsted sites in mesoporous SSZ-13 increases its stability during application as an acid catalyst in the methanol-to-olefins reaction.

On the Mechanism of Lewis Acid Catalyzed Glucose Transformations in Ionic Liquids

A complementary computational and experimental study of the reactivity of Lewis acidic CrCl2, CuCl2 and FeCl2 catalysts towards glucose activation in dialkylimidazolium chloride ionic liquids is performed. The selective dehydration of glucose to 5‐hydroxymethylfurfural (HMF) proceeds through the intermediate formation of fructose. Although chromium(II) and copper(II) chlorides are able to dehydrate fructose with high HMF selectivity, reasonable HMF yields from glucose are only obtained with CrCl2 as the catalyst. Glucose conversion by CuCl2 is not selective, while FeCl2 catalyst does not activate sugar molecules. These differences in reactivity are rationalized on the basis of in situ X‐ray absorption spectroscopy measurements and the results of density functional theory calculations. The reactivity in glucose dehydration and HMF selectivity are determined by the behavior of the ionic liquid‐mediated Lewis acid catalysts towards the initial activation of the sugar molecules. The formation of a coordination complex between the Lewis acidic Cr2+ center and glucose directs glucose transformation into fructose. For Cu2+ the direct coordination of sugar to the copper(II) chloride complex is unfavorable. Glucose deprotonation by a mobile Cl− ligand in the CuCl42− complex initiates the nonselective conversion. In the course of the reaction the Cu2+ ions are reduced to Cu+. Both paths are prohibited for the FeCl2 catalyst.

Towards a Selective Heterogeneous Catalyst for Glucose Dehydration to 5‐Hydroxymethylfurfural in Water: CrCl2 Catalysis in a Thin Immobilized Ionic Liquid Layer

Sugar it up: Stabilization of the CrCl2 active phase in a thin layer of an ionic liquid covalently grafted to mesoporous silica results in a highly selective catalyst for the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in an aqueous medium. Glucose dehydration in water by using the CrCl2-Im-SBA-15 catalyst leads to a 50 % HMF selectivity that can be further increased to up to 70 % by modifying the solvent system.

Coordination Properties of Ionic Liquid-Mediated Chromium(II) and Copper(II) Chlorides and Their Complexes with Glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.

A computational study of the mechanism of CO oxidation by a ceria supported surface rhodium oxide layer.

A mechanism of CO oxidation by a thin surface oxide of Rh supported on ceria is proposed: CO is oxidized by the Rh-oxide film, which is subsequently reoxidized by a ceria surface O atom. The proposed mechanism is supported by in situ Raman spectroscopic investigations.

AC Magnetic Heating of Superparamagnetic Fe and Co Nanoparticles

AC magnetic heating of superparamagnetic Co and Fe nanoparticles for application in hyperthermia was measured to find a size of nanoparticles that would result in an optimal heating for given amplitude and frequency of ac externally applied magnetic field. To measure it, a custom-made power supply connected to a 20-turn insulated copper coil in the shape of a spiral solenoid cooled with water was used. A fiber-optic temperature sensor has been used to measure the temperature with an accuracy of 0.0001 K. The magnetic field with magnitude of 20.6 μT and a frequency of oscillation equal to 348 kHz was generated inside the coil to heat magnetic nanoparticles. The maximum specific power loss or the highest heating rate for Co magnetic nanoparticles was achieved for nanoparticles of 8.2 nm in diameter. The maximum heating rate for coated Fe was found for nanoparticles with diameter of 18.61 nm.

Scale-up of an RF heated micro trickle bed reactor to a kg/day production scale

Abstract The scale-up of a radiofrequency (RF) heated micro trickle bed reactor for hydrogenation of 2-methyl-3-butyne-2-ol (MBY) over a Pd/TiO2 catalyst has been performed. The axial and radial temperature profiles were calculated using a 2D convection and conduction heat transfer model. The effect of the reactor length, tube diameter and number of parallel tubes on the temperature non-uniformity parameter has been studied. The axial scale-up was achieved by repeating a single periodic unit consisting of one heating and one catalytic zone along the reactor length. The catalyst loading can be increased by an order of magnitude following this approach. A radial temperature difference of 2 K was developed in a reactor with an inner diameter of 15 mm. The scale-up by numbering up allows the accommodation of seven parallel tubes inside a single RF coil. It creates a 7 K difference in the average temperature between the central and the outer tubes which results in a 5% difference in MBY conversion. An overall scale-up factor of near 700 is achieved which corresponds to a production rate of 0.5 kg of product/day.

Design of catalytic micro trickle bed reactors

CP Heat capacity CFD Computational fluid dynamics dP Particle diameter dR Reactor diameter DL Axial dispersion coefficient DM Molecular diffusion coefficient h Heat transfer coefficient g Gravity MTBR Micro trickle bed reactor k Rate constant kL Mass transfer coefficient L Reactor length n Reaction order ΔP Pressure drop q Volumetric heat generation rate RF Radio frequency T∞ Ambient temperature T Temperature TBR Trickle bed reactor u Superficial velocity x Fraction Greek Letters εB Bed porosity εL Liquid holdup εLd Dynamic liquid holdup εLs Static liquid holdup εL,t Total liquid holdup μ Micron η Effectiveness factor ρ Density Ω Energy dissipation factor λeff Effective conductivity of the reactor bed βL Liquid saturation σ Surface tension Subscripts L Liquid G Gas p Particle Dimensionless numbers Bo Bodenstein number (uL/DL) Eö Eötvös number ((ρ − ρf)L/σ) Fr Froude number (u2/gL) Mo Morton number (gμ4Δρ/ρ2σ3) Nu Nusselt number (hL/λ) Pe Peclet number (uL/DL) Evgeny V. Rebrov is the corresponding author.