Pcmm Pieter Magusin

N2O decomposition over Fe/ZSM-5: effect of high-temperature calcination and steaming

N2O decomposition over Fe/ZSM-5 made by the sublimation method was investigated. Further calcination or steaming treatment (700°C) increased the decomposition rate of N2O. FTIR showed that such treatments lead to the disappearance of Brønsted acid sites. The various catalysts have different apparent activation energies, confirming the presence of different active Fe species. The observation that after high-temperature calcination a higher activity is obtained while no dealumination occurs indicates a mechanism where neutral Fe oxide clusters occluded in the zeolite micropores react at high temperature with the zeolite protons to form [FeO]+-like species.

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.

The formation of gigantic hollow silica spheres from an EO76–PO29–EO76/butanol/ethanol/H2O quaternary system

Gigantic hollow silica spheres with a hierarchical intra- and inter-particle porosity were obtained from an EO76–PO29–EO76/butanol/ethanol/H2O quaternary system, which is unique in its extremely rapid silica condensation and in the resulting hierarchical morphology.

Thermotropic Phase Behavior of Trialkyl Cyclohexanetriamides

The thermotropic phase behavior of symmetric cyclohexanetriamides carrying various linear and branched alkyl chains was investigated using calorimetry, microscopy, solid-state NMR, dielectric relaxation spectroscopy, and X-ray scattering techniques. Cyclohexanetriamides carrying C(6) or longer linear alkyl chains formed columnar plastic phases with a pseudocentered rectangular lattice. Those with C(8) or longer alkyl chain also showed a nematic liquid crystalline phase. Cyclohexanetriamides carrying branched octyl chains displayed columnar phases with rectangular lattices, except for the triamide with the highly branched tetramethylbutyl group. The occurrence of less symmetrical columnar phases is ascribed to the mode of stacking of cyclohexanetriamides which leads to noncylindrical columns. Dielectric relaxation spectra also featured highly cooperative relaxation processes related to reorientation of the macrodipolar columns in the mesophase, showing the potential of these molecules as building blocks in responsive materials.

T2 distribution spectra obtained by continuum fitting method using a mixed Gaussian and exponential kernel function

Static (1)H NMR Free Induction Decay (FID) signals of polymer solids contain a lot of information about the molecular dynamics. A T2 analysis of the FID has generally been performed in terms of discrete two- or three-component models. However, this requires a priori assumption of the number of proton species before analysis. This paper presents a method of analyzing the FIDs of the polymer solid samples in terms of a continuous T2 distribution. A mixed Gaussian and Exponential kernel function was used to represent the true characteristic of FIDs of the polymer solids. A simple and realistic assumption has been made to reduce the number of degrees of freedom in the continuum fitting and to make the fitting stable. An experimental static (1)H NMR FID of a typical polymer solid sample was analyzed as an example in the end to demonstrate the application of this method.

n-Pentane hopping in zeolite ZK-5 studied with 13C NMR

Using 1D‐ and 2D‐exchange 13C NMR techniques it is shown that n‐pentane translation in zeolite ZK‐5 occurs by hopping between neighboring α and γ cages. Owing to the structure of the ZK‐5 pore network, these techniques give direct information about the translational part of molecular intercage motion, which represents the elementary step of sorbate self‐diffusion. Between 247 and 317 K the hopping rates obtained for n‐pentane in H‐ and K‐ZK‐5 at respective loadings of 8.1 and 9.9 molecules per unit cell are of the order of 1–103 s−1. This corresponds to intra‐zeolite self‐diffusion constants of 10−18–10−15 m2 s−1. Non‐exponential time‐correlation functions indicate heterogeneity, possibly reflecting the different loading states of the individual cages at the microscopic level. The temperature dependence of hopping shows that it is an activated process with a barrier of 28 ± 5, kJ mol−1 for both H‐ZK‐5 and K‐ZK‐5. The apparent activation entropy determined from a two‐site exchange analysis is 130 ± 20 J K−1 mol−1 for both H‐ and K‐ZK‐5. Copyright

Extracting the key fragment in ETS-10 crystallization and its application in AM-6 assembly.

The mechanism of crystallization of microporous titanosilicate ETS-10 was investigated by Raman spectroscopy combined with (29)Si magic-angle spinning (MAS) NMR spectroscopy, DFT calculations, and SEM imaging. The formation of three-membered ring species is shown to be the key step in the hydrothermal synthesis of ETS-10. They are formed by means of a complex process that involves the interaction of silicate species in the reaction mixture, which promotes the dissolution of TiO(2) particles. These insights into the mechanism of ETS-10 growth led to the successful development of a new synthesis route to the vanadosilicate AM-6 that involves the use of intermediates that contain three-membered ring species as an initiator.

Lightweight hydrogen-storage material Mg0.65Sc0.35D2 studied with 2H and 2H–{45Sc} MAS NMR exchange spectroscopy

Using double-quantum (2)H MAS NMR with (45)Sc recoupling and Bloch-Siegert compensated (2)H-{(45)Sc} TRAPDOR we have identified the overlapping NMR signals of deuterium with and without scandium neighbors in Mg(0.65)Sc(0.35)D(2), a candidate lightweight material for hydrogen storage. At room temperature we also observe a third type of mobile deuterium. Deuterium mobility among the three NMR-distinct sites has been investigated by means of one-and two-dimensional exchange spectroscopy (Exsy). Complete deuterium exchange within 0.1s is observed, which indicates that the three NMR-distinct sites are close together in the crystal lattice. The weak temperature- and MAS-rate dependences observed in Exsy are indicative for a combination of chemical exchange and spin diffusion.

Brownian motion in a deformable medium

Abstract Diffusion in a deformable medium shows a remarkable transition at the onset of concerted particle-medium motions. This is derived for Brownian motion in a periodic potential coupled to a broad phonon spectrum, and observed for rotation of organic molecules inside zeolite cavities. Interactions between the particle and local overdamped phonons in the potential wells cause residence-time dependent lattice deformations, which, in our model, decrease the energy barriers. The model explains the non-Arrhenius type of rotational motion of pentane inside zeolite ZK-5 observed with 1 H – 13 C NMR relaxometry.

H2-D2 exchange and migration of Ga in H-ZSM5 and H-MOR zeolites

Trimethylgallium (TMGa) was loaded by chemical vapor deposition (CVD) on two different zeolites, H-ZSM5 and H-MOR. The interaction of TMGa on zeolite acid sites and the effect of reduction and oxidation treatments were characterized by ICP, XPS, FT-IR and 71Ga NMR. The capacity of dissociatively adsorption of H2 and D2 and the resultant HD desorption was analysed by H2−D2 exchange reaction. The oxidation and specially the reduction treatment provoke the migration and redistribution thought zeolite crystals. FT-IR results show that TMGa reacts with both silanol and stericaly accessible Bronsted acid sites. 71Ga NMR spectra show that Ga is presents in two different geometries: octahedral and Ga compensating the negative charged Al from the framework zeolite structure. Hydrogen pretreatment of both zeolites has a positive effect on the distribution of Ga. However, Ga species obtained were less active for H2−D2 exchange than the Ga species obtained after oxidation.