Guy Weber

Characterization of the dealumination effect into H faujasites by adsorption: Part 1. The water molecule as a structural aluminum ion selective probe

The adsorption and desorption isotherms of water vapor are drawn at 25°C for dealuminated HY zeolites upon framework Si/Al ratio. The isotherms are compared to that of the parent NaY zeolite studied in a wide range of temperatures and filling coefficients (0.03 < θ < 1). The isotherm changes in shape from type I to type IV with an hysteresis loop changing from type H4 to type H2, as the Si/Al ratio increases. The Polanyi—Dubinin theory is used to determine the volume accessible to water. It decreases with increasing Si/Al ratios, down to zero at a Si/Al ratio of 35. Such a result is accounted for by the adsorption on the hydrophillic centers, which are the cations (H+) associated with the structural aluminum ions, each cation being coordinated on average by 9 H2O.

Mesoporous Silica‐Confined Manganese Oxide Nanoparticles as Highly Efficient Catalysts for the Low‐Temperature Elimination of Formaldehyde

Manganese(IV) oxide was synthesized through crystallization in confined space by using the SBA‐15 silica support. The evolution of textural, morphological, structural, and redox properties of the manganese phase in the composites has been studied in terms of different parameters such as impregnation route, manganese loading, and activation temperature. High performances of nanoscaled manganese(IV) oxide for low‐temperature formaldehyde oxidation have been obtained. The optimization of preparation parameters enabled the complete conversion of formaldehyde at temperatures as low as 130 °C, which is comparable to the activity of the reference platinum catalyst that demonstrates complete conversion at similar temperatures.

Capture of formaldehyde by adsorption on nanoporous materials

The aim of this work is to assess the capability of a series of nanoporous materials to capture gaseous formaldehyde by adsorption in order to develop air treatment process and gas detection in workspaces or housings. Adsorption-desorption isotherms have been accurately measured at room temperature by TGA under very low pressure (p<2 hPa) on various adsorbents, such as zeolites, mesoporous silica (SBA15), activated carbon (AC NORIT RB3) and metal organic framework (MOF, Ga-MIL-53), exhibiting a wide range of pore sizes and surface properties. Results reveal that the NaX, NaY and CuX faujasite (FAU) zeolites are materials which show strong adsorption capacity and high affinity toward formaldehyde. In addition, these materials can be completely regenerated by heating at 200°C under vacuum. These cationic zeolites are therefore promising candidates as adsorbents for the design of air depollution process or gas sensing applications.

Characterization of adsorbed water in MIL-53(Al) by FTIR spectroscopy and ab-initio calculations

Here, we report ab-initio calculations developed with a twofold purpose: understand how adsorbed water molecules alter the infrared spectrum of the metal-organic framework MIL-53(Al) and to investigate which are the associated physico-chemical processes. The analyzed structures are the two anhydrous narrow (np⊘) and large (lp⊘) pore forms and the hydrated narrow pore form (np-H2O) of the MIL-53(Al). For these structures, we determined their corresponding infrared spectra (FTIR) and we identified the vibrational modes associated to the dominant spectral lines. We show that wagging and scissoring modes of CO2 give flexibility to the structure for facilitating the lp⊘- np⊘ transition. In our studies, this transition is identified by eight vibrational modes including the δCH(18a) vibrational mode currently used to identify the mentioned transition. We report an exhaustive band identification of the infrared spectra associated to the analyzed structures. Moreover, the FTIR for the np-H2O structure allowed us to identify four types of water molecules linked to the host structure by one to three hydrogen bonds.

Thermal effects of water intrusion in hydrophobic nanoporous materials.

Liquid water intrusion in hydrophobic nanoporous silicalite-1, a pure siliceous zeolite, in isothermal conditions under high pressure produces an endothermic effect. After intrusion, confined water in zeolite pores is in a different state from that of the liquid bulk water. Such forced intrusion also chemically modifies the material and tends to render it slightly more hydrophilic.

Experimental and simulated infrared spectroscopic studies of the interaction of ethylene on a MFI zeolite

Infrared spectroscopic studies of ethylene adsorbed on a ZSM-5 zeolite were performed using both experiments and molecular dynamics simulation. The model used for ethylene and for the MFI zeolite was a full atomic one. The potentials employed in this model allowed obtaining a good agreement between experimental and simulated spectra for the adsorptive and the adsorbent. Then aggregates of 18 unit cells of zeolite with two different loadings of ethylene were simulated in contact with gas at 300 K. IR spectra of ethylene, zeolite and ethylene adsorbed on zeolite were then calculated over equilibrium trajectories. Simulated FTIR spectra of a MFI zeolite interacting with ethylene were analyzed as a function of loading and compared with the experimental results.

Confinement of Water in Hydrophobic Nanopores: Effect of the Geometry on the Energy of Intrusion

Water confinement in the hydrophobic nanopores of highly siliceous zeolite having MFI and CHA topology is investigated by high pressure manometry coupled to differential calorimetry. Surprisingly, the intrusion of water is endothermic for MFI but exothermic for CHA. This phase transition depends on the geometry of the environment in which water is confined: channels (MFI) or cavities (CHA). The energy of intrusion is mainly governed by the change in the coordination of water molecules when they are forced to enter the nanopores and to adopt a weaker, hydrogen-bonded structure. At such a nanoscale, the properties of the molecules are governed strongly by geometrical restraints. This implies that the use of classical macroscopic equations such as Laplace-Washburn will have limitations at the molecular level.

Adsorption of a Polar or a Non-Polar Chloroalkene on a ZSM-5 Zeolite at 298 K

The physisorption of trichloroethylene and tetrachloroethylene on ZSM-5 (Si/Al = 339) zeolite was investigated at 298 K using thermogravimetry, differential microcalorimetry and X-ray diffraction. The zeolite always undergoes a monoclinic-orthorhombic structural change during the adsorption of the first molecules. An alignment of the polar trichloroethylene molecules inside all the channels of the zeolite is proposed to account for the experimental results. A phase transition of the non-polar tetrachloroethylene is suggested to produce the stepped isotherm, the steep rise in the heat curve and the high increase in the mobility of the molecules for the loading of 4 molecules per unit cell.

Characterization of the dealumination effect into H faujasites by adsorption: Part 2. The hexane molecule as a pore volume probe

Abstract Thermogravimetric studies under controlled vapor pressure are made at 25°C to measure adsorption and desorption isotherms of n -hexane on a series of dealuminated HY zeolites. These had been characterized by water vapor adsorption in Part 1 of this paper. Contrary to what was observed for water adsorption, isotherms always show a very high adsorption capacity in the very low pressures and a H4 hysteresis loop. The micropore maximal volume accessible to the adsorbate, the mesopore volume, and the adsorption energy are discussed with regard to the dealumination degree of the HY zeolites.

Communication: Evidence of structural phase transitions in silicalite-1 by infrared spectroscopy.

The adsorption of trichloroethylene, perchloroethylene, and p-xylene on a MFI (Mobile-FIve) zeolite is studied using in situ FTIR spectroscopy at 298 K. Spectra of self-supported zeolites in contact with increasing pressures of pure gas were recorded at equilibrium in the mid-infrared domain. Analysis of the evolution of the shape and location of vibrational bands of the zeolite as a function of the amount adsorbed allowed the observation of structural modifications of the adsorbent for the first time by infrared spectroscopy.