Jos Gislain Leon Philippaerts

Siloxane bridges as reactive sites on silica gel. Fourier transform infrared–photoacoustic spectroscopic analysis of the chemisorption of diborane

The reaction of diborane with the silica gel surface has been studied with Fourier transform infrared photoacoustic spectroscopy (FTIR–PAS). After a dissociative adsorption of diborane on the siloxane bridges, borane reacts with the hydroxyl groups of the silica gel surface, evolving hydrogen gas. Besides this general reaction (a), a new reaction (b) is observed, which is competitive with the direct boranation of the hydroxyl groups. The siloxane bridges act as reactive chemisorption sites, resulting in the formation of silane groups. [graphic omitted]

Initial cracking properties and physicochemical characterization of acid-leached small-port (SP) and large-port (LP) mordenites by pulse n-hexane cracking, infrared and 27Al magic angle spinning nuclear magnetic resonance spectroscopy

Small- and large-port mordenite zeolites have been characterized by 27Al m.a.s.n.m.r. and infrared spectroscopy to evaluate the observed changes in catalytic properties as a function of the dealumination degree. As a test reaction, n-hexane cracking was used. A dual Lewis–Bronsted cracking mechanism, together with a specific structural change upon dealumination, is proposed to be responsible for the high activity of some of these H-mordenites.

A new structural modification technique for zeolites: chemisorption of Si2H6

Abstract Chemisorption of disilane on H-mordenite small port causes two types of structural modification: 1) homogeneous intracrystalline implantation of additional groups and/or 2) preferential pore entrance and external surface modification. The obtained type depends of the applied reaction conditions. The second modification process causes an efficient pore size reduction without loss of sorption capacity or acidity. The obtained substrates show a high resistance to a steaming treatment. The properties of these modified zeolites have been evaluated by chemisorption kinetics, gas adsorption experiments and FTIR-PAS spectroscopy.

Fourier-transform infrared photoacoustic spectroscopy of zeolites

Abstract Photoacoustic detection is shown to be very valuable for obtaining infrared-spectroscopic data for samples with characteristics that involve very difficult sampling. The modification reactions on the zeolite mordenite, a highly scattering material, are investigated by this technique and by gas-adsorption experiments. The mechanism of the reactions between borane groups inside the channels of the mordenite and amines at different reaction temperatures is described. At low temperatures, amine- and amino-boranes are formed that polymerize at elevated temperatures if steric hindrance is absent. The implantation of boron-nitrogen compounds inside the channels of the mordenite allow a continuous and controlled variation of the accessibility of the mordenite for gas molecules such as krypton and xenon at 273 K.

The Influence of Structural Modification by Silanation on the Ion-Exchange Properties of Mordenite L.P.

The NH 4 -exchange characteristics of a number of modified sodium-and hyarogen-mordenites were investigated and compared with the behaviour of the unmodified substrates. The modification technique used was a chemisorption of silane on hydroxylgroups within the zeolite channel-system, followed by a hydrolysis of the silylgroups. It has been proven that the modification results in a loss of the cation-exchange capacity. Furthermore, the decrease in capacity is not equal to the number of acidic OH-groups which have reacted during silanation. A portion of the newly formed OH-groups, after the hydrolysis reaction, is acidic enough for cation-exchange purposes. An estimation of this portion has been made. However, certain structural effects have influenced the ion-exchange properties, even at very low levels of modification.

Fourier-Transform Infra-Red Photoacoustic Spectroscopy, A Useful Technique for the Study of Strongly Physisorbed Molecules

Abstract The pore-size modification of Na-mordenite by implantation of boron-nitrogen compounds is investigated by gas-volumetric sorption experiments and by FTIR-photoacoustic spectroscopy (FTIR-PAS). The PAS spectra of a Na-mordenite after physical sorption of diborane show the specific characteristics of the physisorbed borane groups. These reactive species are further treated with ammonia and methylamine at different reaction conditions. The ultimate porosity is tested by adsorption of test gases such as Kr and Xe (at 273 K), and the BN-compounds, formed inside the channels of the substrate, can be characterized with I.R.-spectroscopy.

FTIR-PAS-spectroscopic study of transparent double-layer polymer films

Depth profiling measurements are carried out on aluminum-foil coated with a tie-resin and a polyethylene (P.E.) film. Since the total thickness is constant, an increase of the thickness of the tie-resin brings about a thinner P.E.-film. For a series of different combinations, the photoacoustic signal is investigated for different modulation frequencies. Gradual changes in the intensity of the tie-resin vibrations are observed. Mostly, these peaks are inverted but, in some cases, they can be turned into normal vibration bands. This is caused by phase errors due to a time delay of heat detected at different depths in the sample. The purpose of this study is to determine the thickness of polymer layers on aluminum-foil using photoacoustic measurements at different modulation frequencies.

FTIR-PAS analysis of silica gel modified with amines for the treatment of natural gases contaminated with sulphur compounds

Silica gel samples modified with different amounts of diethanolamine and monoethanolamine molecules are capable to adsorb H2S, CS2, SO2 and CH3SH. Once a complete coverage of the silica surface with amines through interaction with the surface hydroxyl groups has been reached an inactivation of the filter towards mercaptans occurs. FTIR-PAS spectra of the different silica samples are in agreement with these observations.

The Implantation of Boron-Nitrogen Compounds in Mordenite LP and their Influence on the Adsorption Properties

The structural modification of zeolites by chemisorption of diborane followed by reactions with amines (NH 3 , CH 3 NH 2 , C 2 H 5 NH 2 , (CH 3 ) 2 NH) has been proven to be an important method to change in a controlled way the porosity creating new selectivities for different gases. The ultimate porosity of modified mordenite LP substrates was evaluated by the adsorption kinetics of Ar, Kr and Xe. The pore size of the mordenite LP can be changed gradually by variation of the amount of B 2 H 6 chemisorbed, the nature of the amine and other parameters such as the reaction time and temperature. The boron-nitrogen (BN) compounds, formed inside the mordenite, were studied with photoacoustic FTIR-spectroscopy (PAS). These spectra show that at low temperatures amine-boranes are formed; at higher temperatures H 2 is evolved and BN-polymers such as amino-boranes or boron-nitrid-like species are trapped inside the channels of the zeolite.

Ion-Exchange Properties of Silanated and Disilanated Mordenites : The Influence of Different Modification Steps on The Ammonium-Exchange Capacity

Abstract The ammonium-exchange properties of large port (LPM) and small port (SPM) mordenite have been investigated after structural modification with silane and disilane. It has been proven that the new hydroxyl groups, created within the zeolite channels, are acidic enough to take part in ion-exchange processes. The exchangeability of the new hydroxyl groups is a function of the way in which the H-form was obtained, the applied modifying agent and the type of zeolite used. Moreover, the changes in exchange capacity, due to modification, render valuable information on the localisation and polarity of the new built-in entities.