Pierre Grobet

Short-ranged structural rearrangement and enhancement of mechanical properties of organosilicate glasses induced by ultraviolet radiation

The short-ranged bonding structure of organosilicate glasses can vary to a great extent and is directly linked to the mechanical properties of the thin film material. The combined action of ultraviolet (UV) radiation and thermal activation is shown to generate a pronounced rearrangement in the bonding structure of thin organosilicate glass films involving no significant compositional change or film densification. Nuclear magnetic resonance spectroscopy indicates loss of –OH groups and an increase of the degree of cross-linking of the organosilicate matrix for UV-treated films. Fourier transform infrared spectroscopy shows a pronounced enhancement of the Si–O–Si network bond structure, indicating the formation of more energetically stable silica bonds. Investigation with x-ray reflectivity and ellipsometric porosimetry indicated only minor film densification. As a consequence, the mechanical properties of microporous organosilicate dielectric films are substantially enhanced while preserving the organosili...

Isomorphic Substitution of Silicon in SAPO-37

Isomorphic substitution of Al-P pairs for Si occurs in siliceous SAPO-37 crystals. 29Si MAS NMR shows that such crystals are composed of aluminosilicate and silicoaluminophosphate domains. The aluminosilicate parts have unusual Si, Al ordering. Si-enriched SAPO-37 has enhanced catalytic activity.

Parameters Influencing the Preparation and Characterization of Sodium on Zeolite Catalysts

Optimization of a sodium on support catalyst for room temperature isomerization of butenes is reported, in situ ESR spectroscopy of the working catalysts allows to discriminate between the different sodium species present. Sodium azide impregnation using a methanolic slurry on zeolites L, X, Y and alumina followed by slow thermal decomposition of the adsorbed azide, turned out to be the preferred method. Thermoanalytic, ESR and IR characterization of the catalyst showed that neutral sodium clusters “glued” to the wall of the support through a chemical interaction between residual nitrogen and support oxygen.

Study of the silicon tetrachloride dealumination of NaY by a combination of n.m.r. and i.r. methods

NaY was dealuminated with SiCl4 vapour in order to obtain a material with SiAl = 50. This sample 1 was further treated with HCl and then steamed, which gave sample 2 with SiAl = 200. Both samples were characterized with magic angle spinning n.m.r. using 27Al and 29Si. In addition for the latter nucleus the cross-polarization mode was used. The infra-red hydroxyl spectra were recorded for the same samples. The combination of n.m.r. and i.r. showed a detailed insight into the nature of the dominating dealumination reactions and of the dealuminated products. Also an assignment is proposed for the nature of the zeolite hydroxyl groups contributing to the intensity of the 29Si n.m.r. lines.

Silicalite-1 Zeogrid: A New Silica Molecular Sieve with Super- and Ultra-Micropores

Spherical, micrometer-sized particles with a layered structure were obtained by precipitation of a Silicalite-1 zeolite nanoslab suspension upon addition of cetyltrimethylammonium bromide (CTMABr) and subsequent calcination. The material had a specific micropore volume of 0.69 cm3 g–1, distributed over super- and ultra-micropores. The formation process of this peculiar microporous solid was studied using X-ray diffraction (XRD), 29Si MAS NMR spectroscopy, thermogravimetry (TG), and nitrogen adsorption. In the precipitate, the Silicalite-1 nanoslabs were laterally fused into nanoplates and stapled into layers with intercalated surfactant molecules. Removal of the surfactant through calcination caused facial fusion, besides additional lateral fusion, of the nanoplates. Empty spaces left lying laterally between individual nanoplates were responsible for the super-microporosity. The ultra-micropores were zeolitic channels inside the fused nanoplates. The potential of these Silicalite-1 zeogrids as molecular sieves was demonstrated with pulse gas-chromatographic separation of alkane mixtures. The mass-transfer resistance of a packed bed of zeogrid particles was considerably lower than of compacted zeolite powder.

ESR on silver clusters in zeolite A

Abstract ESR results on silver cluster formation in zeolite A with different loadings are presented. Depending on the reduction degree hyperfine spectra with seven and nine lines and two types of conduction electron spin resonance lines are detected. These signals could be assigned to the evolution in silver cluster formation in and outside the zeolite structure. Zeolites are good supports to prove the experimental evidence of the quantum size effect in small metal particles.

Framework and Non-Framework Al Species in Dealuminated Zeolite Y

Abstract The hydrothermal dealumination of zeolite Y was followed by 29Si and 27Al MAS NMR. From deconvoluted MAS NMR spectra the amount of the different silicon and aluminium species, formed during steaming, could be determined. Next to well documented 27Al signals at 60 ppm of tetrahedral framework Al and at 0 ppm of octahedral Al, lines at 50 ppm, 30 ppm and in the region of 4–0 ppm are observed, the chemical nature of which is discussed. Zeolite Y with framework Si/Al ratio from 3.5 to 17 contains non-negligible amounts of extra-framework silicon and aluminium species, which complicate the determination of the framework Si/Al and non-framework:framework Al ratios. A considerable amount of extra-framework aluminium is missing in the 27Al MAS spectra. This ‘NMR-invisible’ aluminium, assigned to oligomeric alumina species, can be made ‘NMR-visible’ by complexation with acetylacetone under specific conditions.

Calorimetric studies of the adsorption thermodynamic properties of the very large pore molecular sieve VPI-5

Calometric measurements of the heat of adsorption of nonpolar molecules on VPI-5 were performed at 303 K and compared with the results of measurements of the same molecules on the silica faujasite (US-Ex). Both microporous adsorbents show similar adsorption behavior, which is due mainly to the fact that both solids are neutral and comparable in the diameter of the pores or cavities, respectively. The heat curves of ethane, n-butane, n-pentane, and n-hexane on VPI-5 are compared also with the corresponding curves on AIPO4-5 and AIPO4-11. From this comparison, it follows that the adsorption heat increases with increasing framework density (or decreasing pore diameter). With decreasing pore diameter, the entropy of the adsorbed molecules also decreases.

The crystal structure of zeolite Linde Q: A proposal based on powder X-ray diffraction and 27Al and 29Si MAS n.m.r. spectroscopy

The BPH topology is proposed for the tetrahedral framework of the synthetic zeolite Linde Q (hexagonal; a = 13.501(9) A; c = 13.403(19) A; P321; unit cell composition (104 °C); 7 K 2 O·7 Al 2 O 3 ·14 SiO 2 ·21.7 H 2 O). The one-dimensional 12-ring channel along [001] intersects with a two- dimensional intersecting channel system parallel to (001) with eight-ring apertures. The “sheetlike” structure accounts for the low framework density and the low thermal stability. The positions of four extraframework cation sites and four water molecules is also proposed. This structure type with completely ordered Si, Al distribution is consistent with 29 Si MAS n.m.r. spectroscopy and with its chemical and physical properties.

Spectroscopy of prismatic and cube- shaped ZSM-5 crystals

Cubic and prismatic single crystals of ZSM-5 were prepared according to the method of Jansen et al. (ACS Symp. Ser. 398, 1989, p. 257) and compared with microcrystalline ZSM-5. From the viewpoint of XRD and i.r. spectroscopy, all the materials are well crystallized. 29 Si MAS n.m.r. shows, however, that the cubic crystals have superior crystallinity. The cubes are composed of oriented prismatic crystals. The Si/Al ratio is 500; most of the Al of the synthesis mixture is incorporated into analcime crystals. The same holds for the prismatic crystals, but not for the microcrystalline material. For the three materials, the number of silanol groups is 3–7%, which is small compared to the numbers given in the literature or theoretically predicted. Cu 2+ is ion-exchanged via a solid-state reaction with Cu or CuCl 2 ·2 H 2 O. The Cu 2+ coordinates at two distinct sites in prismatic and cubic crystals and three sites in the microcrystalline material. The sites have e.s.r. parameters, which are similar to those for Cu 2+ in mordenite.