Y. Ben Taarit

X-ray diffraction study of cupric ion migrations in two Y-type zeolites containing adsorbed reagents

Abstract X-Ray diffraction study of two copper-exchanged Y zeolites (Cu 16 Na 24 Y and Cu 12 Na 5 H 27 Y) in the dehydrated state showed that the cupric ions strongly prefer S I sites in the sodalite cages where they are firmly bonded to three framework oxygen atoms. The effect of sorbed molecules on the cation distribution was studied by adding ammonia, pyridine, naphthalene and butene to the dehydrated zeolite. Adsorption of a small amount of ammonia which can enter the sodalite cages produced slight but significant changes in the copper position. Addition of pyridine, naphthalene or butene induced an important migration of copper ions from S I and S I sites to the supercages where they can interact with sorbed molecules. The nature of the cation-organic molecule associations was investigated: infrared measurements and X-ray results provided evidence of a proton transfer from the organometallic complexes to the framework oxygen atoms.

ESR study of copper(II) ions in Y zeolite: Effect of water, ammonia and pyridine adsorption

Abstract The ESR technique has been used to study the localization of copper(II) ions in the zeolite framework. In the entirely hydrated samples the copper(II) ion is in the form of an hexaaquo complex localized in the centre of the supercage. Dehydration produces the migration of the ion toward the sodalite cage. Water, ammonia and pyridine coordinate with the dehydrated copper(II) ion, and a back migration toward the supercage occurs.

Infrared study of rhodium clusters entrapped within zeolites

Samples containing 0.5 and 1.5% by wt rhodium were prepared by sublimating Rh/sub 6/(CO)/sub 16/, onto Y zeolite, subjected to various outgassing, oxidizing, and reducing treatments, and studied by IR spectroscopy. The IR spectra were compared with spectra of zeolite-supported (Rh(CO)/sub 2/ Cl)/sub 2/, alumina-supported Rh/sub 6/(C0)/sub 16/, and CO adsorbed on metallic rhodium. At sufficiently low rhodium content, the zeolite-supported Rh/sub 6/(CO)/sub 16/ species could be decarbonylated reversibly by oxygen or evacuation without losing the cluster structure. At higher rhodium loadings, a rhodium(I) dicarbonyl species formed as well as the decarbonylated zero-valent rhodium.

Alkylation of benzene with dodecene. The activity and selectivity of zeolite type catalysts as a function of the porous structure

Abstract LAB (Linear Alkyl Benzene) isomers were obtained by the alkylation of benzene with 1-dodecene over FAU, BEA and EMT zeolites in the presence of decane as solvent. The initial activities were compared by fitting the kinetics early data with a pseudo first order law in dodecene. These were in agreement with those determined from the slope of the conversion versus time curve at zero conversion. The activity and stability were discussed in terms of the residual Na + content, Si/Al ratio and porous structure of the catalysts. The selectivity to the most desired 2-phenyl dodecane isomer was found to increase with increased porous constraints. Yields in the preferred isomer over BEA catalysts were very close to those provided by the FAU open structure catalysts in spite of a much lower conversion over BEA catalysts. Deactivation affected not only the alkylation reaction, but the isomerisation of the olefin as well, over BEA catalysts.

Comparison between TS-1 and TS-2 in the hydroxylation of phenol with hydrogen peroxide

Abstract The hydroxylation of phenol with hydrogen peroxide has been carried out over a series of titanium silicalites. Results have shown that the activity of the catalyst strongly depended on the synthesis route and on the crystal size. For TS-1 and TS-2 samples with similar titanium contents and crystal sizes, the influence of the zeolite structure was not observed.

Synthesis and characterization of a chromium silicalite-1

Abstract Chromium silicalites have been synthesized and characterized using several spectroscopic techniques. I.r. measurements associated with e.p.r. and solid-state n.m.r. data tend to indicate an isomorphous substitution of Si 4+ by chromium ions in the silicalite framework. An absorption band at 960 cm −1 on the i.r. spectrum, characteristic of the incorporation in the case of titanosilicalites, is observed. Furthermore, i.r. of adsorbed pyridine reveals the existence of pyridinium ions in the material.

ESR and IR studies on the adsorption and disproportionation of nitric oxide on copper exchanged Y zeolites, and of reduction by carbon monoxide

Abstract Nitric oxide adsorption on copper exchanged Y zeolites is investigated by means of ESR and IR techniques. It is shown that NO disproportionation is copper concentration dependent as well as NO adsorption which occurs on CO-reduced samples on Cu 2+ ions for low exchanged Y zeolites and on Cu + ions for high exchanged Y zeolites.

Formation of iridium carbonyl complex in NaY zeolite

Abstract The structure of iridium carbonyl complexes trapped within the zeolite cavities and the reactivity of these species towards the methanol carbonylation have been investigated. Ir(NH3)5Cl2+-exchanged NaY zeolite upon thermal decomposition is converted into an Ir(OH)x species. The carbonylation of iridium was followed by quantitative measurement of the 12CO uptake, infrared spectra of the reaction with 12CO, 13CO, and a mixture of 12CO13CO. Ir(I)(CO)3 was found to be very active and selective for the vapor phase carbonylation of methanol at atmospheric pressure in the presence of methyl iodide.

Zeolite based catalysts for linear alkylbenzene production: Dehydrogenation of long chain alkanes and benzene alkylation

Abstract Linear alkylbenzenes (LAB) obtained by alkylation of benzene with linear C10–14 olefins. In the present work we have investigated the dehydrogenation of long chain alkanes over Pt-based catalysts. For convenience n-octane dehydrogenation was used to probe the dehydrogenating properties of the catalysts. The catalysts for dehydrogenation of n-octane are constituted by Pt or Pt-In alloys supported on alumina, NaY, KL zeolites and on silicalite. The metal particles were characterized by STEM-EDX, H2 adsorption, and IR of adsorbed CO. The main conclusions are: In Pt-In/silicalite system, very small metal particles, less than 1 nm, are formed that are localized in the silicalite pores and Pt is alloyed with In. These Pt-In particles show unexpected high dehydrogenating activity and very high stability against coking even in the absence of added hydrogen. The alkylation of benzene with 1-dodecene over H-form zeolites was investigated. The reaction temperature was in the range 373–473 K. Batch reactor was chosen for this study. The results indicate that dealuminated HY zeolites are apparently the most suitable catalysts. H-ZSM-5, H-ZSM-12 showed almost no activity for the production of LAB, due to the small size of the channels. The reaction was influenced considerably by diffusion. While H-mordenite also showed very low catalytic activity, dealuminated H-mordenite exhibited a significant activity and a very high selectivity for the production of 2-phenyldodecane which is the less bulky among the other phenyldodecane isomers. The mesoporosity generated within dealuminated mordenite is responsible for these observations.

Synthesis of TS-1 from titanosilicate gels containing TPAOH/TEAOH and TPAOH/NH4OH mixtures

Abstract Titanium silicates of the MFI type (TS-1) have been synthesized using mixtures of tetrapropylammonium (TPA) and tetraethylammonium (TEA) hydroxides. While TPAOH has revealed to be a real templating agent, this is not the case for TEAOH since it was not incorporated in the zeolite structure. Nevertheless, the presence of TEA considerably affects the crystallization of the gel by retarding the nucleation process and, therefore, the morphology of the zeolite crystals. Similar results are obtained with inorganic alkali-free bases such as NH4OH. Physicochemical characterizations show that both products, prepared either with TEAOH or NH4OH, are similar.