J Uytterhoeven

Chemical, surface and catalytic properties of nonstoichiometrically exchanged zeolites

Zeolites X and Y have been exchanged with Ni 2+ and Cu 2+ cations in the presence and absence of acetic acid/acetate buffer, at different ratios of the solid and liquid phases, at different concentrations of the exchange solution, and using successive exchange treatments with fresh solution applying an intermediate treatment or not. Analytical data about the composition of the solid phase have been collected. Well-selected samples have been dehydrated and characterized by TGA, DTA, X-ray diffraction, ir spectra of the hydroxyl groups and of adsorbed CO and CO 2 . The catalytic activity of the samples was investigated for the decomposition of isopropanol and the oxidation of carbon monoxide. Together with the exchange of transition metal ions, protons are exchanged and hydroxylated species of transition metal cations are precipitated in the zeolite giving rise to an excess amount of transition metal. The extent to which all this occurs depends strongly on the manner the samples have been prepared. Application of the above-mentioned physicochemical techniques shows the presence of polynuclear species related in some way to the corresponding hydroxide and oxide. The species are mainly located in the supercages. The catalytic properties of the samples confirm the physicochemical characterization.

Infrared study of deep-bed calcined NH4Y zeolites

Abstract An infrared spectroscopic study has been made of the hydroxyl groups in so-called ultrastable faujasites and deep-bed calcined NH 4 Y samples. The observations include, besides the typical bands at 3650 and 3550 cm −1 generally observed in conventional HY, two additional bands around 3700 and 3600 cm −1 . The intensity of these bands is high, and the hydroxyls involved do not react with NH 3 or pyridine. The bands persist after treatment with water vapor at 400 °C. Extractions with 0.1 N NaOH removed an important fraction of aluminum, but the 3700 and 3600 cm −1 bands were not affected. Thus, these bands are considered to be due to framework hydroxyls created during the deep-bed calcination step. The two frequencies may correspond to distinct locations in the framework. The question is raised whether or not these observations require reinterpretation of former work on faujasites saturated with divalent cations.

Quantitative infrared spectroscopy of amines in synthetic zeolites X and Y: I. Alkylammonium Y zeolites as precursors of acid hydroxyls in deaminated zeolites Y

Abstract Na + ions in zeolite Y have been replaced by the following alkylammonium ions: mono-, di-, and trimethylammonium, mono-, di-, and triethylammonium, propyl-, isopropyl-, and butylammonium, piperidinium and pyridinium. The interaction of the zeolite lattice with the ions has been investigated by infrared spectroscopy. A comparison was made between the ∂NH + and ∂CH frequencies of these ions in the zeolite and the corresponding frequencies in alkylammonium halogenides. Frequency shifts were correlated with structural properties of the zeolite. The zeolites were deaminated by heating in anhydrous conditions, and the creation of hydroxyl groups followed by scanning the hydroxyl stretching spectra. Deamination of the primary alkylammonium zeolites produced a stoichiometric hydrogen Y zeolite. With the secondary and tertiary ions considerable dehydroxylation was observed. The decomposition mechanisms of the ions are discussed. The special behavior of the pyridinium zeolite suggests that the 3550 cm −1 hydroxyl band contains several components. Decomposition of the pyridinium ions results in a dehydroxylated zeolite containing Lewis acid sites of different strength.

Active sites in zeolites: 5. Hydrogen-deuterium equilibration over synthetic faujasites

The rate of isotopic exchange between H 2 and D 2 was followed over NaY, NaX, HY, hydrolyzed HY and LaY zeolites with controlled amounts of iron impurities. Two maxima have been observed in the equilibration rates, one after activation at 520 °C, and another at 670 °C. At the two maxima, a linear correlation was found between equilibration rates and the iron content of the respective catalysts. The active sites at the first maximum were assumed to be cationic iron, while the activity at the second maximum was ascribed to an iron oxide species. Evaluation of the kinetic parameters showed that the data are consistent with a Bonhoeffer-Farkas mechanism.

Influence of temperature on the OH-band intensity in the infrared spectra of decationated zeolites X and Y

Abstract The IR spectra of several decationated zeolites X and Y were studied in the OH stretching region, and the influence of temperature on the intensity of the bands near 3650 and 3550 cm−1 was investigated. The zeolites were derived from samples initially saturated with Li+, Na+, K+, and Mg2+ ions, in case of the Y samples and with Na+ ions in case of the X samples. Some samples had different contents of residual Na+ ions. The exact frequency of the band near 3650 cm−1 was dependent on the amount more than on the nature of the residual cations. The frequency of the OH bands was interpreted in terms of the electrical field in the zeolite cavities. A reversible decrease of the band intensity (20–30%) was observed with increasing temperature below 400 °C together with a small shift to lower frequencies and a broadening of the bands. All these effects are ascribed to the increased thermal motion of the lattice constituents. The ratio of the intensities of the 3550 and 3650 bands was also dependent on the temperature. This was explained by assuming a redistribution of the protons over the different sites. The effect was dependent on the amount of residual ions and the initial value of the band intensity ratio at room temperature.

Complexes of Diethylenetriamine(dien)and Tetraethylene-Pentamine(tetren) with Cu(II) and Ni(II) on Hectorite

The nature of the complexes in aqueous solutions of Cu(II) and Ni(II) with diethylenetriamine (dien) and tetraethylenepentamine tetren) is pH-dependent. At M(II):dien = 2 and M(II):tetren = 1, the main complexes are [M(dien H)2(H2O)2]4+ and [M(tetren H)(H2O)2]3+. In excess ligand (pH = 10.30), the majority species are [M(dien)2]2+ and [M(tetren)(H2O)]2+, and considerable amounts of monoprotonated amines are adsorbed. The surface of hectorite prefers the tetragonally distorted complexes in all cases studied. The complexes readily lose their axially coordinated water molecules to form planar complexes on the interlamellar surface. The planar Ni(II)-complexes are diamagnetic, showing that the surface is a very weak axial ligand. The divalent complexes [M(dien)2]2+ and [M(tetren)(H2O]2+ can also be partially transformed to the corresponding planar forms on the surface, especially in the case of [Cu(dien)2]2+. The driving forces are thought to be the acid nature of the clay-adsorbed water and the gain in crystal field stabilization energy of the transition metal ions.РезюмеПрирода соединений в водных растворах Сu(II) и Ni(II) с диэтилентриамином (диен) и тетраэтиленпентамином (тетрен) зависит от рН. При М(II):диен = 2 и М(II):тетрен = 1, главными соединениями являются [М(диен Н)2(Н2O)2]4+ и М(тетрен Н)(Н2O)2]3+. При избытке лиганда (рН = 10,30) большинство соединений представляют собой [М(диен)2]2+ и [М(тетрен) (Н2O)]2+, при этом адсорбируются значительные количества монопротоновых аминов. Во всех исследованных случаях поверхность гекторита предпочитает тетрагонально искаженные соединения. Эти комплексы легко теряют свои координированные по оси водные молекулы, образуя плоские соединения на межслойной поверхности. Плоские Ni(II)-соединения являются диамагнитными, указывая, что поверхность образована очень слабым осевым лигандом. Двухвалентные соединения [М(диен)2]2+ и [М(тетрен) (Н2O)]2+ также могут быть частично преобразованы на поверхности в соответствующие плоские формы, особенно в случае [Си(диен)2]2+. Предполагается, что движущими силами являются кислотная природа адсорбированной глиной воды и увеличение в поле кристалла стабилизационной энергии ионов переходных металлов.ResümeeDie Natur der Cu(II) und Ni(II) Komplexe mit diäthylentriamin (dien) und tetraäthylen-pentamin (tetren) in wäßrigen Lösungen ist pH abhängig. Bei M(II):dien = 2 und M(II):tetren = 1 sind die hauptsächlichen Komplexe [M(dien H)2(H2O)2]4+ und [M(tetren H)(H2O)2]3+. Bei Überschuß an Ligand (pH = 10,3) sind die Hauptsorten [M(dien)2]2+ und [M(tetren)(H2Ö)]2+ und beträchtliche Mengen monoprotonierter Amine werden adsorbiert. Die Oberfläche des Hektorit bevorzugt in allen untersuchten Fällen die tetraädrisch verformten Komplexe. Die Komplexe verlieren ihre axial koordinierten Wasser Moleküle, um planare Komplexe auf der interlamellaren Oberfläche zu formen. Die planaren Ni(II)-Komplexe sind diamagnetisch und zeigen, daß die Oberfläche ein sehr schwacher axialer Ligand ist. Die divalenten Komplexe [M(dien)2]2+ und [M(tetren)(H2O)]2+ können auch teilweise auf der Oberfläche in die entsprechenden planaren Formen übergehen, besonders im Falle von [Cu(dien)2]2+. Die saure Natur des auf Ton adsorbierten Wassers und die Zunahme in Kristallfeldstabilisierungs-energie der Übergangsmetallionen werden als treibende Kräfte angenommen.RésuméLa nature des complexes en solutions aqueuses de Cu(II) et de Ni(II) avec la diethylene-triamine (dien) et la tétraethylenepentamine (tetren) est dépendante du pH. Pour M(II):dien = 2 et M(II):tetren = 1, les complexes principaux sont [M(dien H)2(H2O)2]4+ et [M(tetren H)(H2O)2]3+. En excès de ligand (pH = 10.30), les espèces majoritaires sont [M(dien)2]2+ et [M(tetren)(H2O)]2+, et des quantités considérables d’aminés monoprotonées sont adsorbées. La surface d’hectorite préfère les complexes déformés tétragonalement dans tous les cas étudiés. Les complexes perdent aisément leurs molécules d’eau coordonnées axialement pour former des complexes planes sur la surface interfeuillet. Les complexes planes Ni(II) sont diamagnétiques, montrant que la surface est un ligand axial très faible. Les complexes divalents [M(dien)2]2+ et [M(tetren)(H2O)]2+ peuvent aussi être partiellement transformés en les formes planes correspondantes sur la surface, surtout dans le cas de [Cu(dien)2]2+. On pense que les forces motrices sont la nature acide de l’eau adsorbée par l’argile et le gain d’énergie de stabilisation du champ cristallin par les ions du métal de transition.

Use of Fischer-Tropsch Synthesis of Hydrocareons for the Characterization of Bidisperse Particle Size Distributions and Bimetallic Clusters in Zeolites

A detailed analysis of Fischer-Tropsch reaction products on ruthenium loaded zeolites Y has shown that the reactivity and the selectivity of the catalyst can yield valuable information on metal particle size distribution. It is demonstrated that inside the zeolite crystals, very uniform particle dimensions exist. Furthermore using the same method evidence is obtained that for RuCuY and RuNiY zeolites alloys are formed outside the zeolite. In the Ni-Ru agglomerates surface sites composed of each metal catalyze the Fischer-Tropsch reaction independently. Information obtained from temperature programmed oxidation of the metal phase confirms the picture.