Hugo Leeman

Active sites in zeolites: I. Cumene cracking activity of NH4Y zeolites after different reactor pretreatments

Abstract The dealkylation of cumene was investigated in a pulse microreactor. The catalysts were zeolites Y in the hydrogen form and partially hydrolyzed HY pretreated at temperatures between 500 ° and 800 °C. The hydroxyl content of the samples was derived from infrared spectra taken from samples pretreated in identical conditions. Bronsted and Lewis sites were determined by adsorption of ammonia and pyridine, and poisoning experiments with pyridine were also carried out. A good correlation was found between the number of hydroxyls and the amount of pyridine needed for complete poisoning. Nevertheless, the initial activity after different pretreatments decreased much more slowly than the concentration of acidic hydroxyls. It was concluded that only a fraction of the hydroxyls are involved in the reaction. The activity varied with the pulse number. This was ascribed to the formation of a polymer by the propylene formed in the reaction. This polymer is catalytically active per se. On the HY samples the presence of the polymer resulted in a decrease of the initial activity. On the hydrolyzed sample the polymeric species had a favorable effect on the catalytic activity.

The Al pillaring of clays; Part II, Pillaring with [Al 13 O 4 (OH) 24 (H 2 O) 12 ] (super 7+)

Hectorite and saponite are exchanged with [Al13O4(OH)24(H2O)12]7+ and the amount of Al3+ adsorbed and Na+ released are followed as a function of the exchange conditions. On saponite the reaction is a pure ion exchange with 2–2.15 mmol Al3+/g adsorbed and release of 0.80 mmol Na+/g. On hectorite the ion exchange is accompanied by supplementary hydrolysis-polymerization of Al13. When excess Al is offered in the form of Al13, ion exchange is incomplete and is accompanied by precipitation and polymerization of Al13 on the surface of both hectorite and saponite. The typical spacing of 1.8 nm is developed after washing, when at least 1.3–1.4 mmol Al3+/g is adsorbed. Above a loading of 2.2–2.5 mmol/g the 1.8 nm spacing is obtained without washing. Only pillared saponite with a loading of at least 1.9 mmol Al3+/g is thermally stable up to 550°C.

Active sites in zeolites: II. Cumene cracking and toluene disproportionation activity of stabilized faujasite structures

Abstract The concentration of acidic hydroxyl groups, sorptive properties, and catalytic activity for cumene cracking and toluene disproportionation were compared for different stabilized catalysts, viz., “deep-bed” “ultrastable,” and aluminum-deficient Y zeolites. It was concluded that only a fraction of the acidic hydroxyls could be catalytically active. The toluene disproportionation reaction requires hydroxyl groups with higher acidity. Several structural properties have a favorable effect on the nature of the active sites for both reactions.

Spectroscopy of Cobalt in COAPO-5

Abstract CoAPO-5 was synthesized hydrothermally in the presence of the templates triethylamine and N,N-diethylethanolamine. On the basis of the TO 2 formula the cobalt content was varied between 0.0004 and 0.04. Diffuse reflectance spectroscopy showed that in the as-synthesized blue materials Co 2+ is in the lattice in a tetrahedral environment of oxygen atoms with a ligand field strength of 3796 cm −1 . Upon calcination in O 2+ the tetrahedral environment is distorted, part of the structural Co 3+ is oxidized to Co 3+ and the samples turn green. This structural Co 3+ is reduced with H 2 at 773°K to the blue CoAPO-5 with Co 2+ in a distorted tetrahedral environment.

ADSORPTION OF PROTAMINE AND PAPAIN PROTEINS ON SAPONITE

Due to the increased importance of bionanocomposites, protamine and papain proteins were adsorbed on Na+- and on Cs+-exchanged saponite from aqueous solution. Protein analysis of equilibrium solutions and thermogravimetric analyses of biocomposites were used to prepare adsorption isotherms. Based on the isotherm shape, and on the amounts of protein adsorbed and the amounts of Na+ and Cs+ released, the initial protein sorption apparently was due to ion exchange. Additional sorbed protein was weakly retained and could be removed by washing with water. From ion exchange, the average charge of the protamine adsorbed was estimated to be +13.1 to +13.5. Similar papain measurements could not be made due to partial decomposition. Quantitatively, protamine was adsorbed at levels up to 400 mg/g on Na+-saponite and 200 mg/g on Cs+-saponite. The maximum protamine adsorption was 650 to 700 mg/g for Na+-saponite and 350–400 mg/g for Cs+-saponite. Protamine was sorbed to edge surfaces and the basal spacing of the interlamellar region of saponite was 1.75 nm. Protamine displaced only 36% of the Cs+ in Cs+-saponite and expanded the interlamellar region by 36% for a basal spacing of 1.6 nm. Papain sorption to Na+-saponite occurred by a two-step process: (1) adsorption to saponite particle external surfaces followed, (2) by partial intercalation. Quantitatively, Papain was adsorbed up to 100 mg/g for Na+-and Cs+-saponite. Greater initial papain concentrations resulted in a 450 mg/g maximum for Na+-saponite, but no increase above 100 mg/g for Cs+-saponite. Papain apparently only sorbed to external Cs+-saponite surfaces that were estimated to be 33–40 m2/g. Step-wise thermal decomposition of the saponite-protein composites occurred between 300 and 800°C.

Facile preparation of Langmuir–Blodgett films of water-soluble proteins and hybrid protein–clay films

Water-soluble protein monolayers have been prepared by spreading protein (lysozyme (Lys) and bovine serum albumin (BSA)) aqueous solutions over water and diluted clay (saponite) dispersions in a Langmuir–Blodgett (LB) trough. LB films of protein and hybrid protein–clay were prepared by vertical upstroke deposition at a desired surface pressure. Surface pressure–time (π–t) curves and surface pressure–area isotherms (π–A) indicate that the equilibrium time between the injection and compression plays an important role in forming a protein monolayer. Atomic force microscopy (AFM) suggests that heterogeneous films, consisting of regions of protein clusters and regions of saponite layers covered with protein clusters, are obtained. Both lysozyme and BSA accumulate particularly well at the edges of the saponite layers. The main difference is that the positively charged lysozyme is much more efficient in attracting negatively charged saponite layers at the air–water interface. The amount of lysozyme immobilized (nS) is 0.2–0.4 ng mm−2 for the water–lysozyme film and 0.5–0.6 ng mm−2 for the saponite–lysozyme film, as determined using UV-Vis spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the presence of clay and proteins in the hybrid LB films. No significant change in the position of amide I or II bands was observed, suggesting little or no conformational changes upon immobilization of the proteins.

Three-Component Langmuir–Blodgett Films Consisting of Surfactant, Clay Mineral, and Lysozyme: Construction and Characterization

The Langmuir-Blodgett (L-B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant-clay L-B film at the air-water interface without phase transition. The UV-visible spectra of the hybrid film ODAH-saponite-Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3+/-0.2) ng mm(-2). The average surface area (Omega) per molecule of lysozyme is approximately 18.2 nm(2) in the saponite layer. For the multilayer film (ODAH-saponite-Lys)(n), the average amount of lysozyme per layer is (1.0+/-0.1) ng mm(-2). The amount of lysozyme found in the hybrid films of ODAH-laponite-Lys is at the detection limit of about 0.4 ng mm(-2). Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm(-1) band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mN m(-1).

Synthesis and spectroscopy of clay intercalated Cu(II) bio-monomer complexes: coordination of Cu(II) with purines and nucleotides

The spectroscopic properties of Cu(bio-monomer)nm+ complexes [BM=bio-monomer (purine, adenine, guanine, hypoxanthine, 5′-ADP and 5′-GMP)] in saponite clays have been investigated by diffuse reflectance spectroscopy (DRS) in the UV-Vis-NIR region and electron paramagnetic resonance (EPR) at X-band. Mono- and/or bis complexes of Cu(purine), Cu(adenine), Cu(5′-ADP) and Cu(5′-GMP) have been intercalated between the layers of saponite by a simple cation exchange procedure from aqueous solutions of pre-formed Cu(BM)nm+ complexes. Successful immobilisation was obtained with a BM:Cu2+ ratio of 5, but the exact coordination geometry of the intercalated complexes was determined by the overall Cu-loading, the pH of the initial exchange solution and the type of BM. Mono Cu(adenine) and Cu(purine) complexes with a NNOO coordination dominate at low Cu-loadings, or at an exchange solution pH between 3 and 4, whereas bis Cu(adenine)22+ and Cu(purine)22+ complexes with a NNNN coordination are exclusively present at higher Cu-loadingswithanexchangesolutionpHbetween5and8.Ontheotherhand, clay-intercalated Cu(5′-ADP)+ and Cu(5′-GMP)+ are always present as mono-complexes, most probably in a NOOO coordination.

Chemisorption of trimethylphosphine on zeolites

PMe 3 reacts with acidic OH-groups to HP + Me 3 with partial dehydroxylation of the 3650 cm −1 OH groups and partial H-bonding to the 3550 cm −1 OH groups. It does not react with nonacidic OH groups. PMe 3 reacts with O 1 oxygens to chemisorbed OPMe 3 . Further oxidation can also occur with formation of OP (OMe) 3 , H 2 O, CO 2 and non-identified decomposition products.

Formation of ruthenium carbonyls in zeolites

The activation of [Ru(NH3)6]3+ in mordenite and in a deep bed calcined LaY zeolite in CO gives at T<373 K monocarbonyl complexes and a dicarbonyl absorbing at 2040–2100 cm−1 and 2030–2095 cm−1 respectively. On deep bed calcined LaY this dicarbonyl is preferentially transformed to a new dicarbonyl (2054–2100 cm−1) and some polycarbonyls at high temperatures and high CO pressures. On mordenite in the same conditions the preferential decomposition pathway is that of a monocarbonyl. These reactions are at variance with those observed during the activation of watergas shift active zeolites (RuNaX and RuNaY). Both the structure and the acidity of the zeolites are at the origin of these differences.