Piet J. Grobet

Catalytic activity and Si, Al, P ordering in microporous silicoaluminophosphates of the SAPO-5, SAPO-11, and SAPO-37 type

The catalytic activity in the conversion of decane on SAPO-5, SAPO-11, and SAPO-37 samples with Si T-atom fractions ranging from 1 to 42% were determined. The relationship of catalytic activity with compositional parameters is discussed. Due to the nonuniform distribution of silicon, aluminium, and phosphorus over individual crystals, the overall chemical composition of a SAPO-n sample is unable to rationalize its catalytic activity. In order to explain the catalytic activity of SAPO-5, SAPO-1 l, or SAPO-37 materials, the contributions of aluminosilicate (SA) and silicoaluminophosphate (SAPO) crystal domains have been determined using 29Si MAS NMR. Acid sites located in the SA and SAPO domains and at their interphases contribute to the catalytic activity. The contribution of the different types of acid sites to the catalytic activity is strongly dependent on the SAPO-n structure type.

Zeosil nanoslabs: building blocks in nPr(4)N(+)-mediated synthesis of MFI zeolite

Tetrapropylammonium (TPA)-containing precursors are the building blocks in the crystallization of silica. In the first steps slab-shaped silicalite nanoparticles are formed by ordered combination of the precursors. These nanoslabs have MFI-type zeolite framework topology and play a key role in TPA-ion-mediated zeolite crystallization from monomeric and polymeric silica sources.

SELECTIVE ALKENE OXIDATION WITH H2O2 AND A HETEROGENIZED MN CATALYST : EPOXIDATION AND A NEW ENTRY TO VICINAL CIS-DIOLS

Covalent anchoring of 1,4-dimethyl-1,4,7-triazacyclononane on silica gel is the first step in the preparation of a heterogenized Mn catalyst. When H2 O2 is used as the oxidant, this material can catalyze the vicinal cis-dihydroxylation of disubstituted olefins, as shown schematically here. Both enantiomers of the product are obtained.

Methylalumoxane MCM‐41 as Support in the Co‐Oligomerization of Ethene and Propene with [{C2H4(1‐indenyl)2}Zr(CH3)2]

Superior to the homogeneous catalyst or physisorbed catalyst system is a system with the ansa-metallocene catalyst [{C2 H4 (1-ind)2 }Zr(CH3 )] on a support formed by covalently anchoring methylalumoxane (MAO) on the internal pore walls of MCM-41. This system is a highly active and shape-selective mesoporous host in the co-oligomerization [shown schematically in Equation (a)] of ethene and propene with ansa-metallocenes. TMA=trimethylaluminum, ind=indenyl.

Sodium Clusters in Zeolites as Active Sites for Carbanion Catalyzed Reactions

The isomerisation of the n-butenes over Y zeolites loaded with ionic and neutral sodium clusters was investigated. These clusters were formed upon thermal activation of the zeolite impregnated with methanolic solutions of sodium azide. Three different sodium particles could be distinguished with ESR spectroscopy: extralattice Naox, intracrystalline Naoy clusters and ionic Na3+4, clusters located in the sodalite cages. The relative intensities of the respective cluster signals are dependent upon the rate of activation and support structure. From kinetic data, it followed that the sodium-on-zeolite Y catalyst was very active in the butene isomerisation reaction and that the reaction intermediates are of a carbanion type. Indeed, substrates without a-hydrogen like 3, 3-dimethyl-l-butene cannot be isomerised at all. In situ ESR spectroscopy of the working catalyst was used to determine the active site. It followed that intra-crystalline metallic clusters are the active entities for double bond shift and cis-trans isomerisation.

PREPARATION OF HIGH-SILICA FAUJASITES BY TREATMENT WITH SILICON TETRACHLORIDE

NaY has been dealuminated in highly controlled conditions by SiCl4. The materials thus obtained, after subsequent washing and ammonium exchange, were characterized by chemical analysis, thermogravimetry, X-ray diffraction, infrared spectroscopy of the framework and surface hydroxyl groups and 29Si nuclear magnetic resonance spectroscopy.In order to obtain highly crystalline materials in a reproducible way, a very specific dealumination and washing procedure has to be followed. The mechanism of the dealumination is complex and always combines direct isomorphic substitution with acid leaching of aluminium. The materials obtained have continuously varying properties as far as unit-cell dimensions and framework vibrations are concerned. In contrast, the amount of extra-lattice aluminium retained in the zeolite reaches a maximum at intermediate degrees of dealumination.

A Heterogeneous cis‐Dihydroxylation Catalyst with Stable, Site‐Isolated Osmium–Diolate Reaction Centers

Involatile OsO4 ! A tetrasubstituted olefin is immobilized on SiO2 and reacts with OsO4 to form a stable osmate(IV) ester, which is a leak-proof heterogeneous catalyst for the cis-dihydroxylation of olefins.

Synthesis and Characterisation of Silicon-Rich Sapo-5

Abstract The synthesis of silicon-rich SAPO-5 is reported. The Incorporation of silicon in the framework of SAPO-5 is demonstrated by 27Al, 29Si and 31P MAS NMR, IR spectroscopy and catalytic test reactions.

Impact of annealing on the susceptibility of wheat, potato and pea starches to hydrolysis with pancreatin

Abstract Native, and one- and two-step annealed wheat, pea and potato starches were subjected to hydrolysis with pancreatin (1.34 nKat/mg starch, 37 °C, pH 6.0). While annealing increases enzyme resistance for wheat, pea and potato starches in the first (rapid) phase of hydrolysis, it increases the extent of degradation in the second (slower) phase for wheat and pea starches. Annealed potato starches, however, are still more resistant than native potato starch in the second phase of hydrolysis. Environmental scanning electron microscopy shows that enzymic degradation of wheat starch granules does not proceed uniformly throughout the granule population. Pancreatin action does not affect differential scanning calorimetry (DSC) gelatinisation characteristics of all studied native and of annealed potato starches. Although enzymic hydrolysis has no great effect on the DSC gelatinisation behaviour of native starches, partial enzymic solubilisation of the granules enhances the effects of annealing. After 2 and 120 h of solubilisation, DSC thermograms of annealed wheat and pea starches show somewhat broader peaks with lower enthalpies than those of the corresponding unhydrolysed starches. 13 C CP/MAS NMR data of extensively (46%) degraded and undegraded native wheat starch granules show no change in double helix content, whereas after 57% solubilisation of one-step annealed wheat starch, a decrease in the proportion of double helices is observed. The 13 C CP/MAS NMR signal at 31 ppm increases by a factor 2.0 for 46% solubilised native wheat starch, and by a factor 2.3 for 57% solubilised annealed wheat starch, indicating resistance of amylose-lipid complexes to pancreatin hydrolysis. Dissociation enthalpies, however, are higher than can be predicted from a concentration of complexes. The enthalpy of dissociation of amylose-lipid complexes, after enzymic hydrolysis, increases more for annealed than for native wheat starch. All the above suggest that, during annealing, molecular changes occur that have an impact on pancreatin hydrolysis.

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.