A. Béres

Layered double hydroxides and their pillared derivatives – materials for solid base catalysis; synthesis and characterization

Abstract Mg–Al and Zn–Al L(ayered) D(ouble) H(ydroxide)s have been prepared and characterized. Thermal and dehydration/rehydration behaviour was studied by thermoanalytical methods (TG, DTG, DTA) and 27 Al M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Acid–base properties of the calcined samples were investigated by T(emperature) P(rogrammed) D(esorption) of preadsorbed CO 2 and the double-bond isomerization reaction of 1-butene. Heat treatment destroyed the layered structure, which could be only partially reconstituted by rehydration. On calcination mixed oxide with the predominance of basic sites were formed. Pillaring of the LDHs with organic (terephtalate, dodecyl sulphate) as well as inorganic (oxometallate, ferrocyanide) anions were also performed. The materials were characterized by infrared (IR) spectroscopy, XRD and BET measurements. Heat stabilities of the pillared substances were investigated too. Pillaring by various methods proved to be successful, however, decreased heat resistance was found in the intercalated materials relative to the host LDHs.

Indium and gallium containing ZSM-5 zeolites: acidity and catalytic activity in propane transformation

Abstract Surface acidity and propane transformation on In-and Ga-containing ZSM-5 type zeolites were investigated to find relation between the acidic character of catalysts prepared by conventional or solid state ion-exchange and the catalytic activity in alkane aromatization. On the basis of the concentration of Brensted and Lewis acid sites measured by IR spectroscopy the In and Ga containing samples may be ordered into three main groups. The presence of Brensted acid sites results in cracking of the hydrocarbon molecules, whereas the aromatization activity is attributed to Lewis acidity associated with the intimate contact of the oxide/zeolite assemblies.

Characterization of alkali metal cluster-containing faujasites by thermal, IR, ESR, multi-nmr and test reaction studies

Summary Characterization of alkali metal clusters in MY-FAU (M=Li + , Na + , K + , Rb + , Cs + ) by a combination of physical-chemical methods revealed the formation of both charged and neutral Na~ and My clusters upon heat treatment of NaN 3 -loaded zeolites. They turned out to be efficient basic catalysts.

Synthesis of layered double hydroxides and their reactivities in 1-butene isomerization after calcination

Layered double hydroxides were synthesized and their catalytic activities tested in 1-butene isomerization after calcination at 723 K. The heat treatment destroyed the hydrotalcite-like structure creating mixed oxides with wide-ranging acid-base properties as revealed by temperature-programmed desorption of carbon dioxide and the double bond isomerization of 1-butene.

Acid-base testing of catalysts using 1-butene isomerization as test reaction

Catalysts tested were classified into two groups according to the initial ratio ofcis- andtrans-2-butene in the products. CaY, Fe-PILC and Al-PILC proved to be acidic while LiY, NaN3/NaY and calcined hydrotalcite (HT) basic materials.

Dehydration-rehydration behaviour of layered double hydroxides: a study by X-ray diffractometry and MAS NMR spectroscopy

Abstract MgAl and ZnAl double hydroxides were synthesized and their dehydration-rehydration behaviour was studied by X-ray diffractometry and 27 Al magic-angle spinning (MAS) NMR spectroscopy. On dehydration the layered structure collapsed, but treatment in water resulted in partial reconstitution of the original structure. On heat treatment part of the octahedrally coordinated aluminium, typical of layered double hydroxides, became tetrahedrally coordinated. On rehydration some of the tetrahedral aluminium became octahedrally coordinated again.

Characterization and catalytic activity of Ni-Al and Zn-Cr mixed oxides obtained from layered double hydroxides

Abstract In this work, the preparation of Ni–Al and Zn–Cr layered double hydroxides (LDHs) and their transformations upon calcination are described. The LDHs were prepared from their nitrate salts by pH controlled precipitation. They were characterized before and after calcination by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and BET surface area measurements. The acid–base properties of the dehydrated materials were also investigated by temperature programmed CO 2 desorption and the double-bond isomerization reaction of 1-butene. It was found that upon calcination mixed oxides with large surface areas were formed, which possessed mainly acidic sites of moderate strength.

Thermal behavior of alkali metal azides in NaY-FAU zeolite

The thermal behavior of pure alkali metal azides and their mechanical mixtures with NaY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. LiN3, KN3, RbN3 and CsN3 were prepared from NaN3 by ion-exchange. The pure azides exhibited low thermal stability, hindering the precise spectroscopic characterization in some cases. The decomposition of each azide in the zeolite took place above the temperature characteristic for the pure azide, demonstrating the stabilization of the azide in the zeolite cavities. This feature was the only common characteristic established for the azide/zeolite systems.

Behaviour of Hydrotalcite and Its Fe (CN)64- Pillared Derivative on Heat Treatment

Mg-Al L(ayered) D(ouble) H(ydroxide) was prepared and its thermal behaviour was characterized by thermoanalytical methods (TG, DTG, DTA), 27Al M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Heat treatment destroyed the layered structure, which could only be partially reconstituted by rehydration. On calcination mixed oxide with the predominance of basic sites were formed. Pillaring the LDH with Fe(CN)64- anions was also performed. The material was characterized by XRD and BET measurements. Heat stability of the pillared substance was investigated, too. Pillaring proved to be successful, however, decreased heat resistance was found in the intercalated material relative to the guest LDH.

STATE OF ALKALI AZIDES IN ZEOLITES STUDIED BY THERMAL ANALYSIS

Thermal behaviour of pure LiN3, NaN3, CsN3 and their mixture with the respective LiY-FAU, NaY-FAU, CsY-FAU zeolite was investigated by means of thermogravimetry and IR spectroscopy. Thermodesorption of CO2 was applied to compare the basicity of the alkali ionexchanged Y zeolites. Two of the investigated systems, the NaN3/NaY-FAU and the CsN3/CsY-FAU gave single, well defined and reproducible azide decomposition features rendering these samples to apply as catalyst precursors for preparation of zeolite with basic character.