NH4Y and NH4LaY-type zeolite catalysts were prepared by cyclic ion-exchange of a synthetic Linde Y-zeolite. The release of ammonia and water were followed by evolved gas analysis (automatic thermogastitrimetric equipment) as well as with a continuous selective water detector.
Authors:B. Gergely, A. Rédey, C. Guimon, A. Gervasini, and A. Auroux
The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry.
The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide
and also ammonia were measured on these catalytic surfaces. NH3, SO2, NO2 are strongly adsorbed while NO is only physisorbed. The supported Ga2O3 samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of
SnO2 decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify
the acidity of titania. In all cases, the basicity, probed by SO2 adsorption, is very strongly affected by the deposition of Ga2O3 or SnO2. The differential heats of NO2 adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and
of the amount of guest oxide.
Authors:H. Nasser, Á. Rédey, Tatiana Yuzhakova, and J. Kovács
In order to explore the influence of CeO2 on the structure and surface characteristics of molybdena, an investigation was undertaken by using N2 adsorption (BET method), thermal analysis and in-situ diffuse reflectance infrared (DRIFT) techniques. In this work, the
Mo/CeO2 and Ce-Mo/Al2O3 samples were prepared by impregnation and co-precipitation methods with high Mo loadings. Combining the results one may notice
that the presence of ceria led to the increase of polymerized surface Mo species so as to forming Mo-O-Ce linkages besides
the formation of coupled O=Mo=O bonds indicative of polymeric MoO3.
From thermal analysis, it can be inferred that Mo/Al2O3 is the thermally most stable material in the temperature range used in the experiment (up to 900°C), whereas Ce-Mo/Al2O3 and Mo/CeO2 samples undergo morphological modifications above 700°C resulting in lattice defects, which motivate the mobility of Mo and
Ce ions and thus enhance the possibility of interaction between them. Additionally, their activity towards CO adsorption needs
reduced ceria and molybdena containing coordinatively unsaturated sites (CUS), oxygen vacancies and hydroxyl groups to form
various carbonate species.
Authors:Elizabet Horváth, J. Kristóf, L. Vázquez-Gómez, Á. Rédey, and V. Vágvölgyi
The thermal evolution process of RuO2–IrO2–SnO2
mixed oxide thin films of varying noble metal contents has been investigated
under in situ conditions by thermogravimetry-mass spectrometry (TG-MS), infrared
emission spectroscopy (IR) and cyclic voltammetry (CV). The gel-like films
prepared from aqueous solutions of the precursor compounds RuOHCl3,
H2IrCl6 and Sn(OH)2(CH3COO)2–xClx on titanium metal support were heated in an atmosphere
containing 20% O2 and 80% Ar up to 600C. Chlorine
evolution takes place in a single step between 320 and 500C accompanied
with the decomposition of the acetate ligand. The decomposition of surface
species formed like carbonyls, carboxylates and carbonates occurs in two stages
between 200 and 500C. The temperature of chlorine evolution and that
of the final film formation increases with the increase of the iridium content
in the films. The anodic peak charge shows a maximum value at 18% iridium
Authors:E. Horváth, J. Kristóf, R. Frost, Á. Rédey, V. Vágvölgyi, and T. Cseh
The thermal behaviour of halloysite fully expanded with hydrazine-hydrate has been investigated in nitrogen atmosphere under
dynamic heating and at a constant, pre-set decomposition rate of 0.15 mg min-1. Under controlled-rate thermal analysis (CRTA) conditions it was possible to resolve the closely overlapping decomposition
stages and to distinguish between adsorbed and bonded reagent. Three types of bonded reagent could be identified. The loosely
bonded reagent amounting to 0.20 mol hydrazine-hydrate per mol inner surface hydroxyl is connected to the internal and external
surfaces of the expanded mineral and is present as a space filler between the sheets of the delaminated mineral. The strongly
bonded (intercalated) hydrazine-hydrate is connected to the kaolinite inner surface OH groups by the formation of hydrogen
bonds. Based on the thermoanalytical results two different types of bonded reagent could be distinguished in the complex.
Type 1 reagent (approx. 0.06 mol hydrazine-hydrate/mol inner surface OH) is liberated between 77 and 103C. Type 2 reagent
is lost between 103 and 227C, corresponding to a quantity of 0.36 mol hydrazine/mol inner surface OH. When heating the complex
to 77C under CRTA conditions a new reflection appears in the XRD pattern with a d-value of 9.6 , in addition to the 10.2
Ĺ reflection. This new reflection disappears in contact with moist air and the complex re-expands to the original d-value
of 10.2 in a few h. The appearance of the 9.6 reflection is interpreted as the expansion of kaolinite with hydrazine alone,
while the 10.2 one is due to expansion with hydrazine-hydrate. FTIR (DRIFT) spectroscopic results showed that the treated
mineral after intercalation/deintercalation and heat treatment to 300C is slightly more ordered than the original (untreated)
Authors:Viorel Chihaia, Karl Sohlberg, M. Scurtu, C. Hornoiu, M. Caldararu, C. Munteanu, G. Postole, N. I. Ionescu, T. Yuzhakova, and A. Redey
The surface dynamics of SnO2/γ-Al2O3 catalysts with different tin dioxide loadings (3 and 20 wt%) prepared by the impregnation method were investigated by using in situ electrical/dielectric measurements. The samples were characterized by BET, inductively coupled plasma atomic emission spectroscopy and X-ray diffraction methods. The propylene oxidation reaction, in the temperature range of 30–400 °C, was used to identify the catalytic activity of SnO2 based catalysts. Results are discussed on the bases of the electrical changes accompanying variation of the active phase content. The conductance/capacitance of supported samples evidenced the reciprocal influence of the support and of the guest oxide.