Agnieszka Węgrzyn

Pillared smectite modified with carbon and manganese as catalyst for SCR of NOx with NH3. Part II. Temperature‐programmed studies

Temperature‐programmed desorption (TPD) and surface reaction (TPSR), and additionally FTIR spectroscopy of adsorbed NO molecules were used to characterise surface sites on pillared smectites modified with carbon and manganese. Much higher adsorption of NH3 than NO was found, but acidic pre‐treatment increased NO sorption to comparable values as well as catalytic performance in SCR of NOx. In this case formation of strongly bound NO3− species was recognised, which reacted with NH3 at a temperature 200 °C higher than weaker adsorbed NO.

Simultaneous removal of dyes and metal cations using an acid, acid-base and base modified vermiculite as a sustainable and recyclable adsorbent

The aim of this work was the modification of vermiculite in order to produce a low cost, efficient and sustainable adsorbent for dyes and metals. Three activation methods consisting of acid, base and combined acid/base treatment were applied to improve the of vermiculites adsorption properties. Adsorbents were tested in single, bi- and tricomponent solutions containing cationic dyes and Cu2+ cations. The raw material showed low adsorption capacity for dyes and metal. The acid/base treated vermiculite had very good adsorption capacity toward dyes while the maximum adsorption capacity for Cu2+ did not change comparing to the starting material. The alkaline treated vermiculite was a good adsorbent for metals, while still being able to remove dyes on the level of the not treated material. Moreover, it was shown that the materials may be regenerated and used in several adsorption-desorption cycles. Furthermore, it was possible to separate adsorbed dyes from metals that were desorbed, using as eluents ethanol/NaCl and 0.05M HNO3, respectively. This opens a possibility for sustainable disposal and neutralization of both of the pollutants or for their further applications in other processes.

The influence of acid treatments over vermiculite based material as adsorbent for cationic textile dyestuffs

The influence of different acid treatments over vermiculite was evaluated. Equilibrium, kinetic and column studies have been conducted. The results showed that vermiculite first treated with nitric acid and then with citric acid has higher adsorption capacity, presenting maximum adsorption capacities in column experiments: for Astrazon Red (AR), 100.8 ± 0.8 mg g(-1) and 54 ± 1 mg g(-1) for modified and raw material, respectively; for Methylene Blue (MB) 150 ± 4 mg g(-1) and 55 ± 2 mg g(-1) for modified and raw material, respectively. Materials characterization by X-ray diffraction, UV-vis-diffuse reflectance spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, X-ray fluorescence, N2 adsorption and CEC determination, has been performed. The results suggest the existence of exchange of interlayer cations, leaching of metals from vermiculites sheets and formation of an amorphous phase in the material. Adsorption follows pseudo 2(nd) order model kinetics for both dyestuffs and equilibrium occurs accordingly to Langmuirs model for AR and Freundlichs model for MB. In column systems Yans model is the best fit. The enhanced properties of acid treated vermiculite offer new perspectives for the use of this adsorbent in wastewater treatment.

SUBSTITUTION OF Fe3+ FOR Al3+ CATIONS IN LAYERED DOUBLE HYDROXIDE [LiAl2(OH)6]2 CO3·nH2O

Synthesis of the Li-Al-Fe layered double hydroxides was performed by the coprecipitation method at constant pH (11.0±0.2) and temperature (40±2°C). Structural features of the as-synthesized samples were investigated by X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy and Mössbauer spectroscopy. The samples consisted of well crystallized [LiFexAl2-x(OH)6]2CO3·nH2O phases with strict ordering of M+ and M3+ cations in the sheets. However, only a proportion of Al3+ could be substituted by Fe3+ ions. The excess Fe3+ cations formed a separate ferrihydrite phase. Incorporation of Fe into the hydrotalcite-like structure resulted in an increase in the a lattice parameter determined by XRD. In addition, a shift of IR absorption bands, ascribed to the stretching vibrations of interlayer CO32− anions as well as the transitional motions of oxygen in the layers, to lower frequencies was observed. The presence of Fe3+ in the octahedral sheets caused a splitting of the band assigned to the stretching vibrations of the layer OH groups. Mössbauer experiments revealed that Fe exists in the synthesized samples in two different chemical environments. A proportion of the Fe3+ cations is incorporated as isolated ions in the [LiFexAl2-x(OH)6]2CO3.nH2O crystal structure. However, Fe3+ ions forming the ferrihydrite phase are dominant in the Fe-rich materials.

Vermiculite-based catalysts for oxidation of organic pollutants in water and wastewater

In presented work natural expanded vermiculite was used as a starting material for synthesis of Fe-doped catalysts. Material was modified with increasing amount of Fe by ion-exchange and precipitation of iron oxide. Composite materials were characterized with respect to their structure (X-ray diffraction, Infrared spectra using Diffuse Reflectance), agglomeration state of Fe (Ultraviolet-Visible spectra using Diffuse Reflectance) and chemical composition. Activity in H2O2 decomposition as well as in phenol oxidation was studied in liquid phase at atmospheric pressure and temperature up to 70 °C. It was shown that doping with Fe increases catalytic activity. However, excess of iron resulted in formation of undesired side-products.

Hydrotalcite-like materials containing manganese – a short review

Numerous hydrotalcite-like or their derivatives have been reported as catalysts for a wide variety of chemical processes including selective reduction of nitrogen oxides with ammonia (SCR, DeNOx) or NOx storage/reduction process, selective ammonia oxidation to nitrogen and water vapour (SCO), N 2 O decomposition (DeN 2 O) and total oxidation for volatile organic compounds (VOCs). Among them manganese-containing hydrotalcite-like materials and their derivatives seems to possess high activity. This paper gives an overview of Mn-containing catalysts, including the catalyst development and their possible applications. The use of mixed metal oxides obtained from synthetic hydrotalcite-like materials mainly in the role of catalysts for the total VOCs decomposition has been reviewed. Achieved results clearly show that tested materials are candidates for potential application in real catalytic processes.

Studies of Zn-Al-Ce mixed oxides as catalysts for diesel soot combustion

Studies of Zn-Al-Ce mixed oxides as catalysts for diesel soot combustion A series of Zn-Al-Ce mixed oxides was synthesized by a co-precipitation method. The obtained samples were characterized with respect to composition (XRF), structure (XRD, FT-IR) and texture (BET). Zn-Al-Ce mixed oxides were tested as catalysts of diesel soot combustion. The best catalytic activity was found for Zn2Ce oxide system, which operated in the temperature range of 350-500°C.