Gönül Gündüz

Heterogeneous Fenton-like degradation of Rhodamine 6G in water using CuFeZSM-5 zeolite catalyst prepared by hydrothermal synthesis.

In this study, heterogeneous Fenton-like degradation of reactive azo dye Rhodamine 6G in water was investigated over a CuFeZSM-5 zeolite catalyst prepared by hydrothermal synthesis. At initial pH of 3.4, a color removal of 100% was achieved after a reaction time of 45 min. TOC elimination was measured to be 51.8% after 2 h of oxidation. Initial decolorization rate was described by an equation of -r(A0) = 4.56 x 10(2) e(-24.83/RT)C(R6G,0)C(0.35)(H2O2,0) where R is in kJ/mol. The leaching of iron and copper cations from zeolite structure into the solution during oxidation was dependent on pH strongly. The regulation of pH from 6.5 (dye solution pH) to 3.4, increased leaching for iron from 0.7 to 0.8 mg/dm3 and for copper from 1.4 to 2.1 mg/dm3. The copper was totally leached from the catalyst during the process at pH 3.4.

Isomerization of α-pinene over ion-exchanged natural zeolites

Abstract Catalysts prepared by ion exchange of clinoptilolite-based natural zeolite tuffs with NH 4 + , Ba 2+ and Pb 2+ were investigated in the isomerization reaction of α-pinene at atmospheric pressure under nitrogen flow. Activity and selectivity to mono-, bi- and tricyclic products were correlated with acidity strength.

Influence of catalyst pretreatment on a-pinene isomerization over natural clays

The kinetics of α-pinene isomerization over natural clays and the influence of catalyst pretreatment with different amounts of sulfuric acid have been investigated in a batch reactor at atmospheric pressure. Contrary to catalytic activity, selectivity was seen to be independent of pretreatment.

Isomerization of Alpha-pinene Over Acid Treated Natural Zeolite

Abstract In this study, isomerization of α-pinene was studied over several acid-treated natural zeolite catalysts rich in clinoptilolite. Zeolite samples were contacted with HCl at different concentrations at 30°C or at 60°C for 3 and 24 hours and tested in isomerization reaction of alpha-pinene. The catalysts prepared were characterized by XRD, nitrogen adsorption, and acidity studies. Acidity strength and the distribution of Lewis and Brönsted acid sites of the catalysts were determined, and their catalytic activities in α-pinene isomerization and selectivities to main reaction products, camphene and limonene, were investigated. Acid treatment improved the selectivity of catalyst samples to camphene, decreasing the selectivity to limonene, probably forcing limonene to secondary reactions at high conversions. The kinetics of α-pinene consumption was described by first-order kinetics. Two kinetic models were tested for the reaction mechanism and one model was found to give a good correlation between the theoretical and experimental data. In the models, the key intermediate was the pinylcarbonium ion, which was formed irreversibly from α-pinene. Number and distribution of Lewis and Brönsted acid sites affect the formation of bicyclic and monocyclic products.

Heterogeneous Fenton-like Degradation of Orange II in Water Using FeZSM-5 Zeolite Catalyst

In this study, Fenton-like degradation of Orange II in water was investigated over an FeZSM-5 zeolite catalyst prepared by ion exchange. A color removal of 99.99 % and a COD elimination of 55.0 % were achieved after a reaction time of 2h at 266.7 mM H2O2 at 323 K for 0.05 g/dm3 of Orange II solution at a pH around 7. Initial decolorization rate was described by an equation of -rAo = 6.4x103 e-30.7/RT COII,o CH2O2,o0.3 where R is in kJ/mol. No significant decay in decolorization efficiency of the used catalyst was observed.

Fe Containing ZSM-5 Zeolite as Catalyst for Wet Peroxide Oxidation of Orange II

This study presents the catalytic performances of iron containing ZSM-5 zeolites, prepared by ion exchange or hydrothermal synthesis, in catalytic Fenton-like oxidation of Orange II in aqueous solution. The catalyst, ZSM-5 zeolite with Si/Al ratio of 42 loaded with iron by ion exchange, showed the highest activity. The decolorization of 99.7 percent, degradation of 87.0 percent and COD removal of 81.2 percent were achieved over this catalyst at an initial pH of 3.5. Incorporation of iron into ZSM-5 structure increased its catalytic activity. The hydrothermally prepared FeZSM-5 catalyst was more stable against leaching at low pH value due to the iron being in the framework.

Catalytic Wet Air Oxidation of Oxalic Acid at Atmospheric Pressure

Catalytic wet air oxidation of oxalic acid in aqueous solution was investigated in a stirred reactor over a Pt (0.7% in wt)/Al2O3 catalyst at atmospheric pressure, in a concentration range of oxalic acid of 500-3000 ppm, and at a temperature range of 313-353 K. The conversions obtained after 5 h were 28.96 %, 45.98 % and 30.74 % for initial concentrations of 500, 1500, 3000 ppm, respectively. A rate equation of oxalic acid oxidation, in mol.h-1.g-1Pt was determined from measurements of initial rates, at different initial concentrations of oxalic acid, temperatures and catalyst mass loads. The activation energy for oxalic acid conversion was found to be 24.6 kJ mol-1.The heterogeneous catalyzed free-radical oxidation of oxalic acid was discussed.

Catalytic Activity of Heteropolytungstic Acid Encapsulated into Mesoporous Material Structure

The paper presents a spectroscopic and catalytic study of encapsulated Keggin type heteropoly acid (12-tungstophosphoric acid, HPW) in the mesopores of MCM-41 molecular sieves. Nitrogen physisorption, FTIR, SEM, XRD and catalytic methods have been used to characterize and compare the properties of the samples. Methanol conversion, ?-pinene isomerization and ethyl acetate oxidation have been applied as model reactions for the evaluation of acid site activity. The combined physicochemical and catalytic investigations clearly show that the introduction of 12-tungstophosphoric acid into MCM-41 causes significant changes in the properties of the sample.

Influence of ultrasound on the heterogeneous Fenton-like oxidation of acetic acid

The main objective of this study is to investigate the effect of ultrasound on the heterogeneous Fenton-like oxidation of acetic acid, which is one of the most resistant carboxylic acids to oxidation. For this purpose, firstly, the degradation of acetic acid was examined by using ultrasound alone and the effects of different parameters such as: type of sonication system, ultrasonic power, and addition of H2O2 were investigated on the degradation of acetic acid. There was no chemical oxygen demand (COD) reduction in the presence of sonication alone. In the presence of the heterogeneous Fenton-like oxidation process alone, at 303 K, COD reduction reached only 7.1% after 2 h of reaction. However, the combination of the heterogeneous Fenton-like oxidation process with ultrasound increased the COD reduction from 7.1% to 25.5% after 2 h of reaction in an ultrasonic bath operated at 40 kHz, while the COD reduction only increased from 7.1% to 8.9% in the ultrasonic reactor operated at 850 kHz. This result indicates that the hybrid process of ultrasound and heterogeneous Fenton-like oxidation is a promising process to degrade acetic acid.