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 ␣-pinene at atmospheric pressure under nitrogen flow. Activity and selectivity to mono-, bi-and tricyclic products were correlated with acidity strength.
In this work, isomerization reaction of ␣-pinene was studied over several heat-treated natural zeolite catalysts, rich in clinoptilolite, from Balýkesir-Bigadic region in Turkey in a batch slurry reactor under nitrogen atmosphere. Zeolite samples were calcined at different temperatures such as 300, 450 and 600• C. All catalysts were tested in the isomerization reaction of ␣-pinene and were characterised by nitrogen adsorption experiments, IR, and XRD measurements. Acidity strength and the distribution of Lewis and Bronsted acid sites of the samples were determined. Selectivities to main reaction products, camphene and limonene, and reaction kinetics were investigated. Catalytic activity, that is total conversion of ␣-pinene, of heat-treated samples decreased with increasing calcination temperatures. Selectivity to limonene is dependent on ␣-pinene conversion at high conversion levels while the selectivity to camphene is not. The formation of heavy products increased with treatment temperature. It was seen that ␣-pinene consumption could be described by a first-order kinetics.
Liquid phase isomerization of ␣-pinene was studied over a number of differently pre-treated montmorillonite clays. The effects of the acid pre-treatment parameters (acid-to-clay ratio (A/C), water-to-acid ratio (W/A), temperature and pre-treatment time) on the product distribution were investigated. It was observed that the pre-treatment with acid improved the catalytic activity of that catalyst which was activated at 200 • C for 4 h at A/C ratios between 0.2 and 0.4. Alpha-pinene consumption was very small over the catalysts prepared with an A/C ratio of 0.8. Characterization studies that were done by nitrogen and water vapor adsorption experiments and by IR measurements showed that catalysts with high differential pore volumes for pores around 2 nm and homogenous mesopore distributions and with low dealumination degrees were good catalysts for the production of camphene. Catalysts having heterogeneous mesoporosity were found to be the preferable ones for limonene production.
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