Catalytic conversion of limonene over acid activated Serra de Dentro (SD) bentonite

A series of acid-activated clay catalysts were prepared from a purified bentonite, rich in structural iron, collected at Serra de Dentro on the island of Porto Santo. The purified bentonite exhibited a surface area of 130 m(2) g(-1) which increased to values as high as 500 m(2) g(-1) following activation with 4M HCl at 95 degrees C for 30 min (SD-W-95-30). The ability of the activated samples to convert limonene to p-cymene was evaluated using a reaction time of 15 min at 80 degrees C. The sample prepared using 3M HCl at 95 degrees C for 30 min (SD-3M-95-30) offered the optimum combination of surface area (470 m(2) g(-1)) and acidity (0.26 mmol g(-1)) and 95% of the limonene was converted to product. About 15% of the product mixture was p-cymene whilst non-volatile products and polymeric species made up 54% of the product mixture. The presence of iron in the octahedral sheet of the SD bentonite appears responsible for the dehydrogenation activity. TG-MS analysis of acid activated samples, saturated with cyclohexylamine, reflected the dehydrogenation capabilities of the catalysts in that SD-3M-95-30 produced the most benzene and aniline as decomposition/transformation products. (c) 2006 Elsevier B.V. All rights reserved.