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Research Project
CLAYCATS - Modified Porto Santo Clays as catalysts for liquid phase organic reactions
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Catalytic conversion of limonene over acid activated Serra de Dentro (SD) bentonite
Publication . Fernandes, C.; Catrinescu, C.; Castilho, P.; Russo, P. A.; Carrott, M. R.; Breen, C.
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 m2 g 1 which increased to values as high as 500 m2 g 1 following activation
with 4M HCl at 95 8C for 30 min (SD-4M-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 8C. The sample prepared using 3M HCl at 95 8C for 30 min (SD-3M-95-30) offered the optimum combination of
surface area (470 m2 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.
Influence of exchange cations on the catalytic conversion of limonene over Serra de Dentro (SD) and SAz-1 clays: correlations between acidity and catalytic activity/selectivity
Publication . Catrinescu, C.; Fernandes, César; Castilho, P.; Breen, C.
A bentonite collected at Serra de Dentro (SD), Porto Santo Island, Portugal, and the source clay SAz-1 (Cheto, Arizona) were ion-exchanged
with different cations (Al3+, Ni2+, Cr3+ and Na+
). Variable temperature diffuse reflectance infrared Fourier transform spectroscopy (VT-DRIFTS)
of pyridine treated samples, thermal desorption of cyclohexylamine and real time mass spectrometry of the evolved gases were used to evaluate the
acidic properties of the prepared catalysts. The catalytic activity of these ion-exchanged clays was tested in the acid-catalysed conversion of
limonene at 150 8C, to yield isomerization products (terpinolene, a-terpinene, g-terpinene and isoterpinolene), disproportionation products ( p cymene and p-menthenes) and high molecular-weight compounds. The possibility of increasing the selectivity toward p-cymene, over a catalyst
with substantial Lewis acid character, was particularly envisaged. Catalysts derived from SD were significantly more active than their SAz-1
counterparts. This was mainly attributed to the greater inherent acidity, to the higher structural iron content (providing dehydrogenation activity)
and to the higher nitrogen surface area of the starting SD clays. Within the Mn+
-SD series, the order of activity decreased as
Ni2+ > Al3+ > Cr3+ > Na+
. A direct comparison between Al3+-SD (with maximized Bro¨nsted acidity) and Ni2+-SD (with predominant Lewis
acid character) provided no support for enhanced p-cymene production over Lewis acid sites.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
POCI
Funding Award Number
POCTI/CTM/47619/2002