Ga-MCM-41 synthesis and catalytic activity in the liquid-phase isomerisation of α-pinene

A procedure to synthesize Ga-MCM-41 materials, using gallium nitrate and tetraethyl orthosilicate (TEOS) as gallium and silica sources, respectively, is reported. Samples were synthesized with a silica/gallium ratio of 40, 30, 20 and 10 and subsequently characterised by XRD, N-2 adsorption, SEM, DRIFT measurements and acid properties as surface acidity using pyridine (PY) and 2,6-dimethylpyridine (DMPY) as probe molecules, as well as, DRIFTs of absorbed pyridine in gas phase. Materials were tested in the liquid-phase-alpha-pinene isomerisation reaction. According to the literature, the isomerisation proceeds via two parallel and competing pathways, one yielding monocyclic products and the other yielding polycyclic products depending on the catalysts acid strength. Camphene and limonene were obtained as major products. Camphene and polycyclic products are formed in weak (Lewis acid sites) whereas stronger (Bronsted) acid sites resulted in limonene and monocyclic derivatives. Materials exhibited an interesting catalytic activity in terms of conversion and selectivity to camphene and limonene under mild reaction conditions (353 K). The highest conversion values (around 60-70%) were achieved after 1 h of reaction and further. reaction times did not seem to increase, significantly, the materials activity. (c) 2007 Elsevier Inc. All rights reserved.