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Influence of exchange cation and layer charge on the isomerization of -pinene over SWy-2, SAz-1 and Sap-Ca

C. BREEN^* and A. J. MORONTA

Materials Research Institute, Sheffield Hallam University, Sheffield S1 1WB, UK

^* E-mail: c.breen{at}shu.ac.uk

(Received 27 November 2000; revised 20 March 2000)

SWy-2 (Wyoming), Sap-Ca saponite (California) and SAz-1 (Cheto, Arizona) were exchanged with different cations (Al, Ni, Mg, Ca and Na). The catalytic activity of these ion-exchanged clays was measured directly using the isomerization of -pinene at 80°C for 2 h to yield camphene, limonene and other minor products. The order of activity for the different cation-exchanged forms was Al > Ni > Mg > Ca > Na, which correlated well with the known polarizing power of these cations and the resulting interlayer acidity. Catalysts derived from Sap-Ca were the most active followed by SWy-2, with SAz-1 the least active by a considerable margin. The greater activity of Sap-Ca over SWy-2 was attributed to the high tetrahedral charge in the former. Reduction of the layer charge of SAz-1 using Li fixation caused a significant improvement in the catalytic activity of the Al-exchanged reduced-charge SAz-1.

KEYWORDS: -pinene, ion-exchanged clays, exchangeable cations, catalysis