ACTIVATION OF SULFATED ZIRCONIA CATALYSTS - EFFECT OF WATER-CONTENT ON THEIR ACTIVITY IN N-BUTANE ISOMERIZATION

effect of water content in sulfated zirconia catalysts on their activi ties for n-butane isomerization was investigated using catalytic testi ng, Fourier transform infrared (FTIR) spectroscopy and thermogravimetr y analysis. It was found that minor amounts of water promote the catal ytic activity while excess water diminishes it. The FTIR spectrum of p yridine adsorbed on the catalysts showed that a decrease in water cont ent resulted in a decrease in Bronsted acidity with a concurrent incre ase in Lewis acidity. In the most active catalyst, approximately two-t hirds of the acid sites are Bronsted sites, and the rest are Lewis sit es; an appropriate amount of water is needed to produce this ratio. Th e Bronsted acid sites presumably contribute to the catalysis by proton ating butene formed at redox sites on the catalyst to create carbocati ons. The high catalytic capability of the Bronsted acid sites requires the presence of adjacent Lewis acid sites, which withdraw electrons f rom bisulfate SO-H bonds through an induction effect, giving rise to m ore acidic protons.