Nature of zirconium phosphite as an acidic catalyst

The nature of acidic sites on layered zirconium phosphite has been characterized by IR spectra, thermal analysis and catalytic dehydration of ethanol. The catalytic behaviour was compared with that of α-zirconium phosphate. The reaction sequences for ether and ethene formation were studied by analysing the kinetic data. The Bronsted acidity of monohydrogen orthophosphate groups was considered to be the common active site on α-zirconium phosphate and the zirconium phosphite sample calcined at 673 K. For the latter compound, the phosphite groups on the exterior surface were found to be oxidised to phosphate by calcination in air. The uncalcined sample of zirconium phosphite exhibited a different catalytic behaviour. Its selectivity for diethyl ether was the highest among the catalysts studied. The dehydration activity of this compound was presumed to be due to the polar P—H bonds in the phosphite groups.