Hydrogen effects on cumene cracking over zirconium oxide promoted by sulfate ion and platinum

The effects of hydrogen on the catalytic activity of zirconium oxide modified with sulfate ion and platinum (Pt/SO42--ZrO2) for cumene cracking were studied with a pulse reactor to examine if the catalytically active protonic acid sites are generated from hydrogen molecules present in the gas phase. In a hydrogen stream, a high conversion was obtained and the deactivation with pulse number was not appreciable. In a helium stream, the activity quickly decreased with pulse number, and the activity gradually recovered when the carrier gas of helium was switched into hydrogen. The formation of carbonaceous residue was extended in the absence of hydrogen, but suppressed in the presence of hydrogen. The effects of hydrogen were examined for other catalysts such as zirconium oxide modified with sulfate ion (SO42--ZrO2) and zirconium oxide modified with platinum (Pt/ZrO2), but no promotion effects of hydrogen on the catalytic activity were observed. The promotion effects of hydrogen for Pt/SO42--ZrO2 are rationalized by the formation of protonic acid sites from hydrogen molecules. The suppression of the carbonaceous residue formation in the presence of hydrogen is also discussed. (C) 1996 Academic Press, Inc.