Alkali-promoted alumina catalysts: I. Chemisorption and oxygen exchange of carbon monoxide and carbon dioxide on potassium-promoted alumina catalysts

Abstract

Some potassium-promoted alumina catalysts were prepared by impregnating alumina with K 2CO 3 solutions. The catalysts were calcined at 620 °C before use. K 2CO 3 decomposed completely during calcination, but no potassium oxides or aluminates were formed on the surface. Oxygen exchange between those catalysts and C 18O 2 and C 18O was measured over a wide temperature range between 50 and 600 °C and compared with results obtained with alumina used as the support. It was found that potassium not only increased the number of exchangeable oxygens on the surface but also weakened the bond between these oxygens and the surface. The chemisorption of carbon monoxide and carbon dioxide was also investigated mainly by infrared spectroscopy. On the present K 2 CO 3 Al 2 O 3 catalysts both gases showed distinctive ir bands, a pair of bands at 1590 and 1320 cm −1 and another pair of bands at 1570 and 1320 cm −1 depending on the temperature. The former pair was assigned to a CO 2 − ion and the latter pair to a bidentate carbonate both attached on the potassium ion. The present results of oxygen exchange on K 2 CO 3 Al 2 O 3 were successfully explained by assuming that the surface species assigned above are the intermediates of the exchange reaction with carbon monoxide and carbon dioxide, respectively.