Development of infrared spectroscopy technique for deposited carbon study

Abstract

Carbonaceous deposit on a Pt-Sn/γ-Al2O3 catalyst used for the dehydrogenation propane to propylene was investigated by infrared spectroscopy technique (IR). Coke characterization was performed in an inert atmosphere at ambient and elevated temperatures. The results revealed that the catalyst strongly adsorbed a significant amount of water and CO2 on its surface. The adsorbed water and CO2 obscure the IR absorption band of coke thus hindering the measurement of IR absorption band of coke deposit on catalyst. Purging sample with dry inert gas at an elevated temperature can improve the appearance of the IR absorption band of coke by removing the signal of the interfering adsorbed species. It was found that the carbonaceous deposit can form aromatic ring structure within a short reaction time. Evidences of IR absorption band of coke as reaction increase indicate that the coke structure had a tendency to transform into more polyaromatic rings.