FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF COKE DEPOSITS ON A CR2O3-AL2O3 CATALYST

The process of coke deposition during the dehydrogenation of butene to butadiene over a chromia-alumina catalyst has been studied by Fourier transform infrared spectroscopy. The study was carried out on samples of coked catalyst dispersed on KBr pellets. The aromatic C=C stretchi ng (1630-1500 cm(-1)) and aliphatic C-H bending (1450-1300 cm(-1)) reg ions of the spectra were examined by curve-fitting analysis in order t o improve the information provided by Fourier transform infrared spect roscopy. Different steps in the process of coke deposition were observ ed. At low temperature the coke is formed by polyolefinic chains rathe r than by aromatic structures. Aromatization of coke takes place with increasing temperature and can be followed by observing the peak at 15 90 cm(-1). The aging of the coke in nitrogen does not produce modifica tions in its aromaticity and the observed dehydrogenation is due to th e loss of aliphatic structures as is revealed by the 1385 cm(-1) band.