Structural characterization of coke deposits on industrial spent paraffin dehydrogenation catalysts

Coke deposition on spent noble metal catalysts used in petroleum/petrochemical industries is of serious concern on account of its impact on the catalyst deactivation and consequent loss in the production yield. In order to counteract the effects of coke deposition, it is vital to know the location as well as the nature and composition coke deposited on the spent catalysts. In the present study, spent Pt-Sn/Al2O3 catalysts used in the industrial reactors for selective dehydrogenation of C10–C13 n-paraffins to mono-olefins at different coke loading (approximately 7–9%, w/w) were characterized. The characterization of coke deposits were analyzed by the combination of analytical techniques including HPLC, solid-state 13CCP/MASNMR,and TGA.Average structural information has been obtained from the quantitative analysis of NMR data. The results indicate that the nature of coke present in the soluble coke extracts of spent catalysts is rich in alkylated mono- and diaromatics with low percentage of polyaromatics whereas the nature of insoluble coke is highly polyaromatic (aromaticity, fa > 0.95). In addition, temperature programmed oxidation studies by TGA reveals that the coke is deposited on the dispersed metal as well as on the support. © 2002 Elsevier Science B.V. All rights reserved