Characterization of coke deposited on spent catalysts for long-chain-paraffin dehydrogenation

The chemistry, morphology, and structure character of coke deposited on spent catalysts for long-chain-paraffin (n-C16–19) dehydrogenation and the effect of coke on the surface structure of the catalysts were studied by several characterization techniques: thermogravimetry/differential thermal analysis (TG-DTA), elemental analysis, UV Raman spectroscopy, temperature-programmed oxidation (TPO), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunaucr–Emmett–Teller (BET), mercury intrusion porosimetry (MIP) and CO-chemisorption. During the dehydrogenation of n-C16–19, coke gradually accumulates on the surfaces of the catalysts while the coking rate and the H/C mole ratio of the coke decrease. After the times on stream (TOS) of 960 h, the coke deposition on the catalysts is up to 6.56 wt.%, and the H/C mole ratio of the coke is only 0.86. The coke is graphited or amorphous nature and contains conjugated olefinic species and polycyclic aromatic hydrocarbons (PAHs). The coke causes a significant deactivation of the active sites. As compared with the fresh catalysts, the surface area, the total pore volume and the Pt dispersion of the spent catalysts are decreased 19.4%, 33.3% and 61.2%.