Determination of probalility of chain growth of coke formation on metals and on supports of Pt/gamma-Al[subscript 2]O[subscript 3] by using the Schulz-Flory distribution theory

Abstract

In this thesis, the main goal was to study the distribution and probability of chain growth of coke on the metal sites and on the support sites. At the beginning, the combination of Pt/SiO2 representing the metal sites and Al2O3 representing the acid sites was investigated. Considering conversion, metal site, H2 uptake and the nature and amount of coke, interestingly, it was found that Pt/SiO2 with 100-120 mesh mixed with Al2O3 60-80 mesh has coking behavior similar to Pt/Y-Al2O3. TPO, ESR, IR, BET, XRD, TEM and Soxhelt extraction analyzed with GC-14B were employed for characterization. It was obvious that the effects of time, temperature, H2/HC ratio and modification of catalysts greatly affected reducing of the amount and probability of chain growth of coke. By considering coke formation on the metal sites and on the support sites, it was found that probabilities of chain growth on both sites were the same. However, the greater accumulation was occurred on the support. This offered the transformation on gas phase of coke intermediates from the metal, which was primarily responsible for producing the coke precursors, to the support as proposed in this model of coke formation. Since coke on the metal has a lower degree of polymerization, the coke was rich in hydrogen.