Aromatization of n-Octane over Pt-Sn/KL catalysts : activity and regeneration

Abstract

Platinum supported on KL zeolite (Pt/KL) is an efficient catalyst for the aromatization of n-hexane into benzene, but is not as effective for n-octane aromatization. The product distribution shows small quantities of C8-aromatics but high amount of benzene and toluene, which are undesired products from the secondary hydrogenolysis reaction. In previous studies, using nano-crystalline KL zeolite (NCL) and the addition of Sn enhanced the activity and selectivity toward C8 aromatics. The advantage of using the NCL is to reduce the diffusion limitations while that of the Sn addition is to break the Pt ensemble by forming the Pt-Sn alloy phase; hence, the hydrogenolysis reaction is inhibited. However, the Pt-Sn alloy may be destroyed during the catalyst regeneration. Therefore, in this work, the combination of using NCL zeolite with the addition of Sn on Pt/KL was studied. It was found that the addition of Sn improved the catalytic activity and selectivity on both Pt/COM and Pt/NCL. However, the PtSn/COM gave higher C8 aromatics than PtSn/NCL. This could be because PtSn/COM has higher fraction of PtSn alloy phase than PtSn/NCL. The effects of regeneration temperature (300-500°C), time (15 min-2h) and air flow rate (10-40 ml/min) on Pt-Sn alloy over COM were also studied. Among the conditions tested, the catalyst regenerated with an air flow rate of 20 ml/min at 400°C for 1 h exhibits the highest degree of PtSn alloy and low residual coke contents, leading to the highest catalytic activity and selectivity in the 2nd cycle which is close to the those observed on the fresh Pt-Sn/COM catalyst.