Effect of cerium and zirconium nanoparticles on the structure and catalytic performance of SAPO-34 in steam cracking of naphtha to light olefins

The effects of cerium and zirconium nanoparticles and their interaction on the structure and catalytic performance of SAPO-34 were investigated in steam catalytic cracking to produce ethylene and propylene from naphtha. The prepared catalysts were characterized by means of XRD, FT-IR, BET, SEM and NH3-TPD techniques. The NH3-TPD results showed that the addition of cerium resulted in the increase of both weak and strong acid sites. However, zirconium addition diminished the weak acid sites and boosted the strong acid sites. The activity measurements indicated that modified catalysts possessing moderate acidity favored ethylene and propylene yield. Response surface methodology in combination with the central composite design was employed to statistically evaluate the effect of cerium (2-8 wt%) and zirconium (2-5 wt%) loading as well as finding an optimum catalyst. By using the desirability function, the optimum SAPO-34 which maximizes the yield of ethylene and propylene simultaneously was found at cerium loading of 2.92 wt% and zirconium loading of 2.98 wt%. Deactivation of SAPO-34 and optimized SAPO-34 were investigated for 10 h of time-on-stream. It was found that the catalytic lifetime of SAPO-34 was poor, but the optimized SAPO-34 showed better resistance to deactivation.