Effect of the acidity of HZSM-5/MCM-41 hierarchical zeolite on its catalytic performance in supercritical catalytic cracking of n-dodecane: experiments and mechanism. Issue 16 (1st August 2018) - Xian, Xiaochao
Abstract : Tuning the acidity of ZSM-5/MCM-41 hierarchical zeolite by ion exchange with NaCl can enhance its stability for supercritical catalytic cracking. Abstract : The effect of the acidity of HZSM-5/MCM-41 hierarchical zeolite on its catalytic performance in the supercritical catalytic cracking of n -dodecane was investigated by controlled ion exchange with NaCl solution under ultrasonic conditions. XRD and nitrogen adsorption–desorption results showed that the crystal and porous properties were not affected, while NH3 -TPD, the probe reaction of n -hexane cracking and temperature-programmed surface reaction (TPSR) of n -dodecane demonstrated that strong Brønsted acid sites were replaced by Na + (weak Lewis acid sites) to different extents with varying concentrations of NaCl solution. Although the initial conversion of n -dodecane during the supercritical catalytic cracking was slightly reduced, its stability was greatly enhanced by ion exchange. An ultrastable catalyst with no obvious deactivation within 3 h of time on stream (TOS) was obtained by ion exchange with 0.8 M NaCl solution. A mechanism describing the role of the acid sites residing in both micropores and mesopores of the hierarchical catalyst was proposed based on coke analysis.