Pt-Zn/HZSM-5 as a highly selective catalyst for the Co-aromatization of methane and light straight run naphtha

Abstract

Selectivity of catalysts has become increasingly important in the petrochemical industry in order to reduce waste, maximize efficiency, and reduce costs. Reported here is a catalyst in the form of Pt-Zn/HZSM-5 with low acidity to reduce over cracking and maximize selectivity of benzene, toluene, and xylene (BTX) during the aromatization of naphtha under methane environment. The Pt-Zn combination when coupled with HZSM-5 support over light straight run naphtha (LSR) and methane, is capable of BTX selectivity of 94.4% with no formation of detrimental polyaromatics and olefins. Such a performance is attributed to the appropriate distribution of acid sites (seen via NH3-TPD and pyridine DRIFT) with regards to strength and type because of loading Pt and Zn as well as Zn’s ability to reduce coke formation as seen via TGA-DSC (1 μg coke/(g cat·h) for Zn/HZSM-5 and 5.9 μg coke/(g cat·h) for HZSM-5). TEM imaging shows that a methane environment effectively suppresses metal particle agglomeration (1.4 nm average metal nanoparticle diameter) compared to nitrogen (2.1 nm average metal nanoparticle diameter) with XRD showing Pt’s ability to maintain catalyst crystallinity during moderate temperature and moderate pressure as well as reaction time of 1 h. It has been seen here that by employing Zn and Pt in tandem over HZSM-5, catalytic performance can be greatly increased (22.4% BTX yield) when compared to sole loading of Zn (13.4%) or Pt (13.1%), thus a positive synergetic effect is witnessed. Such a selective and coke resistant catalyst shows great promise for the future of LSR reformation to valuable products with methane as a very feasible co-reactant capable of contributing to positive liquid products.