Transition metal modified hierarchical ZSM-5 nanosheet for catalytic cracking of n-pentane to light olefins

Abstract

Catalytic cracking of naphtha is an effective way to produce light olefins, in which zeolite catalyst plays an important role. In this work, hierarchical ZSM-5 self-pillared nanosheet (NS) supporting Ca, Fe and Zr is prepared for catalytic cracking of n-pentane to produce ethylene and propylene. Hierarchical pores by self-pillared nanosheet zeolite aggregates delivers enhanced exposed surface, thus giving improved conversion of n-pentane and yield of olefins, in comparison with conventional microporous ones. Moreover, different metal sites intrigue various reaction pathways in cracking. The dehydrogenation-cracking of n-pentane is demonstrated by Ca/NS catalyst with enhanced conversion of reactant and selectivity of olefins. The introduction of Fe on NS (Fe/NS) sacrifices part of acidities and inhibits the hydrogen transfer reaction by monomolecular cracking pathway, leading to enhanced olefin selectivity and catalytic stability, but decreased conversion of n-pentane. Zr incorporation promotes utilization of Brønsted acid sites through bimolecular cracking routes. The interaction between reactants and Brønsted acid sites or olefins carbenium ions could be promoted by the introduced framework Zr, which improves the conversion of n-pentane, but leading to reduced olefin selectivity with relative low stability.