Investigation of n-alkane aromatization over nano-particle nickel supported catalysts

The conversion of n-hexane over nano-particle nickel supported on carbon (petroleum-based and coconut shell) was investigated in a fixed bed reactor. The effect of process parameters (gas hourly space velocity, reaction temperature) and catalyst properties (metal loading, Ni particle size) on the catalytic activity and selectivity of nickel supported catalysts for n-hexane aromatization was investigated. Results were expressed as n-hexane conversion, product selectivity and turnover frequencies. The catalysts were characterized by scanning transmission electron microscopy (STEM), H₂ chemisorption, x-ray photoelectron spectroscopy and propane hydrogenolysis. The main objective of the study was to determine a relationship between nickel particle size and aromatization activity, and, more specifically, the conversion of n-hexane to benzene.; Results for the aromatization of n-hexane to benzene showed an increase in n-hexane conversion and benzene selectivity with an increase in reaction temperature. Over petroleum-based Ni-supported catalysts, activities and selectivities were comparable to existing Pt-supported catalysts. Based on turnover frequencies, it was determined smaller Ni particles were more active and selective for n-hexane aromatization for the conditions investigated in this study. Based on the product distribution, it is believed n-hexane undergoes a distinct unimolecular dehydrocyclization to form benzene.; XPS analysis showed sulfur present on the petroleum-based supported Ni catalyst and these catalysts were more active and selective than their coconut shell counterparts. Experiments in presulfiding the coconut shell Ni-supported catalyst led to an increase in selectivity to benzene, meaning sulfur plays a role in the n-hexane aromatization to benzene.