Hexane Aromatization: Analysis of the K-Edges of S and K Provides New Insight into H2S Poisoning of Pt/KL

Abstract

The purpose of this investigation was to examine the effect of sulfur impurity on 1%Pt/KL-zeolite catalyst by co-feeding 500 ppbv hydrogen sulfide (H2S) during hexane aromatization under industrially relevant conditions using a plug flow reactor. Product selectivity and hexane conversion were measured with time-on-stream and compared to a clean run carried out under otherwise identical conditions. Sulfur addition to the feed accelerated the rate of deactivation as observed by rapid declines in both hexane conversion and benzene selectivity; hexene selectivity, the product of the less structurally sensitive dehydrogenation reaction, increased significantly. After 20 h, which was enough time to observe sufficient deactivation, the reaction was stopped. For the purpose of catalyst characterization, after cooling to 150 °C, the catalyst was preserved in Polywax 725 to prevent catalyst oxidation. XANES analysis at the potassium K-edge suggests that the local environment for potassium was not significantly altered by sulfur addition, while sulfur K-edge results indicate that sulfur bound to platinum to form platinum sulfide (PtS, not PtS2). Platinum sulfide is likely responsible for accelerating Pt growth, as observed in DRIFTS of adsorbed CO and HR-TEM/STEM micrographs.