Poisoning of Pt/KL catalysts even by ppb levels of H<sub>2</sub>S is a major concern in naphtha reforming for the aromatization of hexane. In this investigation, a 1%Pt/KL-zeolite catalyst prepared by CVD was subjected to clean and sulfur-containing feeds (e.g., 500 ppbv H<sub>2</sub>S) during hexane aromatization at industrially relevant conditions using a fixed bed reactor. Soft x-rays were employed at the Canadian Light Source, Inc. to investigate two potential pathways of sulfur poisoning: (1) direct poisoning of Pt by adsorption of sulfur and (2) poisoning of K atoms proposed to be involved in ring closure. As noted by previous authors, sulfur accelerated the rate of deactivation as observed by rapid declines in both hexane conversion and benzene selectivity; in contrast, hexene selectivity, the product of the less structurally sensitive dehydrogenation reaction, increased. Analysis by XANES at the potassium K-edge indicated that the electronic structure of K was not significantly altered by the presence of sulfur; on the other hand, sulfur K-edge results confirmed that platinum sulfide was formed as PtS. In prior investigations, sulfur was proposed to accelerate Pt agglomeration and blocking of L-zeolite channels, and this was suggested to likely involve platinum sulfide. Agglomeration of Pt was observed in both DRIFTS of adsorbed CO and in HR-TEM/STEM micrographs.

Soft x-ray and TEM characterization of sulfur poisoned Pt/KL catalysts for the aromatization of hexane

255th National Meeting (2018)

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