Testing and characterisation of Pt/ASA and PtPd/ASA for deep HDS reactions

Abstract

The development of a dedicated, second stage deep HDS reactor to meet the low sulfur levels in diesel fuel is a challenging option, since it allows to process the feed under low H2S partial pressures. Because ASA supported noble metal catalysts have a high activity in the HDS of 4,6 di-alkylated DBT's in real gas oil, they constitute a new option. The nature of the active sites on ASA supported noble metal catalysts has been studied by electron microscopy and infrared spectrometry on adsorbed CO (FTIR(CO)). It is concluded that the support acidity plays a role in the genesis of active sites for HDS. Alloying Pt and Pd on ASA results in very active catalysts for conversion of 4-E,6-MDBT and DBT. Pt/ASA has a high selectivity for hydrogenolysis whereas PtPd/ASA shows a high selectivity for hydrogenation reactions. FTIR(CO) and the catalytic activity in DBT HDS indicate the presence of two different sites on PtPd/ASA: HDS sites, similar to those present in Pt/ASA and hydrogenation sites. The former consist of electron deficient Pt which facilitates the formation of sulfur vacancies, whereas the latter are are sulfur free, metal-like sites. The strong competitive adsorption between H2S, 4-E,6-MDBT and DBT suggests that the sulfur containing compounds are all adsorbed through the sulfur atom.