Abstract
In the present work, the effect of the citric acid (i.e., adsorption-assisting agent) and the thermal treatment over the citric acid-synthesized CoMo catalyst precursors were investigated. The catalysts were prepared by wet co-impregnation of γ-alumina extrude with citric acid-containing CoMo aqueous solution in acid medium (pH = 2–3) and treated at various temperatures (typically between 110 and 400 °C) in an air atmosphere. The γ-alumina-supported CoMo sulfide catalysts were evaluated using two different feeds (a model feedstock containing various S and N compounds (hereafter feed 1) and a real feedstock (hereafter feed 2). It was found that the synthesis of alumina-supported high loading CoMo catalyst precursor by wet co-impregnation using citric acid as chelating agent in the CoMo impregnation solution takes place mainly through the uniform deposition–precipitation of Co aqueous complex and Mo citrate onto alumina. This process leads to the formation of nanodispersed Co and Mo species that effectively mitigate the formation of β-CoMoO4 during the thermal treatment at high temperature (i.e., 350 °C). The decomposition reaction of Co aqueous-complex and Mo citrate deposited on alumina started at 220 °C. The gradual degradation of the whole metal citrate with increasing treatment temperature decreased the catalyst activity because of the apparent formation of poorly reducible mixed-metal oxides in the catalyst precursor. The use of citric acid to synthesize the CoMo formulations enhances not only the C–S bond scission through the direct desulfurization pathway, but also the hydrogenation route.
Highlights
It is well-established that the combustion of fossil fuels emits harmful gases and compounds into the atmosphere that produce long-term disease in the living organisms and the greenhouse effect
This process leads to the formation of nanodispersed Co and mol L-1 (Mo) species that effectively mitigate the formation of bCoMoO4 during the thermal treatment at high temperature
A series of citric acid-synthesized c-alumina-supported CoMo catalyst precursors treated at various temperatures and sulfided with middle distillate spiked with dimethyl disulfide (4 wt. % sulfur) at 350 °C was catalytically examined for deep HDS and HDN reactions over two different feedstocks
Summary
It is well-established that the combustion of fossil fuels emits harmful gases and compounds into the atmosphere that produce long-term disease in the living organisms and the greenhouse effect. Cation coordinated to the carboxyl groups and terminal oxygen atoms deposited on alumina, whose maximum HDS activity was obtained in the catalyst thermally treated at 220 °C It is well-established in the literature that the use of citric acid as chelating agent can give additional benefit to the HDS catalyst performance as long as the sulfidation is carried out over the catalyst precursors previously treated at low temperatures to preserve the chelating effect over Co (or Ni) and Mo species. We tried to gain further insight into the deposition of high loading of Co and Mo citrate species on alumina surface and their evolution during the thermal treatment by characterizing and testing a series of CoMo catalysts They were synthesized by wet co-impregnation of alumina body with citric acid-containing CoMo aqueous solution. Sulfur/ug.g1 Nitrogen/ug g* Density (15oC)/g cm-3 Boiling point range/oC Mono-aromatics/wt. % Di-aromatics/wt. % Poly-aromatics/wt. % Total aromatics/wt. % Other HCs/wt. % Cetane index
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