Alkali metal nitrates and hydroxides were added to Ni/Mo on gamma-alum
ina hydroprocessing catalysts in order to neutralize surface acidity,
thereby reducing coke deposition on the catalyst and enhancing activit
y. The initial activity of the catalysts was tested by hydroprocessing
Athabasca bitumen in microbatch reactors and a 1 L continuous-feed st
irred reactor. Addition of nitrate salts was not effective. Addition o
f 0.26 mmol alkali metal hydroxide/g of catalyst was sufficient to red
uce the concentration of very acidic sites in the catalyst, as measure
d by thermal desorption of pyridine. At this level of addition, coke d
eposition was reduced and hydrodesulfurization was increased. Experime
nts in a batch reactor showed that Li and Na were similar in activity,
giving 80% sulfur removal compared to 63% with the untreated commerci
al catalyst. Coke content was reduced, with carbon concentration decre
asing from 17.3% in the untreated catalyst to 14.4% with Li or Na at 2
6 to 28 mmol/g. The Na-doped catalyst gave a 40% increase in the hydro
desulfurization rate constant over the untreated catalyst in a continu
ous-feed stirred reactor during a 6 h experiment, consistent with the
batch results. Asphaltene removal was also improved, while hydrodenitr
ogenation, microcarbon residue conversion, and residue conversion were
unaffected.