Comparison of the effects of nitrogen poisoning on molybdenum oxycarbide and Pt/beta-zeolite catalysts in the isomerization of n-heptane

The effect of nitrogen-containing compounds was studied over MoO3-carbon-modified and Pt-(1,5 wt %)/beta-zeolite catalysts using n-heptane isomerization as the test reaction and piperidine and pyridine as the poisoning molecules, n-Heptane isomerization performed over both catalysts under pure feed showed no deactivation as a function of time on stream. At a pressure of 6 bar the MoO3-carbon-modified catalyst exhibited a high resistance to deactivation up to 10 ppm of nitrogen, while the Pt-based catalyst was strongly deactivated down to 30% of its initial activity after 20 h. At higher concentrations of nitrogen (greater than or equal to 40 wt ppm) deactivation occurred over both catalysts as a function of time. Results obtained after different regeneration regimes on the MoO3-carbon-modified deactivated catalyst led to the conclusion that the deactivation observed was essentially due to coke formation. Finally, increasing the total pressure allowed a better resistance to deactivation by hydrogenating the coke residues over the MoO3-carbon-modified catalyst.