| Summary: | Poisoning effect of nitrogen on heterogeneous, supported precious metal catalysts, along with their recycling, was further examined in the liquid-phase hydrogenation of 1-methylpyrrole (<b>MP</b>) to 1-methylpyrrolidine (<b>MPD</b>) over rhodium on carbon or γ-alumina, in methanol, under non-acidic conditions, at 25–50 °C and 10 bar. Reusing a spent, unregenerated 5% Rh/C or 5% Rh/γ-Al<sub>2</sub>O<sub>3</sub> catalyst, it was found that the conversion of this model substrate and the activity of the catalyst were strongly dependent on the amount of catalyst, the type of support, the catalyst pre- or after-treatment, the temperature, and the number of recycling, respectively. An unexpected catalytic behaviour of rhodium was observed when it was used in a prehydrogenated form, because no complete conversion of <b>MP</b> was achieved over even the fresh Rh/C or Rh/γ-Al<sub>2</sub>O<sub>3</sub>, contrary to the untreated one. In addition, there was a significant difference in the reusability and activity of these rhodium catalysts, depending on their supports (activated carbon, γ-alumina). These diversions were elucidated by applying dispersion (O<sub>2</sub>- and H<sub>2</sub>-titration), temperature-programmed desorption of ammonia (NH<sub>3</sub>-TPD), and transmission electron microscopy (TEM) measurements.
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