Ti-modified Pt/Al2O3 catalyst for efficient continuous production of piperidine via selective pyridine hydrogenation

Abstract

Pyridine selective hydrogenation to piperidine is an important alternative to chemical synthesis. The commercial pyridine hydrogenation technologies taking Pt/Pd/Rh supported on carbon material as catalysts suffer from difficult molding and poor mechanical properties, resulting in their inability to be applied to continuous catalytic hydrogenation process. Here, Ti modified Pt-supported Al₂O₃ catalyst used in continuous hydrogenation process was synthesized via a one-pot hydrothermal method. Using a variety of complementary characterization methods, we identified the existence forms of Pt and Ti species in the catalyst. The results revealed that Ti modification decreased the density of strong Lewis acid sites on the catalysts, resulting in a decrease in Pt dispersion. Conversely, the introduction of Ti atoms significantly enhanced the reducibility of Pt species. This can be attributed to the formation of Ti^3 + species, whose presence effectively facilitated the reduction of higher-valent Pt species (Pt²⁺ and Pt⁴⁺) to Pt⁰. The Pt/Ti7.5/Al₂O₃ catalyst with 7.5 wt% TiO₂-containing achieved up to 87.8 % conversion of pyridine and 92.4 % selectivity of target product piperidine at 160 °C, 4.0 MPa, 300 H₂/oil (v/v), and 6 h⁻¹ LHSV in the fixed-bed continuous hydrogenation process, an improvement of 7.5 % and 9.9 % respectively, compared to Pt/Al₂O₃ catalyst. This optimal performance can be attributed to the balanced state of the active metal dispersion and reducibility at this specific Ti loading, where the synergy between these two factors maximized the active metal utilization ratio, thus leading to the catalyst being able to maximize its catalytic efficiency.