Fast catalytic conversion of diethylene glycol to morpholine over thermally stable Zn promoted Cu-NiO/Al2O3 catalyst prepared via combustion approach

Abstract Highly active and thermally stable M-Cu-NiO/Al 2 O 3 catalysts (M represents Al/La/Mg/Zn) were prepared by combustion method and applied in diethylene glycol (DEG) conversion to morpholine (Mp). Copper species preserved relatively small crystallite size (19 nm), high dispersion (40.3%) and high surface area (272 m 2 /g) in M-Cu-NiO/Al 2 O 3 catalysts. High dispersion and intimate contact of copper with Al and La/Mg/Zn synergistically enhanced DEG conversion and Mp selectivity. Addition of promoter i.e. La, Mg, or Zn facilitated the formation of surface defects and isolated species to inhibit migration and aggregation of Cu moities during calcination as well as in high temperature DEG conversion reaction. Compared to other catalysts, Zn-Cu-NiO/Al 2 O 3 combusted catalyst exhibited the highest DEG conversion of 99% (55% higher than impregnated catlayst) and Mp selectivity (95%), even at a high DEG space velocity of 0.8 mL g −1  h −1 . Moreover, Zn-Cu-NiO/Al 2 O 3 exhibited excellent thermal stability i.e. less than 2% decrease in initial DEG conversion after 80 h of reaction. The catalysts followed an overall activity order of: Zn-Cu-NiO/Al 2 O 3  > Mg-Cu-NiO/Al 2 O 3   >  La-Cu-NiO/Al 2 O 3 . The catalysts were characterized by XRD, BET surface area, SEM and XPS techniques. The present study, credited to its cost-effective nature, simplicity of operation and high efficiency, can be effectively applied for DEG conversion to Mp on industrial level.