Abstract: Ru/Al₂O₃-ZrO₂-NiO/cordierite catalysts with an egg-shell-like Ru distribution were prepared by conventional incipient wetness impregnation and ammonia gas absorption deposition. The performance of the catalysts in a modified monolithic fixed-bed reactor was evaluated. The catalysts exhibited good selectivity and stability. Importantly, a maximum yield of 24.7% was achieved at a low concentration of ZnSO₄ (0.5 wt%). The catalysts were characterized by N₂ adsorption, X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy, optical microscopy, and scanning electron microscopy/energy-dispersive X-ray analysis. The introduction of NiO resulted in the formation of NiAl₂O₄ phase during calcination at 1373 K, reducing the proportion of small pores. Meanwhile, the presence of ZrO₂ enhanced the sintering resistance of the coating, and moderate surface area was retained after calcination. The egg-shell distribution of Ru, thin layer thickness indicating short diffusion length, small proportion of nanosized pores (e.g., 1-4 nm), moderate specific surface area, and narrow pore size distribution to facilitate Ru dispersion are thought to be important factors controlling the behavior of the present monolithic catalysts.

Key words: Monolithic catalyst, Washcoat, Benzene, Cyclohexene, Selective hydrogenation, Spinel, Zirconia, Nickel oxide