Ru/Al2O3-ZrO2-NiO/cordierite monolithic catalysts for selective hydrogenation of benzene

Abstract

Ru/Al 2 O 3 -ZrO 2 -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 ZnSO 4 (0.5 wt%). The catalysts were characterized by N 2 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 NiAl 2 O 4 phase during calcination at 1373 K, reducing the proportion of small pores. Meanwhile, the presence of ZrO 2 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. Novel egg-shell-like Ru/Al 2 O 3 -ZrO 2 NiO/cordierite monolithic catalysts with tailored pore structure are fabricated. Mesopores and low pore volume are needed to obtain a reasonable yield of cyclohexene using the monolithic catalysts with a low concentration of ZnSO 4 solution.