Highly effective chainlike Ni/CZ5-x catalysts for catalytic reduction of p-nitrophenol: Effect of Si/Al ratio of ZSM-5 support

Abstract

A series of ZSM-5 supported Ni catalysts with different Si/Al ratios (Si/Al=25, 30, 50 and 70) wzmpregnation method for p-nitrophenol (4-NP) reduction were investigated. The Ni/CZ5-x catalysts with chainlike morphology exhibited higher catalytic activity as compared with cubic aggregating Ni/Z5–25, and the activity gradually increased with decreasing of the Si/Al ratios of catalysts in the order of Ni/CZ5–30 > Ni/CZ5–50 > Ni/CZ5–70. For Ni/CZ5-x catalysts with similar morphology, the Ni/CZ5–30 catalyst showed the optimal activity with TOF value of 4.7995 × 10−3 s−1 and reaction time of 7 min, which was comparable to those of precious metals and significantly superior to cheap metal catalysts have been reported in the identical reaction condition. The excellent performance was mainly attributed to the synergistic effect between the more Ni0 fraction promoting the 4-NP catalytic conversion and strong surface hydrophilicity and acidity effectively accelerating the BH4- adsorption and dissociation in the Ni/CZ5-x catalysts with appropriate Si/Al ratio. The larger Ni0 fraction derived from the better dispersion of Ni species with smaller diameter on the surface of chainlike crystal, benefitting from the elevated hydrophilicity in the aqueous environment with the decreasing Si/Al ratio. This work first provided the influence of Si/Al ratio of support on catalytic performance of 4-NP reduction reaction and a new designing approach of the catalyst with high metal dispersion and good surface hydrophilicity for other catalytic fields in the future.