Sol–gel preparation of crystalline Ni12P5/N-doped carbon and amorphous Ni–P–C catalysts and their high catalytic performances toward hydrogenation reduction reaction of 4-nitrophenol

Abstract

Sol–gel method was used to prepare Ni₁₂P₅/N-doped carbon and amorphous Ni–P–C materials where the dried gel precursors were heated under N₂ atmosphere in a tube furnace. By using ethylene diamine tetraacetic acid (EDTA) as the chelating agent, Ni₁₂P₅/N-doped carbon catalysts can be obtained when the heating temperatures were 700 °C and 800 °C. The Ni₁₂P₅/N-doped carbon nanomaterial heated at 800 °C exhibited high catalytic performance toward the hydrogenation reduction reaction of 4-nitrophenol (4-NP) using NaBH₄ as the reducing agent. Pseudo first-order kinetics of the reaction can be observed, where catalytic activity parameters were 450.0 s⁻¹ g⁻¹ and 54.5 s⁻¹ g⁻¹ when the molar ratios of NaBH₄ : 4-NP were 1000 : 1 and 100 : 1, respectively. When EDTA was replaced by ethylene glycol, amorphous Ni–P–C materials could be obtained when the heating temperatures were 350 °C, 450 °C, 550 °C, 600 °C and 700 °C. Unexpectedly, all the amorphous materials had desirable catalytic performances toward the hydrogenation of 4-NP. However, the kinetics of the reaction was pseudo zero-order over the amorphous catalysts. Our results provide new insight into the design of useful catalysts toward the hydrogenation reactions of 4-NP via the sol–gel method.