Engineering spinel NiMgAlOx catalysts derived from in situ confined Ni into MgAl-LDH for hydrogen production via ammonia decomposition

Abstract

Nickel-based catalysts offer certain advantages, including low cost and a simple preparation process, which renders them suitable for the industrial ammonia decomposition reaction. We synthesized a series of Ni_aMgAlO_x derived from Ni_aMgAl-LDH precursors for hydrogen production by ammonia decomposition. The results demonstrated that the Ni_1.5MgAlO_x catalyst displayed exceptional reaction activity and stability. Structural characterizations revealed that the LDH precursor of the Ni_aMgAlO_x catalyst underwent transformation into a spinel structure after high-temperature calcination, exhibiting a high specific surface area and suitable mesopore distribution. EDX element mapping showed that the nickel species were evenly distributed across the catalyst surface, thereby enhancing the accessibility of active sites and improving catalytic activity. Additionally, nickel doping optimizes the charge distribution on the catalyst surface, balances the acid–base properties, enhances electron transfer within the Ni–O–Al framework, and facilitates the formation of the N–N bond on the surface, thereby promoting catalytic dehydrogenation. Ammonia decomposition tests were conducted in a fixed-bed reactor operating at temperatures ranging from 300 °C to 650 °C, revealing that the Ni_1.5MgAlO_x catalyst attained an ammonia conversion rate exceeding 90% at 600 °C. A comparison of the Ni_1.5MgAlO_x catalyst reported in this study with the catalysts described in the extant literature revealed that the former demonstrated superior intrinsic activity and stability.