A Noble‐Metal‐Free Catalyst Derived from Ni‐Al Hydrotalcite for Hydrogen Generation from N₂H₄⋅H₂O Decomposition

Abstract

Storing hydrogen safely and efficiently is one of the major technological barriers preventing the widespread application of hydrogen-fueled cells, such as proton exchange membrane fuel cells (PEMFCs). Hydrous hydrazine (N 2 H 4 ·H 2 O) is considered as a promising liquid hydrogen storage material owing to the high content of hydrogen (7.9 %) and the advantage of CO-free H 2 produced. [1] In particular, hydrous hydrazine offers great potential as a hydrogen storage material for some special applications, such as unmanned space vehicles and submarine power sources, where hydrazine is usually used as a propellant.The decomposition of hydrazine proceeds by two typical reaction routes: [2] H 2 NNH 2 ! N 2 ðgÞ þ 2 H 2 ðgÞ ð 1Þ 3 H 2 NNH 2 ! 4 NH 3 ðgÞ þ N 2 ðgÞ ð 2ÞReaction (2) not only decreases the yield of H 2 but also complicates the separation process of products, because the ammonia by-product would poison the Nafion membrane and the fuel-cell catalysts. Thereby, it is of crucial importance to develop a highly selective catalyst over which the reaction proceeds only by pathway (1) at low temperatures. To this end, Xu and co-workers [3] synthesized a series of nickelcontaining bimetallic nanoparticles, including Ni-Rh, Ni-Pt, and Ni-Ir, which showed high H 2 selectivity at room temperature. Nevertheless, the incorporation of noble metals to nickel greatly increased the cost of catalysts. In a subsequent study by Xu and co-workers, [4] Ni-Fe nanoparticles were employed as catalysts for this reaction. However, the nanoparticles were only active at 70 8C, and addition of 0.5 mol L À1 NaOH was necessary for the high selectivity. Moreover, the practical application of colloidal nanoparticles will raise significant problems, such as mass production, handling, stability, separation, and recyclability. Therefore, from the viewpoint of practical applications, a supported base metal catalyst is a preferred choice owing to its low cost, good mechanical stability, and easy separation from the reaction medium.Herein, using a Ni-Al hydrotalcite-like compound (Ni-Al-HT) as the precursor, we obtained a highly dispersed nickel catalyst that presented 100 % conversion of N 2 H 4 ·H 2 O and up to 93 % selectivity to H 2 for the decomposition of N 2 H 4 ·H 2 O at ambient temperature. To our knowledge, this is the first report in which supported base metal catalysts show such high selectivity towards the formation of H 2 .It is well-known that supported noble metal catalysts, especially iridium catalysts, are very active for the decomposition of hydrazine. Compared with Ir, Ni is less active. [5] Accordingly, to obtain a high activity over Ni catalysts, a very high loading of Ni is required while maintaining a high degree of dispersion. Hydrotalcite-like compounds have been demonstrated to be excellent precursors for the preparation of highly dispersed and high-loading metal catalysts. [6] Herein, we synthesized binary Ni-Al-HT with interlayer CO 3 2À anions by a co-precipitation method. [7] After reduction in a H 2 atmosphere at...

Remarkably efficient CoGa catalyst with uniformly dispersed and trapped structure for ethanol and higher alcohol synthesis from syngas

“…LDHs, unique two-dimensional nanostructured materials with metal cations distributed in a highly ordered manner in brucite-like layers [47], are an effective precursor for supported metal catalysts with high-density catalytic sites well dispersed [48][49][50][51]. The CoGa catalyst prepared in this work displays a selectivity of more than 90% to ethanol and higher alcohols in total alcohol products, with a CO conversion of 43.5%, and especially a stable catalytic performance in the reaction.…”

Surface modification of Ni/Al2O3 with Pt: Highly efficient catalysts for H2 generation via selective decomposition of hydrous hydrazine

“…During the reduction in the Ni/ Al 2 O 3 precursor, there was a broad hydrogen consumption peak centered at 490°C. This peak is assigned to the reduction of highly dispersed NiO, which interacts strongly with the alumina support [18]. It is noted that the ratio of reduced Ni was only 93% based on Ni content according to the hydrogen consumption calculation, which indicates that 7% of Ni 2+ ions were located deep in the Al 2 O 3 lattice as a solid solution and became hard-to reduce Ni 2+ species.…”

“…In particular, hydrotalcite and/or its calcination product is very relevant as a solid base, which is increasingly regarded as a good alternative to these corrosive dissolved catalysts (e.g., NaOH, KOH): easy separation from the reactant, recycling possibility, decreased corrosion of the reactor, and so forth. Recently, we have reported that a basic Ni-based catalyst, derived from Ni-Al hydrotalcite precursor, could catalyze the selective decomposition of hydrous hydrazine with H 2 selectivity up to 93% [18]. This unique catalysis is due to the cooperation of Ni nanoparticles and strong basic sites derived from the alumina support.…”

“…It was prepared by a co-precipitation method as described elsewhere [18][19][20] ). Afterward, a green suspension was obtained, and the pH value was adjusted to 10 by introducing 3 mol L À1 NaOH aqueous solution.…”

Highly efficient Ni@Ni–Pt/La2O3 catalyst for hydrogen generation from hydrous hydrazine decomposition: Effect of Ni–Pt surface alloying

“…To this end, a number of group Ⅷ transition metal/alloy catalysts have been prepared using chemical reduction [5e12], coprecipitation [13e17] and wetness impregnation [18e21] methods. Some of them, like NieAl 2 O 3 eHT [13], Ir/g-Al 2 O 3 [18], and NieM alloys (M ¼ Rh, Ir, Pt, Pd, Fe, Mo) [6e12,15e21], enable selective decomposition of N 2 H 4 $H 2 O to generate H 2 at mild conditions. But in a general view, the currently available catalysts exhibit only moderate performance in catalytic activity, selectivity and durability, which results in slow H 2 generation kinetics and problematic controllability of N 2 H 4 $H 2 O decomposition.…”