Top-Down Syntheses of Nickel-Based Structured Catalysts for Hydrogen Production from Ammonia

Abstract

We report the fabrication and catalytic performance evaluation of highly active and stable nickel (Ni)-based structured catalysts for ammonia dehydrogenation with nearly complete conversion using nonprecious metal catalysts. Lowtemperature chemical alloying (LTCA) followed by selective aluminum (Al) dealloying was utilized to synthesize foam-type structured catalysts ready for implementation in commercial-scale catalytic reactors. The crystalline phases of Ni−Al alloy (NiAl 3 , Ni 2 Al 3 , or both) in the near-surface layer were controlled by tuning the alloying time. The best-performing catalyst was obtained from a Ni foam substrate with a NiAl 3 /Ni 2 Al 3 overlayer synthesized by LTCA at 400 °C for 20 h. The developed Ni catalyst exhibited an activity enhancement of 10-fold over the nontreated Ni foam and showed outstanding activities of 15 800 mol H2 mol Ni −1h −1 (TOF: 4.39 s −1 ) and 19 978 mol H2 mol Ni −1 h −1 (TOF: 5.55 s −1 ) at 550 and 600 °C, respectively. This performance is unprecedented compared with previously reported Ni-based ammonia cracking catalysts with higher-end performance (TOFs of 0.08−1.45 s −1 at 550 °C). Moreover, this catalyst showed excellent stability for 100 h at 600 °C while discharging an extremely low NH 3 concentration of 1034 ppm. The NH 3 concentration in the exhaust gas was further reduced to 690 and 271 ppm at 700 and 800 °C, respectively, while no deactivation was observed at these elevated temperatures. Through material characterizations, we clarified that controlling the degree of Al alloying in the outermost layer of Ni is a crucial factor in determining the activity and stability because residual Al possibly modifies the electronic structure of Ni for enhanced activity as well as transforming to acidic alumina for increased intrinsic activity and stability.

The Direct Reduction of Iron Ore with Hydrogen

“…Research and development of catalysts are done on precious metals, bimetallic materials, and metal oxides [38][39][40][41][42]. The bimetallic compound is proven to improve catalytic performance even though the manufacturing is complicated.…”

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes

“…Additionally, the centralization of industrial NH 3 synthesis around H 2 feedstocks contributes to geopolitical disparities in affordable fertilizer access . Nascent efforts to utilize NH 3 as a carbon-free energy vector similarly reckon with the unsustainability of NH 3 mass production. , Yet, NH 3 oxidation methods such as H 2 cracking or electrocatalytic oxidation − may be key in availing strategies to tackle the microscopic reverse: sustainable N 2 reduction to NH 3 . The nearly thermoneutral N 2 reduction and NH 3 oxidation suggests proton-coupled electron transfer (PCET) as an attractive approach to minimize kinetic barriers between intermediates.…”

Ammonia Can be Currently Considered as one of the Best Green Energy Ally

“…An alternative to avoid using two separate storage fuel systems is to generate hydrogen from the ammonia decomposition. The cracking of ammonia has been studied by several authors [167][168][169], proposing the use of thermal catalytic reactors that allow reducing reaction temperature. Catalysts commonly employed contain noble metals (Rh, Ru, Pd, Pt, among others), but also Fe and Ni have been tested in order to reduce costs and dope the catalyst with rare earth metals to increase activity or using bimetallic configurations [170,171].…”