COx-free hydrogen generation via decomposition of ammonia over al, Ti and Zr−Laponite supported MoS2 catalysts

Review of the Decomposition of Ammonia to Generate Hydrogen

“…The first kinetic expressions proposed considered that the decomposition of ammonia followed a first order kinetics, 381,382 which in some cases is still used today. 131,184,250,317,321,341 However, other authors proposed that the reaction rate is a combination of zero order and first order as a function of temperature, 383,384 while more recent studies have shown that the reaction is inhibited by the presence of H 2 . 238,385 The inhibition is manifested particularly at low temperatures, and it has been proposed that it is due to the hydrogen that accumulates on the surface of the catalyst.…”

“…In recent years, a large number of studies have been carried out on the kinetics of ammonia decomposition using different catalysts to determine the expression of the reaction rate and to understand the decomposition mechanism. The first kinetic expressions proposed considered that the decomposition of ammonia followed a first order kinetics, , which in some cases is still used today. ,,,,, However, other authors proposed that the reaction rate is a combination of zero order and first order as a function of temperature, , while more recent studies have shown that the reaction is inhibited by the presence of H 2 . , The inhibition is manifested particularly at low temperatures, and it has been proposed that it is due to the hydrogen that accumulates on the surface of the catalyst . Different methods have been used to determine the expression of the reaction rate; on the one hand, the Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach, which considers coverage-independent parameters. ,,− On the other hand, the Temkin–Pyzhev model considers that the associative desorption of nitrogen is the rate-limiting step, and that if the influence of the inverse reaction can be neglected the reaction rate is expressed as a power law. ,− Finally, the Tamaru model considers that a different model is applied depending on the pressure and temperature conditions. ,, The model proposed by Tamaru et al was verified for a W catalyst − and confirmed to be valid for other types of catalysts as well, such as Pt, VN, Mo 2 N, and TiN x O y .…”

“…340 In successive cycles, the catalyst increased its catalytic activity due to the formation of molybdenum nitride, which is catalytically active and is formed during the reaction. Santhana Krishnan et al 341 tested catalysts with MoS 2 as the active phase supported on laponite and laponite modified with Al, Ti, and Zr, obtaining the best results with the support modified with Zr, reaching a conversion of 94% at 600 °C. They concluded that the modification of the support with heteroatoms allows an increase in both the dispersion of MoS 2 and the basicity of the catalyst.…”

Recent Advances in Bimetallic Catalysts for Hydrogen Production from Ammonia

“…Initially, the studies reflected that the proposed ammonia decomposition rate expressions were based on first-order kinetics [82] still being applied in recent studies. [38,69,83,84] However, temperature-dependent combinations of zero and first-order reaction rates are also reported elsewhere. [85,86] More recently, studies have revealed that the presence of hydrogen inhibits the reaction rate.…”

“…The researchers have proposed different kinetic expressions for this reaction. Initially, the studies reflected that the proposed ammonia decomposition rate expressions were based on first‐order kinetics [82] still being applied in recent studies [38,69,83,84] . However, temperature‐dependent combinations of zero and first‐order reaction rates are also reported elsewhere [85,86] .…”