High‐Temperature Stable, Iron‐Based Core–Shell Catalysts for Ammonia Decomposition

Abstract

High-temperature, stable core-shell catalysts for ammonia decomposition have been synthesized. The highly active catalysts, which were found to be also excellent model systems for fundamental studies, are based on α-Fe(2)O(3) nanoparticles coated by porous silica shells. In a bottom-up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, L-lysine, and water with adjustable average sizes of 35, 47, and 75 nm. Secondly, particles of each size could be coated by a porous silica shell by means of the base-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) with cetyltetramethylammonium bromide (CTABr) as porogen. After calcination, TEM, high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray (EDX), XRD, and nitrogen sorption studies confirmed the successful encapsulation of hematite nanoparticles inside porous silica shells with a thickness of 20 nm, thereby leading to composites with surface areas of approximately 380 m(2) g(-1) and iron contents between 10.5 and 12.2 wt %. The obtained catalysts were tested in ammonia decomposition. The influence of temperature, iron oxide core size, possible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 750 °C with a space velocity of 120,000 cm(3) g(cat)(-1) h(-1) and maintained conversions of around 80 % for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 800 °C, the system was investigated by in situ XRD, in which body-centered iron was determined, in addition to FeN(x), as the crystalline phase under reaction conditions above 650 °C.

H2 Production via Ammonia Decomposition Using Non-Noble Metal Catalysts: A Review

“…The US Department of Energy has clearly indicated that the feasibility of ammonia as hydrogen storage molecule relies on its decomposition at temperatures aligned with those of the PEM fuel cell, in the range of 150-180°C making necessary the development of catalysts active under these conditions [18]. To date, the most effective catalyst for ammonia decomposition consists of ruthenium particles supported on carbon nanotubes (CNT) due to their high conductivity (6353 mol H 2 mol…”

“…In this context, it is important to note that the most popular commercial catalysts for the large-scale production of ammonia are based on iron promoted with K 2 O, CaO, SiO 2 , and Al 2 O 3 , active at temperatures above 400°C [29]. While most of the fundamental research regarding catalyst development for ammonia decomposition is on rutheniumbased systems, the bulk price of iron is 50,000 times lower than that of ruthenium, giving rise to an obvious significant cost benefit associated to the development of effective ironbased catalysts with similar activity than ruthenium ones [18]. The relatively lower activity of iron with respect to ruthenium-based catalysts can be explained by the stronger bond enthalpy of Fe-N compared to Ru-N which can lead to the formation of surface nitrides which slows down the reaction rate and eventually deactivates the catalysts by poisoning.…”

“…Corresponds to metallic surface area when value followed by (M) [18,45]. The silica shell provides high thermal stability versus sintering.…”

Asymmetric Colloidal Janus Particle Formation Is Core-Size-Dependent

“…17 A common route of synthesis for Janus particles is using electrostatic assembly 18−23 and spontaneous formations. [6][7][8][9][10]24 This method is frequently used to make hierarchical templates that can then be selectively coated to make asymmetric colloidal structures. 18−23 Such templates are usually synthesized by mixing in the same solution a core particle of one charge and satellites of the opposite charge.…”

Mesoporous spherical silica encapsulating Pd nanoparticles prepared by CO 2 -induced mircoemulsion and catalytic application in Suzuki coupling reaction

“…In addition, welldispersed palladium nanoparticles in mesoporous SBA-15 were also prepared with sol-gel route, and the resulting nanocomposites exhibit a highly catalytic activity and reused ability for both the Suzuki and Heck coupling reactions [17]. Moreover, core-shell structure materials had also been prepared for the sake of enhancing the catalytic stability [18,19]. Recently, Opanasenko provided an outstanding overview on the heterogeneous Pd catalysts [20].…”