Ammonia Decomposition Activity Research Articles

Promotional Effect of Carbon on Fe Catalysts for Ammonia Decomposition: A Density Functional Theory Study

Density functional theory calculations have been performed to investigate the recombinative desorption of N on terraced Fe(100) and Fe(110) as well as stepped Fe(111) and Fe(211) surfaces. The results showed that the stepped surfaces, especially the Fe(111) surface, are more active than the terraced surfaces, which could be related to the presence of so-called C7 sites for the stepped surfaces. Carbon atoms were found to stabilize the thermodynamically unstable stepped surfaces to be the energetically favored facets and thus facilitate the preferential exposure. As these carbon atoms incorporated into the stepped surfaces in the form of surface or subsurface carbon, the activation energy for the recombinative desorption of N was lowered, which was mainly ascribed to the decrease in the d band center of surface Fe atoms. In addition, a relation between the electronic and structural properties of Fe catalysts in the absence or presence of carbon and ammonia decomposition activity was also correlated.

Ammonia decomposition over titanium carbides

Ammonia decomposition over titanium carbides were investigated using eight different samples which have been synthesized by TPR (temperature-programmed reduction) method of titanium oxide (<TEX>$TiO_2$</TEX>) with pure <TEX>$CH_4$</TEX>. The resulting materials which were synthesized using wo different heating rates and space velocity exhibited the different surface areas. These results indicated that the structural properties of these materials have been related to heating rates and space velocity employed. The titanium carbides prepared in this study proved to be active for ammonia decomposition, and the activity changed with the particle size/surface area. These showed the relationship between ammonia decomposition activity and the different active species. Compared to molybdenum carbide, the titanium carbides were one order of magnitude less active, suggesting the correlation between the activity difference and the degree of electron transfer between metals and carbon in metal carbides.

Ammonia decomposition over Ni/La2O3 catalyst for on-site generation of hydrogen

Ammonia decomposition is a promising process for on-site generation of hydrogen. In this study, various nickel catalysts supported on metal oxides were prepared and their catalytic activity for ammonia decomposition was investigated. Ni/Al2O3 catalyst achieved the highest ammonia conversion among catalysts investigated due to the high surface area of Al2O3 support (200m2g−1). Despite the low surface area of support material (4.7m2g−1), the catalytic activity of Ni/La2O3 was comparable to that of Ni/Al2O3. The basicity of support materials was not specifically related with the catalytic activity. For Ni/La2O3 catalyst, the small nickel particles were deposited over La2O3 from LaNiO3 during the reduction treatment. When the Ni loading amount was changed in the range of 10–70wt% for Ni/La2O3 catalyst, the sample with 40wt% Ni exhibited the highest conversion of 78.9% at 550°C. The catalytic performance of Ni/La2O3 was also affected by the preparation method and calcination temperature. The LaNiO3 formation was responsible for the high activity of Ni/La2O3 catalyst for the ammonia decomposition.

MCM-41 supported Co[sbnd]Mo bimetallic catalysts for enhanced hydrogen production by ammonia decomposition

MCM-41 supported Co, Mo and CoMo bimetallic catalysts with different Co/Mo atomic ratios were prepared by incipient wetness impregnation, and the channels of MCM-41 acted as nano-reactor. The catalysts without pre-nitridation treatments were directly used to catalyze ammonia decomposition. The characterization of the catalysts was carried out by N2 physisorption, H2-TPR, Raman, XRD, TEM and XPS. The results show that the catalysts have the similar size distribution of metallic particles. Due to the synergistic effect between Co and Mo, MCM-41 supported CoMo bimetallic catalysts show higher ammonia decomposition activity compared to Co or Mo alone. The CoMo bimetallic catalyst with the Co/Mo atomic ratio of about 7/3 exhibits the highest NH3 conversion. Moreover, the Co7Mo3/MCM-41 catalyst shows good thermal stability.

Ammonia decomposition activity on monolayer Ni supported on Ru, Pt and WC substrates

Catalyst design for specific reactions currently involves using atomic or molecular descriptors to identify promising catalysts. In this paper, we explore three surfaces that have similar computed nitrogen binding energies, which is a descriptor for the ammonia decomposition reaction. The surfaces studied include a monolayer of Ni on Pt(111), Ru(0001) and tungsten monocarbide (WC). The activity of these surfaces toward the ammonia decomposition reaction was compared using density functional theory and temperature programmed desorption. It was found that while the NHx–H bond scission is similar on each of the surfaces, the temperature of nitrogen desorption is very different. The differences are explained and the implications for ammonia decomposition activity and catalyst design are discussed.

Experimental and theoretical studies of ammonia decomposition activity on Fe-Pt, Co-Pt, and Cu-Pt bimetallic surfaces

We investigate the decomposition of ammonia on bimetallic surfaces prepared by the deposition of a monolayer of Fe, Co, or Cu on a Pt(111) surface computationally and experimentally. We explore the correlation between predicted activities based on the nitrogen binding energies with experimental decomposition activity on these bimetallic and corresponding monometallic surfaces. Through density functional theory calculations and microkinetic modeling, it is predicted that the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces, with a monolayer of Fe or Co on top of Pt(111), are active toward decomposing ammonia. In contrast, the corresponding subsurface configurations, Pt-Fe-Pt(111) and Pt-Co-Pt(111) are inactive. These predictions were confirmed experimentally through temperature programmed desorption experiments. Decomposition was seen at temperatures below 350 K for the Fe-Pt-Pt(111) and Co-Pt-Pt(111) surfaces. For the Cu∕Pt(111) system, the surface, subsurface and parent metals were each predicted to be inactive, consistent with experiments, further validating the model predictions. The stability of these bimetallic surfaces in the presence of adsorbed nitrogen is also discussed.

Präparation und Charakterisierung von SiO2-geträgerten Zirconiumoxidnitriden mit hoher Oberfläche und Untersuchung ihrer katalytischen Aktivität bei der Ammoniakzersetzung / Synthesis, Characterization, and Catalytic Activity of Zirconium Oxide Nitrides Supported on High-surface SiO2

Zirconium oxide nitrides are active ammonia decomposition catalysts for the production of hydrogen. We present a route to zirconium oxide nitrides with high surface area. The precursor used consisted of a high-surface-area silica material coated with zirconium alkoxide. Subsequent hydrolysis and calcination resulted in ZrO2 supported on SiO2. The high surface area of the material could be maintained in the following ammonolysis procedure leading to the corresponding zirconium oxide nitride. In contrast to the as-prepared ZrO2, the zirconium oxide nitrides exhibited a significant catalytic activity in ammonia decomposition, but compared to an iron oxide-based reference material, the new oxide nitrides showed a rather low activity. Nevertheless, zirconium oxide nitrides constitute suitable model systems for elucidating the effect of nitrogen in the anion substructure on the activity and selectivity of oxide-based ammonia decomposition catalysts.

Catalytic decomposition of ammonia in simulated coal-derived gas over supported nickel catalysts

As a hot gas clean-up technology for integrated coal gasification combined-cycle (IGCC) power plants, the catalytic decomposition of ammonia using simulated coal-derived gas was studied. Based on the selective catalytic oxidation of ammonia to nitrogen and water, the characteristics of five kinds of supported nickel catalysts were investigated. Ammonia decomposition experiments were carried out at 0.9 MPa, and the surface properties of the catalysts were investigated through surface area measurement, the temperature programmed desorption of ammonia (NH 3-TPD), carbon analysis, XRD analysis, and transmission electron microscope (TEM) observation. The results showed that a nickel catalyst supported on ZSM-5 zeolite has the highest activity and selectivity for ammonia decomposition to nitrogen without carbon deposition from 250–400 °C among the tested catalysts.

Spatially and Size Selective Synthesis of Fe-Based Nanoparticles on Ordered Mesoporous Supports as Highly Active and Stable Catalysts for Ammonia Decomposition

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.

Catalytic clean-up of gasification gas with precious metal catalysts – A novel catalytic reformer development

Several precious metal catalysts were prepared on modified zirconia and tested for the selective catalytic clean-up of the gasification gas. The activity of the precious metal catalysts were compared to that of the modified zirconia supported nickel catalyst and to the support. The activities of the catalysts were tested in a monolithic form in a quartz laboratory reactor at temperatures of 600–900 °C under atmospheric pressure using synthetic sulfur containing gas mixture. In addition, the stability of the Ni and Rh catalysts was examined by measuring the activities at 800 °C for 10 h using sulfur containing gas. The simulated gas contained CO, CO 2, CH 4, C 2H 4, H 2, N 2, H 2O, H 2S, NH 3 and a tar model compound, i.e. a mixture of naphthalene and toluene. The addition of metal on the support promoted the activity in tar model compound decomposition only at the temperature range of 850–900 °C. The order of activity was Rh ≈ Ni > Pd > Ir > Ru > Pt. Almost complete tar model compound conversion was achieved with Rh, as well as with Ni, at 900 °C. At lower temperatures, the support showed higher activity in tar model compound decomposition compared to the metal/support catalysts tested. Only Ni and Ru showed moderate activity in ammonia decomposition. In regard to sulfur tolerance at 800 °C, Rh was activated during the 10 h experiment while the activity of Ni decreased. The performance of both was restored after the overnight N 2 flush and the conversion of the tar model compound was higher for Rh (64%) than for Ni (46%).

Microfibrous entrapped Ni/Al2O3 using SS‐316 fibers for H2 production from NH3

AbstractUsing a high‐speed and low‐cost papermaking technology combined with subsequent sintering process, sinter‐locked three‐dimensional microfibrous networks consisting of ∼2 vol % of 6‐μm‐diameter SS‐316 microfibers were utilized to entrap ∼25 vol % of 100–200‐μm‐diameter porous Al2O3 support particulates. Nickel, a most active component for ammonia decomposition, was then dispersed onto the pore surface of the entrapped Al2O3 support particulates by incipient wetness impregnation method. The resulting microfibrous catalysts took advantage of large void volume, entirely open structure, high heat/mass transfer, good thermal stability, and unique form factors, thereby leading to good activity for ammonia decomposition and significant reduction of overall bed weight and volume. This composite bed reactor was capable of producing 215 sccm hydrogen over per cm3 bed volume with ammonia conversion of 99.5% at 650°C. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Novel microfibrous composite bed reactor: high efficiency H2production from NH3 with potential for portable fuel cell power supplies

A novel microfibrous composite bed reactor was developed and was demonstrated for high efficiency hydrogen production by the decomposition of ammonia at moderate temperatures in portable fuel cell power system applications. By using a high-speed and low-cost papermaking technology combined with a subsequent sintering process, sinter-locked three-dimensional microfibrous networks consisting of approximately 3 vol% 8 microm (dia.) nickel microfibers were utilized to entrap approximately 35 vol% 100-200 microm dia. porous Al(2)O(3) support particulates. A CeO(2) promoter and active Ni component were then dispersed onto the pore surface of the entrapped Al(2)O(3) support particulates by a stepwise incipient wetness impregnation method. The microfibrous structure took advantage of a large void volume, entirely open structure, high heat/mass transfer, high permeability, good thermal stability, and unique form factors. Addition of ceria significantly promoted the low-temperature activity of Ni/Al(2)O(3) catalyst particulates incorporated into the micorfibrous structure. The use of fine particles of catalyst significantly attenuated the intraparticle mass transport limitations. As a result, the present novel microfibrous composite bed reactor provided excellent activity and structure stability in ammonia decomposition, as well as low pressure drop and high efficiency reactor design. At a 90% conversion of a 145 sccm ammonia feed rate, the microfibrous entrapped Ni/CeO(2)-Al(2)O(3) catalyst composite bed could provide a 4-fold reduction of catalytic bed volume and a 5-fold reduction of catalytic bed weight (or 9-fold reduction of catalyst dosage), while leading to a reduction of reaction temperature of 100 degrees C, compared to a packed bed with 2 mm dia. Ni/CeO(2)-Al(2)O(3) catalyst pellets. This composite bed was capable of producing roughly 22 W of hydrogen power, with an ammonia conversion of 99% at 600 degrees C in a bed volume of 0.5 cm(3) throughout a 100 h continuous test. These initial and promising results established that the microfibrous nickel-based catalyst composites were effective for high efficiency production of hydrogen by ammonia decomposition, while achieving a significant reduction of overall catalytic bed weight and volume. We anticipate our assay to be a new point for small-scale hydrogen production, where the microfibrous catalytic reactors considered in isolation can satisfy several of the most fundamental criteria needed for useful operation.

Hydrogen Generation by Ammonia Cracking with Iron Metal-Rare Earth Oxide Composite Catalyst

A series of fine powders of Fe-MO x (M = Ce, Al, Si, Sr, and Zr) composite were prepared by the conventional coprecipitation method from their nitrate solutions. The activity of hydrogen extraction from ammonia over these composite powders as ammonia cracking catalyst was characterized. The catalytic activity for ammonia decomposition observed on the composite powders of Fe-(Ce, Zr)O 2 was high because of the electron donation to the iron metal from Ce 3+ due to the reduction of CeO 2 through the reaction. In addition to this effect, the additive (Ce, Zr)O 2 solid solution supports worked as a solid acid to enhance the ammonia adsorption and reaction probability of Fe component. These were effective to generate hydrogen through the ammonia decomposition at relatively low temperature.

Monopropellant decomposition catalysts. I. Ageing of highly loaded Ir/Al 2O 3 catalysts in oxygen and steam. Influence of chloride content

Alumina supported iridium catalysts used in satellite thrusters are prepared several years before satellite launch and the ageing of such catalysts is an important parameter for the lifetime of the satellite. The ageing has been studied using two procedures and different characterization methods: metal dispersion through hydrogen chemisorption followed by oxygen and hydrogen titrations, powder X-ray diffraction, transmission electron microscopy and catalytic activity in ammonia decomposition. Long term storage during six months and one year under static argon, air or hydrogen atmosphere led to the same slight decrease of the metallic dispersion. After accelerated ageing using dynamic oxygen or water vapor flow, the samples display the same dispersion drop and the same evolution of the crystallite size distribution with a drop of the smallest crystallites due to sintering effects or to formation of oxichloride surface species. The catalytic activity discloses a difference between the ageing treatments: the treatment with oxygen leads to an increase of the measured activity while a treatment with water vapor gives the opposite behavior. The removal of surface chloride ions stabilizes the catalyst against water vapor ageing effects without any modification of dispersion, size distribution and catalytic activity.