Low-temperature Ammonia Synthesis Research Articles

Enhanced Catalytic Ammonia Synthesis with Transformed BaO

We report that a simple mixture of BaO and CaH2 powders with ruthenium nanoparticles acts as an effective heterogeneous catalyst for low-temperature ammonia synthesis with a very small activation energy (41 kJ mol–1). The high catalytic performance of this material is not due to either the original CaH2 or BaO particles but to BaO transformed by reaction with CaH2. The transformed BaO contains BaH2, a stable and strong electron-donating material that facilitates a reversible hydrogen storage-release reaction and significantly enhances electron donation to Ru, which results in high catalytic performance.

Ammonia Synthesis Over Co Catalyst in an Electric Field

Ammonia is an important chemical feedstock and is produced by Ru or Fe catalyst so far. We investigated Co catalyst for low temperature ammonia synthesis in an electric field. Well-reduced Co/Ce0.5Zr0.5O2 catalyst showed high activity for ammonia synthesis even at 473 K in the electric field. Various characterizations including kinetic tests, operando DRIFTS measurements, TEM observations, and XAFS measurements, revealed that the active site is the interface between supported Co and Ce0.5Zr0.5O2 oxide support, thanks to the surface protonics derived from an electric field.

Self-organized Ruthenium-Barium Core-Shell Nanoparticles on a Mesoporous Calcium Amide Matrix for Efficient Low-Temperature Ammonia Synthesis.

A low-temperature ammonia synthesis process is required for on-site synthesis. Barium-doped calcium amide (Ba-Ca(NH2 )2 ) enhances the efficacy of ammonia synthesis mediated by Ru and Co by 2 orders of magnitude more than that of a conventional Ru catalyst at temperatures below 300 °C. Furthermore, the presented catalysts are superior to the wüstite-based Fe catalyst, which is known as a highly active industrial catalyst at low temperatures and pressures. Nanosized Ru-Ba core-shell structures are self-organized on the Ba-Ca(NH2 )2 support during H2 pretreatment, and the support material is simultaneously converted into a mesoporous structure with a high surface area (>100 m2 g-1 ). These self-organized nanostructures account for the high catalytic performance in low-temperature ammonia synthesis.

Elucidation of the role of electric field on low temperature ammonia synthesis using isotopes

We have found that an electric field brings high yield on low temperature catalytic ammonia synthesis over Cs/Ru/SrZrO3 catalyst. The role of the electric field is investigated based on kinetics and isotope effects.Results show that the electric field promotes proton hopping on the catalyst surface, and it brings a change in the reaction mechanism from the conventional one to the N2H+ intermediate mechanism. In the electric field, N2H+ intermediate plays an important role, enabling low-temperature ammonia synthesis.

Nitrogen Photofixation over III-Nitride Nanowires Assisted by Ruthenium Clusters of Low Atomicity.

In many heterogeneous catalysts, the interaction of supported metal species with a matrix can alter the electronic and morphological properties of the metal and manipulate its catalytic properties. III-nitride semiconductors have a unique ability to stabilize ultra-small ruthenium (Ru) clusters (ca. 0.8 nm) at a high loading density up to 5 wt %. n-Type III-nitride nanowires decorated with Ru sub-nanoclusters offer controlled surface charge properties and exhibit superior UV- and visible-light photocatalytic activity for ammonia synthesis at ambient temperature. A metal/semiconductor interfacial Schottky junction with a 0.94 eV barrier height can greatly facilitate photogenerated electron transfer from III-nitrides to Ru, rendering Ru an electron sink that promotes N≡N bond cleavage, and thereby achieving low-temperature ammonia synthesis.

The inhibitor role of NH3 on its synthesis process at low temperature, over Ru catalytic nanoparticles

Single catalysts containing 3, 5 and 7wt.% of Ru (Ru3/Al2O3, Ru5/Al2O3 and Ru7/Al2O3) were prepared via impregnation of alumina with RuO2 colloidal suspensions. Two mechanical mixtures, containing Ru3/Al2O3+Ru5/Al2O3 and Ru3/Al2O3+Ru7/Al2O3, were also prepared. Catalytic activity was measured during low-temperature ammonia synthesis reaction. Three different tests were performed after reduction pretreatment of the catalysts: 1) Standard test, the catalytic activity of ammonia synthesis; 2) Test under NH3+He treatment, following ammonia decomposition; 3) Test under NH3+He+H2 treatment, following ammonia decomposition in presence of hydrogen. Standard tests were additionally used to study the effect of the different treatments (NH3+He and NH3+He+H2) on the catalytic activity of ammonia synthesis. Catalysts were characterized by N2 physisorption, XRD and XPS spectroscopy. The size of Ru nanoparticles influences their performance during ammonia synthesis. The important role of the average size and size distribution of Ru nanoparticles in their activity for ammonia synthesis has been confirmed. Catalysts having a broad size distribution of Ru nanoparticles are more active than those having a narrow size distribution of Ru nanoparticles. Ammonia treatment has a negative effect in ammonia synthesis: results suggest that NHx intermediates remaining strongly adsorbed on the surface inhibit the activity of catalysts during ammonia synthesis. The presence of hydrogen during NH3 treatment inhibits ammonia decomposition and induces weaker adsorption of NHx intermediates. The presence of large particles is necessary to reach and maintain a high catalytic activity during ammonia synthesis. Taking into account previous studies, it could be suggested that large Ru nanoparticles activates mobile hydrogen atoms that migrate towards small Ru nanoparticles, promoting NHx hydrogenation. When mixing two catalysts having different mean Ru sizes, there is a significant synergistic effect in the catalytic activity, due to a more effective hydrogenation of NHx intermediates.

Electrocatalytic synthesis of ammonia by surface proton hopping.

Highly efficient ammonia synthesis at a low temperature is desirable for future energy and material sources. We accomplished efficient electrocatalytic low-temperature ammonia synthesis with the highest yield ever reported. The maximum ammonia synthesis rate was 30 099 μmol gcat-1 h-1 over a 9.9 wt% Cs/5.0 wt% Ru/SrZrO3 catalyst, which is a very high rate. Proton hopping on the surface of the heterogeneous catalyst played an important role in the reaction, revealed by in situ IR measurements. Hopping protons activate N2 even at low temperatures, and they moderate the harsh reaction condition requirements. Application of an electric field to the catalyst resulted in a drastic decrease in the apparent activation energy from 121 kJ mol-1 to 37 kJ mol-1. N2 dissociative adsorption is markedly promoted by the application of the electric field, as evidenced by DFT calculations. The process described herein opens the door for small-scale, on-demand ammonia synthesis.

Kinetics of hydrogen adsorption and mobility on Ru nanoparticles supported on alumina: Effects on the catalytic mechanism of ammonia synthesis

Relevant findings on hydrogen adsorption and mobility are provided in this work to elucidate the mechanism of low-temperature ammonia synthesis, catalyzed by polydispersed Ru nanoparticles supported on alumina. H/D isotopic exchange technique, complemented by DRIFTS analysis, was applied to study the kinetics of hydrogen adsorption/desorption on metallic Ru and hydrogen diffusivity on alumina, for catalysts presenting different size distributions of Ru nanoparticles. H atoms adsorbed on large Ru nanoparticles present higher mobility and they migrate on alumina via exchange with OH groups. A broad size distribution of Ru nanoparticles leads to synergy in the rate of ammonia synthesis, and also in hydrogen mobility. The mechanism of catalytic cooperation involves transfer of H atoms from large to small nanoparticles, where the reaction rate is promoted. Considering dynamic catalytic processes in the formulation of kinetic models is crucial for a more accurate description of processes and the development of large-scale processes.

Breaking scaling relations to achieve low-temperature ammonia synthesis through LiH-mediated nitrogen transfer and hydrogenation.

Ammonia synthesis under mild conditions is a goal that has been long sought after. Previous investigations have shown that adsorption and transition-state energies of intermediates in this process on transition metals (TMs) scale with each other. This prevents the independent optimization of these energies that would result in the ideal catalyst: one that activates reactants well, but binds intermediates relatively weakly. Here we demonstrate that these scaling relations can be broken by intervening in the TM-mediated catalysis with a second catalytic site, LiH. The negatively charged hydrogen atoms of LiH act as strong reducing agents, which remove activated nitrogen atoms from the TM or its nitride (TMN), and as an immediate source of hydrogen, which binds nitrogen atoms to form LiNH2. LiNH2 further splits H2 heterolytically to give off NH3 and regenerate LiH. This synergy between TM (or TMN) and LiH creates a favourable pathway that allows both early and late 3d TM-LiH composites to exhibit unprecedented lower-temperature catalytic activities.

Carrying Agent Influence on the Ruthenium Catalyst Activity of the Ammonia Synthesis

The paper examined the catalysts of low-temperature ammonia synthesis Ru-Cs/Sibunit in which Sibunit, mesoporous carbon carrying agents, vary considerably in specific surface area and pore volume, but the pore sizes are similar. According to Raman spectroscopy, the Sibunit structures are same. Applied ruthenium dispersiveness, determined by CO chemisorption, are also close (∼ 13 - 16%) for all the examined catalysts. The difference in the activity of the samples is due to the different direct contact probability of the particles of ruthenium and modifier (CsOx). This probability decreases with increasing specific surface area (SBEТ Sibunit) that are supposed to cause the decrease of catalyst activity on high-superficial Sibunit in the ammonia synthesis reaction.

P.1.g.076 The neuroprotective effect of Erythrina velutina on cerebral ischemia in mice

The paper examined the catalysts of low-temperature ammonia synthesis Ru-Cs/Sibunit in which Sibunit, mesoporous carbon carrying agents, vary considerably in specific surface area and pore volume, but the pore sizes are similar. According to Raman spectroscopy, the Sibunit structures are same. Applied ruthenium dispersiveness, determined by CO chemisorption, are also close (∼ 13 - 16%) for all the examined catalysts. The difference in the activity of the samples is due to the different direct contact probability of the particles of ruthenium and modifier (CsOx). This probability decreases with increasing specific surface area (SBEТ Sibunit) that are supposed to cause the decrease of catalyst activity on high-superficial Sibunit in the ammonia synthesis reaction.

Catalysis by Enzymes: The Biological Ammonia Synthesis

Enzymes are nature’s own catalysts and fundamental for life, as they catalyze essentially all biological processes. Compared to inorganic catalysts, however, their structure and function is immensely more complicated. Computational modeling has played an increasing role in elucidating enzyme mechanisms, as it can provide information complementary to experimental techniques. Elucidating enzyme structure and mechanism is not only important to understand the basic functions of life, they can also help to find and develop inorganic catalysts. In this review, an overview of recent computational developments for the enzyme nitrogenase will be given. Nitrogenase catalyzes ammonia synthesis, which is also a very important reaction in inorganic catalysis, and insight on enzyme structure and function could provide understanding on how to design biomimetic catalysts for low temperature ammonia synthesis.

On the path to catalysts for the low-temperature ammonia synthesis

A nontraditional approach to the development of catalysts for low-temperature ammonia synthesis is considered. The approach is characterized by application of catalysts representing heterogeneous analogs of the known homogeneous nitrogen-fixing systems based on transition metal compounds and strong electron donors. The use of this approach led to the development of catalysts that considerably surpass in their activity (at atmospheric pressure) the industrial catalyst for the ammonia synthesis. Some of the developed catalysts are active in the formation of ammonia from dinitrogen and dihidrogen even at 110–150°C. The mechanisms of activation and hydrogenation of dinitrogen over these new catalysts are discussed.

ChemInform Abstract: Development of Novel Low Temperature and Low Pressure Ammonia Synthesis Catalyst.

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Development of novel low temperature and low pressure ammonia synthesis catalyst

A novel catalyst based on Fe 1− x O (wustite) has been developed for ammonia synthesis. The technology has been without precedent. Its features are as follows: among all the iron catalysts for ammonia synthesis including Fe Co catalyst, the catalyst has the highest activity, the easiest reduction and stronger mechanical strength. The cost is much lower than that of the catalyst containing cobalt. The industrial use of the catalyst indicated that it has remarkable effect of saving energy. The performance figures have reached the world leading level and the catalyst has been widely used in industry in China.