Catalytic Ammonia Research Articles

Integration between energy and exergy analyses to assess the performance of furnace regenerative and ammonia decomposition systems

Energy and exergy analyses were performed on a glass furnace regenerator and hydrogen production via thermal catalytic ammonia decomposition. A novel integration between energy and exergy analyses was suggested to predict the performance of thermodynamic and hydrogen production systems. It was found that the heat recovered by the combustion air of the south side regenerator was higher than that on the north side because of the fouling effect of the deposit materials and the heat lost through the regenerator walls. The maximum energy and exergy efficiencies of the south side regenerator were 98% and 93%, respectively, while those of the north regenerator side were 96.3% and 80%, respectively. The integration between energy and exergy analyses was also applied to investigate the performance of H2 production from the catalytic NH3 decomposition system. The conversion rate results proved that an increase in the ammonia feeding pressure was unfavorable. Moreover, the maximum energy and exergy efficiencies of the NH3 thermal decomposition system were 73.5% and 13.34% at a feeding pressure of 100 kPa, respectively. Furthermore, the non-equilibrium of the system is identified from the integrated effectiveness and entropy generation number.

Catalytic Ammonia Formation with Electrochemically Reduced Samarium Diiodide from Samarium Triiodide and Water from Dinitrogen

Ammonia was catalytically formed from dinitrogen using samarium diiodide (SmI2), which was electrochemically reduced from samarium triiodide (SmI3) as a reductant and water as a proton source. The process was assessed as a model reaction for the electrochemical reduction of dinitrogen to ammonia under ambient reaction conditions. In this reaction system, electrochemical energy could be converted to chemical energy through ammonia using samarium iodide with high Faradaic efficiency.

Catalytic ammonia decomposition over Ni-Ru supported on CeO2 for hydrogen production: Effect of metal loading and kinetic analysis

Ceria-supported Ni-Ru bimetallic catalysts with different metal loadings have been prepared by co-impregnation, characterized and tested in the production of hydrogen from the catalytic decomposition of ammonia. The bimetallic catalysts showed an excellent catalytic performance in long-term stability tests with respect to monometallic Ru/CeO2 and Ni/CeO2 and in multicycle tests under pure ammonia. The best catalytic performance has been obtained over catalysts with 2.4−5 wt.% Ni, 0.4−0.6 wt.% Ru, and a Ni/Ru wt.% ratio of ca. 7. TOFH2 values exceeding 2 s−1 have been obtained, which are among the highest reported for ammonia decomposition at 400 °C. Raman spectroscopy, XRD, HRTEM, XPS, TPR and H2 chemisorption have revealed the existence of an intimate contact between Ni and Ru and CeO2, which is considered the reason of the excellent catalytic activity and stability observed. A kinetic model has been developed using the Langmuir-Hinshelwood-Hougen-Watson approach for the decomposition of ammonia in a fixed bed reactor. The reaction rate expression of the ammonia decomposition on Ni-Ru bimetallics supported on ceria suggests that the dehydrogenation of the ammonia adsorbed on the surface of the catalyst is the limiting step of the reaction and that ammonia decomposition is inhibited by the presence of H2.

The Opportunities and Challenges for NH3 Oxidation with 100% Conversion and Selectivity

The selective catalytic oxidation of ammonia (SCO) to N2 seems to be the most promising technology to remove NH3. Compared with electrocatalytic and photocatalytic ammonia oxidation technology, the thermal catalytic oxidation ammonia technology was sufficient to support large-scale commercial and industrial applications. The NH3-SCO reaction was strongly obeyed the reaction routes of imide, hydrazinium-type and iSCR mechanism. Further, in situ (electron paramagnetic resonance) EPR spectroscopy combined with DFT calculation could provide a foundation for the design and construction of highly efficient ammonia oxidation catalyst. Finally, important ideas for NH3-SCO should be given the 100% N2 selectivity and higher NH3 conversion at lowest temperature. If Ag single-atoms were inserted in the tunnels of zeolites or MOF to result in single Ag atoms anchored at the tunnel, this single-atom Ag particles exhibited super NH3 conversion, N2 selectivity and hydrothermal durability at low temperatures.

Ru nanoparticles on a Cs-loaded MgO superbase as highly efficient catalysts for ammonia synthesis.

Cs-Loaded MgO, a typical type of solid superbase, was used as a support to disperse and anchor Ru nanoparticles. Much enhanced Ru dispersion together with electron donation of Cs-loaded MgO enables Ru nanoparticles on Cs-loaded MgO to exhibit excellent activity and intrinsic activity for ammonia synthesis, superior to the conventional Ru/MgO catalyst and the state-of-the-art Cs modified Ru/MgO catalyst under identical reaction conditions.

High spin polarized Fe2 cluster combined with vicinal nonmetallic sites for catalytic ammonia synthesis from a theoretical perspective

Compared to other Fen (n > 2) clusters, Fe2 cluster catalysts combined with vicinal nonmetallic sites are expected to be an ideal catalyst for ammonia synthesis with a lower N–H formation (0.47 eV) and N–N dissociation (0.50 eV) energy barrier at the same time.

Catalytic Ammonia Combustion over the Surface as well as Perimeter

Catalytic Ammonia Combustion over the Surface as well as Perimeter

Applications of rare earth oxides in catalytic ammonia synthesis and decomposition

Due to their unique structural and electronic properties, rare earth oxides have been widely applied as supports and promoters in catalytic ammonia synthesis and decomposition.

Insights on cold plasma ammonia synthesis and decomposition using alkaline earth metal-based perovskites

Plasma catalytic ammonia synthesis & decomposition on perovskites. The blend of intrinsic properties (Mg electronegativity) with plasma awakens properties (plasma homogeneity induced by the dielectric constant) leads to high ammonia synthesis rates.

Behaviour and speciation of inorganic trace pollutants in a coal-fired power plant equipped with DENOX-SCR-ESP-NH3FGD controls

The behaviour and speciation of inorganic trace pollutants were studied in a 270 MWh coal-fired power station equipped with denitrification (DeNOx)-based selective catalytic reduction (SCR), electrostatic precipitators (ESP) and ammonia flue gas desulphurisation (NH3-FGD) controls. The aqueous (NH4)2SO4 slurry (pH 3.2) showed remarkably high concentrations of SO42−, Cl−, Fe, NH4+, PO43−, and F− and was substantially enriched in multiple trace pollutants, e.g. Mn, Ni, Zn, and As, which can be ascribed to the diffusion of gaseous pollutants released during combustion and to the partial dissolution of fly ash (FA) particles entrained in the flue gas FGD. These processes were favoured by the iteration of the FGD water re-circulation cycles within the scrubber. Three major unresolved performance issues remain for the NH3-FGD with respect to the retention efficiency of major and trace pollutants: (i) the high concentration of soluble salts and major and minor trace elements in the aqueous (NH4)2SO4 slurry could lead to entrainment of droplets and particles with the outgoing (OUT)-FGD gas; (ii) the ionic strength, as a result of the high concentration of the elements associated with soluble salts and major and minor elements, could lead to diminishing diffusivity of gaseous pollutants into the aqueous phase, where these are supposed to dissolve; and (iii) the acidic conditions of the aqueous (NH4)2SO4 slurry, caused by Fe-hydrolysis, could lead to low FGD efficiencies. Operating conditions at this power station affect Hg partitioning and fate across the PCC-SCR-ESP-NH3-FGD.

Identifying Surface Reaction Intermediates in Plasma Catalytic Ammonia Synthesis

Ammonia synthesis by plasma catalysis has emerged as an alternative process for decoupling nitrogen fixation from fossil fuels. Plasma activation can potentially circumvent the limitations of conve...

Hydrogen production by ammonia decomposition over ruthenium supported on SiC catalyst

A series of ruthenium catalysts using β-SiC as a support was synthesized with different metal loading (1−5wt.% of Ru). Catalysts were characterized and tested with hydrogen production by catalytic ammonia decomposition. Additionally, the influence of calcination conditions as well as reduction temperatures (673K and 873K) was studied. Ru dispersion and metallic particle size were found to greatly influence catalytic activity. Moreover, calcination in a nitrogen atmosphere could remove a higher proportion of chlorine species derived from the precursor, thereby enhancing catalytic activity. Furthermore, a lower reduction temperature resulted in smaller particle sizes of ruthenium, which were more active in ammonia decomposition. Maximum intrinsic activity was obtained for a Ru size of around 5nm. The catalyst containing 2.5wt.% Ru, calcined in a N2 atmosphere and reduced at 673K resulted in excellent H2 production from ammonia decomposition, with ammonia conversion close to 100% at 623K was obtained. Porous SiC proved to be a suitable support for the nanosized Ru catalyst and was highly active in hydrogen production from ammonia decomposition. Moreover, this support provided good performance stability after one day of reaction.

A silica-supported Ni-based catalyst prepared using TEPA for the plasma synthesis of ammonia

Ammonia is a potential hydrogen carrier and can be used as an alternative fuel. In this study, plasma cooperative catalytic synthesis ammonia was used. The catalyst consisted of Ni impregnated into silica, using one of three complexing agents (TEPA, EDTA and GLY) and compared with conventional impregnation methods. The unsaturated coordinated Ni(tepa)2+ will coordinate with the hydroxyl groups on the silica surface. When using the catalyst prepared by TEPA, the ammonia synthesis rate was 3.8 times higher than with no catalyst, and 1.4 times higher than the catalyst made by conventional impregnation method. XRD and TEM show that the catalyst prepared using TEPA exhibited the smaller metal particle size, the higher dispersion and the stronger interaction between metal and support than other catalysts. XPS indicate that the good metal dispersion of the catalyst facilitate form more Ni3N during the reaction, which will greatly improve the activity of the catalyst.

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Electrochemical Reduction of Samarium Triiodide into Samarium Diiodide

Electrochemical reduction of samarium triiodide (SmI3) into samarium diiodide (SmI2) is investigated as a model reaction to reuse samarium compounds in catalytic ammonia production under ambient re...

Exhaust energy recovery via catalytic ammonia decomposition to hydrogen for low carbon clean vehicles

The work presented here, demonstrates the on-board exhaust assisted catalytic ammonia (NH3) conversion to H2-N2 using either only exhaust heat (decomposition) or by direct reaction with part of the exhaust gas (reforming). The resultant H2-N2 gas mixture from the exhaust heat driven thermochemical energy recovery processes contains up to 15% more energy than the reactant NH3 (i.e. for 1 kW of NH3 used in the reaction up to 1.15 kW of H2 is produced). Experimental studies using a rhodium-platinum (Rh-Pt) catalyst and equilibrium calculations in Chemkin using Konnov’s 0.6 and Nozari’s reduced mechanisms have revealed that complete NH3 conversion occurs at typical gasoline direct injection (GDI) engine exhaust gas temperatures (450 °C–550 °C).By partially replacing gasoline in GDI engine with the resultant (H2-N2 products, up to 30% reduction in CO2 and fuels consumption can be achieved. Additional benefits can be gained under real engine operation when the benefits of reduced pumping losses, due to intake dilution with H2-N2 gas, are also considered. Furthermore, the work demonstrates additional benefits in CO2 life cycle for the NH3 use as an energy carrier in transportation and broader combustion power generation systems.

The role of heterogeneous catalysts in the plasma-catalytic ammonia synthesis

Ammonia, being the second largest produced industrial chemical, is used as a raw material for many chemicals. Besides, there is a growing interest in the applications of ammonia as electrical energy storage chemical, as fuel, and in selective catalytic reduction of NOx. These applications demand on-site distributed ammonia production under mild process conditions. In this paper, we investigated 16 different transition metal and oxide catalysts supported on γ-Al2O3 for plasma-catalytic ammonia production in a dielectric barrier discharge (DBD) reactor. This paper discusses the influence of the feed ratio (N2/H2), specific energy input, reaction temperature, metal loading, and gas flow rates on the yield and energy efficiency of ammonia production. The optimum N2/H2 feed flow ratio was either 1 or 2 depending on the catalyst – substantially above ammonia stoichiometry of 0.33. The concentration of ammonia formed was proportional to the specific energy input. Increasing the reaction temperature or decreasing gas flow rates resulted in a lower specific production due to ammonia decomposition. The most efficient catalysts were found to be 2 wt% Rh/Al2O3 among platinum-group metals and 5 wt% Ni/Al2O3 among transitional metals. With the 2 wt% Rh catalyst, 1.43 vol% ammonia was produced with an energy efficiency of 0.94 g kWh−1. The observed behaviour was explained by a combination of gas-phase and catalytic ammonia formation reactions with plasma-activated nitrogen species. Plasma catalysts provide a synergetic effect by activation of hydrogen on the surface requiring lower-energy nitrogen species.

Effect of rare earth elements (La, Y, Pr) in multi-element composite perovskite oxide supports for ammonia synthesis

A series of BaCeO3 modified with different rare earth elements (La, Y, Pr) were synthesized by co-precipitation and calcination and the effect of rare earth elements for catalytic ammonia synthesis under mild conditions was studied. The ammonia synthesis performance tests show that 2.5% Ru/BaCe0.9La0.1O3–δ catalyst (All the percentages of Ru in this article are in mass fraction) exhibits the highest ammonia synthesis rate (34 mmol/(g·h)) at 3 MPa, 450 °C, and no sign of deactivation after 100 h of reaction. H2-TPR and XPS analyses indicate that the introduction of La increases the amount of oxygen vacancies of the catalyst, which is beneficial to increasing the electron density of Ru surface. HRTEM analysis shows that the Ru particle size is reduced greatly after La is introduced, which facilitates the catalyst generating more B5-type sites (active sites of Ru species for NN dissociation). CO2-TPD analysis indicates that BaCe0.9La0.1O3–δ has stronger basicity, which promotes electrons transfer from support to Ru. This work provides an effective method for design and synthesis of Ru-based multi-element composite perovskite oxide catalysts.

Ru-doped phosphorene for electrochemical ammonia synthesis

The electrochemical ammonia synthesis has attracted increasing attention due to its energy saving characteristics. However, developing novel electrocatalysts and their mechanism remain great challenges. Here, several transition metal (TM) atoms doped on phosphorene were studied as N2 fixation electrocatalysts by using density functional theory (DFT) calculations. The results demonstrate that single Ru atom doped phosphorene shows an excellent catalytic activity for ammonia synthesis via the enzymatic pattern. A small overpotential of 0.696 V is achieved for this process. The effect of oxidation in the catalyst was also discussed in our work. Oxidation deactivates the catalyst, which should be avoided in the experiment. Our outcomes offer a novel perspective for single-atom catalytic ammonia synthesis with phosphorene as a substrate.

Progress on Selective Catalytic Ammonia Oxidation (NH3‐SCO) over Cu−Containing Zeolite‐Based Catalysts

AbstractThe selective catalytic oxidation of ammonia into nitrogen and water vapor (NH3‐SCO) has proven to be the most efficient technique for the removal of NH3 from the oxygen‐containing diesel exhausts. Until now, two reviews over investigated catalysts have been published in 2015–2016 (Jabłońska et al., RCS. Adv. 2015; Appl. Catal. B: Environ. 2016). Among various NH3‐SCO catalysts, Cu‐ and/or Fe‐containing zeolites are considered as promising candidates due to their benign nature, NH3 storage capacity, very high NH3 conversion and N2 selectivity. The present review focusses only on the Cu‐containing zeolites (mainly on chabazite (CHA): SSZ‐13, SAPO‐34) catalysts) applied in NH3‐SCO starting from 2015. The synthesis/preparation methods and the state of Cu in catalysts on the activity and selectivity are highlighted. The advantages of the understanding of the reaction mechanism are reviewed. Finally, an outlook is given together with expected inspirations for future research directions in developing zeolite‐based catalysts.