Activation of nitrogen by alkali metal promoted transition metal I. Ammonia synthesis over ruthenium promoted by alkali metal
Abstract
The rate of ammonia synthesis over ruthenium was found to be remarkably promoted by addition of alkali metal, particularly when ruthenium is supported by active carbon (AC) or alumina. The synthesis rate over the 5% RuACK catalyst can be raised to about 10 times that of conventional doubly promoted iron (Fe Al2O3K2O) catalyst at 250 °C. RuACCs gives even greater activity than RuACK. The catalytic activity increases with decrease in ionization potential of added alkali (Cs > K > Na) and with increase in the added amount of alkali metal, approaching a plateau value at around 3–4 mg-atom alkali/g-catalyst. Unsupported ruthenium is also remarkably promoted by addition of alkali metal. It is accordingly concluded that the promoter action is provided by a charge transfer from alkali metal to transition metal which brings about a higher electron density in the transition metal, a favorable state for the activation of nitrogen. The specific synthesis rates per surface ruthenium are higher over active carbon and alumina than other supports, suggesting a role of these supports as a medium of electron transfer.
References (14)
- K Aika et al.
J. Catal.
(1969) - K Aika et al.
J. Catal.
(1970) - K Aika et al.
J. Catal.
(1970) - J.W Gadzuk
Surface Sci.
(1967) - R.L Gerlach et al.
Surface Sci.
(1970) - K Aika et al.
J. Catal.
(1969) - B.D Flockhart et al.
J. Catal.
(1967)
Cited by (443)
Ammonia synthesis over cesium-promoted mesoporous-carbon-supported ruthenium catalysts: Impact of graphitization degree of the carbon support
2024, Applied Catalysis B: EnvironmentalCarbon-supported ruthenium catalysts facilitate electrically-assisted Haber–Bosch ammonia synthesis. However, the relationship between carbon supports and catalytic performance remains ambiguous. We developed ordered mesoporous carbon plates (MCPs) with varying graphitization degrees as Cs-promoted Ru catalyst supports, examining correlations between ammonia synthesis rate and key structural parameters, included graphitization degree, Ru nanoparticle size, and Cs/Ru ratio. High-graphitization-degree carbon supports resisted methanation and facilitated formation of reductive activation enabled dynamic Cs0 species as electronic promotor, induced by spillover hydrogen from the Ru surface to CsOH. Density functional theory calculations further revealed that CsOH alleviated hydrogen poisoning. Notably, the catalyst supported on MCP-1100—which exhibited the highest graphitization degree among the supports and superior stability—with 10 wt% 2.3-nm-sized Ru nanoparticles and Cs/Ru = 2.5 achieved high ambient-pressure ammonia synthesis rates (7.9–43 mmolNH3·g−1·h−1) below 410 °C. Furthermore, it functioned under intermittent operating conditions, potentially integrating renewable-electricity-based electrolytic hydrogen production.
A comprehensive assessment of ammonia synthesis reaction kinetics and rate equations
2023, International Journal of Hydrogen EnergyIn this study, the ammonia formation analytical rate equations were described well at pressures from 107 to 320 atm and different flow rates. The surface adsorption and desorption of nitrogen over iron-type catalysts were investigated according to the reaction kinetics of ammonia synthesis. The kinetic reaction rate equations of Temkin & Pyzhev, Langmuir–Hinshelwood, Ozaki et al., and the power rate law predicted the behaviour of the system and evaluated closeness to the experimental data. The microkinetic model rate (I and II) results were compared with other analytical and experimental rate equations. All proposed models showed excellent fits with experimental data. This result implies that the rate equation correlates to the overall dissociation rate of adsorbed nitrogen and the equilibrium constant for all ammonia formation reaction steps. The Temkin & Pyzhev rate results showed deficiencies at low ammonia synthesis operating pressures. Also, the nitrogen partial pressure reaction order was highly influenced by the power rate law results. The rate results from microkinetic models I and II were nearly the same. In addition, the Ozaki et al. rate equation could be used to predict the ammonia synthesis rate. The rapid computation time of the ammonia synthesis rate requires a simple rate equation. Therefore, calculating the rate based on the Temkin & Pyzhev and power rate laws is appropriate for fitting experimental measurements.
Prospects of solar-powered nitrogenous fertilizers
2023, Renewable and Sustainable Energy ReviewsNitrogenous fertilizer is integral to the food system for better yield of crops, and urea is the most common one. It requires ammonia as the primary reactant, while ammonia requires hydrogen for its production. Synthesis of these products is based on fossil fuels and is very carbon intensive, and pose many environmental threats. To reduce these, this review aims at understanding major solar energy-based pathways for three scenarios of producing solar fertilizers; producing urea using ammonia synthesized via solar hydrogen through water using thermolysis, photocatalytic, thermochemical, or electrolysis processes; using solar-powered ammonia using nitrogen and air/water by thermochemical, electrochemical, or photoelectrochemical methods; or directly producing urea using solar energy via photocatalytic and electrochemical processes. The potential of solar fertilizers, along with their advantages and disadvantages in agriculture, have also been highlighted. Besides this, an estimate of the land required (percent) to produce urea for all the scenarios using solar energy has been carried out for India with typical values of 0.119–0.130% for hydrogen production, 0.003–0.010% for ammonia and least for urea production. The review of techno-economic analysis and life cycle assessment for different hydrogen and ammonia production methods has been presented, and a comparative life cycle assessment study for certain hydrogen, ammonia, and nitrogenous fertilizer production methods using GaBi software was undertaken. Global warming potential, acidification potential, and eutrophication potential for 1 kg solar urea production were found as 0.092 kg CO2 equivalent, 0.014 mol of H+, and 1.869×10-6 kg phosphate equivalent.
Definitive adsorption states of intermediates on Ru nanocatalysts for progress of ammonia synthesis discovered by modulation excitation spectroscopy under reaction conditions
2023, Journal of CatalysisDiffuse reflectance infrared Fourier transform spectroscopy combined with modulation excitation spectroscopy realized observation of NH3 production process on a Ru nanoparticle supported on MgO under operation conditions in the presence of both H2 and N2 (∼400 °C, 0.1 MPa). Our study clearly indicated that N2 dissociation is developed via transition from vertically adsorbed states of N2 (N2-Ver) on an on-top Ru site to horizontally adsorbed states via N2-Ver on a bridge site, which is a critical step for the progress of AS reactions on Ru catalysts at low temperatures and persists in the presence of both N2 and H2.
Elucidating the dissociative and associative mechanisms on the surface-anchored Fe<inf>3</inf> cluster under the effect of external electric field
2023, Applied Surface ScienceIn the Haber-Bosch process, the direct dissociation of the N-N bond requires harsh reaction conditions. Three-atom metal clusters exhibit excellent catalytic performance in ammonia synthesis under mild conditions. They are considered potential catalysts to promote the associative hydrogenation of NN*. Moreover, it has been reported that electric fields can be a powerful tool for enhancing the performance of heterogeneously catalyzed reactions. Whether electric fields can further promote ammonia synthesis on three-atom metal clusters and its regulation mechanism needs to be investigated. In this work, we illustrate the effects of the electric fields on the N2 adsorption process, the NN* associative hydrogenation process, the N-N bond direct dissociation process, and the NNH* dissociation process for Fe3 cluster. The results show that the positive external electric field promotes the N2 adsorption process and activates the N-N bond of the NN* and NNH* species. With the increase of electric fields, the initial and final states of the N2 adsorption and NNH* dissociation processes become more stable. In addition, the electric field impedes electron transfer during the N2 adsorption process and the NN* associative hydrogenation process. This research will guide future work on applying electric fields to ammonia synthesis catalyzed by three-atom metal clusters.
Selective oxidation of 5-HMF to DFF over alkali promoted Mn nanocomposite
2023, Applied Catalysis A: GeneralVarious compositions of Cs promoted Mn catalysts were synthesized and investigated for selective oxidation of 5-HMF to DFF, among which Mn-Cs(80:20) was found to be most efficient giving 91 % conversion of 5-HMF and 99 % selectivity to DFF. Detail characterization like N2-sorption, BET surface area, TG-DTA, XRD, XPS, FE-SEM-EDX, TEM, HR-TEM, CO2-TPD, H2-TPR, O2-TPO, FTIR, Raman spectra and CH3OH-IR were done to establish structure-activity correlation. Enhanced surface area, porosity, thermal stability, dual morphologies were observed due to inclusion of Cs in Mn lattice domain which further enhanced the crystallinity, and oxygen diffusion on the surface. Mixed morphologies comprising nanoparticles (4–5 nm) and nanocubes (50–60 nm) were observed with enhanced redox potential and reduced work function due to weakening of Mn-O bonds. Significant increase in the basicity of catalyst, interfacial redox properties and lattice oxygen led to highly efficient oxidation of 5-HMF to DFF via Mars-van Krevelen mechanism at relatively milder conditions i.e. T = 90 °C and PO2= 200 psig. The catalyst was easily recyclable up to 7 times with minor loss in activity which was regenerated heat treatment protocol.