Sustainable Fertilizers: Publication Landscape on Wastes as Nutrient Sources, Wastewater Treatment Processes for Nutrient Recovery, Biorefineries, and Green Ammonia Synthesis.

The ability of modern agriculture to meet future food demand imposed by accelerating growth of the world's population is a major challenge, and fertilizers play a key role by replacing nutrients in agricultural soil. Given the need for fertilizers, their cost in nonrenewable resources and energy, and the consequences of the greenhouse gas emissions required to make them, people have begun to explore ways to make fertilizer manufacturing and use more sustainable. Using data from the CAS Content Collection, this review examines and analyzes the academic and patent literature on sustainable fertilizers from 2001 to 2021. The breakdown of journal and patent literature publication over time on this topic, country or region of publications, the substances included in published research, among other things allow us to understand the general progress in the field as well as the classes of materials and concepts driving innovation. We hope that this bibliometric analysis and literary review will assist researchers in relevant industries to discover and implement ways to supplement conventional fertilizers and nutrient sources while improving the efficiency and sustainability of waste management and ammonia production.

Comparing Molecular Mechanisms in Solar NH3 Production and Relations with CO2 Reduction.

Molecular mechanisms for N2 fixation (solar NH3) and CO2 conversion to C2+ products in enzymatic conversion (nitrogenase), electrocatalysis, metal complexes and plasma catalysis are analyzed and compared. It is evidenced that differently from what is present in thermal and plasma catalysis, the electrocatalytic path requires not only the direct coordination and hydrogenation of undissociated N2 molecules, but it is necessary to realize features present in the nitrogenase mechanism. There is the need for (i) a multi-electron and -proton simultaneous transfer, not as sequential steps, (ii) forming bridging metal hydride species, (iii) generating intermediates stabilized by bridging multiple metal atoms and (iv) the capability of the same sites to be effective both in N2 fixation and in COx reduction to C2+ products. Only iron oxide/hydroxide stabilized at defective sites of nanocarbons was found to have these features. This comparison of the molecular mechanisms in solar NH3 production and CO2 reduction is proposed to be a source of inspiration to develop the next generation electrocatalysts to address the challenging transition to future sustainable energy and chemistry beyond fossil fuels.

Changing perspectives in marine nitrogen fixation.

Nitrogen fixation, the reduction of atmospheric dinitrogen gas (N2) to ammonia, is critical for biological productivity but is difficult to study in the vast expanse of the global ocean. Decades of field studies and the infusion of molecular biological, genomic, isotopic, and geochemical modeling approaches have led to new paradigms and questions. The discovery of previously unknown N2-fixing (diazotrophic) microorganisms and unusual physiological adaptations, combined with diagnostic distributions of nutrients and their isotopes as well as measured and modeled biogeographic patterns, have revolutionized our understanding of marine N2 fixation and its role in the global nitrogen cycle. Anthropogenic upper-ocean warming, increased dissolved carbon dioxide, and acidification will affect the distribution and relative importance of specific subgroups of N2 fixers in the sea; these changes have implications for foodwebs and biogeochemical cycles.

Catalytic N2-to-NH3 (or -N2H4) Conversion by Well-Defined Molecular Coordination Complexes.

Nitrogen fixation, the six-electron/six-proton reduction of N2, to give NH3, is one of the most challenging and important chemical transformations. Notwithstanding the barriers associated with this reaction, significant progress has been made in developing molecular complexes that reduce N2 into its bioavailable form, NH3. This progress is driven by the dual aims of better understanding biological nitrogenases and improving upon industrial nitrogen fixation. In this review, we highlight both mechanistic understanding of nitrogen fixation that has been developed, as well as advances in yields, efficiencies, and rates that make molecular alternatives to nitrogen fixation increasingly appealing. We begin with a historical discussion of N2 functionalization chemistry that traverses a timeline of events leading up to the discovery of the first bona fide molecular catalyst system and follow with a comprehensive overview of d-block compounds that have been targeted as catalysts up to and including 2019. We end with a summary of lessons learned from this significant research effort and last offer a discussion of key remaining challenges in the field.

Unconventional Catalytic Approaches to Ammonia Synthesis.

Ammonia is a critically important industrial chemical and is largely responsible for sustaining the growing global population. To provide ammonia to underdeveloped regions and/or regions far from industrial production hubs, modular systems have been targeted and often involve unconventional production methodologies. These novel approaches for ammonia production can tap renewable resources at smaller scales located at the point of use, while decreasing the CO2 footprint. Plasma-assisted catalysis and electrochemical ammonia synthesis have promise owing to their atmospheric pressure and low-temperature operation conditions and the ability to construct units at scales desired for modularization. Fundamental and applied studies are underway to assess these processes, although many unknowns remain. In this review, we discuss recent developments and opportunities for unconventional ammonia synthesis with a focus on plasma-stimulated systems.

Production of [13N]ammonia from [13C]methanol on a 7.5 MeV cyclotron using 13C(p, n)13N reaction: Detection of myocardial infarction in a mouse model.

[13N]Ammonia is commonly produced using 16O(p, α)13N reaction but one of the limiting factor of this reaction is the relatively small nuclear cross-section at proton energies of <10 MeV. An alternative production method using 13C(p, n)13N reaction, which has a higher nuclear cross-section at low proton energies, is more suitable for a preclinical PET imaging facility equipped with a <10 MeV cyclotron. Here, we report a novel method to produce [13N]ammonia from [13C]methanol for preclinical use on a 7.5 MeV cyclotron. A tantalum solution target (80 µl) consisting of a havar window supplied by the cyclotron manufacturer for the production of [18F]fluoride was used without any modifications. The final bombardment parameters were optimized as follow: [13C]methanol concentration in target solution - 10%, bombardment time - 8 min, and beam current - 2.2 µA. These parameters provided doses of [13N]ammonia which were sufficient to conduct preclinical PET imaging studies in a mouse model of myocardial infarction. Under optimized conditions, the operational lifetime of the target was approximately 150 µAmin. Radionuclide identity of the product as 13N was confirmed by measuring the decay half-life and its radionuclide purity was confirmed by γ-ray spectroscopic analysis. Gas chromatography revealed that the final [13N]ammonia dose was not distinguishable from water, showing no traces of methanol. As expected, PET/CT imaging in healthy CD-1 mice indicated the accumulation of [13N]ammonia in myocardial tissue; mice with myocardial infarction created by left ascending coronary ligation showed clear perfusion deficit in affected tissue. This work demonstrates the proof-of-concept of using 13C(p, n)13N reaction to produce [13N]ammonia from [13C]methanol with a <10 MeV cyclotron, and its diagnostic application in imaging cardiac perfusion.

Carbon-Based Metal-Free Catalysts for Electrocatalytic Reduction of Nitrogen for Synthesis of Ammonia at Ambient Conditions.

The electrocatalytic nitrogen reduction reaction (NRR) is a promising catalytic system for N2 fixation in ambient conditions. Currently, metal-based catalysts are the most widely studied catalysts for electrocatalytic NRR. Unfortunately, the low selectivity and poor resistance to acids and bases, and the low Faradaic efficiency, production rate, and stability of metal-based catalysts for NRR make them uncompetitive for the synthesis of ammonia in comparison to the industrial Haber-Bosch process. Inspired by applications of carbon-based metal-free catalysts (CMFCs) for the oxygen reduction reaction (ORR) and CO2 reduction reaction (CO2 RR), the studies of these CMFCs in electrocatalytic NRR have attracted great attention in the past year. However, due to the differences in electrocatalytic NRR, there are several critical issues that need to be addressed in order to achieve rational design of advanced carbon-based metal-free electrocatalysts to improve activity, selectivity, and stability for NRR. Herein, the recent developments in the field of carbon-based metal-free NRR catalysts are presented, along with critical issues, challenges, and perspectives concerning metal-free catalysts for electrocatalytic reduction of nitrogen for synthesis of ammonia at ambient conditions.

Wet NH3-Triggered NH2-MIL-125(Ti) Structural Switch for Visible Fluorescence Immunoassay Impregnated on Paper.

This work has looked to explore an innovative and powerful visible fluorescence immunoassay method through wet NH3-triggered structural change of NH2-MIL-125(Ti) impregnated on paper for the detection of carcinoembryonic antigen (CEA). Gold nanoparticles heavily functionalized with glutamate dehydrogenase (GDH) and secondary antibody were used for generation of wet NH3 with a sandwiched immunoassay format. Paper-based analytical device (PAD) coated with NH2-MIL-125(Ti) exhibited good visible fluorescence intensity through wet NH3-triggeried structural change with high accuracy and reproducibility. Moreover, NH2-MIL-125(Ti)-based PAD displayed two visual modes of fluorescence color and physical color with the naked eye and allowed the detection of CEA at a concentration as low as 0.041 ng mL-1. Importantly, the PAD-based assay provides promise for use in the mass production of miniaturized devices and opens new opportunities for protein diagnostics and biosecurity.

A Unique Historical Case to Understand the Present Sustainable Development.

Every innovation seeks to become a profitable business, with this considered to be the engine for economic prosperity. When an innovation is revolutionary, its long-term consequences can be revolutionary too. The Haber-Bosh process for ammonia synthesis is arguably the twentieth century's most significant innovation, and its importance to global food production and its impact on the environment are not expected to diminish over the coming decades. The historical case of the ammonia synthesis process invented by Fritz Haber and the ensuing innovation provides an incomparable opportunity to illustrate the interactions across contemporary needs, prominent scientists, political concerns, moral dilemmas, ethics, governance and environmental implications at a time when the concept of sustainability was still in its infancy. Despite its high economic and environmental costs, no cleaner or more efficient sustainable alternative has so far been found, and so replacing this "old" innovation that still "feeds" a large part of the world's population does not appear to be on the cards in the near future.

Electrochemical Synthesis of Ammonia from Water and Nitrogen: A Lithium-Mediated Approach Using Lithium-Ion Conducting Glass Ceramics.

Lithium-mediated reduction of dinitrogen is a promising method to evade electron-stealing hydrogen evolution, a critical challenge which limits faradaic efficiency (FE) and thus hinders the success of traditional protic-solvent-based ammonia electro-synthesis. A viable implementation of the lithium-mediated pathway using lithium-ion conducting glass ceramics involves i) lithium deposition, ii) nitridation, and iii) ammonia formation. Ammonia was successfully synthesized from molecular nitrogen and water, yielding a maximum FE of 52.3 %. With an ammonia synthesis rate comparable to previously reported approaches, the fairly high FE demonstrates the possibility of using this nitrogen fixation strategy as a substitute for firmly established, yet exceedingly complicated and expensive technology, and in so doing represents a next-generation energy storage system.

Ammonia Synthesis at Low Pressure.

Ammonia can be synthesized at low pressure by the use of an ammonia selective absorbent. The process can be driven with wind energy, available locally in areas requiring ammonia for synthetic fertilizer. Such wind energy is often called "stranded," because it is only available far from population centers where it can be directly used. In the proposed low pressure process, nitrogen is made from air using pressure swing absorption, and hydrogen is produced by electrolysis of water. While these gases can react at approximately 400 °C in the presence of a promoted conventional catalyst, the conversion is often limited by the reverse reaction, which makes this reaction only feasible at high pressures. This limitation can be removed by absorption on an ammine-like calcium or magnesium chloride. Such alkaline metal halides can effectively remove ammonia, thus suppressing the equilibrium constraints of the reaction. In the proposed absorption-enhanced ammonia synthesis process, the rate of reaction may then be controlled not by the chemical kinetics nor the absorption rates, but by the rate of the recycle of unreacted gases. The results compare favorably with ammonia made from a conventional small scale Haber-Bosch process.

Catalytic Conversion of Dinitrogen into Ammonia under Ambient Reaction Conditions by Using Proton Source from Water.

Molybdenum-catalyzed conversion of molecular dinitrogen into ammonia under ambient reaction conditions has been achieved by using a proton source generated in situ from the ruthenium-catalyzed oxidation of water in combination with visible light and a photosensitizer. The preset reaction system is considered as a new model for the nitrogen fixation by photosynthetic bacteria.

An Fe-N2 Complex That Generates Hydrazine and Ammonia via Fe═NNH2: Demonstrating a Hybrid Distal-to-Alternating Pathway for N2 Reduction.

Biological N2 fixation to NH3 may proceed at one or more Fe sites in the active-site cofactors of nitrogenases. Modeling individual e(-)/H(+) transfer steps of iron-ligated N2 in well-defined synthetic systems is hence of much interest but remains a significant challenge. While iron complexes have been recently discovered that catalyze the formation of NH3 from N2, mechanistic details remain uncertain. Herein, we report the synthesis and isolation of a diamagnetic, 5-coordinate Fe═NNH2(+) species supported by a tris(phosphino)silyl ligand via the direct protonation of a terminally bound Fe-N2(-) complex. The Fe═NNH2(+) complex is redox-active, and low-temperature spectroscopic data and DFT calculations evidence an accumulation of significant radical character on the hydrazido ligand upon one-electron reduction to S = (1)/2 Fe═NNH2. At warmer temperatures, Fe═NNH2 rapidly converts to an iron hydrazine complex, Fe-NH2NH2(+), via the additional transfer of proton and electron equivalents in solution. Fe-NH2NH2(+) can liberate NH3, and the sequence of reactions described here hence demonstrates that an iron site can shuttle from a distal intermediate (Fe═NNH2(+)) to an alternating intermediate (Fe-NH2NH2(+)) en route to NH3 liberation from N2. It is interesting to consider the possibility that similar hybrid distal/alternating crossover mechanisms for N2 reduction may be operative in biological N2 fixation.

Versatile Protecting-Group Free Tetrazolomethane Amine Synthesis by Ugi Reaction.

The use of ammonia in the Ugi reaction is often problematic due to low yields and multiple side reactions. Here, we report the use of ammonia in the tetrazole Ugi variation providing a clean, good-to-high yielding reaction, especially with ketones as oxo components. The scope and limitations of this reaction and a structure-reactivity relationship are provided by performing >85 reactions. The primary amine component of the α-amino tetrazole is a versatile starting material for further reactions.

The Challenge of Electrochemical Ammonia Synthesis: A New Perspective on the Role of Nitrogen Scaling Relations.

The electrochemical production of NH3 under ambient conditions represents an attractive prospect for sustainable agriculture, but electrocatalysts that selectively reduce N2 to NH3 remain elusive. In this work, we present insights from DFT calculations that describe limitations on the low-temperature electrocatalytic production of NH3 from N2 . In particular, we highlight the linear scaling relations of the adsorption energies of intermediates that can be used to model the overpotential requirements in this process. By using a two-variable description of the theoretical overpotential, we identify fundamental limitations on N2 reduction analogous to those present in processes such as oxygen evolution. Using these trends, we propose new strategies for catalyst design that may help guide the search for an electrocatalyst that can achieve selective N2 reduction.

Evaluating molecular cobalt complexes for the conversion of N2 to NH3.

Well-defined molecular catalysts for the reduction of N2 to NH3 with protons and electrons remain very rare despite decades of interest and are currently limited to systems featuring molybdenum or iron. This report details the synthesis of a molecular cobalt complex that generates superstoichiometric yields of NH3 (>200% NH3 per Co-N2 precursor) via the direct reduction of N2 with protons and electrons. While the NH3 yields reported herein are modest by comparison to those of previously described iron and molybdenum systems, they intimate that other metals are likely to be viable as molecular N2 reduction catalysts. Additionally, a comparison of the featured tris(phosphine)borane Co-N2 complex with structurally related Co-N2 and Fe-N2 species shows how remarkably sensitive the N2 reduction performance of potential precatalysts is. These studies enable consideration of the structural and electronic effects that are likely relevant to N2 conversion activity, including the π basicity, charge state, and geometric flexibility.

Promotion effect of H2 on ethanol oxidation and NOx reduction with ethanol over Ag/Al2O3 catalyst.

The catalytic partial oxidation of ethanol and selective catalytic reduction of NOx with ethanol (ethanol-SCR) over Ag/Al2O3 were studied using synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). The intermediates were identified by PIMS and their photoionization efficiency (PIE) spectra. The results indicate that H2 promotes the partial oxidation of ethanol to acetaldehyde over Ag/Al2O3, while the simultaneously occurring processes of dehydration and dehydrogenation were inhibited. H2 addition favors the formation of ammonia during ethanol-SCR over Ag/Al2O3, the occurrence of which creates an effective pathway for NOx reduction by direct reaction with NH3. Simultaneously, the enhancement of the formation of ammonia benefits its reaction with surface enolic species, resulting in producing -NCO species again, leading to enhancement of ethanol-SCR over Ag/Al2O3 by H2. Using VUV-PIMS, the reactive vinyloxy radical was observed in the gas phase during the NOx reduction by ethanol for the first time, particularly in the presence of H2. Identification of such a reaction occurring in the gas phase may be crucial for understanding the reaction pathway of HC-SCR over Ag/Al2O3.

A 10(6)-fold enhancement in N2-binding affinity of an Fe2(µ-H)2 core upon reduction to a mixed-valence Fe(II)Fe(I) state.

Transient hydride ligands bridging two or more iron centers purportedly accumulate on the iron-molybdenum cofactor (FeMoco) of nitrogenase, and their role in the reduction of N2 to NH3 is unknown. One role of these ligands may be to facilitate N2 coordination at an iron site of FeMoco. Herein, we consider this hypothesis and describe the preparation of a series of diiron complexes supported by two bridging hydride ligands. These compounds bind either one or two molecules of N2 depending on the redox state of the Fe2(µ-H)2 unit. An unusual example of a mixed-valent Fe(II)(µ-H)2Fe(I) is described that displays a 10(6)-fold enhancement of N2 binding affinity over its oxidized congener, quantified by spectroscopic and electrochemical techniques. Furthermore, these compounds show promise as functional models of nitrogenase as substantial amounts of NH3 are produced upon exposure to proton and electron equivalents. The Fe(µ-H)Fe(N2) sub-structure featured herein was previously unknown. This subunit may be relevant to consider in nitrogenases during turnover.

RETRACTED: Ammonia synthesis. Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3.

The Haber-Bosch process to produce ammonia for fertilizer currently relies on carbon-intensive steam reforming of methane as a hydrogen source. We present an electrochemical pathway in which ammonia is produced by electrolysis of air and steam in a molten hydroxide suspension of nano-Fe2O3. At 200°C in an electrolyte with a molar ratio of 0.5 NaOH/0.5 KOH, ammonia is produced at 1.2 volts (V) under 2 milliamperes per centimeter squared (mA cm(-2)) of applied current at coulombic efficiency of 35% (35% of the applied current results in the six-electron conversion of N2 and water to ammonia, and excess H2 is cogenerated with the ammonia). At 250°C and 25 bar of steam pressure, the electrolysis voltage necessary for 2 mA cm(-2) current density decreased to 1.0 V.