Renewable ammonia for sustainable energy and agriculture: vision and systems engineering opportunities

Drivers and Pathways for the Recovery of Critical Metals from Waste-Printed Circuit Boards

The ever-increasing importance of critical metals (CMs) in modern society underscores their resource security and circularity. Waste-printed circuit boards (WPCBs) are particularly attractive reservoirs of CMs due to their gamut CM embedding and ubiquitous presence. However, the recovery of most CMs is out of reach from current metal-centric recycling industries, resulting in a flood loss of refined CMs. Here, 41 types of such spent CMs are identified. To deliver a higher level of CM sustainability, this work provides an insightful overview of paradigm-shifting pathways for CM recovery from WPCBs that have been developed in recent years. As a crucial starting entropy-decreasing step, various strategies of metal enrichment are compared, and the deployment of artificial intelligence (AI) and hyperspectral sensing is highlighted. Then, tailored metal recycling schemes are presented for the platinum group, rare earth, and refractory metals, with emphasis on greener metallurgical methods contributing to transforming CMs into marketable products. In addition, due to the vital nexus of CMs between the environment and energy sectors, the upcycling of CMs into electro-/photo-chemical catalysts for green fuel synthesis is proposed to extend the recycling chain. Finally, the challenges and outlook on this all-round upgrading of WPCB recycling are outlined.

Nanoporous copper titanium tin (np-Cu2TiSn) Heusler alloy prepared by dealloying-induced phase transformation for electrocatalytic nitrate reduction to ammonia

Heusler alloys are a series of well-established intermetallic compounds with abundant structure and elemental substitutions, which are considered as potentially valuable catalysts for integrating multiple reactions owing to the features of ordered atomic arrangement and optimized electronic structure. Herein, a nanoporous copper titanium tin (np-Cu2TiSn) Heusler alloy is successfully prepared by the (electro)chemical dealloying transformation method, which exhibits high nitrate (NO3-) reduction performance with an NH3 Faradaic efficiency of 77.14 %, an NH3 yield rate of 11.90 mg h-1 mg-1cat, and a stability for 100 h under neutral condition. Significantly, we also convert NO3- to high-purity ammonium phosphomolybdate with NH4+ collection efficiency of 83.8 %, which suggests a practical approach to convert wastewater nitrate into value-added ammonia products. Experiments and theoretical calculations reveal that the electronic structure of Cu sites is modulated by the ligand effect of surrounding Ti and Sn atoms, which can simultaneously enhance the activation of NO3-, facilitate the desorption of NH3, and reduce the energy barriers, thereby boosting the electrochemical nitrate reduction reaction.

Advanced Modeling and Optimization Strategies for Process Synthesis

This article provides a systematic review of recent progress in optimization-based process synthesis. First, we discuss multiscale modeling frameworks featuring targeting approaches, phenomena-based modeling, unit operation-based modeling, and hybrid modeling. Next, we present the expanded scope of process synthesis objectives, highlighting the considerations of sustainability and operability to assure cost-competitive production in an increasingly dynamic market with growing environmental awareness. Then, we review advances in optimization algorithms and tools, including emerging machine learning-and quantum computing-assisted approaches. We conclude by summarizing the advances in and perspectives for process synthesis strategies.

Tuning the Selectivity of Nitrate Reduction via Fine Composition Control of RuPdNP Catalysts

Herein, aqueous nitrate (NO3 -) reduction is used to explore composition-selectivity relationships of randomly alloyed ruthenium-palladium nanoparticle catalysts to provide insights into the factors affecting selectivity during this and other industrially relevant catalytic reactions. NO3 - reduction proceeds through nitrite (NO2 -) and then nitric oxide (NO), before diverging to form either dinitrogen (N2) or ammonium (NH4 +) as final products, with N2 preferred in potable water treatment but NH4 + preferred for nitrogen recovery. It is shown that the NO3 - and NO starting feedstocks favor NH4 + formation using Ru-rich catalysts, while Pd-rich catalysts favor N2 formation. Conversely, a NO2 - starting feedstock favors NH4 + at ≈50 atomic-% Ru and selectivity decreases with higher Ru content. Mechanistic differences have been probed using density functional theory (DFT). Results show that, for NO3 - and NO feedstocks, the thermodynamics of the competing pathways for N-H and N-N formation lead to preferential NH4 + or N2 production, respectively, while Ru-rich surfaces are susceptible to poisoning by NO2 - feedstock, which displaces H atoms. This leads to a decrease in overall reduction activity and an increase in selectivity toward N2 production. Together, these results demonstrate the importance of tailoring both the reaction pathway thermodynamics and initial reactant binding energies to control overall reaction selectivity.

Resistive gas sensors for the detection of NH3gas based on 2D WS2, WSe2, MoS2, and MoSe2: a review

Transition metal dichalcogenides (TMDs) with a two-dimensional (2D) structure and semiconducting features are highly favorable for the production of NH3gas sensors. Among the TMD family, WS2, WSe2, MoS2, and MoSe2exhibit high conductivity and a high surface area, along with high availability, reasons for which they are favored in gas-sensing studies. In this review, we have discussed the structure, synthesis, and NH3sensing characteristics of pristine, decorated, doped, and composite-based WS2, WSe2, MoS2, and MoSe2gas sensors. Both experimental and theoretical studies are considered. Furthermore, both room temperature and higher temperature gas sensors are discussed. We also emphasized the gas-sensing mechanism. Thus, this review provides a reference for researchers working in the field of 2D TMD gas sensors.

Integrated optimization modelling framework for low-carbon and green regional transitions through resource-based industrial symbiosis

The development and utilization of bulk resources provide the basic material needs for industrial systems. However, most current resource utilization patterns are unsustainable, with low efficiencies and high carbon emissions. Here, we report a quantitative tool for resource-based industries to facilitate sustainable and low-carbon transitions within the regional economy. To evaluate the effectiveness of this tool, the saline Qinghai Lake region was chosen as a case study. After optimizing the industrial structure, the benefits of economic output, resource efficiency, energy consumption, solid waste reduction, and carbon emission reduction can be obtained. The scenario analyses exhibit disparities in different transition paths, where the carbon mitigation, economic output, and resource efficiency that benefit from optimal development paths are significantly better than those of the traditional path, indicating the urgency of adopting cleaner technology and industrial symbiosis for regional industries.

Li-Mediated Electrochemical Nitrogen Fixation: Key Advances and Future Perspectives

The electrochemical nitrogen reduction reaction holds great potential for ammonia production using electricity generated from renewable energy sources and is sustainable. The low solubility of nitrogen in aqueous media, poor kinetics, and intrinsic competition by the hydrogen evolution reaction result in meager ammonia production rates. Attributing measured ammonia as a valid product, not an impurity, is challenging despite rigorous analytical experimentation. In this regard, Li-mediated electrochemical nitrogen reduction is a proven method providing significant ammonia yields. Herein, fundamental advances and insights into the Li-mediated strategy are summarized, emphasizing the role of lithium, reaction parameters, cell designs, and mechanistic evaluation. Challenges and perspectives are presented to highlight the prospects of this strategy as a continuous, stable, and modular approach toward sustainable ammonia production.

Optimizing Renewable Ammonia Production for a Sustainable Fertilizer Supply Chain Transition

Local renewable ammonia production using electrolytic hydrogen is an emerging approach to alleviate emissions attributed to synthetic nitrogen fertilizer production while also insulating against fluctuations in fertilizer prices and mitigating transportation costs and emissions. However, replacing ammonia currently produced using fossil fuels will not be immediate. To this end, we develop a supply chain transition model, which first optimizes the design and hourly operation of new renewable ammonia facilities to minimize production costs and then optimizes the annual installation timing, production scale, and location of these new renewable facilities along with ammonia transportation to meet county resolution demands. The objective is to augment and eventually replace conventional ammonia market imports in an economically competitive manner. We performed a case study for Minnesota's ammonia supply chain and found that a full transition to in-state renewable production by 2032 is optimal. This is incentivized by the U.S. federal government's clean hydrogen production credits. This transition results in 99 % reduction in carbon intensity along with stable supply costs below $475 per metric tonne. New renewable production facilities are an order of magnitude smaller than existing conventional plants. They use both wind and solar resources and operate dynamically to minimize expensive battery and hydrogen storage capacities.

Ammonia Production Using Bacteria and Yeast toward a Sustainable Society

Ammonia is an important chemical that is widely used in fertilizer applications as well as in the steel, chemical, textile, and pharmaceutical industries, which has attracted attention as a potential fuel. Thus, approaches to achieve sustainable ammonia production have attracted considerable attention. In particular, biological approaches are important for achieving a sustainable society because they can produce ammonia under mild conditions with minimal environmental impact compared with chemical methods. For example, nitrogen fixation by nitrogenase in heterogeneous hosts and ammonia production from food waste using microorganisms have been developed. In addition, crop production using nitrogen-fixing bacteria has been considered as a potential approach to achieving a sustainable ammonia economy. This review describes previous research on biological ammonia production and provides insights into achieving a sustainable society.

Nano-fertilizers: A sustainable technology for improving crop nutrition and food security

Excessive use of synthetic fertilizers cause economic burdens, increasing soil, water and atmospheric pollution. Nano-fertilizers have shown great potential for their sustainable uses in soil fertility, crop production and with minimum or no environmental tradeoffs. Nano-fertilizers are of submicroscopic sizes, have a large surface area to volume ratio, can have nutrient encapsulation, and greater mobility hence they may increase plant nutrient access and crop yield. Due to these properties, nano-fertilizers are regarded as deliverable 'smart system of nutrients'. However, the problems in the agroecosystem are broader than existing developments. For example, nutrient delivery in different physicochemical properties of soils, moisture, and other agro-ecological conditions is still a challenge. In this context, the present review provides an overview of various uses of nanotechnology in agriculture, preference of nano-fertilizers over the conventional fertilizers, nano particles formation, mobility, and role in heterogeneous soils, with special emphasis on the development and use of chitosan-based nano-fertilizers.