Nitric acid production is a cornerstone of the chemical industry, yet it presents considerable environmental challenges, primarily due to greenhouse gas emissions such as nitrous oxide (N2O) and nitrogen oxides (NOx). This manuscript critically examines the key performance indicators (KPIs) that define the gate-to-gate environmental sustainability of nitric acid plants. Quantitative metrics and related benchmarks achieved in modern plants, e.g., energy efficiency (ca. 2 GJ exported per ton of HNO3) and NOx/N2O reduction (95-99%), are presented. Strategies to enhance these KPIs are discussed, including process integration, intensification, advanced emission control technologies, and operational optimization. Special attention is given to the chemical conversion processes of NOx and N2O, highlighting their roles in minimizing overall emissions. The review also synthesizes recent literature to showcase emerging trends, regulatory developments, and technological innovations that facilitate the transition toward more sustainable nitric acid production. Finally, the article identifies current research gaps and outlines future directions for the field.

Ammonia (NH3) can be synthesized directly from N2 and H2O using plasma micro-discharges formed at the water-electrode interface, offering a promising alternative to both conventional electrocatalysis and nonthermal plasma processes. However, discharge performance and stability are strongly affected by device engineering. This study reports the development and engineering of a hybrid electrochemical device that integrates a micro-plasma cathode for sustainable NH3 production under ambient temperature and pressure. Solvated electrons generated through plasma-liquid interactions, particularly within interfacial aerosol microdroplets, act as highly reducing species, eliminating the need for catalysts or external chemical reagents. The effects of the plasma-liquid gap, gas feed flow rate, discharge current, and cathode inner diameter on NH3 yield are systematically investigated. Optimizing these factors enables Faradaic efficiency exceeding 70% and significantly enhances the instantaneous N2-to-NH3 yield, outperforming previously reported plasma-liquid systems. These findings highlight the importance of system engineering optimization for advancing sustainable plasma-assisted nitrogen fixation and for progressing toward industrial scale-up.

The carbonation of K2CO3 to KHCO3 is an interesting CO2 capture process due to its low material cost, high selectivity, and substantial CO2 capacity. Traditionally, KHCO3 is regenerated into K2CO3 through thermal decomposition. However, plasma-assisted decomposition presents a promising alternative, enabling not only CO2 desorption but also the concurrent production of valuable products such as H2 and CO. In this study, KHCO3 particles in a size range of 250–355 µm were packed in a dielectric barrier discharge reactor and exposed to plasma. It was found that the decomposition of KHCO3 in the plasma reactor is mainly driven by a thermal mechanism, and the decomposition rate was controlled by temperature increase via plasma heating. The energy consumption for decomposition is more than one order of magnitude higher compared to the thermal approach reported in the literature. However, production of CO and H2 was achieved during plasma treatment, highlighting the potential advantage of an integrated CO2 capture and utilization process, and the best CO2 conversion and energy efficiency achieved were 9.0

Anthropogenic air pollution is one of the major threats to planetary and human health. In this view, nitrogen oxides (NOx) and nitrous oxide (N2O) are among the key responsible by contributing to photochemical smog, acid rain, eutrophication, and a variety of health issues. Effective after-treatment abatement technologies like selective catalytic reduction and decomposition routes exist, but the simultaneous conversion of NOx and N2O remains under-explored. This perspective addresses the challenges and opportunities in optimizing catalytic technologies for individual and simultaneous NOx, N2O, and NH3 conversion. The integration of advanced catalytic systems in both established industrial processes and emerging technologies relying on the use of NH3 as a fuel is crucial for achieving sustainable and environmentally friendly solutions. Addressing these challenges can significantly reduce greenhouse gas emissions and ensure ammonia's promise as a low-impact carbon-free fuel. This publication emphasizes the importance of continuous innovation in the field of catalytic conversion strategies to meet stringent environmental regulations and mitigate the impacts of NOx and N2O emissions. Developing cost-effective, high-performance catalysts under real industrial conditions is essential for the widespread adoption of these technologies and the transition to a more sustainable future.

The Li-N2 cell represents a fascinating device that opens a new pathway for ammonia electrosynthesis. It combines the unique property of lithium, which can spontaneously react with N2 under mild conditions, with an energy-efficient solution to the challenging N2 fixation reaction. However, such a battery-inspired setup may be susceptible to false-positive results and present some pitfalls. This work elucidates some critical aspects of Li-N2 cells, aiming at identifying a reliable methodology to assess the electrochemical reduction of N2 at the cathodic surface, avoiding misleading pathways. Despite the spontaneous nature of the reaction between lithium and N2, it remains uncertain whether it is feasible to promote the electrochemical fixation of N2 before reaching the lithium plating potential. This would involve lithium as an ion in the electrolyte, which should activate and enable N2 reduction on the carbonaceous surface before any Li+ reduction occurs, i.e., at a potential higher than the lithium plating potential (-3.04 V vs SHE). This study discusses this possibility, searching for setup limitations, such as the presence of metallic lithium at the anode, and pitfalls, such as the use of cyclic voltammetry in different testing environments as a methodology to evaluate the formation of Li3N before lithium plating occurs.

Fe-exchanged zeolites are heterogeneous catalysts that can potentially ensure simultaneous conversion of nitrous oxide (N2O) and nitric oxide (NO) using ammonia (NH3) as a selective reducing agent through their selective catalytic reduction reaction (N2O-NO-SCR). In this study, we rationalize the origin of the beneficial effect of N2O on the NO conversion by combining catalytic experiments with ex situ characterization and in situ/operando X-ray absorption spectroscopy (XAS) and infrared spectroscopy in diffuse reflectance mode (DRIFTS) on a series of Fe-ZSM-5 catalysts where we attempted to control Fe speciation at constant Fe content. The catalytic activity data revealed that N2O can promote NO conversion at different temperatures and to different extents. This behavior was found to be related to the activity of the catalysts in the NO-mediated N2O decomposition reaction, which ensures the oxidative transformation of NO and thus sustains the N2O-NO-SCR chemistry. The oxidation activity is in turn determined by processes of N2O activation and NO adsorption, which are a function of the Fe speciation and are likely catalyzed by a minority of isolated Fe2+ sites coordinated in different cationic environments. In agreement, the concentrations of the Fe species able to activate N2O (Cα) and of the Fe species able to coordinate NO (CFe-NO) decrease with an increasing degree of Fe agglomeration and govern especially the promotion of the NO conversion induced by N2O in this dual-site mechanism. Maximization of the concentration of both species is therefore essential to design Fe-exchanged zeolites with the highest activity toward the N2O-NO-SCR reaction.

Iron-exchanged zeolites are often deployed industrially to remediate nitric oxide (NO) and nitrous oxide (N2O) emissions. The nature of the active site and the reaction mechanism involved in the simultaneous removal of NO and N2O remain largely unknown, primarily because of the heterogeneity of Fe species. Here we combined catalytic experiments with transient operando X-ray absorption spectroscopy, electron paramagnetic resonance and diffuse reflectance infrared Fourier transform spectroscopy to disentangle the nature of Fe species and elementary reaction steps. We identified spectroscopically the square-planar Fe2+ sites in the beta-cationic position responsible for N2O activation and the related redox cycle. These sites communicate with tetrahedrally coordinated Fe2+ sites in the adjacent gamma-cationic position, accounting for adsorption and redox-mediated oxidation of NO. The availability of NH3 adsorbed on neighbouring Br & oslash;nsted acid sites regulates the overall reaction rate of this dual-site mechanism by intercepting the NO oxidation sequence. The cooperation between these redox processes ensures enhanced conversion of both NO and N2O. Fe-exchanged zeolite catalysts are known for their ability to remediate NOx and N2O emissions, but their reactivity in mixed streams of NO and N2O remains unclear. Now a suite of operando spectroscopies reveals the active Fe species involved in the process and their synergistic effect during the simultaneous conversion of these pollutants.

Electrochemical N-2 reduction reaction (E-NRR) has recently gained increasing interest within the scientific community, due to the ongoing energy crisis and pursuit of process sustainability. In this scenario, emerging lithium-mediated (Li-m) strategies are obtaining promising Faradaic efficiency (FE) and NH3 production rate values. In this work, the Li-m scenarios are classified and explained toward a more sustainable process. Continuous processes, with a lithium salt and a proton donor in an electrolytic cell, are analyzed and compared with stepwise pathways. Different parameters are summarized in relation to the system stability, for which the importance of a tailored solid electrolyte interphase (SEI) layer emerged. Among stepwise processes, the thermochemical direct nitridation of lithium is discussed together with the recently developed Galvanic Li & horbar;N-2 cell strategy.

Electrochemical Nitrogen Reduction Lithium can boost the production of ammonia and fertilizers through renewable energy-powered processed. In article number 2400076, Federico Bella, and co-workers showcase the cutting-edge approaches towards Li-mediated nitrogen electroreduction, highlighting advanced materials and newly conceived devices that can speed-up the ongoing energy and ecological transition.

The cleavage of the N2 triple bond on the Fe(111) surface is believed to be the rate limiting step of the famed Haber-Bosch ammonia catalysis. Using a combination of machine learning potentials and advanced simulation techniques, we study this important catalytic step as a function of temperature. We find that at low temperatures our results agree with the well-established picture. However, if we increase the temperature to reach operando conditions the surface undergoes a global dynamical change and the step structure of the Fe(111) surface is destroyed. The catalytic sites, traditionally associated with the Fe(111) surface appear and disappear continuously. Our simulations illuminate the danger of extrapolating low-temperature results to operando conditions and indicate that the catalytic activity can only be inferred from calculations that take dynamics fully into account. More than that, they show that it is the transition to this highly fluctuating interfacial environment that drives the catalytic process.

The Sabatier principle and the scaling relations have been widely used to search for and screen new catalysts in the field of catalysis. However, these powerful tools can also serve as limitations of catalyst control and breakthrough. To overcome this challenge, this work proposes an efficient method of studying catalyst control by support polarization from first-principles. The results demonstrate that the properties of catalysts are determined by support polarization, irrespective of the magnitude of spontaneous polarization of support. The approach enables elucidating the scaling relations between binding energies at various polarization values of support. Moreover, we observe the breakdown of scaling relations for the surface controlled by support polarization, without requiring ensemble modification. By studying the surface electronic structure and decomposing the induced charge into contributions from different atoms and orbitals, we identify the inherent structural property of the interface that leads to the breaking of the scaling relations. Specifically, the displacements of the underlying oxide support impose its symmetry on the catalyst, causing the scaling relations between different adsorption sites to break.

Dynamics has long been recognized to play an important role in heterogeneous catalytic processes. However, until recently, it has been impossible to study their dynamical behavior at industry-relevant temperatures. Using a combination of machine learning potentials and advanced simulation techniques, we investigate the cleavage of the N 2 triple bond on the Fe(111) surface. We find that at low temperatures our results agree with the well-established picture. However, if we increase the temperature to reach operando conditions, the surface undergoes a global dynamical change and the step structure of the Fe(111) surface is destabilized. The catalytic sites, traditionally associated with this surface, appear and disappear continuously. Our simulations illuminate the danger of extrapolating low-temperature results to operando conditions and indicate that the catalytic activity can only be inferred from calculations that take dynamics fully into account. More than that, they show that it is the transition to this highly fluctuating interfacial environment that drives the catalytic process.

Transition-metal-modified zeolites have recently gained the greatest interest among scientists. Ab initio calculations within the density functional theory were used. The exchange and correlation functional was approximated with the Perdew-Burke-Ernzerhof (PBE) functional. Cluster models of ZSM-5 (Al2Si18O53H26) zeolites were used with Fe particles adsorbed above aluminum. The adsorption of three iron adsorbates inside the pores of the ZSM-5 zeolite-Fe, FeO and FeOH-was carried out with different arrangements of aluminum atoms in the zeolite structure. The DOS diagram and the HOMO, SOMO and LUMO molecular orbitals for these systems were analyzed. It has been shown that depending on the adsorbate and the position of aluminum atoms in the pore structure of the zeolite, the systems can be described as insulators or conductors, which significantly affects their activity. The main aim of the research was to understand the behavior of these types of systems in order to select the most efficient one for a catalytic reaction.

The cleavage of the N2 triple bond on the Fe(111) surface is believed to be the rate limiting step of the famed Haber-Bosch ammonia catalysis. Using a combination of machine learning potentials and advanced simulation techniques, we study this important catalytic step as a function of temperature. We find that at low temperatures our results agree with the well-established picture. However, if we increase the temperature to reach operando conditions the surface undergoes a global dynamical change and the step structure of the Fe(111) surface is destroyed. The catalytic sites, traditionally associated with the Fe(111) surface appear and disappear continuously. Our simulations illuminate the danger of extrapolating low-temperature results to operando conditions and indicate that the catalytic activity can only be inferred from calculations that take dynamics fully into account. More than that, they show that it is the transition to this highly fluctuating interfacial environment that drives the catalytic process.

Despite the Haber-Bosch process being more than 100 years old, only incremental improvements have been achieved until recently. Now, by combining the catalyst expertise of CLARIANT and the engineering knowledge of CASALE, a breakthrough has been realized. AmoMax®-Casale is a new ammonia synthesis catalyst jointly developed by Casale and Clariant particularly for use in Casale ammonia converters. AmoMax®-Casale is a customized evolution of the well-known, wustite-based catalyst, AmoMax® 10. While retaining the same superior resistance to ageing, poisoning and mechanical strength, AmoMax®-Casale is significantly more active. This feature allows to reduce the loop recycle rate and the loop pressure and/or to increase the ammonia production. The higher activity of AmoMax®-Casale contributes to improve the overall operating efficiency either by saving energy, or by increasing significantly the plant capacity. This article will describe in detail the successful development of AmoMax®-Casale, explain advantages and commercial benefits based on concrete plant simulations and share the start-up experience of the first commercial reference.

Two commercial Fe-zeolite catalysts used for N 2 O abatement from nitric acid production plants are analysed before and after hydrothermal aging for their structure and activity towards N 2 O conversion in complex feed.

The effect of an alumina-based binder on the structure of a commercial Fe-ZSM-5 catalyst has been investigated. Several ex-situ characterization techniques were used to show that the binder in the catalyst formulation allows obtaining a material that possesses improved features in terms of Fe species dispersion, framework Al content and acidity. UV–Vis and X-ray absorption spectroscopy showed that the extent of Fe agglomeration in the extruded catalyst was significantly lower compared to that in the catalyst without binder. 27Al and 29Si-MAS NMR spectroscopy demonstrated a remarkable difference in terms of framework Al migration. NH3-TPD experiments corroborated the NMR results suggesting a retention of Brønsted acidity in the extruded catalyst. We tentatively propose that by providing extra-framework Al species prior to the treatment at elevated temperature, the binder hinders the framework Al dislodgment and Fe agglomeration during calcination.

Liquid holdup is a crucial parameter when operating catalytic trickle bed reactors related to wetting efficiency and residence time. Most of the classical methods are expensive, time-consuming, or not valid for high pressures. Liquid holdup by gravimetric recirculation (LHGR) measurement method determines the average total liquid holdup using a closed loop with total recirculation of liquid. The recirculating liquid is contained in a vessel that is weighed instantaneously with a known amount of liquid. The difference between the initial amount of liquid and the instantaneous weight gives the liquid holdup. Main benefits are the following: first, the measurement takes only the time of stabilization that at laboratory scale is 2 S min; second, the system is ready for the next measurement without any modification (the bed is not disturbed nor modified); third, it works for high pressures; finally, it gives values comparable to those from classical techniques like RTD or conductivity methods.

Hydrogen peroxide direct synthesis was studied using different concentrations of NaBr and H3PO4 (promoters) with a commercial Pd/C catalyst. The aim of the study was to understand the role of the acids and bromide on the catalyst and thus the effect on the direct synthesis. The experimental work was done in a continuous trickle bed reactor (TBR) using different concentrations of promoters. The effect of the promoters on the catalyst (Pd leaching and bromide adsorption) was monitored by inductively coupled plasma (ICP) on the solution obtained from the reaction environment. ICP analysis coupled with the monitoring of conversion, selectivity, and productivity helped to understand the effect of the promoters possibility to discriminate better the reaction network mechanism with different reaction conditions. Pd leaching was correlated to catalyst activity and bromide/phosphoric acid ratio. This work provides new and original evidence on the role of promoters, allowing one to understand better how to push the direct synthesis and how to control the catalyst ability to produce H2O2 rather than H2O.

G. Gallina 1, Juan García-Serna 1*, P. Biasi 2, H. Grenman 2, T. Salmi 2 1Valladolid University, High Pressure Processes Grou p, Department of Chemical Engineering and Environmental Technology, Escuela de Ingeniería s Industriales, Valladolid, Spain. 2Johan Gadolin Process Chemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering, Åbo Akademi University, Turku, Finlan d. jgserna@iq.uva.es