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Environmental assessments in green chemistry often rely on simplified metrics that enable comparisons between alternative routes but fail to shed light on whether they are truly sustainable in absolute terms, viz. relative to the Earth's ecological capacity. To expand our currently limited knowledge of the extent to which chemicals are environmentally sustainable, here we analyse 492 chemical products through the lens of seven planetary boundaries representing critical biophysical limits that should never be exceeded. We found that most of them transgress these environmental guardrails, mainly the ones strongly connected to greenhouse gas emissions (i.e., climate change, ocean acidification and biosphere integrity). However, their levels of transgression fail to correlate with their carbon footprints, currently the focus of most studies, implying that chemicals entailing higher greenhouse gas emissions are not necessarily less environmentally sustainable in absolute terms. Our work points towards the need to embrace absolute sustainability criteria in current environmental assessments, which will require agreeing on how to allocate shares of the planet's ecological capacity among anthropogenic activities, including chemicals' production. This work's absolute environmental sustainability assessment (AESA) method, which could complement standard life cycle assessment approaches, might help experimental researchers working in green chemistry develop truly 'green' products. The AESA method should be taken as a starting point to devise holistic approaches for quantifying the absolute environmental impact of chemicals to guide research and policymaking more sensibly. [ABSTRACT FROM AUTHOR]

The use of ethane as a platform molecule for the manufacture of polyvinyl chloride (PVC) is a longstanding challenge, which would allow to reduce the raw material costs and CO2 emissions to produce this plastic. Herein, we discover that rare earth oxychlorides catalyze in a selective (up to 90 %) and stable (>50 h on stream) manner the reaction of ethane and molecular chlorine into 1,2‐dichloroethane, which, upon established cracking, will translate into an order of magnitude higher vinyl chloride productivity compared to ethane oxychlorination technologies. In addition, representative europium oxychloride was supported on suitable carriers and was demonstrated to be selective (up to 90 %) and stable (>40 h on stream) in extrudate form. These findings bring the ethane‐based production of PVC one step closer to implementation. [ABSTRACT FROM AUTHOR]

The use of ethane as a platform molecule for the manufacture of polyvinyl chloride (PVC) is a longstanding challenge, which would allow to reduce the raw material costs and CO2 emissions to produce this plastic. Herein, we discover that rare earth oxychlorides catalyze in a selective (up to 90 %) and stable (>50 h on stream) manner the reaction of ethane and molecular chlorine into 1,2‐dichloroethane, which, upon established cracking, will translate into an order of magnitude higher vinyl chloride productivity compared to ethane oxychlorination technologies. In addition, representative europium oxychloride was supported on suitable carriers and was demonstrated to be selective (up to 90 %) and stable (>40 h on stream) in extrudate form. These findings bring the ethane‐based production of PVC one step closer to implementation. [ABSTRACT FROM AUTHOR]

Natural gas is widely considered as the key feedstock to enable the transition from the oil to the renewables era. Despite its vast reserves, the use of this resource to produce energy and chemicals does not match its full potential. The main reason lies in the nature of its wells, which are often found in remote locations around the globe, rendering access and transportation challenging. To aid this development, several technologies for energy and energy carrier production have been developed, all of which have in common the goal of upgrading natural gas directly at the source of extraction. Following this direction, this review firstly analyses the advances in process design towards decentralised generation of electricity and of liquefied natural gas. Subsequently, recent efforts in progress made in catalysed alkane transformations using heterogeneous catalysts are reviewed for small-scale chemicals and fuels production. The presented analysis identifies that techno-economic and life-cycle assessments should be widely performed to enable proper technological benchmarking of these technologies. The integration of these multidisciplinary fields is key to foster synergies between researchers in the areas of decentralised energy and energy carrier generation in view of developing effective and efficient processes for valorising natural gas directly on-site. [ABSTRACT FROM AUTHOR]

The efficient utilization of biomass, the only globally available, renewable and abundant carbon-neutral source, is of high significance in green and sustainable chemistry. Polyoxometalates (POMs) and POM-based composites have been widely applied in green catalytic reactions, due to their tunable Brønsted/Lewis-acidity and redox properties enabling high reactivity in a wide range of chemical transformations. This review covers recent advances in the chemocatalytic conversion of biomass into chemicals and fuels over POMs and POM–metal composites. For biomass valorisation over POMs, the advances of acid catalysis including hydrolysis, dehydration, etherification, alcoholysis, transesterification and esterification are summarised. Furthermore, applications in chemical oxidation for the synthesis of organic acids and furan chemicals are discussed. For biomass valorisation over metal–POM composites, an overview of tandem reactions (e.g. hydrolysis–hydrogenation, hydrolysis–oxidation, and hydrogenolysis–hydrodeoxygenation) is highlighted. The future prospects of biomass valorisation over POM-based catalysts are finally presented. [ABSTRACT FROM AUTHOR]

Catalytic conversion of CO2 to produce fuels and chemicals is attractive in prospect because it provides an alternative to fossil feedstocks and the benefit of converting and cycling the greenhouse gas CO2 on a large scale. In today's technology, CO2 is converted into hydrocarbon fuels in Fischer–Tropsch synthesis via the water gas shift reaction, but processes for direct conversion of CO2 to fuels and chemicals such as methane, methanol, and C2+ hydrocarbons or syngas are still far from large-scale applications because of processing challenges that may be best addressed by the discovery of improved catalysts—those with enhanced activity, selectivity, and stability. Core–shell structured catalysts are a relatively new class of nanomaterials that allow a controlled integration of the functions of complementary materials with optimised compositions and morphologies. For CO2 conversion, core–shell catalysts can provide distinctive advantages by addressing challenges such as catalyst sintering and activity loss in CO2 reforming processes, insufficient product selectivity in thermocatalytic CO2 hydrogenation, and low efficiency and selectivity in photocatalytic and electrocatalytic CO2 hydrogenation. In the preceding decade, substantial progress has been made in the synthesis, characterization, and evaluation of core–shell catalysts for such potential applications. Nonetheless, challenges remain in the discovery of inexpensive, robust, regenerable catalysts in this class. This review provides an in-depth assessment of these materials for the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2 into synthesis gas and valuable hydrocarbons. [ABSTRACT FROM AUTHOR]

In some applications, where it is not necessary to ensure a constant power supply, it is possible to use photovoltaic systems without batteries. A typical application is the pumping water and subsequent use or for water desalination and storage for later use. Due to the absence of batteries, it is important to carry out an adequate sizing of each part of the system for the correct functioning of the system. This paper presents the modeling of single-phase full bridge inverter for grid isolated photovoltaic systems without the use of batteries for electrical energy storage. The function of the inverter is to take the energy from the photovoltaics modules and deliver it to an ac load, in which the delivered power will be variable due to the fact that storage batteries are not contemplated. The paper focuses on the procedure for obtaining a low frequency averaged model to analyze the effect of the current ripple on the input capacitor for the correct dimensioning of the capacitive filter. Simulation results are shown to validate the presented analysis. [ABSTRACT FROM AUTHOR]

An interview with Javier Pérez-Ramírez, full professor of catalysis engineering at ETH Zurich in Switzerland, is presented. Topics discussed include the main challenges for the future of catalytic materials, his thoughts about catalysis digitalization, and development of science and technology needed to obtain catalytic materials from feedstocks on which people can rely forever with zero environmental impact.

Back Cover: Ethane-Based Catalytic Process for Vinyl Chloride Manufacture (Angew. Catalytic ethane chlorination, ethylene dichloride, natural gas, polyvinyl chloride, rare-earth oxychlorides Keywords: catalytic ethane chlorination; ethylene dichloride; natural gas; polyvinyl chloride; rare-earth oxychlorides EN catalytic ethane chlorination ethylene dichloride natural gas polyvinyl chloride rare-earth oxychlorides 24332 24332 1 10/27/21 20211102 NES 211102 B Gas-to-PVC b In their Research Article on page 24162, Guido Zichittella and Javier Pérez-Ramírez show the outstanding performance of rare earth oxychloride catalysts for the selective conversion of ethane into 1,2-dichloroethane, a precursor of vinyl chloride monomer. [Extracted from the article]

Rücktitelbild: Ethane-Based Catalytic Process for Vinyl Chloride Manufacture (Angew. Catalytic ethane chlorination, ethylene dichloride, natural gas, polyvinyl chloride, rare-earth oxychlorides Keywords: catalytic ethane chlorination; ethylene dichloride; natural gas; polyvinyl chloride; rare-earth oxychlorides EN catalytic ethane chlorination ethylene dichloride natural gas polyvinyl chloride rare-earth oxychlorides 24536 24536 1 10/27/21 20211102 NES 211102 B Gas-to-PVC b Im Forschungsartikel auf S. 24291 berichten Guido Zichittella und Javier Pérez-Ramírez über die herausragende Aktivität von Seltenerd-Oxychlorid-Katalysatoren für die selektive Umwandlung von Ethan in 1,2-Dichlorethan, einen Vorläufer des Vinylchlorid-Monomers. [Extracted from the article]

We report the synthesis of HKUST-1 (Cu3(btc)2; btc=benzene-1,3,5-tricarboxylate) and its growth kinetics by dynamic light scattering completely at room temperature without prior nucleation-induction steps. Upon an increase in concentration of the starting solutions, the generation of a pure phase requires adjustment of the H2O/EtOH ratio. The presence of DMF is important to avoid competitive side phases. Replacement of DMF by a minimal amount of diethylamine resulted in the instantaneous formation of pure HKUST-1 upon mixing at room temperature. Additionally, the synthesis parameters strongly influence the final crystallite size and porous properties. [ABSTRACT FROM AUTHOR]

Abstract: Selectivity control in heterogeneously catalyzed hydrogenation of conjugated hydrocarbons (ene-yne and diene compounds) is a challenging task. Available studies on the topic mainly encircle 1,3-butadiene as the substrate and palladium as the catalyst, while more elaborated playground molecules and other metals remain largely unexplored. This study investigates the gas-phase hydrogenation of valylene (2-methyl-1-butene-3-yne) and isoprene (2-methyl-1,3-butadiene) over Pd, Pb-poisoned Pd, CO-modified Pd, Cu, Ni, and bimetallic Custs. Chemoselectivity, regioselectivity, full hydrogenation, and Crmation/scission footprints of the catalytic systems at different inlet hydrogen-to-hydrocarbon ratios and conversion degrees have been rationalized. Complementary studies of 3-methylbutyne and 1-penten-4-yne hydrogenation were carried out in order to analyze (i) the impact of isomerization on the observed mono-olefin distribution in valylene/isoprene hydrogenation and (ii) the conjugation issue in partial ene-yne hydrogenation. Our results lead to an improved understanding of hydrogenation of polyunsaturated hydrocarbons and open doors to design more selective heterogeneous catalysts and related processes for this practically important class of reactions. [Copyright &y& Elsevier]

The article discusses the first large-scale preparation of hierarchically structured zeolite catalysts aimed at reproducibly introducing extensive intracrystalline mesoporosity into ZSM-5. Controlled silicon extraction in alkaline medium was done on a zeolite at laboratory, middle and pilot scales. It cites the successful demonstration of a large-scale preparation of hierarchical zeolites which clearly established the robustness of the desilication route.

Abstract: We study the application of hierarchical ZSM-5 zeolites, combining micropores and intracrystalline mesopores, as carriers for lipase enzymes compared with purely microporous ZSM-5 and mesoporous MCM-41. Strategies to improve enzyme immobilization by modification of the support porosity and surface properties (e.g. by reaction with organosilane, or by treatment with the enzyme cross-linking agent glutaraldehyde) are also reported. Spectroscopic screening of catalyst activity and recyclability for the aqueous phase hydrolysis of p-nitrophenyl esters, permits evaluation of the influence of support properties and immobilization conditions on the performance of the resulting biocatalysts. An excellent correlation is observed between the mesopore surface area, the enzyme uptake, and the corresponding biocatalyst activity, demonstrating the functional character of mesopores in hierarchical zeolites. Modification of the mesopore walls prior to enzyme immobilization is essential to attain an active and recyclable biocatalyst. Enzymes immobilized on purely inorganic supports exhibit rapid loss of activity attributed to enzyme leaching. Despite the high mesopore surface area of surface-functionalized MCM-41, the mono-dimensionality of the mesopores results in restricted accessibility and a reduced enzyme uptake. In comparison, the interconnected mesopores of the hierarchical zeolites remain accessible after surface functionalization showing good adsorption properties. Lipase immobilized on thiol-functionalized mesoporous ZSM-5 was found to be the most efficient biocatalyst. [Copyright &y& Elsevier]

Abstract: Previous works have opened the debate on the importance of dawsonite in CO2 sequestration by mineral trapping, although there is a lack of systematic studies assessing its long-term stability. With an open eye to this application, we have systematically investigated the stability of synthetic dawsonites (MAlCO3(OH)2, M= , Na+, and K+) in a variety of aqueous media (, Cl−, , , and OH−) at ambient pressure and 323K. The three compositions dissolved under strong acid (pH 2) and basic (pH 14) conditions. In water (pH 7), dawsonites were not stable, evolving into boehmite (NH4-form) and bayerite (Na and K-forms). The most interesting transformations occurred upon contacting the synthesized dawsonites with ammonium, potassium, and sodium carbonate solutions. NH4-dawsonite was converted into Na-dawsonite and K-dawsonite in Na2CO3 and K2CO3 (pH 12), respectively. Na-dawsonite transformed into NH4-dawsonite in (NH4)2CO3 (pH 10). The NH4-dawsonite and Na-dawsonite can be successively inter-converted in the appropriate carbonate solution. These transformations are thought to follow a dissolution-precipitation mechanism. In the pH range of 10–12, K-dawsonite was the most stable among the three synthesized samples. Besides structural changes, the treatment of dawsonites in carbonate solutions caused remarkable morphology and porosity alterations of the product samples. Our study provides an improved understanding of the chemistry of dawsonite-type compounds. In particular, the narrow pH range at which they are stable poses serious constraints in their potential use for geochemical fixation of CO2. [ABSTRACT FROM AUTHOR]

Abstract: A two-step route comprising treatment in sodium aluminate followed by acid washing was developed to introduce secondary mesoporosity in ZSM-5 zeolites with different Si/Al ratios. The parent and treated zeolites were characterized by ICP-OES (solids and filtrates), XRD, TGA, TEM, gas adsorption (N2 at 77K and Ar at 87K), FTIR, and NH3-TPD. The contact of the zeolite with NaAlO2 solutions induced mild leaching of framework silicon, viz. desilication. However, the porosity of the resulting samples was mostly blocked by NaAlO2-derived deposits and Si-containing debris. A subsequent acid washing with HCl or oxalic acid removed the blocking species, largely regaining the native microporosity and further uncovering the extensive intracrystalline mesoporosity generated in the first step. In order to maximize the micro- and mesoporosity in the final zeolites, the conditions of the NaAlO2 and acid treatments were varied with respect to concentration, temperature, and time. The efficiency of the two-step treatment was remarkable for zeolites with Si/Al=25 and 40. The mesopore surface area of the hierarchical ZSM-5 was 3–4 times higher than in the parent zeolites, while other intrinsic properties like crystallinity and acidity were largely preserved. The physico-chemical properties of hierarchical ZSM-5 obtained by the two-step route and by conventional desilication in NaOH were compared. Both desilication variants led to equivalent mesopore surface areas, although the two-step route presented a higher solid yield and produced smaller mesopores due to the much lower amount of silicon leached compared to the treatment in sodium hydroxide. Mechanistic and kinetic aspects of silicon dissolution and porosity development in ZSM-5 were discussed on the basis of alkaline treatments in mixtures of NaOH and NaAlO2. [Copyright &y& Elsevier]

Abstract: The mechanism of ammonia oxidation over Pt, Pd, and Rh wires has been investigated in the Temporal Analysis of Products (TAP) reactor at relevant temperatures in industrial ammonia burners. The results of primary and secondary () interactions with isotopically labeled ammonia at 1073 K enable to conclude that the overall reaction pathways to NO, N2O, and N2 are equivalent on the three noble metals. NO is a primary reaction product, while N2 and N2O originate from consecutive NO transformations. The extent of the secondary reactions determines the net NO selectivity. Rhodium is the most active catalyst for the unwanted reduction of NO by NH3, while platinum shows the lowest activity. This explains the superior NO selectivity attained over Pt and, therefore, its industrial application. The TAP-derived selectivity ranking was substantiated by Density Functional Theory calculations on the (100) facets of the noble metals. We proved experimentally that NO selectivity approaching 100% at complete NH3 conversion can be equivalently attained over Pt, Pd, and Rh by increasing the oxygen content in the feed. For a feed of , both N2O and N2 production are suppressed due to the impeded NO dissociation and favored NO desorption at high oxygen coverage. [Copyright &y& Elsevier]

The selective catalytic reduction of N2O over steam-activated FeZSM-5 zeolite has been investigated at 473-823 K using C1-C3 hydrocarbons (methane, ethane, ethene, ethyne, propane, and propyne). The assessment of the hydrocarbons for nitrous oxide abatement is discussed according to different criteria: (i) de-N2O activity and operation temperature, (ii) hydrocarbon utilization, that is, the selectivity to react with N2O in O2 excess, (iii) emission of CO and CO2. (iv) sensitivity to NO and NH3, and (v) cost Alkanes are generally more effective reducing agents than unsaturated hydrocarbons. In particular, alkynes require higher temperature to activate N2O and are unselective because of their proneness to react with O2. Ethane is an optimal reductant, featuring a high de-N2O activity, high selectivity, and compared to methane, a lower degree of inhibition by NO. [ABSTRACT FROM AUTHOR]

Abstract: Remarkable progress towards implementation of catalytic technology for N2O mitigation in nitric acid plants has been experienced in recent years. EnviNOx®, one of the commercial processes developed by Uhde, accomplishes the tail-gas abatement of N2O and NO x over a single reactor using iron-containing zeolite catalysts. Two variants of the process are available depending on the tail-gas temperature. This manuscript evaluates the low-temperature abatement process (<700K), where NO x and N2O are selectively reduced by NH3 and CH4, respectively. To this end, activity tests in mixtures with N2O, O2, NO, NH3, and CH4 at different temperatures and partial pressures of reactants were carried out over steam-activated FeZSM-5. Ammonia and nitric oxide strongly inhibit the selective catalytic reduction (SCR) of N2O by CH4, shifting the temperature for N2O conversion over 700K. Controlled ammonia dosing is required for the efficient operation of the low-temperature EnviNOx® variant over the particular iron zeolite used in this study. The optimal inlet NH3 concentration is determined by the NO concentration in the tail-gas and its temperature. In the absence of NO and NH3, the CH4-SCR of N2O over FeZSM-5 is effective above 623K. Still, this process cannot retrofit a number of existing plants with lower tail-gas temperatures. [Copyright &y& Elsevier]

Abstract: A temporal analysis of products (TAP) reactor was used to study the mechanism of ammonia oxidation at high temperature (1073 K) over Fe2O3, Cr2O3, and CeO2. The results were compared with those obtained over the industrially applied Pt95–Rh5 alloy. Analysis of characteristic times of the transient responses of N2 and NO made it possible to gain insight into the sequence of their formation. A common feature of both metal oxide and noble metal catalysts is that NO is a primary product of NH3 oxidation, whereas N2 results mainly from secondary transformations of NO. The amount of N2O formed over the oxides was minimal. Multipulse NH3 experiments in the absence of gas-phase O2 give unequivocal evidence of the participation of surface lattice oxygen of the metal oxides in the reaction of NH3 to NO. The degree of reduction of the oxide surface determines the product distribution but does not alter the catalytic activity for NH3 conversion. Greater reduction favors the reaction channel to N2 over that to NO. The desired reaction follows a Mars–van Krevelen-type scheme involving the participation of lattice oxygen in the NH3 conversion to NO and regeneration of the so-formed vacancies by gas-phase O2 and bulk lattice oxygen. Replenishment of surface vacancies by the diffusion of bulk oxygen occurs to a significant extent over Fe2O3. However, when NH3 and O2 are fed together, dissociative adsorption of gas-phase oxygen can be considered the main mechanism for vacancy regeneration. [Copyright &y& Elsevier]

Abstract: This manuscript concisely reviews the significance of the temporal analysis of products (TAP) technique in catalysis research from its introduction to the scientific community in the late 1980s. Evolutionary aspects of this time-resolved transient pulse method are presented, highlighting its relevance for elucidation of mechanistic and kinetic aspects of adsorption, diffusion, and reaction in gas–solid systems. The high-temperature ammonia oxidation over noble metal catalysts is used to underline key advantages of the TAP reactor in mechanistic studies, narrowing the often-encountered pressure and materials gaps between techniques operating at ambient pressure and in ultra-high vacuum. Perspectives to further enhance the capabilities of this technique are briefly put forward. [Copyright &y& Elsevier]

Mechanistic and kinetic aspects of the direct decomposition of N2O over steam-activated Fe-silicalite were investigated by transient experiments in vacuum (N2O peak pressure of ca. 10 Pa) using the temporal analysis of products (TAP) reactor in the temperature range of 773–848K. The transient responses of N2O, N2, and O2 obtained upon N2O decomposition were fitted to different micro-kinetic models. Through model discrimination it was concluded that both free iron sites and iron sites with adsorbed mono-atomic oxygen (*O) species are active for N2O decomposition. Oxygen formation occurs via decomposition of bi-atomic (*O2) oxygen species adsorbed over the iron site. This bi-atomic oxygen species originates from another bi-atomic oxygen species (O*O), which is initially formed via interaction of N2O with iron site possessing mono-atomic oxygen species (*O). Based on our modeling, the recombination of two mono-atomic oxygen (*O) species or direct O2 formation via reaction of N2O with *O can be excluded as potential reaction pathways yielding gas-phase O2. The simulation results predict that the overall rate of N2O decomposition is controlled by regeneration of free iron sites via a multi-step oxygen formation at least below 700K. [Copyright &y& Elsevier]

Abstract: European authorities consider that N2O emissions from nitric acid plants can be reduced to a large extent at a relatively low cost. Two regulation approaches can have major implications for the fertilizer industry in Europe. The EU integrated pollution prevention and control (IPPC) directive will be effective from October 2007 for existing plants. In this, emission permits will be based on best available techniques (BAT). Additionally, the EU commission will shortly consider whether the emission trading directive should be applicable to cover other greenhouse gases besides CO2. This paper discusses advantages and drawbacks of these approaches, with emphasis on how emission trading with N2O can be turned into a win–win situation both for European governments and for the fertilizer industry. [Copyright &y& Elsevier]

Abstract: Transient isotopic studies in the temporal analysis of products (TAP) reactor evidenced the importance of the lifetime of oxygen species generated upon N2O decomposition on extraframework iron sites of Fe-silicalite for methane oxidation at 723K. Fe-silicalite effectively activates CH4 when N2O and CH4 are pulsed together in the reactor. However, these oxygen species gradually become inactive for methane oxidation as the time delay between the N2O and CH4 pulses is increased from 0 to 2s. [Copyright &y& Elsevier]

Abstract: The influence of steam activation of Mg–Al hydrotalcite on the properties of the resulting mixed oxides has been investigated and compared with the typically performed thermal decomposition under dry conditions. The as-synthesized hydrotalcite was treated at 723K and 1bar in nitrogen flow containing steam partial pressures in the range of 0–800mbar. Thermal analysis indicated that the hydrotalcite decomposition was not affected by the presence of steam in the feed gas. The average crystallite size and morphology of the dry and steam-activated materials, as determined by XRD and TEM, respectively, were very similar too. The porous properties of the resulting oxides present significant differences. The BET surface area decreased ca. 20% when small amounts of steam were present as compared to the dry-decomposed product, but was not further reduced upon increasing the steam partial pressure. This has been attributed to the disappearance of small mesopores (<4nm) due to the hydrolysis of Al–O–Al bonds from adjacent layers and platelets. [Copyright &y& Elsevier]

Abstract: Various commercially available zeolite frameworks (MFI, FER, BEA, MOR, FAU) with iron impurities ranging from 85 to 780ppm and nominal Si/Al ratios of 10–15 have been tested in direct N2O decomposition after calcination and steam treatment. Our results show a significant impact of the framework type on the catalytic activity at these high degrees of iron dilution (Fe/Al<0.01). H-beta was the most effective material in the reaction, followed by the other pentasyl-type H-ferrierite and H-ZSM-5 zeolites. [Copyright &y& Elsevier]

Abstract: For the first time, we report on the application of a tapered element oscillating microbalance (TEOM) as a novel technique to investigate the thermal decomposition of hydrotalcite-like compounds (HTlcs) in air. Experiments were performed in the temperature range of 323–973K with Mg–Al, Ni–Al, and Co–Al-HTlcs. The TEOM technique measures mass changes based on inertial forces, presenting important advantages over conventional thermogravimetric analyzers, such as the very rapid time response and the well-defined flow pattern. In general terms, excellent agreement between TEOM, TGA, and DTA techniques during HTlc decomposition was obtained. Interestingly, transition temperatures in the TEOM were lower than in TGA and DTA, particularly for removal of interlayer water but also for dehydroxylation of the brucite-like layers and decarbonation. This was attributed to the flow-through operation in the tapered element of the TEOM as compared to the recognized gas stagnancy and bypass in sample crucibles of conventional thermogravimetric analyzers. Our results conclude that the TEOM technique is suitable for temperature-programmed studies. However, due to its operation principle, blank runs are required in contrast to the more automatic operation in commercial thermogravimetric units. Besides, a careful sample loading and packing in the micro-reactor is essential for reproducible results. [Copyright &y& Elsevier]

Abstract: The high-temperature catalytic partial oxidation (CPO) of methane over a platinum gauze reactor was modeled by three-dimensional numerical simulations of the flow field coupled with heat transport as well as detailed gas-phase and surface reaction mechanisms. Model results agree well with data of CPO experiments over Pt-gauzes in the literature, confirming the presence of strong mass and heat-transport limitations. The conversions of CH4 and O2 increase with an increased contact time and were practically constant in the temperature range of 1000–1200K. The selectivity to CO linearly increases with temperature. H2 was only observed above 1200K, below this temperature H2O was the only hydrogen-containing product. The contribution of heterogeneous steps in the overall process is prominent, but in the later stages of the reactor, gas-phase reactions become significant at certain conditions of temperature, pressure, and residence time. For example, simulations predicted some gas-phase production of ethane and ethylene via methane oxidative coupling at elevated pressure and residence time. The study shows that today''s CFD tools allow the implementation of detailed homogeneous and heterogeneous reaction schemes even for complex catalyst geometries. [Copyright &y& Elsevier]

Abstract: Transient isotopic studies in the Temporal Analysis of Products (TAP) reactor evidenced a clear mechanistic regularity between methane and propane for N2O reduction over Fe-silicalite in the temperature range of 623–773K. The lifetime of the oxygen species generated by N2O decomposition on extraframework iron sites was found to be crucial for alkane oxidation. When N2O and CH4 or C3H8 were pulsed together over Fe-silicalite, oxygen species deposited on iron sites effectively activated the hydrocarbon. However, these oxygen species become inactive for alkane oxidation if the pulses of N2O and the alkane were separated by more than 0.1s. Transient studies have indicated that C3H8 is more efficient for N2O reduction than CH4, as expected from the facilitated activation of the Con increasing the carbon number in alkanes. The performance derived from the TAP reactor agrees well with experiments under flow conditions at ambient pressure. [Copyright &y& Elsevier]

A novel process for the direct ammoxidation of propane over steam-activated Fe-silicalite at 723–823 K is reported. Yields of acrylonitrile (ACN) and acetonitrile (AcCN) below 5% were obtained using N2O or O2 as the oxidant. Co-feeding N2O and O2 boosts the performance of Fe-silicalite compared to the individual oxidants, leading to AcCN yields of 14% and ACN yields of 11% (propane conversions of 40% and products selectivity of 25–30%). The beneficial effect of O2 on the propane ammoxidation with N2O contrasts with other N2O-mediated selective oxidations over iron-containing zeolites (e.g. hydroxylation of benzene and oxidative dehydrogenation of propane), where a small amount of O2 in the feed dramatically reduces the selectivity to the desired product. It is shown that the productivity of ACN and especially AcCN, expressed as mol product h−1 kg, is significantly higher over Fe-silicalite than over active propane ammoxidation catalysts reported in the literature. Our results open new perspectives to improve the performance of alkane ammoxidation catalysts. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the application of mixed conducting perovskite membranes for simultaneous in situ O2 separation and catalytic oxidation of ammonia to nitric oxide. Calcium and strontium-substituted lanthanum ferrite perovskites (La1−x A x FeO3−δ , with A=Ca, Sr and x =0.1–0.2) were prepared by a conventional wet complexation route with citric acid. Dense membrane disks were obtained by uniaxial pressing of the calcined powders followed by sintering. The oxidation of ammonia over these catalytic membranes in the temperature range of 1000–1333K leads to NO selectivities up to 98% with no N2O production, showing stable performance during several days on stream. This novel process demonstrates the great potential for intensification of nitric acid manufacture into miniaturized plants and is considered to be particularly attractive for on-site production of this important bulk chemical. [Copyright &y& Elsevier]

Abstract: The effect of oxygen on the activity and selectivity of the NO reduction by NH3 over Pt–Rh (95–5wt.%) alloy gauze at 1023–1073K has been investigated. To this end, the Temporal Analysis of Products (TAP) reactor in combination with isotopic tracers was applied. Single pulse experiments evidenced the rapid activation of NH3 over the catalyst surface covered by adsorbed oxygen. Contrarily, NO requires an essentially reduced surface in order to be dissociated. Adsorbed oxygen species in the O2-pretreated gauze accelerate the reaction of NH3 with NO with respect to the as-received gauze. N2 was the main reaction product and traces of N2O were comparatively formed (N2O/N2 ∼ 10−3). Pulsing of an equimolar O2–15NH3–NO mixture over the Pt–Rh gauze mainly produces 15NO, while the formation of N2 is largely suppressed. The selectivity to 15NO and N2O in the ternary O2–15NH3–NO system diminished upon decreasing the O2/(15NH3 +NO) ratio, in favor of N2. This ratio was qualitatively varied by changing the time delay between O2 and 15NH3–NO in sequential pulse experiments. Our results indicate that the NH3 oxidation by O2 to NO is much faster than the NO reduction by NH3 at similar concentrations of oxygen and nitric oxide. This explains the low production of N2 and N2O in ammonia burners within nitric acid manufacture. [Copyright &y& Elsevier]

Abstract: The mechanism of the reaction of N2O and 13CO over Fe-silicalite was investigated with the use of the temporal analysis of products (TAP) reactor and compared with that of the reaction of N2O and C3H8 previously reported (Appl. Catal. A 267 (2004) 181). Upon direct N2O decomposition at 523–573 K, Fe-silicalite stored ca. 1018 atoms of oxygen per gram, with a ratio of 1 O atom per each 30–60 Fe atoms in the sample. Only a small fraction of the deposited oxygen was reactive for CO oxidation. Pump-probe experiments at different time delays (0–2 s) between the pulses of nitrous oxide and the reducing agent indicated the markedly different mechanisms of the N2O–13CO and N2O–C3H8 reactions in the temperature range of 623–673 K. Fe-silicalite is active for propane oxidation in the presence of short-lived oxygen species, that are produced when N2O and C3H8 are pulsed simultaneously. Time delays between the N2O and C3H8 pulses greater than 0.1 s are sufficient to transform these active oxygen species for hydrocarbon conversion into inactive ones. In contrast, the oxidation of CO by N2O does not depend on the lifetime of the oxygen species in the range of time delays investigated. The mechanisms of the N2O-mediated 13CO and C3H8 oxidations differ as a consequence of the different interactions of the two reducing agents with iron species in the zeolite. Pulse experiments support the occurrence of the scavenging mechanism with both propane and carbon monoxide. In this mechanism, short-lived oxygen deposited by N2O is efficiently eliminated by the reductant. Distinctive to propane, the strikingly high affinity of carbon monoxide for isolated Fe3+ ions in the zeolite gives rise to an additional pathway for N2O reduction in the presence of chemisorbed CO species. These particular Fe3+–CO species were identified by in situ UV/vis and EPR spectroscopies (J. Catal. 223 (2004) 13). [Copyright &y& Elsevier]

Abstract: The performance of differently prepared Fe-ZSM-5 zeolites in the N2O-mediated propane oxidative dehydrogenation to propylene has been investigated at 723K using a tapered element oscillating microbalance (TEOM) coupled to on-line GC analysis. Catalysts were prepared by hydrothermal synthesis followed by calcination and steam treatment, liquid-ion exchange, and chemical vapor deposition, and contain molar Fe/Al ratios in the range of 0.26–1. Propylene yields in the range of 22–25% were attained over steam-activated Fe-ZSM-5, much higher over the iron zeolites prepared by post-synthesis methods (9–16%), with propylene selectivities around 40%. The deactivation behaviour due to coking differs among the catalysts investigated. Calcined H-ZSM-5 with impurities of iron (Fe/Al=0.007) leads to an initial yield of propylene of 8%, and is increased to 16% upon steam treatment, obtaining a selectivity to propylene of 90%. The turnover frequency for propylene production is up to three orders of magnitude higher in steamed H-ZSM-5 than in the synthesized iron zeolites. Our results suggest that traces of well-isolated (mononuclear) Fe species released from framework positions by steaming are extremely active in the oxidative dehydrogenation of propane to propylene, while large iron clusters enhance deep oxidation of important reaction intermediates to COx. [Copyright &y& Elsevier]

The relation between the intrinsic mechanism of various N2O conversions over FeMFI catalysts and the nature of the active iron site(s) has been analyzed. To this end, direct N2O decomposition and N2O reduction with CO in the absence or presence of NO were investigated using a combination of transient pulse and steady-state techniques over steam-activated FeMFI zeolites with a similar iron content (0.6–0.7 wt% Fe) and different framework compositions (Si–Al, Si–Ga, Si–Ge, and Si). The forms of iron in the catalysts were characterized by UV/vis and HRTEM. The intrinsic reaction mechanism determines the optimal iron site distribution, which can be modulated by tuning the steaming temperature during activation. Oligonuclear iron oxo clusters in the zeolite channels are essential in direct N2O decomposition due to a faster desorption of O2 as compared to isolated ions. Such forms of active iron can be achieved at a lower steam-activation temperature over FeAlMFI and FeGaMFI (900 K) than over FeGeMFI and FeMFI (1150 K). Contrarily, zeolites with a more uniform distribution of isolated iron species lead to higher activities in N2O reduction with CO as compared to highly clustered catalysts. In this case, O-removal as CO2 is strongly accelerated vis-à-vis O2 desorption in direct N2O decomposition. The dual role of NO as a promotor in N2O decomposition and as an inhibitor in N2O reduction also supports the participation of different sites in both types of conversions. NO selectively inhibits N2O reduction over isolated iron ions, further evidencing the essential role of oligonuclear iron clusters in the NO-assisted N2O decomposition. [Copyright &y& Elsevier]

An increasing number of contributions aiming at the development of advanced or modified porous materials for improved performance in various applications incorporate unreliable analyses of N2 adsorption data. As a result, well-defined peaks at 2 and 4 nm in the pore size distribution are attributed to physical mesopores, while being strictly associated with the nature of the adsorbed phase. These erroneous claims often comprise the main conclusion of related publications and should be firmly prevented. A better fundamental insight on the adsorption methods and related physical phenomena is required. [Copyright &y& Elsevier]

The effect of the iron distribution in steam-activated FeZSM-5 and Fe-silicalite on their catalytic performance for direct N2O decomposition and for the oxidative dehydrogenation of propane (ODHP) with N2O and O2 was investigated by means of steady-state and transient pulse experiments. Steam-activated FeZSM-5, containing a large fraction of iron as oligonuclear FexOy clusters, is more active and selective in ODHP and direct N2O decomposition than steam-activated Fe-silicalite, where isolated iron species predominate. This suggests that the same type of iron centers is involved in both conversions. The higher activity of steam-activated FeZSM-5 is associated to the higher mobility of atomic oxygen species attached to oligonuclear iron species, which lead to a faster oxygen desorption in direct N2O decomposition as well as to a faster transfer to propane in the ODHP reaction. Steam-activated FeMFI zeolites were found to be highly effective catalysts for ODHP with N2O, with initial propene yields up to 24%. Relatively high yields of propionaldehyde are also obtained, which mainly originates from the selective oxidation of propene. The unique ODHP performance of iron zeolites requires the use of N2O as monooxygen donor. Such species cannot be created by O2. Only a fraction of oxygen species deposited over iron sites of FeMFI upon N2O activation was found to be active towards propane oxidation under transient vacuum conditions. This is explained by a fast transformation of short-living highly reactive atomic oxygen species into less reactive ones. [Copyright &y& Elsevier]

Steam-activated Fe-zeolites (MFI and BEA) are efficient catalysts for the N2O-mediated oxidative dehydrogenation of propane, with initial propylene yields up to 25% at 723 K, but deactivate as a result of coke formation. A tapered element oscillating microbalance (TEOM) coupled to GC analysis has been applied to correlate activity and deactivation by simultaneous measurements of reaction and coking. The presence of extraframework iron species, generated during steam treatment, is essential for producing active catalysts. The nature and distribution of extraframework iron species, the zeolite host, and the catalyst acidity have no significant effect on the initial propene yield, but strongly influence the deactivation behavior. FeZSM-5 shows a remarkable resistance against deactivation, while a very rapid and complete deactivation occurred in FeBEA. The initial propene yield over FeZSM-5 and FeBEA was remarkably higher than over commercial H-ZSM-5 and H-BEA (with 30–40 times lower iron content), although the residual activities after 400 min on stream were very similar. [Copyright &y& Elsevier]

The reduction of N2O by CO was investigated over FeMFI zeolites prepared by different methods including sublimation, liquid ion exchange, and hydrothermal synthesis followed by steam activation. This leads to catalysts with different nature and distribution of iron species, as characterized by HRTEM, UV/vis, and EPR techniques. A common denominator in the FeZSM-5 samples is the heterogeneous iron constitution, with a significant degree of clustering in the form of iron oxide particles. Iron clustering was suppressed in steam-activated Fe-silicalite, presenting a remarkable uniform distribution of isolated iron species. In the presence of CO, the conversion of N2O over the catalysts is strongly accelerated with respect to direct N2O decomposition. The reaction rate increases linearly with the molar CO/N2O feed ratio and strongly depends on the preparation method applied. A correlation was found between the fraction of isolated Fe(III) species in the as-prepared catalysts and the activity for N2O reduction with CO. Steam-activated Fe-silicalite, containing mostly isolated iron ions in extraframework positions, shows the highest activity per mole of iron, while the highly clustered liquid-ion-exchanged catalyst presents the lowest activity. In situ UV/vis and EPR studies evidence the participation of mononuclear iron ions in the N2O–CO reaction, and also support the involvement of oligonuclear FexOy species. The reaction mechanism is iron site dependent. Over isolated sites, the reduction of N2O with CO occurs via coordinated CO species on Fe3+ ions. The reaction over oligonuclear sites proceeds via a redox Fe3+/Fe2+ process with intermediate formation of O− radicals. [Copyright &y& Elsevier]

Selective catalytic reduction (SCR) of N2O with C3H8 over Fe-zeolites (MFI, BEA, USY) under excess oxygen is strongly inhibited by NO. The assistance of the hydrocarbon in N2O reduction vanishes at high partial NO pressures, approaching the activity of the N2O+NO system at molar NO/C3H8 ratios of 1.5–2, with N2O/C3H8=1. This effect is opposite to the NO promotion in direct N2O decomposition over these catalysts at temperatures >625 K. At lower temperatures and in the absence of NO, propane is oxydehydrogenated to propene by N2O over the catalysts. Extraframework iron sites are essential for N2O and C3H8 conversions, in particular iron in isolated positions is most effective. Propane activates on N2O-oxidized iron sites, while acidic sites play a minor role in the overall process. In the absence of NO, N2O and C3H8 conversions are coupled in temperature. Addition of NO uncouples the N2O and C3H8 conversion profiles and shifts them to higher temperature. NO inhibits N2O decomposition over iron sites by competitive adsorption at temperatures where N2O reduction with C3H8 typically starts (>525 K). At these temperatures, adsorbed NO blocks the isolated Fe-sites for N2O activation. The relatively low activity for NOx reduction to N2 (<20%) and the lower optimal operation temperature for this process (550 K) compared to N2O reduction (725 K) makes the simultaneous removal of NO and N2O with hydrocarbons unfeasible over Fe-zeolites. [Copyright &y& Elsevier]

For elucidating the mechanistic aspects of oxygen formation during N2O decomposition over commercial woven Pt–Rh gauze, transient experiments were carried out in the temporal analysis of products (TAP) reactor by pulsing N216O over 18O-pretreated gauze catalyst at temperatures typical of industrial ammonia burners (1073–1273 K). The transient responses of N2O and the products of its decomposition (O2 and N2) were fitted to two different mechanistic models. From the isotopic studies and the fitting of transient experiments, two separate routes of oxygen formation during catalytic N2O decomposition have been identified. Oxygen is produced via both (i) interaction of N2O with adsorbed oxygen species formed from N2O and (ii) recombination of adsorbed oxygen species on the catalyst surface. The relative contribution of these reaction pathways depends on the reaction temperature. [ABSTRACT FROM AUTHOR]

Preparation of steam-activated Fe-silicalite containing mainly isolated iron species in extraframework positions was essential for deriving structure-activity relationships in various N2O conversion reactions over iron zeolite catalysts. Characterization by UV–Vis/DRS revealed that any significant clustering of iron did not occur in this sample. Other steam-activated FeMFI zeolites, with different framework compositions or treated at higher temperatures, showed various degrees of clustering. The activity of the cluster-free Fe-silicalite was significantly higher in N2O reduction with C3H8 and CO. However, some level of association of iron species leads to higher activities in direct N2O decomposition. Due to the intrinsic reaction mechanism, this result demonstrates the sensitivity of reactions for the form of the iron species in Fe-zeolites, rather than the existence of a unique active site. [Copyright &y& Elsevier]

Selective catalytic reduction (SCR) of N2O with C3H8 over FeZSM-5 under excess oxygen is strongly inhibited by NO. The assistance of the hydrocarbon in N2O reduction vanishes at high partial NO pressures, approaching the activity of the N2O + NO system at molar NO/N2O ratios of 1.5–2, with N2O/C3H8=1. This effect differs from the NO promotion in direct N2O decomposition over Fe-zeolite catalysts. The negative effect of NO on the N2O reduction has a significant impact in the design and operation of catalytic reactors in tail-gases of nitric acid plants and other sources where NO comes along with N2O. [Copyright &y& Elsevier]

Chemistry, a vital tool for sustainable development, faces a challenge due to the lack of clear guidance on actionable steps, hindering the optimal adoption of sustainability practices across its diverse facets from discovery to implementation. This Scientific Perspective explores established frameworks and principles, proposing a conciliated set of triple E priorities anchored on Environmental, Economic, and Equity pillars for research and decision making. We outline associated metrics, crucial for quantifying impacts, classifying them according to their focus areas and scales tackled. Emphasizing catalysis as a key driver of sustainable synthesis of chemicals and materials, we exemplify how triple E priorities can practically guide the development and implementation of processes from renewables conversions to complex customized products. We summarize by proposing a roadmap for the community aimed at raising awareness, fostering academia–industry collaboration, and stimulating further advances in sustainable chemical technologies across their broad scope. [ABSTRACT FROM AUTHOR]

Chemistry, a vital tool for sustainable development, faces a challenge due to the lack of clear guidance on actionable steps, hindering the optimal adoption of sustainability practices across its diverse facets from discovery to implementation. This Scientific Perspective explores established frameworks and principles, proposing a conciliated set of triple E priorities anchored on Environmental, Economic, and Equity pillars for research and decision making. We outline associated metrics, crucial for quantifying impacts, classifying them according to their focus areas and scales tackled. Emphasizing catalysis as a key driver of sustainable synthesis of chemicals and materials, we exemplify how triple E priorities can practically guide the development and implementation of processes from renewables conversions to complex customized products. We summarize by proposing a roadmap for the community aimed at raising awareness, fostering academia–industry collaboration, and stimulating further advances in sustainable chemical technologies across their broad scope. [ABSTRACT FROM AUTHOR]

New and enhanced processes will not be the only drivers toward a sustainable chemical industry. Implementing climate policies will impact all components of the chemical supply chain over the following decades, making improvements in energy generation, material extraction, or transportation contribute to reducing the overall impacts of chemical technologies. Including this synergistic effect when comparing technologies offers a clearer vision of their future potential and may allow researchers to support their sustainability propositions more strongly. Ammonia and methanol production account for more than fifty percent of the CO2 emissions in this industry and are, therefore, excellent case studies. This work performs a prospective life cycle assessment until 2050 for fossil, blue, wind, and solar-based technologies under climate policies aiming to limit the global temperature rise to 1.5 °C, 2 °C, or 3.5 °C. The first finding is the inability of fossil-based routes to reduce their CO2 emissions beyond 10% by 2050 without tailored decarbonisation strategies, regardless of the chemical and climate policy considered. In contrast, green routes may produce chemicals with around 90% fewer emissions than today and even with net negative emissions (on a cradle-to-gate basis), as in the case of methanol (up to −1.4 kg CO2-eq per kg), mainly due to the contributions of technology development and increasing penetration of renewable energies. Overall, the combined production of these chemicals could be net-zero by 2050 despite their predicted two to fivefold increase in demand. Lastly, we propose a roadmap for progressive implementation by 2050 of green routes in 26 regions worldwide, applying the criterion of at least 80% reduction in climate change impacts when compared to their fossil alternatives. Furthermore, an exploratory prospective techno-economic assessment showed that by 2050, green routes could become more economically attractive. This work offers quantitative arguments to reinforce research, development, and policymaking efforts on green chemical routes reliant on renewable energies. [ABSTRACT FROM AUTHOR]

Single‐atom heterogeneous catalysts (SACs) hold promise as sustainable alternatives to metal complexes in organic transformations. However, their working structure and dynamics remain poorly understood, hindering advances in their design. Exploiting the unique features of droplet‐based microfluidics, we present the first in‐situ assessment of a palladium SAC based on exfoliated carbon nitride in Suzuki–Miyaura cross‐coupling using X‐ray absorption spectroscopy. Our results confirm a surface‐catalyzed mechanism, revealing the distinct electronic structure of active Pd centers compared to homogeneous systems, and providing insights into the stabilizing role of ligands and bases. This study establishes a valuable framework for advancing mechanistic understanding of organic syntheses catalyzed by SACs. [ABSTRACT FROM AUTHOR]

Single‐atom heterogeneous catalysts (SACs) hold promise as sustainable alternatives to metal complexes in organic transformations. However, their working structure and dynamics remain poorly understood, hindering advances in their design. Exploiting the unique features of droplet‐based microfluidics, we present the first in‐situ assessment of a palladium SAC based on exfoliated carbon nitride in Suzuki–Miyaura cross‐coupling using X‐ray absorption spectroscopy. Our results confirm a surface‐catalyzed mechanism, revealing the distinct electronic structure of active Pd centers compared to homogeneous systems, and providing insights into the stabilizing role of ligands and bases. This study establishes a valuable framework for advancing mechanistic understanding of organic syntheses catalyzed by SACs. [ABSTRACT FROM AUTHOR]

C1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure‐dependent product distributions driven by CO‐induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co‐feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure. [ABSTRACT FROM AUTHOR]

C1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure‐dependent product distributions driven by CO‐induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co‐feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure. [ABSTRACT FROM AUTHOR]