Dehydrogenation Reaction Research Articles

Impact of Catalysis-Relevant Oxidation and Annealing Treatments on Nanostructured GaRh Alloys.

In this study, we examine the surface-derived electronic and chemical structures of nanostructured GaRh alloys as a model system for supported catalytically active liquid metal solutions (SCALMS), a novel catalyst candidate for dehydrogenation reactions that are important for the petrochemical and hydrogen energy industry. It is reported that under ambient conditions, SCALMS tends to form a gallium oxide shell, which can be removed by an activation treatment at elevated temperatures and hydrogen flow to enhance the catalytic reactivity. We prepared a 7 at. % Rh containing the GaRh sample and interrogated the evolution of the surface chemical and electronic structure by photoelectron spectroscopy (complemented by scanning electron microscopy) upon performing surface oxidation and (activation treatment mimicking) annealing treatments in ultrahigh vacuum conditions. The initially pronounced Rh 4d and Fermi level-derived states in the valence band spectra disappear upon oxidation (due to formation of a GaOx shell) but reemerge upon annealing, especially for temperatures of 600 °C and above, i.e., when the GaOx shell is efficiently being removed and the Ga matrix is expected to be liquid. At the same temperature, new spectroscopic features at both the high and low binding energy sides of the Rh 3d5/2 spectra are observed, which we attribute to new GaRh species with depleted and enriched Rh contents, respectively. A liquefied and GaOx-free surface is also expected for GaRh SCALMS at reaction conditions, and thus the revealed high-temperature properties of the GaRh alloy provide insights about respective catalysts at work.

Well-Defined Supported ZnOx Species: Synthesis, Structure, and Catalytic Performance in Nonoxidative Dehydrogenation of C3-C4 Alkanes.

ConspectusZinc oxide (ZnO) is a multipurpose material and finds its applications in various fields such as rubber manufacturing, medicine, food additives, electronics, etc. It has also been intensively studied in photocatalysis due to its wide band gap and environmental compatibility. Recently, heterogeneous catalysts with supported ZnOx species have attracted more and more attention for the dehydrogenation of propane (PDH) and isobutane (iBDH) present in shale/natural gas. The olefins formed in these reactions are key building blocks of the chemical industry. These reactions are also of academic importance for understanding the fundamentals of the selective activation of C-H bonds. Differently structured ZnOx species supported on zeolites, SiO2, and Al2O3 have been reported to be active for nonoxidative dehydrogenation reactions. However, the structure-activity-selectivity relationships for these catalysts remain elusive. The main difficulty stems from the preparation of catalysts containing only one kind of well-defined ZnOx species.In this Account, we describe the studies on PDH and iBDH over differently structured ZnOx species and highlight our approaches to develop catalysts with controllable ZnOx speciation relevant to their performance. Several methods, including (i) the in situ reaction of gas-phase metallic Zn atoms with OH groups on the surface of supports, (ii) one-pot hydrothermal synthesis, and (iii) impregnation/anchoring methods, have been developed/used for the tailored preparation of supported ZnOx species. The first method allows precise control of the molecular structure of ZnOx through the nature of the defective OH groups on the supports. Using this method, a series of ZnOx species ranging from isolated, binuclear to nanosized ZnOx have been successfully generated on different SiO2-based or ZrO2-based supports as demonstrated by complementary ex/in situ characterization techniques. Based on kinetic studies and detailed characterization results, the intrinsic activity (Zn-related turnover frequency) of ZnOx was found to depend on its speciation. It increases with an increasing number of Zn atoms in a ZnmOn cluster from 1 to a few atoms (less than 10) and then decreases strongly for ZnOx nanoparticles. The latter promote the formation of undesired C1-C2 hydrocarbons and coke, resulting in lower propene selectivity in comparison with the catalysts containing only ZnOx species ranging from isolated to subnanometer ZnmOn clusters. In addition, the strategy for improving the thermal stability of ZnOx species and the consequences of mass-transport limitations for DH reactions were also elucidated. The results obtained allowed us to establish the fundamentals for the targeted preparation of well-structured ZnOx species and the relationships between their structures and the DH performance. This knowledge may inspire further studies in the field of C-H bond activation and other reactions, in which ZnOx species act as catalytically active sites or promoters, such as the dehydroaromatization of light alkanes and the hydrogenation of CO2 to methanol.

Insight into dehydrogenation mechanism of methanol to aromatics over GaO+/HZSM-5: Which is the active center, Lewis acid site or Brønsted−Lewis synergistic site?

The mechanisms of dehydrogenation reactions as important processes in methanol to aromatics (MTA) have been controversial. Recent work on the active center for dehydrogenation at either Lewis acid site (LAS) or Brønsted−Lewis (B−L) acid synergistic site is a matter. The dehydrogenation processes on L−acid site (GaO+) or B−L acid site (H+−GaO+) over GaO+/HZSM-5 with different Lewis acid locations for n-hexene to 1,5-hexadiene, as well as cyclohexene to benzene have been researched by applying the density functional theory (DFT) method. The results reflect that active center of dehydrogenation reactions is B−L acid synergistic site through B−L acid synergy mechanism. All elementary steps including C−H bond activation, the formation of H2, hydrogen transfer as well as the regeneration of B−acid site are easy to proceed. However, the isomerization for carbonium ions from GaO+ to skeleton oxygen of zeolites is relatively difficult. The analysis shows that isomerization is influenced by the structural and electronic properties of carbonium ions chemisorbed on zeolites. Lewis acid strength of GaO+/HZSM-5 and energy gap between HOMO and LUMO on adsorption complexes are appropriate descriptors for the C−H bond activation. The rate constants analysis indicates that increasing temperature is more favorable for C−H bond activation. Further considering that C−H bond activation occurred preferentially than isomerization, it could be a critical initial step to primarily screen catalysts.

Full-period operation optimization of the semi-regenerative reactor based on dehydrogenation reaction and deactivation kinetics

Semi-regenerative reactors are adopted in many catalytic processes. Based on industrial data, a one-dimensional pseudo-homogeneous reactor model was established for the semi-regenerative reactor of the dehydrogenation of heavy paraffins. The validation results show high accuracy of the model prediction. The Sequential Quadratic Programming (SQP) algorithm was employed for the full-period operation optimization of the reactor, resulting in a 3.04% increase in the yield of mono-olefins, but the optimized operation conditions are not consistent with common combination according to the practical production experience described in the literature. Further investigations for semi-regenerative reactors with different dehydrogenation systems show that the optimized combination of operation conditions in a full period is dependent on the depth of dehydrogenation, the rate of catalyst deactivation, and the duration of the period.

Electrochemical Activation of Surface Oxygen for Efficient Oxidative Dehydrogenation Reaction at Elevated Temperatures

Electrochemical Activation of Surface Oxygen for Efficient Oxidative Dehydrogenation Reaction at Elevated Temperatures

Thermally induced in situ fabrication of TiO2/CN heterojunction dopant for enhancement of hydrogen storage properties of LiAlH4

Herein, a novel TiO2/CN heterojunction material has been prepared by one-step bubble template-assisted calcination to enhance the hydrogen storage capability of LiAlH4. The TEM, XPS and UPS analysis confirm that a heterostructure is formed between TiO2 and g-C3N4 successfully. The experimental findings indicate that the TiO2/CN significantly enhances the dehydrogenation performance of LiAlH4. For instance, the LiAlH4-7 wt% TiO2/CN starts to dehydrogenize at 76 °C (94 °C less than pure LiAlH4) and releases 6.5 wt% H2 at 200 °C. Meanwhile, LiAlH4-7 wt% TiO2/CN releases 4.9 wt% H2 at 120 °C within 50 min. The mechanism analysis illustrates that AlTi3N is formed in situ during ball-milling. And density functional theory (DFT) calculation results reveal that the AlTi3N can weaken the Al-H bonds in LiAlH4 through interfacial charge transfer. Furthermore, the TiO2/CN heterostructure creates an internal electric field that generates an electron-rich layer. As a result, the negative electron layer at one end of the TiO2/CN heterojunction has an increased affinity for H, which enhances the dehydrogenation reaction of LiAlH4. Clearly, both the TiO2/CN heterostructure and AlTi3N contribute to the improvement of the dehydrogenation properties of LiAlH4.

Highly efficient and stable hydrogen permeable membrane reactor for propane dehydrogenation

The synthesis of SAPO-34 hollow fiber membranes employs the ball-milling assistant method to enhance membrane yield and quality. These membranes are then combined with CrOx/Al2O3 catalyst to create a packed bed membrane reactor (PBMR) for propane dehydrogenation (PDH). The study investigates the impact of operating temperatures, weight hourly space velocities (WHSV), and sweep gas flow rates on the SAPO-34 zeolite membrane reactor's performance, comparing it to a traditional packed bed reactor (PBR). The removal of hydrogen from the reaction side significantly improves propane conversion, surpassing thermodynamic equilibrium. In PBMR, propylene selectivity slightly exceeds that in PBR, influenced by side reactions like hydrogenolysis and cracking after hydrogen removal. Furthermore, the SAPO-34 zeolite membrane reactor undergoes a prolonged stability test with frequent regeneration using pure propane as feedstock to simulate industrial conditions. It exhibits consistent performance over 120 regeneration cycles within 240 h, maintaining similar H2 permeability and H2/C3H8 selectivity as the fresh membrane post long-term testing.

Disproportionation of Rosin Driven by 4,4′-Thio-bis(3-Methyl-6-Tert-Butylphenol): Kinetic Model Discrimination

Herein, a phenomenological kinetic modeling of the disproportionation of rosin with a well-known antioxidant and bleaching agent, antioxidant 300, also known as 4,4′-thio-bis(3-methyl-6-tert-butylphenol) under thermal conditions adequate for rosin esterification with polyols such as glycerol or pentaerythritol, is studied. The temperature was varied in the 260–280 °C range, while the catalyst was either absent or added till a 2% w/w amount relative to rosin. The composition of the reaction liquid was followed by GC-MS to identify the rosin acids present in each sample and GC-FID to quantify them. Gas chromatography analyses indicated that abietic acids were involved in dehydrogenation, isomerization and disproportionation reactions, while pimaric acid underwent a number of isomerization reactions, dehydroabietic acid being the main product of the disproportionation process, while abietic acid almost disappeared in the more reactive conditions. Several kinetic models featuring direct hydrogenation, disproportionation, isomerization, and dehydrogenation reactions were proposed and fitted, step by step, to all relevant data. Physicochemical and statistical discrimination allowed for the selection of the most adequate model, which includes abietic, neoabietic and palustric acid dehydrogenation to dehydroabietic acid, abietic acid disproportionation to di- and dehydroabietic acid, and pimaric acid isomerization. In any case, a model with isomerization of all abietic-type acids towards abietic acid before its further transformation via dehydrogenation and disproportionation reactions seems statistically valid as well.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Digital light processing of TixOy@Ti/HA biomaterials by oxidation of TiH2 and dehydrogenation of TiO2@TiH2/HA precursors

AbstractThe complex structure of Ti/HA (HA: hydroxyapatite) implants prepared by additive manufacturing technology plays an essential role in its application in bone repair. Digital light processing (DLP) is widely used to prepare bioceramics with complex structures. However, it is a challenge to prepare Ti/HA biomaterials by DLP due to the high ultraviolet (UV) absorption of Ti powder. In the present work, TiH2 powder coated with a TiO2 layer is selected to reduce the UV absorption and improve the curing depth for DLP printed green bodies of TiO2@TiH2/HA, because the TiO2@TiH2 powder can be reduced by 12.7% compared to the TiH2 powder without any oxidation. Then, the shell layer of TiO2 undergoes dehydrogenation and reduction reaction with the core phase of TiH2 during the sintering process to transfer TiO2@TiH2/HA into TixOy@Ti/HA. In addition, the effects of HA content on compressive strength and biocompatibility are investigated in the TixOy@Ti/HA biomaterials. The results show that when adding 60 vol%HA, the maximum monolayer curing depth of the slurry reaches 90.1 ± 3.5 µm. 40%TixOy@Ti/60%HA shows the maximum effect in promoting the pre‐osteoblast differentiation and a relatively high compressive strength of 48.7 ± 3.5 MPa. This work provides an experimental basis for the preparation of ceramic–metal composites with high UV absorptivity using DLP.

On the nature of Con±/0 clusters reacting with water and oxygen

Bulk cobalt does not react with water at room temperature, but cobalt nanometals could yield corrosion at ambient conditions. Insights into the cobalt cluster reactions with water and oxygen enable us to better understand the interface reactivity of such nanometals. Here we report a comprehensive study on the gas-phase reactions of Con±/0 clusters with water and oxygen. All these Con±/0 clusters were found to react with oxygen, but only anionic cobalt clusters give rise to water dissociation whereas the cationic and neutral ones are limited to water adsorption. We elucidate the influences of charge states, bonding modes and dehydrogenation mechanism of water on typical cobalt clusters. It is unveiled that the additional electron of anionic Con– clusters is not beneficial to H2O adsorption, but allows for thermodynamics- and kinetics-favourable H atom transfer and dehydrogenation reactions. Apart from the charge effect, size effect and spin effect play a subtle role in the reaction process. The synergy of multiple metal sites in Con– clusters reduces the energy barrier of the rate-limiting step enabling hydrogen release. This finding of water dissociation on cobalt clusters put forward new connotations on the activity series of metals, providing new insights into the corrosion mechanism of cobalt nanometals.

Thermally manageable and scalable reactor configurations towards efficient hydrogen release from liquid organic hydrogen carriers

In the global pursuit to minimize carbon emissions, hydrogen has emerged as a prominent alternative energy solution. This research introduces a thermally efficient, scalable, and potentially carbon–neutral system for releasing hydrogen, employing methylcyclohexane as a liquid organic hydrogen carrier (LOHC). Our heat supply mechanism utilizes benzyltoluene as a liquid–gas phase change material (PCM) to facilitate effective heat transfer from the heating units to the reactor. We have developed catalysts with high dispersion and Pt loading of Pt/γ-Al2O3 that maintain performance over extended periods, achieving a hydrogen extraction rate of 2.3 Nm3H2(g)/h (equivalent to 5 kgH2/day) in a bench-scale reactor. The bench-scale setup achieves near-equilibrium conversion at a space velocity of 2 LLOHC/(Lcat-h) and 310 °C. The PCM-enhanced system supports a scalable catalytic bed design and simplifies heat supply and startup through the use of various heating methods. We then compare catalytic dehydrogenation reactor setups using single and hybrid heat sources; the former includes an internal Joule heater, offering simplicity and reduced heat loss but depends heavily on electrical energy, while the latter combines the internal Joule heater with an external fuel combustor, facilitating rapid startup albeit with increased heat loss. Lastly, we suggest future research directions to address existing technological hurdles and to expand the application of this system in scaling up hydrogen release processes.

Hydrothermal synthesis of highly cross‐linked PtZn@Silicalite‐1 structured catalysts for propane dehydrogenation

AbstractStructured catalysts coatings exhibit excellent performance on non‐adiabatic gas–solid process, deriving from their enhanced heat and mass transfer properties. However, the coating catalysts prepared by traditional hydrothermal method of zeolite encapsulating noble metal are prone to spalling, especially under conditions of large flow rate and high temperature. Herein, we prepared PtZn clusters encapsulated in silicalite‐1 zeolite coating on stainless steel with high bonding strength by an improved in situ growth method. The optimized catalyst exhibited ultra‐thin, uniform, continuous, and high degree of crosslinking, thereby enhancing mass transfer and thermal stability. In propane dehydrogenation reaction, the optimized PtZn@S‐1‐R showed a high specific activity of 14.7 molPt−1 s−1 and a propylene selectivity above 99% at 600°C with a high weight hourly space velocity of 120 h−1. The metal‐encapsulated zeolite coating catalysts broaden the application avenue for heterogeneous catalysis with great application prospects.

Tricoordinated Single-Atom Cobalt in Zeolite Boosting Propane Dehydrogenation.

Propane dehydrogenation (PDH) reaction has emerged as one of the most promising propylene production routes due to its high selectivity for propylene and good economic benefits. However, the commercial PDH processes usually rely on expensive platinum-based and poisonous chromium oxide based catalysts. The exploration of cost-effective and ecofriendly PDH catalysts with excellent catalytic activity, propylene selectivity, and stability is of great significance yet remains challenging. Here, we discovered a new active center, i.e., an unsaturated tricoordinated cobalt unit (≡Si-O)CoO(O-Mo) in a molybdenum-doped silicalite-1 zeolite, which afforded an unprecedentedly high propylene formation rate of 22.6 molC3H6 gCo-1 h-1 and apparent rate coefficient of 130 molC3H6 gCo-1 h-1 bar-1 with >99% of propylene selectivity at 550 °C. Such activity is nearly one magnitude higher than that of previously reported Co-based catalysts in which cobalt atoms are commonly tetracoordinated, and even superior to that of most of Pt-based catalysts under similar operating conditions. Density functional theory calculations combined with the state-of-the-art characterizations unravel the role of the unsaturated tricoordinated Co unit in facilitating the C-H bond-breaking of propane and propylene desorption. The present work opens new opportunities for future large-scale industrial PDH production based on inexpensive non-noble metal catalysts.

Study on combustion mechanism of methanol/nitromethane based on reactive molecular dynamics simulation

Oxygenated fuels and nitro fuels are effective strategies for addressing incomplete combustion by increasing the oxygen-fuel ratio. A computational approach based on reactive molecular dynamics simulations reveals oxidation mechanisms of temperature-induced effects on a mixed fuel of methanol and nitromethane. The method enables the demonstration of the initial reaction scheme of a binary fuel mixture, even for complicated interplay and coupling reactions. The results showed that the first reaction step of nitromethane was homolysis in poor-oxygen conditions, mainly via CH3NO2 → CH3 + NO2 (Net flux = 183, ratio = 92.89%). Methanol undergoes dehydrogenation reaction with the assistance of active radicals (OH, HO2, CH3, NO, and NO2), and the participation rates of these active groups are 60%, 17.14%, 8.57%, 7.62%, and 6.67%, respectively. The decomposition of nitromethane provided NO2 and CH3 radicals and significantly increased the amount of OH and NO via a reaction of NO2 + H → HNO2 → OH + NO. By fragment analysis, the main C1 intermediates are formed by pyrolysis of methanol/nitromethane such as formaldehyde, hydroxymethyl radical, and formyl radical. The CH3OH and CH2O are relatively stable, and the dehydrogenation is mainly highly active groups such as OH and NO. In contrast, the dehydrogenation of CH2OH and CHO free radicals is completed by self-cleavage or with the help of O2, NO2, etc. Our findings shed light on the oxidation behaviors of methanol/nitromethane mixed fuel in combustion.

Synthesis of 2-substituted quinoline derivatives using [RuCl2(p-cymene)]2-ferrocene thioamide catalytic system via acceptorless dehydrogenative coupling

The substituted quinolines were synthesized via acceptorless dehydrogenative coupling (ADC) of 2-aminobenzyl alcohol with ketones/secondary alcohols, which was accomplished using the in situ catalytic activity of [RuCl2(p-cymene)]2 and ferrocene thioamide (Fc-TA) ligands. The catalysis was extended to aromatic and heterocyclic ketones and secondary alcohols, with unsubstituted and chloro‑substituted 2-aminobenzyl alcohols. The Fc-TA ligands (L1-L3) were synthesized, and characterized using spectroscopic techniques such as FT-IR, UV–Vis, NMR and HRMS. The influence of ligands on the catalysis was studied. Overall, the synthesis of quinolines was accomplished with good to moderate yields, via both mono and double dehydrogenation reactions along with hydrogen and water as only by-products.

From waste to raw chemicals: Catalytic transformation of fusel oil by mixed metal oxides

In this study, we detail a catalytic process for the conversion of fusel oil (FO), a by-product of ethanol production considered as waste, into valuable organic compounds, including aldehydes, alkenes, ketones, and alkylbenzenes spanning a carbon chain length from C6 to C12. The reaction was carried out in a fixed bed flow reactor at atmospheric pressure, employing mixed metal oxides (MMO) derived from hydrotalcites (HTC) as catalysts. The HTC were readily synthesized by co-precipitation method involving Mg2+ and Al3+, wherein 20 mol% Mg2+ was substituted by M2+ = Mn, Fe, Co, Ni, Cu, and Zn, and MMO obtained by HTC calcination. These catalysts offer cost-effectiveness compared to noble metal-containing ones while exhibiting remarkable activity in dehydrogenation, hydrogenation, and dehydration reactions pivotal for alcohol reactivity. The proposed methodology holds promise for large-scale industrial use and pioneers a fresh avenue for deriving value-added raw chemicals from a renewable carbon source.

Calcium additives enhance coke migration and catalyst stability for Pt-based catalysts in ethane dehydrogenation

Understanding and mitigating catalyst deactivation in high-temperature alkane dehydrogenation reactions is critical toward improving their energy and atom efficiency. In this work, we show that a partial overcoat of calcium oxide on a Pt-In alloy catalyst reduces the rate of catalyst deactivation by 10-fold during the non-oxidative dehydrogenation of ethane to ethylene. During 20 h of time-on-stream at 600 °C in 5 % C2H6, the Ca-doped PtIn2 catalyst retains >85 % of its initial activity while the undoped PtIn2 deactivates to <20 %. Temperature-programmed oxidation and spatially-resolved Raman spectroscopy reveal that the improved catalyst stability stems from enhanced migration of coke precursors away from the catalytically-relevant Pt sites to the silica support. Strikingly, the Ca overcoat does not alter the inherent rate and selectivity of coke formation but rather its crystallinity and localization, which nonetheless has a dramatic impact on the long-term performance of the catalyst.

Mechanistic insights into chemical conditioning on transformation of dissolved organic matter and plant biostimulants production during sludge aerobic composting

Inorganic coagulants (aluminum and iron salt) are widely used to improve sludge dewaterability, resulting in numerous residues in dewatered sludge. Composting refers to the controlled microbial process that converts organic wastes into fertilizer, and coagulant residues in dewatered sludge can affect subsequent compost efficiency and resource recycling, which remains unclear. This work investigated the effects of two typical metal salt coagulants (poly aluminum chloride [PAC] and poly ferric sulfate [PFS]) conditioning on sludge compost. Our results revealed that PAC conditioning inhibited composting with decreased peak temperature, microbial richness, enzymatic reaction intensities, and compost quality, associated with decreased pH and microbial toxicity of aluminum. Nevertheless, PFS conditioning selectively enriched Pseudoxanthomonas sp. and resulted in more fertile compost with increased peak temperature, enzymatic reaction intensities, and humification degree. Spectroscopy and mass difference analyses indicated that PFS conditioning enhanced reaction intensities of labile biopolymers at the thermophilic stage, mainly comprising hydrolyzation (H2O), dehydrogenation (-H2, -H4), oxidation (+O1H2), and other reactions (i.e., +CH2, C2H4O1, C2H6O1). Unlike the common composting process primarily conducts humification at the cooling stage, PFS conditioning changed the main occurrence stage to the thermophilic stage. Non-targeted metabolomics revealed that indole (a humification intermediate) is responsible for the increased humification degree and indoleacetic acid content in the PFS-conditioned compost, which then promoted compost quality. Plant growth experiments further confirmed that the dissolved organic matter (DOM) in PFS-conditioned compost produced the maximum plant biomass. This study provided molecular-level evidence that PFS conditioning can promote humification and compost fertility during sludge composting, enabling chemical conditioning optimization for sustainable management of sludge.

Cu(I) Complexes Catalyzed the Dehydrogenation of N-Heterocycles.

A copper-catalyzed method for the dehydrogenation of various nitrogen-containing heterocycles to furnish quinolines and indoles has been developed. A range of 1,2,3,4-tetrahydroquinolines underwent dehydrogenation by employing 2 mol % of copper complex Cat 3 as a catalyst and using O2 as an oxidant at 120 °C in 1,2-dichlorobenzene to afford the desired quinolines. The method enables the dehydrogenation of a variety of indolines in the presence of 2 mol % of copper complex Cat 2, using 10 mol % of TEMPO as an additive and O2 as an oxidant under room temperature in tetrahydrofuran to furnish indoles in high yields. Mechanistic studies suggested that the dehydrogenative activity is ascribed to the formation of a copper(II) active species from copper(I) complexes oxidized by O2, which was proved by high-resolution mass spectrometry (HRMS). The copper-catalyzed dehydrogenation reaction proceeds via a superoxide radical anion (·O2-) as proved by electron paramagnetic resonance (EPR) spectrometry. In situ infrared spectroscopy revealed that the dihydroquinoline intermediate was formed in the dehydrogenation of 1,2,3,4-tetrahydroquinolines.