Ammonia catalytic combustion technology enables the efficient conversion of NH3 into nitrogen (N2) and water (H2O), offering a reliable carbon-free fuel utilization strategy. This approach effectively addresses the inherent challenges associated with NH3 combustion, including high ignition temperatures, low N2 yields, and combustion instability. This study focuses on the catalytic process characteristics and mechanism of NH3 combustion over spherical CeO2-supported transition metal catalysts. Cu/CeO2, Mn/CeO2, and Ni/CeO2 catalysts were synthesized by impregnation method. The catalytic performance for NH3 combustion revealed a clear activity trend of Mn/CeO2 > Cu/CeO2 > Ni/CeO2. However, the most active catalyst, Mn/CeO2, also showed the least N2 yield. In contrast, Cu/CeO2 emerged as the balanced performer, coupling high NH3 conversion (~100%) with good N2 yield (88.7%–90.4%) over 10 hours, and achieving self-sustained combustion at 7.1% NH3. Mechanistic studies attribute Mn/CeO2’s high activity to a synergistic interplay where Ce4+ oxidizes Mn2+ to Mn3+, stabilizing more oxygen vacancies, which confirmed by Density Functional Theory (DFT) calculation. The low N2 yield of Mn/CeO2 is linked to its inferior reduction ability and diminished NH3 adsorption capacity, as revealed by H2 temperature-programmed reduction (H2-TPR) and temperature-programmed desorption of NH3 (NH3-TPD-MS). In-situ infrared transmission spectroscopy (IR) results found that the adsorbed NHx can react with HNO species in Mars-van-Krevelen (M-K) mechanism over Cu/CeO2 catalyst. And a rapid consumption of NOx indicates an intensive internal selective catalytic reduction (i-SCR) pathway, which effectively accounts for the high N2 yield observed in Cu/CeO2. But the Mn/CeO2 exhibited weaker HNO formation and lower i-SCR activity, in consistent with its inferior N2 yield. These results provide a guidance for the design of advanced catalysts and promote insight into the mechanistic pathways of ammonia catalytic combustion.

To address the issues of insufficient activity and stability in transition metal catalysts for the catalytic oxidation of volatile organic compounds (VOCs), this study adopted a high-entropy strategy, successfully constructing a Mn-based high-entropy spinel oxide catalyst (Mn-HEO) through the doping of multiple metal atoms (Co, Mg, Zn, Cu) at the A site. Experimental results indicate that Mn-HEO exhibits significantly enhanced catalytic performance with a significant T90 reduction of 122 degrees C compared with Mn3O4. Stability test (450 degrees C) proves that Mn-HEO maintains 100% complete benzene conversion while Mn3O4 decreases to 80%. Combining characterization with density functional theory (DFT) calculations, high-entropy metal doping induces lattice distortion and electronic structure modulation in Mn-HEO, causing the d band center (-4.76 eV) to shift upward, significantly enhancing the adsorption capacity for gaseous oxygen (-2.83 eV) and benzene (-1.46 eV). Importantly, the surface chemical adsorption oxygen ratio of Mn-HEO is 1.15 times that of Mn3O4, and the O-O bond (1.48 & Aring;) is more prone to be weakened, promoting the activation and migration of oxygen species, thereby enhancing the catalytic activity of Mn-HEO.

The cracking of polyolefins into liquid fuels is a critical pathway for the resource utilization of plastic waste. However, coke deposition readily occurs on the catalyst surface during the catalytic cracking process, leading to the blockage of active sites, deterioration of product selectivity, and shortened catalyst lifespan, which severely restricts the industrial scale-up and stable operation of this technology. Consequently, addressing catalyst coking has become a research hotspot and core challenge in the field of polyolefin cracking. To tackle this issue, this review systematically summarizes the formation mechanisms and detrimental characteristics of catalyst coking during liquid fuel production from polyolefin cracking. It also, for the first time, integrates three strategies to address this problem: (i) strategies for Inhibiting coke formation at the source, including modulation of catalyst acidity, optimization of topological structure, and design of bifunctional metal-acid sites; (ii) discussion of coke removal and regeneration methods, such as high-temperature calcination, hydrogenation removal method, and plasma regeneration techniques; (iii) proposal of the concept of utilizing coke as a potential carbon resource for high-value applications. Finally, the review summarizes the advantages and disadvantages of existing strategies and provides an outlook on future research directions. These include the development of novel anti-coking catalysts, improvement of efficient catalyst regeneration methods, and advancement of high-value conversion routes for coke. The aim is to provide theoretical guidance and technical references for achieving an efficient and stable polyolefin catalytic cracking process.

Chemical Looping Combustion (CLC) is a combustion technology that enables efficient and low-energy CO2 capture. However, the cyclic regeneration capability of oxygen carriers represents a critical bottleneck restricting the development of this technology. This study investigates the CO chemical looping combustion (CO-CLC) behavior of inverse CeO2/Cu2O and pure Cu2O as oxygen carriers, focusing on lattice oxygen regeneration. DFT calculations and Redhead kinetics analyses pinpoint the Cu-Ce interface as the key promoter for oxygen activation. Electron transfer across this interface weakens Cu-O bonds, lowering both the oxygen vacancy formation energy to 2.54 eV at surface and the lattice oxygen migration barrier by 16 kJ/mol relative to pure Cu2O, which consequently improves the oxygen mobility markedly. The modified electronic structure, evidenced by a d-band center shift closer to the Fermi level, also weakens the adsorption of CO and O2 by 1.7 eV and 0.17 eV, thereby enhancing the overall reactivity. The Cu-Ce synergy enhances CO oxidation, oxygen activation/migration, and lattice oxygen replenishment, significantly boosting the cyclic regeneration capability of oxygen carriers.

This study investigates the low-temperature synergistic removal of soot and NOx using a sol-gel synthesized CuCeOy catalyst. Compared to model Printex-U carbon black, real diesel soot (SO) exhibits higher reactivity owing to its disordered structure and abundant oxygen-containing functional groups. The CuCeOy catalyst significantly lowered peak oxidation temperature of SO to 342 degrees C in an O2/NO/Ar atmosphere. NO plays a dual role: it lowers ignition temperature via NO2 formation, but its competitive adsorption with O2 limits the reaction rate by favoring an indirect pathway. Using isotope tracing, a bidirectional oxygen spillover mechanism was directly observed-gas-phase O2 refills oxygen vacancies, and the replenished lattice oxygen spills over to oxidize soot. This pathway is competitively inhibited by NO. DFT validates NO/O2 competitive adsorption at vacancies and surface lattice oxygen reacting preferentially over bulk. The findings provide new insights into designing efficient non-noble metal catalysts for low-temperature soot and NOx control.

Chemical looping combustion (CLC) is a promising technology for efficient CO2 capture. However, the intrinsic relationship between lattice oxygen migration and the cycling stability of oxygen carriers (OCs) remains insufficiently understood. In this study, we systematically investigated the structural evolution of Cu2O model OCs with well-defined morphologies, emphasizing the critical role of lattice oxygen migration in governing their cycling stability. Carbon monoxide (CO) was used as a probe molecule to induce the reduction of Cu2O, while oxygen (O2) facilitated its oxidation, thereby completing the CLC cycles. Cu2O in cubic and dodecahedral forms, which have closed surfaces, exhibit incongruent inward and outward lattice oxygen migration, triggering irreversible structural changes that ultimately result in ineffective cycles. In contrast, octahedral Cu2O, possessing an open surface and one-coordinate unsaturated Cu atoms, facilitates both CO oxidation and O2 activation. This open-surface configuration enables congruent lattice oxygen migration during redox cycling, thereby maintaining structural integrity and catalytic activity over ten consecutive cycles at 200 °C. These findings reveal a positive feedback mechanism between lattice oxygen migration and structural stabilization, providing fundamental insights into the origin of the superior cycling stability of well-defined Cu2O model OCs in CLC.

To meet the demand for simultaneous purification of multi-component volatile organic compounds (VOCs) from industrial emission sources, this study systematically investigated the catalytic oxidation behaviors of benzene, toluene and cyclohexane over regular Cu2O model catalysts, aiming to explore the mixing reaction mechanism.The results demonstrates that octahedral Cu2O possesses the best activity and competitive adsorption on the catalyst surface is the primary factor influencing the multi-component VOCs interactions. Specifically, toluene, due to its higher polarity, inhibits the benzene oxidation through competitive adsorption. Toluene and cyclohexane exhibit mutual promotion in catalytic oxidation attributing to the distinct adsorption configurations and weak competition. The cyclohexane oxidation generates benzene as a by-product, which increases benzene concentration and consequently suppresses its oxidation. DFT calculations reveals that toluene possesses the highest adsorption energy (-0.93 eV), followed by benzene (-0.86 eV) and cyclohexane (-0.52 eV), corresponding to the competitive adsorption ability. It should be noted that toluene shows the strongest hybridization between its molecular orbitals and Cu 3d and O 2p orbitals, leading to a reconfiguration of the electronic structure of the catalyst, which enhance the electron transfer efficiency and competitive advantage during the multi-component VOCs oxidation.

Tuning the oxygen vacancy concentration of non-noble metal catalysts is crucial for harnessing environmental catalytic oxidation reactions. Oxygen vacancy-induced reactive oxygen species (ROS) cycling capacity is modulated by catalyst modification using non-thermal plasma (NTP) for toluene oxidation. In this work, NTP treatment of spherical CuO/CeO2 catalysts accelerates electron transfer between Cu-O-Ce, resulting in the formation of more oxygen vacancies while maintaining the structural stability of the catalyst. This strategy facilitates the adsorption and activation of gaseous O2, generating highly mobile ROS that participate in the catalytic oxidation of toluene to form CO2. Compared with the untreated 7 %CuO/CeO2 catalyst (T90 = 272 degrees C), the NTPtreated 7 %CuO/CeO2-P exhibits a 41.5 % increase in oxygen vacancy concentration, along with improvements of 55.8 % and 54.7 % in oxygen storage and release performance, respectively, which ultimately unveil the remarkable toluene oxidation activity (T90 = 260 degrees C). Oxygen vacancy significantly enhances ROS mobility and reactivity, thereby accelerating the O2-OV-ROS cycling. Abundant oxygen vacancies allow an acceleration of the catalytic oxidation of toluene. This work provides a credible understanding of the catalyst performance enhancement achieved through NTP treatment of modified catalysts, which is effective in developing a pathway to enhance the catalytic oxidation activity of volatile organic compounds (VOCs).

Photothermal catalysis has received extensive attention as an effective strategy to enhance the energy efficiency of volatile organic compounds (VOCs) treatment. However, how to design photothermal catalysts in a reasonable way for efficient degradation of VOCs is one of the attractive and challenging goals at present. Density Functional Theory (DFT) theoretical calculations can assist experiments in conducting a comprehensive evaluation of catalytic materials, guiding the targeted and efficient design of catalysts. Hence, different surface models of five metal oxides were established, and through calculations of surface formation energy, adsorption energy chlorobenzene (CB) and work function, materials such as CeO2 (111), MnO2 (211), CuO (111), Fe2O3 (104) and Co3O4 (311) with thermodynamic stability and excellent intrinsic activity were determined. The above five metal oxides were synthesized by controlling the growth orientation of crystal planes. The dual-metal catalytic material prepared by the composite of CeO2 and MnO2 was determined through catalytic performance tests and characterization, as it possesses both low-temperature activity and photothermal conversion properties. Under the irradiation of 600 mW/cm2, the complete conversion temperature of CB by CeMnOx was 160 degrees C (i.e., furnace temperature), which was 80 degrees C lower than that of thermal catalysis. The orbital hybridization of Ce and Mn affected the electronic arrangement and energy level distribution of the material. The increased Mn3+ content made the coordination environment more inhomogeneous, facilitating the formation of oxygen vacancies and enhancing the oxygen activation capacity and adsorption of CB. Furthermore, the broadened band gap structure improved the utilization rate of photo-energized carriers, and the thermal electron transport mechanism strengthens the bond-breaking ring-opening and deep oxidation processes of & sdot;OH, enabling it to exhibit superior performance under photothermal synergy. This work presents a DFT-assisted experimental method, providing new strategy for the degradation of VOCs under milder conditions.

Catalytic NH3 combustion presents a promising strategy to overcome the challenges of high ignition temperature and excessive NOx emissions in the clean utilization of carbon-free NH3 fuel. This investigation elucidated distinct structure-activity relationships and combustion pathways of CuCe/S catalysts prepared via different synthesis methods. The catalyst synthesized by rapid Joule heating (CuCe/S-J, T90=330 °C) significantly outperforms its conventionally mixed counterpart (CuCe/S-M, T90=396 °C) in NH3 combustion activity. Series of characterizations (in situ ESEM and XAFS etc.) reveal that the superior activity of CuCe/S-J originates from its highly dispersed CuO dispersion (83.5%) on the SAPO support, and stronger Cu–Ce interaction induced by the rapid thermal process, which facilitates efficient electron transfer (Cu⁺+Ce4⁺–O→Cu2⁺+Ce3⁺–OV), generate more active Cu2⁺ species (0.76) and Ce3⁺–OV sites at the interface. As evidenced by H2-TPR and NH3-TPD-MS, these features collectively enhance the redox ability and NH3 adsorption-activation. In situ IR and isotopic (18O2) transient experiments delineate the reaction pathways: NH3 adsorbed on active sites (Cu-OH+ and Cu2+) reacts with activated lattice oxygen to form key intermediates (HNO, NH4⁺, NH2), which subsequently decompose to produce N2 and H2O at lower temperature on CuCe/S-J. These findings not only confirm the viability of environmentally friendly catalytic combustors for ammonia fuel, but provide fundamental insights for designing high-performance catalyst.Novelty and significance statement: Catalytic combustion of high-concentration NH3 is a prospective technology to address the high ignition temperature and increased NOx production in direct gaseous NH3 combustion, but is rarely reported so far. This work proposes an innovative rapid Joule heating method to prepare CuCe/-J catalyst, and the enhanced structure-activity relationship of CuCe/S-J is thoroughly elucidated. The activity of CuCe/S-J (T90=330 °C) is better than CuCe/S-M (T90=396 °C) by traditional Muffle furnace heating prepared method, attributed to the former exhibits stronger metal-metal and metal-support interactions, reflecting the higher Cu dispersity (83.5%) and more Cu2⁺+Ce3⁺–OV interface on CuCe/S-J. The M-K reaction mechanism was precisely revealed by in situ IR and isotopic (18O2) transient tracer. The significance of this research lies in demonstrating the feasibility of environmentally friendly catalytic combustors for ammonia fuel, while also advancing the understanding of advanced catalyst design and reaction mechanism underlying heterogeneous catalytic ammonia combustion systems.

The catalytic combustion of NH3 under fuel-rich conditions offers a promising route to carbon-neutral energy, but precise NOx suppression remains challenging due to competing redox pathways under extreme thermal gradients. Unlike steady-state NH3-SCR, this process involves dynamic Cu-site evolution in Cu/SSZ-13 catalysts. We elucidate the temperature-dependent mechanism of Cu species and develop a quantitative kinetic model linking Cu+ /Cu2+ valence transitions to NOx formation. Integrating quasi-in-situ XPS/AES, in-situ FTIR, synchrotron XAFS, and DFT calculations, we identify a critical "dynamic redox equilibrium window" (400-600 degrees C), where ammonia solvation mobilizes Cu species, enabling balanced Cu+/ Cu2+ coexistence. Isolated Cu+ sites drive rapid NO reduction via an E-R mechanism, while Cu2+ sites promote NH3 oxidation, achieving high N2 selectivity. Exceeding 600 degrees C induces catastrophic "selectivity collapse," triggered by lattice oxygen activation in Cu-oxo clusters (distinct from zeolite framework), which re-oxidizes Cu+ to static Cu2+ and causes a three-orderof-magnitude NO surge. Oxygen vacancy formation energy and O2 adsorption energy serve as key descriptors for this thermodynamic drive. Kinetic modeling shows rapid heating rates bypass this collapse, providing a practical startup strategy for low-NOx reactors.

Despite the excellent CO catalytic performance of Pt-0, it tends to suffer oxidation in real high-temperature environments, leading to decrease in activity. Therefore, it is necessary to study the catalytic performance of Pt-based catalysts in their unreduced state. In this study, the structure-activity relationship of high concentration CO oxidation over unreduced platinum supported catalysts (Pt/CeO2, Pt/TiO2, Pt/SnO2, Pt/ZrO2, Pt/La2O3) were investigated. The results indicate that due to the strong interaction between Pt and Ce, the valence changes of support element Ce facilitate the formation of redox pairs of Pt2+/Pt4+ and Ce3+/Ce4+ at the Pt-Ce interface, culminating in a catalytic activity superior to that of other catalysts. Furthermore, the O-18(2) isotope experiment achieved quantification of different lattice oxygens. Surface cycle lattice oxygen in the Pt/CeO2, possessing the highest Turnover Frequency (4.75 x10(-3) s(-1)), accounts for optimum catalytic activity. Both Mars-van Krevelen (M-K) mechanism and Langmuir-Hinshelwood (L-H) mechanism coexist in the CO catalytic oxidation, but the former predominates the reaction. The contribution proportion of the M-K mechanism decreases in the order of Pt/CeO2 (83 %) > Pt/TiO2 (79 %) > Pt/SnO2 (76 %) > Pt/ZrO2 (73 %) > Pt/La2O3 (70 %), which corresponds to the activity results.

The utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications. To achieve this, minimizing NO formation while maximizing energy release is essential. In this study, we investigated the catalytic performance of catalysts with different acid site characteristics, including a non-acidic catalyst, CuO-CeO2 supported on TiO2 providing only Lewis acid (LA) sites, and a catalyst with both Brønsted acid (BA) and LA sites at the same active sites. These catalysts were used to examine the synergistic effects of BA and LA sites in NH3 catalytic combustion. Results show that proton transfer at BA sites, where H+ protonates NH3 to form NH+4, stabilizes NH3, reducing reactive NHx intermediates and enhancing NO reduction efficiency by interacting with N2O.In-situ impedance spectroscopy and diffuse reflectance infrared spectroscopy reveal that NH+4 formed on BA sites migrates, interacting with reductive NO species to prevent nitrate decomposition and limit NHx formation. The 18O2 isotope tracing of O species in NO reveals that NH+4 promotes NO conversion to N2 via an internal selective catalytic reduction (i-SCR) mechanism, maintaining NO concentrations below 50 ppm at temperatures below 550°C. Based on this specially designed catalyst, the combination of advanced in-situ analytical techniques and isotopic tracing highlights a crucial pathway for NH+4-mediated NOx reduction at acidic sites. The utilization of carbon-free NH3 gas can be extended from low-concentration environmental applications to high-concentration energy applications, requiring minimized NO formation alongside maximized energy release.

In recent years, the adsorption and separation of ammonia (NH3) from airflow have attracted growing attention. However, there is a need to further enhance the adsorption capacity of adsorbents. In this study, the aminofunctionalization of UiO-66 was investigated to evaluate its dynamic NH3 adsorption performance by varying the type and proportion of organic ligands. It was observed that the introduction of amino groups significantly enhanced the ammonia adsorption capacity by 78.5 %, despite a minor reduction in specific surface area and pore size. Combined with the results of density functional theory and in-situ infrared, the enhanced adsorption ability can be ascribed to the functionalization increasing the polarity within the pore, thereby strengthening interactions with ammonia molecules through weak hydrogen bonding.

VOCs oxidation over transition metal catalyst is commonly understood via the Mars-van Krevelen mechanism involving the crucial role of lattice oxygen (OL) activity, however, how it is influenced by atomic coordination is still unclear. Herein, we use model catalysts of Cu2O-cub, Cu2O-oct and Cu2O-dod with crystal planes of (100), (111) and (110), respectively, to investigate the OL activity and catalytic oxidation of toluene. The activity of Cu2O-oct is found to be the highest, followed by Cu2O-cub and Cu2O-dod. Experiments results combined with density functional theory show that, although low di-coordinated O atoms leads to the lowest surface oxygen vacancy formation energy (2.47eV) and the highest surface OL activity of Cu2O-cub, it cannot determine the activity. The lowest bulk oxygen vacancy formation energy (3.16eV) in Cu2O-oct terminated with tri-coordinated O atoms and open surface can accelerate the migration and replenishment of OL, thereby promoting the catalytic activity.

Cobalt-nickel-based catalysts are among the most promising non-noble metal catalysts for hydrogen production via ammonia decomposition. However, attaining the optimal bonding ratio at the CoNi alloy-support interface remains a significant challenge for ensuring sufficient catalytic activity in ammonia decomposition. To address this issue, this study investigates the enhancement of catalytic activity through the interface effects between CoNi alloy nanoparticles and different supports (ZSM-5, Al2O3, and TiO2), as well as the role of Lewis acid sites within the supports. It is found that the CoNi alloy particles supported on the carriers form CoNi-O bonds with oxygen atoms, creating an oxide-metal interface that facilitates charge transfer from the carrier to the alloy, promoting catalytic activity. In the CoNi/ZSM-5 catalyst, the abundant formation of CoNi-O bonds enhances the interfacial effects and promotes charge transfer, thereby improving catalytic performance. Besides, the plentiful Lewis acid sites in ZSM-5 improve the ammonia adsorption and the increasing local ammonia concentration ensures more effective contact and enhances catalytic efficiency.

Regenerative cooling technologies are recognized as an effective and feasible thermal protection method in liquid oxygen/methane engines. This paper presents a comprehensive review of regenerative cooling applications in engine thrust chambers. The current research on regenerative cooling, including its flow and heat transfer characteristics, is summarized. Additionally, the interrelationships among influential factors, dimensional analysis, transcritical flow and heat transfer mechanisms, as well as heat transfer and pressure drop correlations, are thoroughly examined through numerical simulations and experimental validation. Despite advancements, the cooling capacity of regenerative systems remains insufficient for engines due to the complex operating conditions within thrust chambers and the limited coolant mass flow rate. To mitigate heat transfer deterioration, the paper discusses physical property models, criteria for heat transfer enhancement and deterioration, and predictions based on heat transfer correlations. Furthermore, inconsistencies in descriptions near the pseudo-critical region significantly limit the applicability of existing heat transfer mechanisms and correlations. In light of this, further research is necessary to elucidate heat transfer deterioration mechanisms, cyclic life sensitivity, the combined effects of mini-channel scale and transcritical conditions, and methods to enhance cooling performance. These investigations will lay the groundwork for fundamental research and the development of reusable launch vehicles.

The selective catalytic oxidation (SCO) has proved to be one of the most effective strategies for NH3 removal, and the corresponding reaction mechanism remains a key and challenging issue. This study provides the NH3-SCO reaction pathways at different reaction stages on Cu-Ce/SSZ-13 catalysts mainly based on kinetic experiments and quantitative analysis of active sites. Mars-van Krevelen (M-K) mechanism is determined to dominate the whole SCO reaction by the kinetic model. At low-temperature, the dehydrogenated NH3 (NHx) reacts with lattice oxygen first to generate the key imide -HNO (-NH pathway), whereas, NHx species tend to be coupled on the catalyst surface to form N2H4 (hydrazine pathway) with temperature rising. i-SCR reaction at high temperature reduces NOx production and improves nitrogen selectivity. Ce ions can promote the migration of Cu2+ in SSZ-13 skeleton from [Cu2+(OH)]+-Z in eight-membered rings to Cu2+-2Z in six-membered rings which facilitates the N2 selectivity at high temperature.

Studying the mechanisms of bagasse conversion into syngas is essential to sustain the growing use of biomass in energy economy production. In this work, the precise kinetics of bagasse gasification with various gasification agents was firstly investigated employing in-situ infrared spectra with Coats-Redfern integration, combining qualitative infrared spectroscopy allowed for kinetic analysis, so as to explore how the intermediate species vary in each basic reaction. The results demonstrate that the CO2 agent reduces the activation energy of nitryl after amino oxidation, making the lignin involved in gasification more easily as well as causing higher gasification efficiency. On the one hand, steam serving as a gasification agent enhances the concentration of hydroxyl groups and produces H2-rich syngas. On the other hand, the strong oxidizing hydroxyl group reduces the energy barrier of carbonyl and carboxyl groups in cellulose, which facilitates the gasification process. Furthermore, this study compared the effects of gasification agent (H2O or CO2) on syngas composition, reactor temperature distribution, carbon conversion rate, gasification efficiency, as well as low calorific value, providing essential information for understanding the micro-reaction pathways and pathway regulation during bagasse gasification.