Catalysts For Combustion Research Articles

Efficient synergistic effect of B-acid and oxygen species on CuCe + ZSM-5 for selective catalytic combustion of DMF

The main indicators in the catalytic combustion of nitrogen-containing volatile organic compounds (NVOCs) are high activity at low temperatures and high N2 yield. In this study, CuCe+ZSM-5 catalyst, formed by preferentially forming the complex oxides of Cu species with Ce species and then grinding it with ZSM-5 support, exhibited optimum activity and the high N2 yield during the catalytic N,N-Dimethylformamide (DMF) combustion. The addition of Ce species allowed Cu species to bind to them, preventing Cu species from agglomeration and improving redox capacity. Therefore, for CuCe+ZSM-5 catalyst, the majority of Cu species were present in combination with Ce species, thereby enhancing the reactivity of the oxygen species. This promoted the cleavage of the amide bond, thereby enhancing the activity at low temperatures. In addition, B-acid site facilitated the preferential dissociation of the N-CH3 bond, resulting in the formation of the N–H bond. This resulted in the N species remaining unoxidized, thereby enhancing N2 yield. CuCe+ZSM-5 catalyst avoided the covering of B-acid sites during the calcination, in comparison to CuCe/ZSM-5 catalyst, promoting the selective oxidation of N species. This work provides a new strategy for designing efficient catalysts for catalytic NVOCs combustion.

Microwave-absorbing property, chemical adsorption, and catalytic activity of monolithic LamMnnOx catalyst in microwave catalytic combustion of toluene

To verify the catalytic activity of LamMnnOx (m,n = 1,2; x = 2.5 ∼ 5.5) catalyst in microwave catalytic combustion of volatile organic compounds (VOCs), monolithic LamMnnOx catalysts were prepared and applied in toluene oxidation in this study. The research demonstrated that the LamMnnOx catalysts had strong microwave-absorbing properties due to first dielectric loss and secondary magnetic loss. The bed temperature rose rapidly due to the formation of hotspots under microwave irradiation. Furthermore, LamMnnOx catalysts chiefly adsorbed toluene by chemical adsorption, and the adsorption capacity of Mn was much stronger than that of La. Based on the activity tests, La1Mn1Ox (x = 2.5 ∼ 3.5) catalyst exhibited the highest catalytic activity among the four catalysts, and toluene was converted and mineralized completely at 259 ℃ and 315 ℃, respectively, under the conditions of an initial toluene concentration of 1000 mg/m3, bed height of 150 mm, and gas velocity of 2.5 L/min. Highly active LaMnO3 perovskite, uniform distribution of active particles, and abundant oxygen vacancies ensured the high activity of the La1Mn1Ox catalyst. Hence, the La1Mn1Ox catalyst was stable after a total of 600 min of activity test. According to electron transfers on the active Mn surface, the adsorption and activation of gaseous oxygen, and the transformation of Oads to Olatt on the oxygen vacancies, toluene oxidation speculates to follow the Langmuir-Hinshelwood and the Mars-van Krevelen mechanisms simultaneously. Therefore, this work provides further technological support for applying LamMnnOx catalysts in microwave catalytic combustion of industrial VOCs waste gas.

Enhanced NOx-assisted soot combustion by cobalt doping to weaken mullite Mn-O bonds for lattice oxygen activation

Catalytic combustion is widely regarded as the most efficient technique for removing soot particulates from diesel engine exhaust, with its efficiency largely dependent on the performance of catalysts. In this study, a series of YMn1−xCoxO5-ζ catalysts were synthesized using a hydrothermal method to investigate their catalytic properties in soot oxidation. Among these catalysts, YMCo-0.2 exhibited the highest catalytic activity, achieving 90 % soot conversion at 392 °C and demonstrating robust tolerance in the presence of water vapor and SO2. Structural characterization revealed that Co doping did not alter the fundamental crystal structure of YMn2O5 mullite. Through some characterization comprehensive analysis, and DFT calculations further supported the experimental findings, indicate that Co substitution significantly increased the lattice oxygen mobility and surface active oxygen content. Compared to the surface lattice oxygens at other positions, the weakening of the Mn-O bond results in the lattice oxygens in the Co-O-Mn4+ sites in the catalysts exhibiting higher reactivity. Additionally, the catalyst displayed strong NO and O2 adsorption and activation capabilities, indicating its potential for efficient NOx-assisted soot combustion. This study provides insights for designing and optimizing mullite catalysts for soot combustion.

High‐Throughput Screening of Dual‐Atom Catalysts for Methane Combustion: A Combined Density Functional Theory and Machine‐Learning Study

AbstractCeria‐supported precious metal catalysts have undergone extensive investigation for the catalytic methane combustion. However, it remains a significant challenge to achieve both highly synergistic oxidation activity and efficient atom utilization remains a challenge for commonly used supported nanoparticles and single‐atom catalysts. Dual‐atom catalysts (DACs) emerges as a frontier of advanced catalysts, presenting unique catalytic properties that benefit from the synergy of neighboring metal sites. In this study, 361 ceria‐supported DACs (M1M2/CeO2) encompassing combinations of 19 transition metals are systematically explored. Using high‐throughput density functional theory calculations, the structures, stability as well as activity of M1M2/CeO2 are assessed. Notably, Au1Ga1/CeO2 is identified as a promising DAC exhibiting high activity for methane total oxidation, substantiated by comprehensive DFT‐calculated reaction pathways. Furthermore, employing six machine‐learning algorithms, the structure‐properties relationship is explored within ceria‐based DACs and highlight the importance of oxidation states and atomic radii of doped metals as the descriptors. The trained model by computational dataset exhibits high accuracy and predict a more active Mn1Au1/CeO2 than those screened using only DFT datasets. The high‐throughput strategy demonstrated in this work not only provides insights into the rational design of methane oxidation catalysts, but also paves the way for exploring DACs for diverse applications.

Captivating Combustion Traits of Bio-Oil Droplets Enriched with Bio-Additives from the Areca Shell Waste

Fuel derived from crude vegetable oil, such as coconut oil, holds promise as an alternative energy source to mitigate the increasing reliance on fossil fuels driven by population growth and industrial activities. The experiment involved suspending a single droplet of crude coconut oil mixed with activated carbon from areca shell waste and placed at the junction on R-type thermocouple (Pt/Pt-Rh13%). The droplets were ignited using a hot wire and subjected to atmospheric pressure and room temperature. Coconut oil comprises a saturated triglyceride carbon chain compound of approximately 91%, and areca shell waste possesses a porous structure that fosters favorable interactions between fuel molecules. The droplet combustion method was selected to streamline the process and enhance the contact area between air and fuel, thereby boosting the reactivity of fuel molecules. The research found that adding activated carbon shortens the carbon chain, making it more reactive and easier for the fuel to ignite. Specifically, activated carbon significantly enhances fuel performance at a concentration of two parts per million (ppm). At this level, the fuel absorbs heat more effectively and ignites faster compared to one ppm and three ppm levels. Moreover, the results show that heat absorption occurs slowly at one ppm, while at three ppm, the increased molecular mass of the fuel can strengthen carbon-bonding forces. These factors contribute to a longer ignition time for the fuel. The findings suggest that the activated carbon from areca shell waste can play a good role as a combustion catalyst, where overall, fuel performance increases.

Boosting catalytic activity of Pd/LaxCe1-xMnO3 catalysts in methane combustion by a plasma-treated strategy

An innovative plasma-treated strategy was employed to prepare LaxCe1-xMnO3 (LCMO) perovskite oxides. Pd nanoparticles were loaded onto plasma-treated (P) and air-calcined (T) LCMO respectively, forming the corresponding Pd/LCMO catalysts. The results indicated that the introduction of Pd and plasma treatment largely boost the catalytic activity in methane combustion. Among these catalysts, the Pd/LCMO-P catalyst shows the best performance in CH4 oxidation, giving T90 of 425 °C. It was revealed that the morphology structure and surface defects were strongly affected by plasma treatment, further affecting the dispersion and chemical state of Pd species via surface interaction. The superior performance should be ascribed to the good redox properties (high Mn4+/Mn3+ ratio), rich surface-active oxygen species, and enhanced oxygen mobility (weakened Pd-O and Mn-O chemical bonds). Besides, the distributions of cerium in the surface and crystal lattice of LMO also improved metal-support interaction and the oxygen mobility, that boosted CH4 oxidation. This plasma-treated strategy provided an effective path to develop the efficient combustion catalyst for superior performance.

Synergistic effect as a function of preparation method in CeO2-ZrO2-SnO2 catalysts for CO oxidation and soot combustion

The development of catalysts based on environmentally desirable components is a topical challenge. In the present work, we consider the effects of the preparation method on phase composition, porous structure, nature and distribution of active sites as well as synergistic behavior of components in two series of CeO2-ZrO2-SnO2 catalysts for soot combustion and CO oxidation. The catalysts prepared by the citrate method feature rather large SnO2 aggregates distributed on CeO2 and/or ZrO2 oxides. On the contrary, the catalysts prepared by the CTAB-templated approach feature a uniform distribution of oxide species and usually show higher activity in both CO oxidation and soot combustion. In both series, the activity and characteristics of catalysts are enhanced due to the synergistic effects arising when two or more oxide components coexist in their composition, and the degree of synergy is a function of the preparation method. The features of the most active catalysts combine (1) high specific surface area and pore volume, (2) high microstrain values, (3) coexisting oxygen vacancies of different nature, (4) high H2 consumption at low temperatures, and (5) high fraction of adsorbed active oxygen species.

Ceria-zirconia solid solution supported platinum catalysts for toluene oxidation: Studying the improved catalytic activity by tungsten addition

The catalytic oxidation of toluene at low temperatures is still an urgent issue to be solved. The key to addressing this issue is the preparation of a high-efficiency catalyst. Herein, ceria-zirconia (CZ) solid solution supported platinum (Pt) catalysts were prepared by citric acid (C)-assisted impregnation method. Surprisingly, the catalytic oxidation activity of the catalyst for toluene combustion significantly improved after introducing W into Pt-C/CZ. In addition, introducing W improved the redox property of the Pt-based catalyst, optimized the distribution of the oxygen vacancies, increased the average particle size of the catalyst particle, modulated the valence state and electronic structure of Pt, elevated the surface lattice oxygen activity, increased the number of surface moderate acidic sites and enhanced toluene adsorption capacity. In this study, the electronic structure of the Pt active site is modulated by introducing a W promoter, providing valuable guidance for the rational design of efficient noble metal catalysts.

Surface in situ Co-Mn modification over LaMnO3 perovskite with enhanced activity for ethane combustion

Catalytic combustion is one of effective ways to remove short-chain alkanes. In this study, we elaborately designed a novel catalyst of in situ Co-Mn decorated LaMnO3 perovskite for ethane catalytic combustion, in which extra Mn and Co species were introduced via acidic KMnO4 and Co(NO3)2 solution precipitation method. The addition of Mn and Co could not only slightly etch LaMnO3, thereby increasing specific surface area and redox property, but also generate new active phase CoMn2O4, thus accelerating reaction. Among all the as-prepared catalysts, CMO/LMO-0.5 exhibited admirable ethane removal efficiency with a T90 of 365 °C, a reaction rate of 0.46 mmol·g−1·h−1, a TOF value of 0.64 mmol·g−1·h−1, and excellent hydrothermal stability and reusability. Moreover, according to in situ DRIFTS, a possible pathway was proposed. This work can rationalize an alternative approach to develop an active catalyst for short-chain alkanes catalytic combustion or other catalytic systems.

The impact of support selection and Co loading amount on the catalytic performance for methane combustion

Methane (CH4) is a key component of natural gas and is essential for energy production and utilization. However, due to its strong greenhouse effect, efficient catalytic combustion methods are needed to convert it into CO2 and H2O. This study systematically evaluates the catalytic performance of Co, CoO, and Co3O4 in methane catalytic combustion, particularly highlighting the superior activity of Co3O4. To improve catalytic efficiency, this paper examines the effects of SiO2, Al2O3, and CeO2 as support materials using co-precipitation and impregnation methods. The results show a significant improvement in the catalytic activity of Co3O4 supported on CeO2, attributed to CeO2's unique redox properties and high oxygen storage capacity. Additionally, the study explores the impact of different loading amounts (5%, 10%, 15%, 20%) of Co3O4(x)-CeO2 catalysts on their performance. The optimal 10%wt Co3O4–CeO2 catalyst achieves methane conversion rates of 10%, 50%, and 90% at temperatures of 376 °C, 473 °C, and 578 °C, respectively, demonstrating exceptional stability during a 20-h stability test and the ability to adapt to fluctuations in CH4 concentrations in low-oxygen environments, while also exhibiting significant catalytic activity across a range of methane concentrations from 0.5% to 2.5%. These findings provide important theoretical and experimental guidance for the application of cobalt-based catalysts in CH4 combustion, paving the way for future catalyst design and optimization.

Synthesis of uniform-sized spherical monodisperse K2Ba[Ni(NO2)6] via polymer-assisted anti-solvent crystallization method for the enhanced catalytic pyrolysis of HNIW

Nitro complexes (NCs) have been selected as combustion catalysts for propellants due to their synergistic behavior. However, NCs prepared by traditional methods suffer from poor dispersion and irregular shape, which limit their catalytic potential. Hence, a polymer-assisted anti-solvent crystallization (PAASC) strategy was developed to fabricate potassium barium hexanitronickelate (K2Ba[Ni(NO2)6], PBHNN) crystals. In this method, emulsion particles created by mixing the solvent with the poor solvent serve as spherical templates. The particle size and monodispersity of PBHNN are controlled by PVP content. With 0.042 mol/L PVP, PBHNN were monodisperse with a particle size of 1.05±0.03 μm, which showed the best catalytic behavior for increasing the exothermic amount of hexanitrohexaazaisowurtzitane (HNIW) by 100.6 %. The high catalytic performance is due to the large specific surface area and improved contact efficiency. The in-situ TG-FTIR-MS test revealed that the procedure of PBHNN enhanced the pyrolysis of HNIW. The N-NO2 bonds of HNIW are weakened by the strong attraction of metal oxides to electrons, which accelerates the formation of NO2. Consequently, increased NO2 promotes subsequent oxidation reactions and improves the pyrolysis efficiency of individual HNIW. Therefore, the PAASC method is crucial for the fabrication of spherical monodisperse NCs with uniform particle size and high catalytic activity.

Tuning the oxygen storage capacity and oxygen release properties of CeO2-based catalysts for catalytic combustion of toluene

CeO2 with varied doping transition metal was investigated to understand the oxygen storage capacity and oxygen release property of CeO2-based catalysts for toluene combustion. The order of catalytic activity was as follows: CuCeOx ≈ CoCeOx > MnCeOx > FeCeOx > NiCeOx > ZrCeOx > CeO2. Kinetic studies showed that the reaction on CuCeOx proceed via an MvK mechanism and the oxygen of catalyst was crucial factor for the toluene combustion. H2-TPR and XPS showed the addition of transition metal to CeO2 could modify the surface lattice oxygen. Moreover, the oxygen storage capacity and oxygen release properties showed the transition metal additive not only change the amount of oxygen, but also affect the oxygen mobility. A linear relationship was observed between the catalytic activity and oxygen storage capacity. Diffuse reflectance infrared fourier transform spectroscopy showed the toluene first adsorbed on the surface of catalyst, and then reacted with oxygen of catalyst to form benzyl, benzoate and benzyl carbonate species. All these results provided a new strategy to develop high performance catalyst.

Theory-driven design of graphene-nickel gallate nanocomplex as functional catalyst for composite modified double base propellant

New graphene-nickel gallate nanocomplex (G-M-Ni) was designed, synthesized and characterized to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of propellant, structural analysis of catalyst and simulation results of quantum mechanics. The positive effect of G-M-Ni is not only reflected in the significantly increased burning rate, but also reflected in the reduction of friction sensitivity of composite modified double base (CMDB) propellant. The G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and the burning rate of propellant at 20 MPa enhanced from 23.15 to 29.07 mm·s−1. Besides, the friction sensitivity of propellant reduced from 64 % to 36 % after addition of 0.5% G-M-Ni. The positive effect of G-M-Ni on CMDB propellant combustion is mainly attributed to its promotion impact on nitroglycerin (NG) pyrolysis, which significantly increased the differential charge density and decreased the decomposition activation energy (from 1.89 eV to 1.38 eV). The gas products produced by the rapid pyrolysis of NG are conducive to the heat feedback between the gas phase and the combustion surface, which makes the propellant have higher burning rate, bright flame, thin dark zone and flocculated quenching surface morphology. The findings in this study confirm the potential of G-M-Ni as a functional combustion catalyst for CMDB propellants, which has guiding significance and inspiration for the development of new combustion catalysts from the view of molecular-level insights. Novelty and significance statementRecently, graphene based functional combustion catalysts have attracted much attention in the field of solid propellants due to their excellent catalytic combustion performance, reduced sensitivity, and improved mechanical properties. Herein, novel graphene-nickel gallate nanocomplex (G-M-Ni) were designed, synthesized and characterized to deal with the to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of CMDB propellant, structural analysis of new material and simulation results of quantum mechanics. By taking graphene as the benchmark, the G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and excellent effect on the reduction of friction sensitivity. The relationship between molecular structure of G-M-Ni and combustion characteristics of CMDB propellant were disclosed. The theory-driven design mode of this work may provide new pathways to tune combustion behaviors of CMDB propellants from the view of molecular-level insights.

Considerable enhancement of nanothermites propagation through worm-like expansion of expandable graphite

Metastable intermolecular composites (MICs) are known for their high energy density, high burn rate, and low diffusion distance, and they have various applications in military and civilian equipment and tasks. However, the introduction of binders, which facilitate shaping, during the processing of MICs for practical applications can lead to a decrease in the energy release rate and an increase in the required ignition energy. Herein, we incorporated graphene nanoplatelets (GNPs), multi-walled carbon nanotubes (MWCNTs), and expandable graphite (EG) into 90- wt% Al/CuO nanothermites stick using simple extrusion-based direct ink writing to improve their overall performance. The high-temperature expansion characteristics and unique structure after expansion caused EG to perform an important role during Al/CuO nanothermites system combustion, which effectively promotes heat transfer and considerably increases the burn rate (81.6%) and pressure rising rate (103.0%). This study demonstrated EG as a low-cost and efficient combustion catalyst for MICs and introduced a simple approach to modulate the energy release rate, combustion pressure and semiconductor bridge (SCB) ignition performance of MICs through incorporation of small amounts of carbon materials.

A highly active and stable palladium zeolite catalyst for wet methane combustion

Natural gas engines are the most viable alternative to diesel and gasoline ones. However, the current state-of-art catalyst, palladium (Pd) on alumina, for eliminating unburnt methane from engine exhaust suffers from high light-off temperature (> 400 °C) and poor water tolerance. Here we systematically investigated the effects of zeolite structure and Si/Al ratio, catalyst calcination temperature and extra-framework cation type on catalytic performance of zeolite-supported Pd catalysts for wet methane combustion to overcome these limitations. We found that a 3.0 wt% Pd catalyst supported on Na+-post-exchanged 500 °C-calcined IWV zeolite with a Si/Al ratio of 45 has a light-off temperature as low as 290 °C for methane combustion in the presence of 10 % water vapor while maintaining ca. 85 % methane conversion at 330 °C for 100 h. This study provides a new direction for bringing supported Pd catalysts close to real-world applications.

Preparation, characterization, and thermal decomposition catalytic activity of novel combustion rate catalysts

Abstract The study successfully synthesized a combustion catalyst consisting of copper atoms anchored onto a carbon black support. The 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20), 1,1-diamino-2,2-dinitroethylene (FOX-7), cyclotetramethylene-tetranitramine, and ammonium perchlorate energetic materials were studied and analyzed using high-temperature pyrolysis process and catalytic oxidation thermal decomposition kinetics analysis. The research results indicate that the addition of the catalyst CB@Cu significantly reduces the activation energy during the pyrolysis process of energetic materials, leading to an earlier decomposition temperature and a significant catalytic effect. After adding catalyst CB@Cu, the endothermic peaks of the three energetic materials shifted toward lower temperatures, but the magnitude of the movement was relatively small. The maximum thermal decomposition temperature has been reduced by 3–5°C compared to that before the addition of the catalyst. At lower temperatures, the catalyst has a better catalytic effect on the energetic materials. The catalyst indicates the formation of electron transfer and the presence of metal Cu ligands, increasing the number of active sites with energetic materials, making the heat release of energetic materials more concentrated and increasing the degree of thermal decomposition.

Exploration of TKX-50-M (M=Pb, Bi and Cu) as insensitive high-energy combustion catalysts of HMX-CMDB propellant

In order to deal with the long-standing contradiction between safety and performance for propellent combustion catalyst, the TKX-50-M (M=Pb, Bi and Cu) were designed, synthesized and characterized. The density, thermal decomposition, mechanical sensitivity and energy performance of the prepared TKX-50-M were studied systemically. By taking NTO-Pb as the benchmark, the TKX-50-M exhibited much better energetic and safety properties. Besides, the combination of TKX-50-Pb, TKX-50-Cu and carbon black is conductive to the combustion of HMX-CMDB propellant. The burning rate of HMX-CMDB propellant increases from 16.80 to 21.28 mm s−1 at 20 MPa, and the pressure index reduces from 0.87 to 0.39 in the pressure range of 10–20 MPa. The catalytic mechanism of TKX-50-M were explored according to the results of combustion wave structure, flame image and characteristics of burning out surface. The catalytic effect of TKX-50-Pb is mainly reflected in the gas phase region, and the introduction of TKX-50-Cu and carbon black shows a significant synergistic catalytic effect. The results of this study not only help to explore insensitive high-energy combustion catalyst, but also helps to improve the combustion, energy and safety performance of CMDB propellants.

Regulation of Catalysts on Tightly Packaged Solid Propellant Energetic Particles: High Combustion Performance with Low Temperature Sensitivity.

Although the effectiveness of combustion catalysts promoting the combustion performance of solid propellant (SP) was identified in many research studies, its regulation on the temperature sensitivity coefficient of burning rate (δp) has been rarely explored, where SP with low δp is a big challenge with little progress. Herein, several ammonium perchlorate (AP)-enriched (>70 wt %) pomegranate-structured SP energetic particles (SPPs), AP/nitrocellulose (NC)/Al (SPP), SPP/CoWO4-rGO (SPP-Co), SPP/Bi2WO6-rGO (SPP-Bi), and SPP/CuCo2O4/GO (SPP-Cu), were prepared by the electrospray granulation method, tightly packaging AP with high-efficiency catalysts to promote its reactivity and reduce temperature sensitivity. The pressurization rates of SPPs in a constant volume combustion chamber at 50, 0, and -40 °C were obtained to determine δp. The burning rates of SPP-Co, SPP-Bi, and SPP-Cu loose strips are 0.319, 0.312, and 0.356 m/s, which are increased by 11.1%, 8.7%, and 24.0% compared to that of SPP (0.287 m/s), respectively. The peak pressures and pressurization rates of SPP-Co, SPP-Bi, and SPP-Cu at 0 °C are increased by 18.8%, 10.1%, and 9.1% and 62.3%, 67.1%, and 64.1% compared with SPP, respectively, indicating that these catalysts significantly accelerate the combustion process. Compared with SPP, the δp of SPP-Co, SPP-Bi, and SPP-Cu decreased by 26.6%, 60.6%, and 24.7% at 0-50 °C and 19.5%, 61.6%, and 27.6% at -40-0 °C, respectively. It suggests that the Bi2WO6-rGO catalyst reduces the δp by 61% at -40-50 °C, exhibiting the optimal δp regulation performance. This research introduces a novel approach to lower the δp from the chemical by tightly packaging temperature-sensitive AP with high-efficiency catalysts.

Ce–Zr–Mn Oxide Catalysts for Soot Combustion: The Role of Preparation Method

Ce–Zr–Mn Oxide Catalysts for Soot Combustion: The Role of Preparation Method

Effect of Ba Addition on the Catalytic Performance of NiO/CeO2 Catalysts for Methane Combustion

Effect of Ba Addition on the Catalytic Performance of NiO/CeO2 Catalysts for Methane Combustion