Catalysts For Combustion Research Articles

Construction of nanoflowers combustion catalyst NiO@g-C3N4 for improving thermal decomposition performance of AP

Thermal decomposition of ammonium perchlorate (AP) typically requires high temperatures and activation energy, but the introduction of combustion catalysts will improve its thermal decomposition performance. Therefore, it is crucial to rationally design combustion catalysts for enhancing the thermal decomposition performance of AP. Herein, 3D NiO nanoflowers@2D graphite-phase carbon nitride (g-C3N4) nanosheets (NiO@x%CN, x = 1, 3, 5, 7, 9) composite catalysts were constructed by solvothermal and calcination methods, and characterized by a series of analyses. NiO@5%CN displayed the best ability to catalyze the thermal decomposition of AP, which reduced the high decomposition temperature of AP by 113.8 °C and the activation energy by 21.67 kJ mol−1. The combustion rate of NiO@5%CN-CSP has increased by 118 % compared to that of composite solid propellants. This work provides a new insight for the design of NiO-based high-efficiency combustion catalysts.

Adjustment mechanism of Co3+ performance in Co3O4-LaOx catalyst for high-efficiency catalytic combustion of toluene

This study employed the sol–gel method to fabricate Co-La catalysts under various calcination temperatures were used to the catalytic oxidation of toluene. The investigation on the impact of calcination temperature on the Co3+ content and the resultant catalytic activity was studied. The CoLa-550 catalyst (calcined at 550 °C) exhibited the highest concentration of Co3+ and optimal catalytic performance for toluene oxidation (T90 = 195 °C). In situ DRIFTS technology confirmed the ring-opening of benzoic acid was the rate-determining step. Comprehensive analyses utilizing XPS, H2-TPR, and O2-TPD revealed the significance of optimizing Co3+ content to enhance catalytic activity. This research provided crucial theoretical and experimental support for the development of efficient non-noble metal catalysts.

Enhancing combustion performance of solid propellants using synergistic effect of energetic metal–organic framework with cage-like [Bi6(µ3-O)3(µ3-OH)5] clusters and copper-iron hetero-metallic compound

This study explores the potential of energetic metal–organic frameworks (E-MOFs) to enhance the combustion performance of solid propellants. A {[Bi6O3(tza)5(NO3)2(OH)5]·H2O}n (Bi-MOF) incorporating the energetic ligand tetrazole-1-acetic acid (Htza) was synthesized and evaluated for structural characteristics and properties. The catalytic thermal decomposition of cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX) by mixed systems was investigated. These systems consisted of Bi-MOF and copper-iron hetero-metallic compound ({[CuFe3O(tza)6(H2O)3]·Cl·(NO3)2·4H2O}n, CuFe-MOF), previously reported by our group in different ratios. The effect of the mixed system with the highest synergy index on the combustion performance of composite modified double-base propellant (RDX-CMDB) and nitrate ester plasticized polyether propellant (HMX-NEPE) was investigated. The impact of varying carbon black (CB) contents on the catalytic performance of the mixed system was also examined. The results showed that Bi-MOF exhibits good thermal stability (Tdec = 226.9 °C) and insensitivity (IS>40 J, FS>360 J). The mixed system, comprising Bi-MOF and CuFe-MOF in a 2:1 ratio (M2), exhibited the highest synergistic indices (3.35 and 3.24) on thermal decomposition for RDX and HMX. RDX-CMDB and HMX-NEPE propellant formulations containing M2 and a small amount of CB exhibited significant improvements in combustion performance. RDX-CMDB propellant exhibited up to an 80.6 % increase in burning rate and up to a 59.6 % reduction in pressure index. The pressure indices of NEPE without and with aluminum were reduced from 0.65 and 0.50 to 0.38 and 0.40, respectively (10–20 MPa, 1–20 MPa). These findings highlight the promise of the mixed system, formed by Bi-MOF and CuFe-MOF, as a potential combustion catalyst for RDX-CMDB and HMX-NEPE propellants.

Low-Temperature Methane Combustion Using Ozone over Coβ Catalyst.

Catalytic methane (CH4) combustion is a promising approach to reducing the release of unburned methane in exhaust gas. Here, we report Co-exchanged β zeolite (Coβ) as an efficient catalyst for CH4 combustion using O3. A series of ion-exchanged β zeolites (Co, Ni, Mn, Fe, and Pd) are subjected to the catalytic test, and Coβ exhibits a superior performance in a low-temperature region (<100 °C). The results of X-ray absorption spectroscopy (XAS) and catalytic tests for Coβ with different Co loadings indicate the isolated Co species is the plausible active site. The reaction mechanism of CH4 combustion over the isolated Co2+ cation is theoretically investigated by the single-component artificial force-induced reaction (SC-AFIR) method to thoroughly search for possible reaction routes. The resulting path toward CO2 formation shows an activation energy of 73 kJ/mol for the rate-determining step and an exothermicity of 1025 kJ/mol, which supports the experimental results. During a long-term catalytic test for 160 h without external heating, the CH4 conversion gradually decreases from 80 to 40%, but the conversion fully recovers after dehydration at 500 °C (0.5 h). The copresence of H2O and CO exhibits a negative impact on the catalytic activity, while NO and SO2 do not markedly change the catalytic activity.

Facile preparation of alkali metal‐modified hollow nanotubular manganese‐based oxide catalysts and their excellent catalytic soot combustion performance

AbstractThe soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment, so treating diesel engine exhaust is critical. At present, the most effective method for eliminating soot particles is post‐treatment technology. Preparation of economically viable and highly active soot combustion catalysts is a pivotal element of post‐treatment technology. In this study, different single‐metal oxide catalysts with fibrous structures and alkali metal‐modified hollow nanotubular Mn‐based oxide catalysts were synthesized using centrifugal spinning method. Activity evaluation results showed that the manganese oxide catalyst has the best catalytic activity among the prepared single‐metal oxide catalysts. Further research on alkali metal modification showed that doping alkali metals is beneficial for improving the oxidation state of manganese and generating a large number of reactive oxygen species. Combined with the structural effect brought by the hollow nanotube structure, the alkali metal‐modified Mn‐based oxide catalysts exhibit superior catalytic performance. Among them, the Cs‐modified Mn‐based oxide catalyst exhibits the best catalytic performance because of its rich active oxygen species, excellent NO oxidation ability, abundant Mn4+ ions (Mn4+/Mnn+ = 64.78%), and good redox ability. The T10, T50, T90, and CO2 selectivity of the Cs‐modified Mn‐based oxide catalyst were 267°C, 324°C, 360°C, and 97.8%, respectively.

Introducing attapulgite to prepare manganese-based monolithic catalyst for catalytic combustion of toluene

A series of attapulgite-loaded manganese oxides cordierite monolithic catalysts with different KMnO4/Mn(NO3)2 molar ratios (3:1, 1:1, and 1:3 for KMnO4/Mn(NO3)2, respectively) were prepared by a hydrothermal-ball mill impregnation method. According to the analysis of the characterization findings, the main active species of the catalyst was Mn4+ species. By incorporating acid-treated attapulgite (HATP) and adjusting the molar ratio of KMnO4/Mn(NO3)2, the content of Mn4+ and surface-adsorbed oxygen species on the catalyst surface increased, subsequently enhancing catalytic activity at low temperatures. Experimental results revealed that the Mn/HATP/cordierite catalyst with a KMnO4 to Mn(NO3)2 molar ratio of 3:1, Mn loading amount of 30 wt%, and active coating deposition of 250 g/L exhibited the highest catalytic activity, achieving a 90 % conversion of toluene at 298 °C (T90 = 298 °C, GHSV = 10000 h−1). These findings will provide valuable support for the design of highly efficient monolithic catalysts for toluene removal.

Constructing asymmetric active Fe3+-OV-Mn4+ sites at the Fe2O3-MnO2 interface for low-temperature soot combustion

Promoting the generation of reactive oxygen species by adjusting the strength of metal-oxygen bonds and constructing interfacial active sites has been proven to effectively enhance soot combustion. Herein, Fe2O3-MnO2 bimetallic oxides (FMO) with a heterogeneous interface were prepared using a simple PBA (Prussian blue analogue) derivation method. The catalysts exhibited superior active oxygen content and strong electron transport capacity. The Fe3+-OV-Mn4+ structure, an asymmetric oxygen vacancy, formed at the interface, and the strength of the metal-oxygen bonds was further regulated at different calcination temperatures, significantly activating lattice oxygen. The FMO-HA catalyst showed the highest activity, with soot conversion temperatures reaching 90 % at 289 °C under tight contact and 382 °C under loose contact. This work offers a dual regulatory strategy to enhance the production of reactive oxygen species and proposes a rational design for high-performance catalysts for soot combustion.

Theory-driven design of graphene schiff base iron nanocomplex as catalyst for composite propellant

New graphene Schiff base iron nanocomplexes (S-792-Fe, S-550-Fe, and S-590-Fe) were designed and fabricated based on investigations of reactions mechanisms of AP pyrolysis, structural analysis of new materials and simulation results of quantum mechanics to deal with the long-standing contradiction between safety and performance for composite propellent combustion catalyst. By taking traditional catalyst Catocene as the benchmark, the S-550-Fe nanocomplexes exhibited competitive catalytic performances, much better anti-migration properties and significantly reduced impact and electrostatic sensitivities. After adding S-550-Fe, the burning rate of propellant enhanced from 13.87 to 19.77 mm s−1 at 15 MPa, and the impact and electrostatic sensitivities are improved to 50.2 cm and 172.12 mJ, respectively. The excellent catalytic performance of S-550-Fe is closely related to its molecular structure, which is manifested by an increase in charge density and a decrease in NH3 oxidation energy barriers. The promotion effects of S-550-Fe on desorption and oxidation of NH3 from the surface of AP is conducive to the rapid and complete pyrolysis of AP, which is reflected in the improvement of combustion rate and temperature gradient. The theory-driven design mode of this work may provide new pathways to tune combustion behaviors of composite propellants from the view of molecular-level insights.

Robust Ru/Ce@Co Catalyst with an Optimized Support Structure for Propane Oxidation.

Short carbon chain alkanes, as typical volatile organic compounds (VOCs), have molecular structural stability and low molecular polarity, leading to an enormous challenge in the catalytic oxidation of propane. Although Ru-based catalysts exhibit a surprisingly high activity for the catalytic oxidation of propane to CO2 and H2O, active RuOx species are partially oxidized and sintered during the oxidation reaction, leading to a decrease in catalytic activity and significantly inhibiting their application in industrial processes. Herein, the Ru/Ce@Co catalyst is synthesized with a specific structure, in which cerium dioxide is dispersed in a thin layer on the surface of Co3O4, and Ru nanoparticles fall preferentially on cerium oxide with high dispersity. Compared with the Ru/CeO2 and Ru/Co3O4 catalysts, the Ru/Ce@Co catalyst demonstrates excellent catalytic activity and stability for the oxidation of propane, even under severe operating conditions, such as recycling reaction, high space velocity, a certain degree of moisture, and high temperature. Benefiting from this particular structure, the Ru/Ce@Co (5:95) catalyst with more Ce3+ species leads to the Ru species being anchored more firmly on the CeO2 surface with a low-valent state and has a strong potential for adsorption and activation of propane and oxygen, which is beneficial for RuOx species with high activity and stability. This work provides a novel strategy for designing high-efficiency Ru-based catalysts for the catalytic combustion of short carbon alkanes.

Patterns of Formation of Binary Cobalt–Magnesium Oxide Combustion Catalysts of Various Composition

In order to establish the formation patterns of the Co–Mg oxide system, samples with different Co:Mg ratios and heat treatment temperatures were synthesized and studied. A study of the samples confirmed the phase transition of MgxCo2–xO4 spinels into the corresponding solid solutions at 800–900 °C. The similarity of the formation patterns for different compositions is shown. The rocksalt oxide in low-temperature samples is an anion-modified paracrystalline phase that forms a “true” solid solution only upon spinel decomposition. The TPR profiles of the decomposed Co3O4 spinel show surface Co3O4 peaks and a wide peak corresponding to the well-crystallized CoO, while partial Co3O4 TPR up to 380 °C results in dispersed and amorphous CoO. The high-temperature non-stoichiometric samples are poorly reduced, indicating their low oxygen reactivity. Spinel reoxidation after heat treatment to 1100 °C by calcination at 750 °C showed complete regeneration for MgCo2O4–Co3O4 samples and its absence in case of an excess of MgO relative to stoichiometry.

Boosting the removal of diesel soot particles by regulating the Pr−O strength over transition metal doped Pr6O11 catalysts

The content of active lattice oxygen and oxygen vacancies is crucial for the catalytic oxidation of soot. Herein, we adjust the Pr-O bond strength in Pr6O11 by doping several common transition metals (Mn, Fe, Co, Ni) to promote the formation of oxygen vacancies and the activation of lattice oxygen. This strategy does not compromise its crystal structure, allowing for improved catalytic performance while maintaining stability. The Mn-doped Pr6O11 catalyst shows the best soot catalytic oxidation performance. Its T50 (the temperature of soot conversion reaching 50 %) value is 396 °C under loose contact. Further characterizations and density functional theory (DFT) calculations demonstrate that PMO possesses a large specific surface area. Additionally, the weakening the strength of the Pr-O bond leaded to an increase in oxygen vacancies, which in turn enhanced the redox ability of catalyst. This work will provide a reference for the development of Pr-based catalysts for soot combustion.

Energetic transition metal complexes based on 1‐allylimidazole and nitrocyanamide: Syntheses, characterizations and catalytic performances on the thermal decomposition of ammonium perchlorate

AbstractTo explore combustion catalysts for solid propellants, four novel energetic coordination compounds were prepared with the anion of nitrocyanamide (NCA) as the ligand and 1‐allyl‐imidazole (AIM) as the ligand, and transition metals Mn, Co, Ni, and Cu as the central ions. The structures of these compounds were [Mn(AIM)4] (NCA)2 (1), [Co(AIM)4](NCA)2 (2), [Ni(AIM)4](NCA)2 (3), [Cu(AIM)4](NCA)2 (4). The results showed that all of the compounds possessed high energy density, and compound 2 had a mass energy density (Eg) of 17.9 kJ g−1 and a volume energy density (Ev) of 25.59 kJ cm−3. The catalytic effect of these compounds on the thermal decomposition of ammonium perchlorate (AP) was studied using DSC. The addition of 5 % catalyst to AP samples advanced the high‐temperature decomposition temperature and significantly increased the heat release. Compound 4 exhibited the best catalytic performance, with an increased heat release of 1739 J g−1, decomposition temperature advanced by 88.2 °C, and activation energy reduced to 74.74 kJ mol−1. These results demonstrate the potential of these compounds as combustion catalysts for solid propellants.

Removal and complete combustion of 1,4-dioxane in water by a two-step reaction combining adsorption and catalytic combustion

Catalytic wet air oxidation is not so effective to decompose 1,4-dioxane in water, while there have been several studies on this reaction. As an alternative, we propose a two-step purification system for removal and complete combustion of 1,4-dioxane, where the first step is removing 1,4-dioxane from water by adsorption, and in the second step, the adsorbent is heated to release 1,4-dioxane, and the released 1,4-dioxane is completely combusted by gas-phase catalytic reaction. We had searched for adsorbents and combustion catalysts suitable for the system and found a high-silica MFI zeolite and Pt/SiO2, respectively. The high-silica MFI zeolite adsorbed up to 121 mg g−1 of 1,4-dioxane, and 1.1 mmol L−1 of 1,4-dioxane in water was almost completely removed by 10 g L−1 dose. The zeolite was reusable for adsorption-desorption cycles at least five times without any loss of the performance. Pt/SiO2 was highly active for the complete combustion of 1,4-dioxane even at 200 °C. By using the high-silica MFI zeolite and Pt/SiO2, we conducted the release of 1,4-dioxane from the zeolite by heating and the gas-phase catalytic combustion of 1,4-dioxane using two reactors connected in series, which were filled with the zeolite and Pt/SiO2, respectively, and demonstrated that all 1,4-dioxane was released by 300 °C and was completely combusted in the upstream and downstream reactors, respectively.

Mn/carbon aerogels derived from the water-induced self-assembly of UIO-66 (Mn) for the thermal decomposition of ammonium perchlorate.

In solid propellants, combustion catalysts play a crucial role. Here, we introduce a convenient method for the self-assembly of UIO-66 (Mn) in the presence of water, leading to the preparation of Mn/C aerogels. The aerogels were successfully utilized in the thermocatalytic decomposition of ammonium perchlorate (AP). The results indicate that the incorporation of 2% mass fraction of Mn/C aerogels enhances the peak temperature of AP decomposition by approximately 87.5°C. Mn/C aerogels demonstrate excellent catalytic performance. In combination with kinetics, we propose a thermal catalytic mechanism.

Identifying the active sites and their interaction mechanism in the CO catalytic combustion process over Co3O4

Co3O4 is one of the most promising catalysts for CO catalytic combustion. Nevertheless, the roles of Co2+ and Co3+ in the catalytic combustion process are still incompletely explored. Existing studies mostly focused on the role of Co3+, but the role of Co2+, and the interactions between the Co3+ and Co2+ are ignored. The catalytic activity of different Co sites is always affected by the electronic structure and the adsorption ability towards gas molecule, but clarifying the role of a single site is difficult due to the coexistence of Co2+ and Co3+. Herein, for exploring the role of single Co2+ or Co3+ site and their interaction, the Co2+ and Co3+ sites were replaced by Zn2+ and Al3+, respectively, which are more inert in CO catalytic combustion. According to catalytic activity measurement, the catalytic performance follows the order that: Co3O4(T90 = 153 °C) > ZnCo2O4(T90 = 189 °C) > CoAl2O4(T90 = 292 ℃). The experimental and calculation results showed that both Co2+ and Co3+ could act as active sites for CO catalytic combustion. CO and O2 are more prone to be absorbed over Co3+ and Co2+ sites, respectively. Co2+ and Co3+ make adsorbed oxygen and surface lattice oxygen highly reactive, respectively. The interaction between Co3+ and Co2+ is also important. The coexistence of Co2+ and Co3+ could increase the ratio of lattice oxygen and avoid the competitive adsorption between CO and O2, thereby Co3O4 showed the excellent catalytic performance.

Silicate-induced high-temperature-resistant small-crystallite ceria support enhancing palladium-catalyzed low-concentration methane combustion

High-performance Pd/CeO2 catalysts for the purification of low-concentration methane in waste gases by catalytic combustion have long been pursued, given that methane is a potent greenhouse gas. The reduction in ceria oxygen supply and palladium dispersion, caused by ceria crystallite sintering, deactivates the catalyst. Here, we report an enhanced palladium catalyst supported on a silicate-induced small-crystallite ceria (7.2 nm) calcined at 800 °C, compared to the pristine ceria (50.7 nm). The catalyst was coated on a cordierite monolith for 0.1 vol% methane combustion, achieving 90 % methane conversion at 336 °C, which is 84 °C lower than the temperature required for Pd/CeO2 reference. The small-crystallite ceria exhibited a high oxygen supply capacity due to abundant oxygen vacancies, facilitating the conversion of carbon-containing intermediates from methane dissociation on palladium species, thereby enhancing the catalyst’s intrinsic activity. The catalyst, with increased palladium dispersion, demonstrated a methane reaction rate 6.7 times higher than that of the Pd/CeO2 at 280 °C. This study provides new insights into designing highly efficient Pd/CeO2-based catalysts for low-concentration methane combustion.

Mn-Ag bimetals supported on plate-like ZSM-5 as efficient and stable catalysts for the catalytic combustion of toluene: Synergistic effects and catalytic mechanisms

Ag-modified MnO2 loaded on plate-like ZSM-5 (PZ5) with different Ag/Mn ratios were synthesized by an in-situ growth method and used as catalysts for toluene combustion, as a probe molecule of volatile organic compounds (VOCs). The results showed that Ag doping greatly enhanced the toluene combustion activity (Mn50Agy/PZ5). Among them, Mn50Ag0.04/PZ5 showed the highest catalytic activity for toluene combustion with 90 % conversion of toluene at 234 °C (T90), and the reaction rate calculated per unit mass of Mn was 1.22×10−7 at 220 °C, which was 2.7 times higher than that of MnO2. In addition, Mn50Ag0.04/PZ5 exhibited excellent long-term stability and water resistance. Various characterizations indicated that the excellent performance of Mn50Ag0.04/PZ5 was attributed to its higher Mn2++Mn3+/Mn4+ ratios, higher reducibility, and more active surface adsorbed oxygen species. Finally, in-situ DRIFTS studies confirmed that Ag doping did not alter the catalytic combustion pathway of toluene over the Mn50Ag0.04/PZ5 catalyst but could accelerate the rate of conversion of toluene to the final products because the transfer of electrons from Ag+ to lattice oxygen persuaded the weaken of the Mn-O bond, and then made it easier for bulk lattice oxygen to migrate towards the Ag-MnO2 interface or catalysts’ surface, thus showing the better catalytic performance for toluene combustion.

Mechanistic insights into the support effects of Cu catalysts in hydrogen combustion

Mechanistic insights into the support effects of Cu catalysts in hydrogen combustion

Electron transferring with oxygen defects on Ni-promoted Pd/Al2O3 catalysts for low-temperature lean methane combustion

Methane (CH4) is the second most consequential greenhouse gas after CO2, with a substantial global warming potential. The CH4 catalytic combustion offers an efficient method for the elimination of CH4. However, improving the catalytic performance of Pd-based materials for low-temperature CH4 combustion remains a big challenge. In this study, we synthesized an enhanced Pd/5NiAlOx catalyst that demonstrated superior catalytic activity and improved water resistance compared to the Pd/Al2O3 catalyst. Specifically, the T90 was decreased by over 100 °C under both dry and wet conditions. Introducing Ni resulted in an enormously enhanced number of oxygen defects on the obtained 5NiAlOx support. This defect-rich support facilitates the anchoring of PdO through increased electron transfer, thereby inhibiting the production of high-valence Pd(2+δ)+ and stimulating the generation of unsaturated Pd sites. Pd0 can effectively activate surface oxygen and PdO plays a significant role in activating CH4, resulting in high activity for Pd/5NiAlOx. On the other hand, the increased water resistance of Pd/5NiAlOx was mainly due to the generation of *OOH species and the lower accumulation of surface -OH species during the reaction process.

Crystalline phase-modulated PtOx nanoparticles exhibit superior methane combustion performance and sulfur poisoning resistance: Multi-interaction regulation

Up to now, methane combustion catalysts generally suffer from issues such as poor reaction stability and susceptibility to sulfur poisoning, which have become the key factors restricting their application, so it is necessary to construct catalysts with excellent chemical stability of the active center and strong sulfur resistance. Here, we showed the crystal phase-modulated state of PtOx nanoparticles (PtOx NPs) on TiO2 and investigated their effects on the reactivity of methane catalytic combustion and anti-SO2 poisoning properties. It was found that Pt/r-TiO2 showed superior activity, stability, and resistance to SO2 poisoning. Transmission electron microscope (TEM) images showed that the PtOx NPs on the surface of r-TiO2 were much more stable than a-TiO2 for the reason that the Ostwald ripening of PtOx NPs on a-TiO2 was facilitated due to the strong metal-support interaction (MSI) between PtOx NPs and TiO2 and the low migration energy of the PtOx NPs on TiO2, while they were moderate of Pt/r-TiO2, and then the active sites were stabilized during methane combustion. The activity was controlled by the size and electronic structure of PtOx NPs, which were stable on the surface of r-TiO2 with a higher Pt4+ content, and the density functional theory (DFT) calculations further revealed the role of r-TiO2 in increasing the quantities of surface oxygen vacancies. Moreover, the SO2 tolerance of Pt/r-TiO2 was also the best among all kinds of Pt-based catalysts prepared, which was attributed to the minimal adsorption energy (Ead) of SO2 on r-TiO2, and the absence of sulfate and sulfite deposition on the Pt/r-TiO2 catalyst confirmed by TGA and in-situ DRIFTS studies on SO2 adsorption. In this research, the anti-SO2 poisoning and reaction stability were realized by adjusting the interaction between SO2, active components, and supports, which provided a new insight for the design of stable Pt-based SO2-resistant catalysts.