Catalysts For Combustion Research Articles

The Affects of Ce Doping Cr\(_2\)O\(_3\) Based Catalysts Supported on Activated Carbon for 1,2-Dichloroethane Abatement

Hydrothermal method is used to prepare activated carbon (AC) supported chromium-based catalysts for the catalytic combustion of 1,2-dichloroethane (DCE). The physicochemical properties relating catalysts are evaluated by several characterization techniques such as XRD, SEM, XPS, N2 adsorption-desorption isotherms, H2-TPR and NH3-TPR. The outcomes demonstrated that the Cr2O3 is the perfect targeted base catalyst adding to the facts that the hydrothermal approach is an appropriate way to create catalysts with superior properties. The textural characteristics, reducibility, and acidity of the Cr-based catalysts were all enhanced by the addition of cerium (Ce) and AC. Nevertheless, the research shows how crucial the Ce doping amount is for adjusting the physicochemical characteristics and catalytic efficacy of Cr-based catalysts. The catalyst 20Ce-Cr/AC has the maximum catalytic activity when it came to DCE combustion, where its T50 and T90 attaining of 247°C and 269.5°C, correspondingly. This is explained by the ideal Ce doping level, which improves the redox characteristics and revealed more active sites.

Redox-induced controllable engineering of MnO2-MnxCo3-xO4 interface to boost catalytic oxidation of ethane

Multicomponent oxides are intriguing materials in heterogeneous catalysis, and the interface between various components often plays an essential role in oxidations. However, the underlying principles of how the hetero-interface affects the catalytic process remain largely unexplored. Here we report a unique structure design of MnCoOx catalysts by chemical reduction, specifically for ethane oxidation. Part of the Mn ions incorporates with Co oxides to form spinel MnxCo3-xO4, while the rests stay as MnO2 domains to create the MnO2-MnxCo3-xO4 interface. MnCoOx with Mn/Co ratio of 0.5 exhibits an excellent activity and stability up to 1000 h under humid conditions. The synergistic effects between MnO2 and MnxCo3-xO4 are elucidated, in which the C2H6 tends to be adsorbed on the interfacial Co sites and subsequently break the C-H bonds on the reactive lattice O of MnO2 layer. Findings from this study provide valuable insights for the rational design of efficient catalysts for alkane combustion.

Silica-assisted Pt1/CeO2 single-atom catalyst for enhancing the catalytic combustion performance of VOCs by inducing H2O activation

Due to the competitive adsorption of water and reactants at the active sites, especially the water toxicity of platinum-based single-atom catalysts, it is of great importance to improve the low-temperature activity and the water resistance of catalysts for the catalytic combustion of benzene. In this work, it was found that constructing a SiO2 shell layer on the catalyst not only "immobilized" the Pt single atoms, but also effectively weakened the adsorption of H2O on the Pt active sites, which resulted in excellent water resistance of the Pt single-atom catalysts. The comprehensive characterization results demonstrated that the participation of water molecules in the catalytic oxidation reaction of benzene could be effectively promoted by enhancing the strong metal-support interactions (SMSI) at the core-shell interface, which would change the electronic structure of the catalyst surface. As a result, the Pt1/CeO2@SiO2-4 catalyst with a Pt-O-Si active interface exhibits good activity (T = 190 °C) as well as excellent water resistance under the wet condition (10 vol%). This project provides a promising strategy for the design of Pt-based core-shell catalysts with excellent water resistance.

Novel strategy to regulate the geometric and electronic structure of Pt catalyst for efficient propane combustion

The geometric and electronic structure of Pt active sites plays a crucial role in determining the catalysts performance, but precise regulation remains challenging. Herein, we propose a novel approach to modulate the nature of Pt active sites by combining photo-deposition of Pt nanoparticles with ultra-low Mo loading (0.1 wt%) modification on Pt/SiO2 catalysts. The addition of ultra-low loading Mo promoter not only effectively reduces the size of Pt particles but also donates electrons to the Pt particles. Furthermore, the photo-deposited Pt particles exhibit a higher proportion of metallic Pt species, which is more stable than that metallic Pt species obtained by H2 reduction, compared to those prepared using traditional wetness impregnation methods. Propane oxidation activity evaluations confirm that the photo-deposited and Mo-modified Pt/0.1Mo/SiO2-P catalyst exhibits the highest activity among all the prepared catalysts. Combined with experiments of C3H8-TPSR and in-situ DRIFT spectra of propane oxidation, it is found that the Pt/0.1Mo/SiO2-P catalyst remarkably promotes propane activation and C-H bond cleavage due to the nature change of Pt active sites, and the presence of gaseous oxygen benefits propane cleavage on active sites. Our primary results provide a promising strategy for designing superior platinum catalysts by regulating Pt active sites nature for efficient propane complete oxidation.

Ammonia and toluene oxidation: Mutual activating effect of copper and cerium on catalytic efficiency

Copper and cerium containing hydrotalcite-like precursors Cux-Cey-Mg-Al were synthesized by mutual co-precipitation followed by calcination at 800 °C. The obtained mixed metal oxides were studied as catalysts for selective ammonia oxidation (NH3-SCO) and toluene combustion. Various techniques, such as temperature-programmed reduction with hydrogen, temperature-programmed desorption of toluene, scanning electron microscopy and reactive frontal chromatography were used to characterize the catalysts. Series 800-Cux-Ce2.5 showed the highest catalytic efficiency in both reactions, allowing complete NH3 and C7H8 conversion below 350 °C and 500 °C, respectively. CeO2 crystallites (12–18 nm), as well as dispersed CuO oxide forms were found in the most active samples. Both phases affect pollutants conversion, however, for ammonia oxidation the occurrence of Cu2+ is essential, while for toluene oxidation, the formation of Ce4+ is sufficient. Over the most active sample (800-Cu5-Ce2.5) the complete conversion in mutual oxidation of NH3 and toluene was achieved below 450 °C.

MOF-74 derivatives spinel CuCo2O4/C with d-band center modulation for accelerating ammonium perchlorate thermolysis

As one of main components of solid propellant, ammonium perchlorate (AP) shows slow sluggish decomposition kinetics with unconcentrated heat release. In the past, researchers have done a lot of work using spinel oxides as combustion modifiers to improve the combustion performance of AP. However, AP decomposition process is very complicated, and the relationship between intrinsic activity of cobalt-based spinel catalysts and AP combustion process is still unclear. In this paper, a series of cobalt-based spinel structure catalysts, MCo2O4/C, were prepared by pyrolysis of cobalt-containing bimetal MOF-74 and used as AP combustion catalysts. All of them showed excellent catalytic performance, among which CuCo2O4/C had the best catalytic activity. It effectively reduces the activation energy of the reaction, speeds up the reaction rate, and reduces the peak temperature of the AP decomposition reaction by 161.2 ℃, and the reaction rate k is 10.28 times of Co3O4/C. XPS and NH3-TPD tests indicate that substitution CoTd2+ with Cu2+ increases the ratio of Co3+/Co2+ and enhance interaction between NH3 and catalyst. The essential reason is that Cu–O-Co corner sharing effect changes electron distribution and enhances CoOh3+ Lewis acidity accompanied with the proximity of d-band center to EF by density functional theory calculations.

Boosting catalytic combustion of diesel soot particles over potassium-promoted CoMn-Co3O4 dual spinel structure catalyst

Catalytic oxidation is an effective method to remove soot particles from diesel exhaust, and the key aspect of this technology is to develop highly effective catalysts. In this work, a potassium-promoted dual spinel structure was prepared for soot elimination with the self-sacrificing template strategy. The highest activity was presented by the CoMn-0.2 H-10%K catalyst under a loose contact mode, with the temperature of soot conversion reaching 90% and turnover frequency value of 365 °C and 3.76×10−3 s−1, respectively. The catalyst was found to have a high content of oxygen vacancy and a superior ability for lattice oxygen migration, which led to elevated performance for soot combustion. The formation of K-OMS-2 at the interface between the CoMn spinel and the Co3O4 spinel was one of the reasons for the elevated lattice oxygen migration at low temperatures. This work provides an effective way to prepare transition metal catalysts for soot combustion.

Chemical compatibility of energetic metal complexes with polymers by thermal analytical techniques

Energetic metal complexes have been established to be effective combustion catalyst for energetic composites and propellants with improved performance. Chemical compatibility is an important aspect in the development of novel energetic composites which are related to safe processing, handling, and storage. In the present paper, the compatibility of energetic metal complexes [Zn(atrz)(DNBA)2(H2O)2]n (complex 1) and [Cd(atrz)(DNBA)2(H2O)2]n (complex 2) with Viton A and epoxy resin as polymer binder are studied by thermal analytical techniques. The compatibility was studied through vacuum stability test (VST), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) according to standardization agreement (STANAG) 4147 method. Furthermore, physicochemical methods including powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR) are used to support the thermal analytical methods. The VST results indicate that the volume of gases evolved for complex 1/Viton A, complex 1/epoxy resin, complex 2/Viton A, and complex 2/epoxy resin is found to be 0.545 mL/g, 0.86 mL/g, 0.403 mL/g, and 0.884 mL/g, respectively, indicating high compatibility with one another. According to the STANAG 4147 criteria, the DSC/DTG data demonstrate that the difference in Tmax is less than 2 °C for all the admixtures, suggesting that the polymer binders under investigation are compatible with complexes. TG results demonstrate that the mass loss difference is less than 4 % for all admixtures, indicating good compatibility. The essential additional information offered by the supplementary non-thermal FTIR and PXRD techniques confirm that no reaction occurs between metal complex and polymer. SEM micrographs exhibit that metal complex crystals are embedded in the polymer matrix.

Synthesis and testing of active and water resilient low temperature methane combustion catalysts

Synthesis and testing of active and water resilient low temperature methane combustion catalysts

Fabrication of porous and highly defective CeO2-based catalysts for soot combustion with the strategy of soft-template addition and matrix doping by multiple rare earth elements

In this study, aiming to optimize the reactivity of CeO2 for soot combustion, rare earth elements (La, Pr, Sm and Y) co-doped CeO2 catalysts were synthesized via polyvinylpyrrolidone (PVP) and glycine (GNC) combustion methods. The PVP-CeO2-Re catalyst maintains a high specific surface area (82.9 m2 g−1) and abundant porous structure, thus being able to enhance the soot contact efficiency. The co-doping of multiple rare earth ions improves also the redox properties of the catalyst and increases the surface defects/vacancies, which is crucial to form the active surface O2- and O22- species to participate in soot combustion. The oxygen exchange rate over the catalyst with gaseous O2 can be accelerated by raising the temperature, and the exchange mechanism changes from a mixture of the R1 and R2 mechanisms to a domination by the R2 mechanism. Notably, PVP-CeO2-Re catalyst shows not only excellent activity (T50=373 °C) but also good stability. Our work could provide some reference for the design of promising catalysts applied in diesel particulate filters.

Characterizing of Nano Activated Bio-Carbon of Sago Waste as a Homogeneous Combustion Catalyst

Alternative fuels were developed by blending crude coconut oil and bio-carbon nanoparticles. Bio-carbon, derived from sago waste via pyrolysis and ground using a ball mill, underwent FTIR testing to assess its energy absorption capabilities. SEM analysis was conducted to examine the surface morphology of bio-catalyst with and without crude coconut oil. The findings indicate that incorporating bio-catalyst can enhance mechanical properties, facilitating rapid heat absorption, as evidenced by reduced flashpoint and viscosity. In addition, the results show an increase in fuel mass, broadening of molecular contacts, increased reactivity, and increased heat absorption for easier ignition. This phenomenon indicates that bio-carbon of sago waste have great potential for biofuel use as a homogeneous combustion catalyst.

Modulation mechanism of Mn-O strength in α-MnO2 catalyst for high-efficiency catalytic combustion of propane

The cleavage of C-H with high energy impedes the catalytic combustion of propane. Herein, α-MnO2 with modulation of Mn-O strength by changing the calcination temperature was applied in propane catalytic combustion. α-MnO2 calcinated at 350 °C (α-MnO2-350) exhibited superior performance (T20=150 °C, T90= 220 °C) in propane oxidation due to the synergistic effect of oxygen vacancies (OVs) and Lewis acidity. Density functional theory (DFT) calculations revealed that the lowest o-vacancy formation energy on α-MnO2-350 (Evo=0.74 eV) with its lowest Mn-O strength prompted the existence of abundant OVs and propane oxidation. Moreover, the highest Lewis acidity in α-MnO2-350 displayed the strongest propane adsorption, promoting the activation of C-H. The mineralization of propane on α-MnO2-350 dropped steeply after 68 h while could recover to 90 % in long-term water vapor stability test owing to the H2O adsorbed at OVs and the carbonaceous intermediates adsorbed at the Lewis acid sites.

Combustion characteristics of water-oil emulsion droplets with special additives

Relevance. Fuel oil application in power plants is characterized by increased values of underburning and anthropogenic emissions. One way to reduce anthropogenic emissions is the use of oil-water emulsions. Also, additional specialized additives are used to reduce anthropogenic emissions and improve fuel combustion characteristics. Aim. To determine the optimal fuel oil additive to reduce anthropogenic emissions and ignition delay times. Methods. The following additives: ION-M, Rosneft R503V3, Rosneft R502V1 (relative mass concentration 0.5%) were added to the water-oil fuel. The physicochemical properties of fuel oil M-100, as well as the elemental composition of CHNSO, were determined. The rheological characteristics of water-oil fuel compositions were established. Using high-speed photography, the droplet ignition delay times were determined. Using the gas analyzer, it was possible to prevent anthropogenic emissions. Results and conclusions. The results of the study showed that the additive based on a special combination of positively and negatively charged ions (ION M) reduces ignition delay times by 20–60%, when the gas temperature varies in the range from 700 to 900 °C. The addition of the additive based on fatty vegetable acids (P502B3) reduced the ignition delay times by 7–10%, when the temperature changed in the range from 700 to 900 °C relative to water-oil fuel. It was found that when using the P502B1 additive in water-oil fuel, it was possible to reduce the ignition delay times by 15–50%. It was determined that in the presence of combustion catalysts, water binds with heavy hydrocarbons and thus the release of volatile substances occurs faster, i. e. the supplied heat is not wasted on heating water into droplets, but evenly affects the entire volume of fuel. The results of the study of anthropogenic emissions showed that the use of additives when burning water-oil fuel reduces the concentrations of CO, CO2, NO, SO2 by 8, 6, 10 and 13%, respectively, compared to fuel oil.

Effects of graphene organic iron nanocomplex on the pyrolysis and laser ignition performance of TKX-50

Novel graphene iron tannate and graphene iron gallate nanocomplex (G-D-Fe and G-M-Fe) were designed, prepared and characterized by SEM, EDS, FTIR, RAMAN and XPS equipment. The catalytic property of the G-D-Fe and G-M-Fe for energetic TKX-50 was explored by DSC, kinetic calculation and laser ignition. The synthesized G-D-Fe and G-M-Fe present a positive impact on pyrolysis and ignition combustion of TKX-50, resulting in the significantly reduced decomposition temperature, activation energy (Ea) and ignition delay time. After adding G-D-Fe (G-M-Fe), the first and second decomposition peak temperatures (TFDP and TSDP) of TKX-50 were decreased by 42.3 °C (43.9 °C) and 45.0 °C (49.6 °C), respectively. At the conversion degree of 0.2–0.8, the nonlinear kinetic data showed that after adding G-D-Fe and G-M-Fe, the Ea of TKX-50 decreased from 163.5 to 141.3 and 145.4 kJ·mol−1 respectively. Additionally, after adding G-D-Ni and G-M-Ni, the laser ignition delay time of TKX-50 was reduced from 58 ms to 26 ms and 28 ms, respectively. The possible catalytic mechanism of preferred combustion catalyst G-D-Fe was disclosed by in-situ FTIR and gas-phase MS-FTIR analysis. The results are helpful to broaden the catalysts for pyrolysis and ignition combustion of TKX-50 and to disclose the catalytic mechanism.

High-temperature resistant BaO-Y2O3 catalysts with different morphologies for NO decomposition and mechanism study

The high-temperature reaction is a common phenomenon in combustion society, and its catalytic response remain a tremendous challenge hampered by the activity and resistance of the catalyst to high temperatures exceeding 1000 ℃. Three distinct forms of BaO-Y2O3 catalysts—nanosphere, nanorod, and rod—were created using a hydrothermal method and high-temperature annealing to enable direct decomposition of NO. To gather reaction-relevant structural and property information for BaO-Y2O3, we combined reactor activity measurements, chemisorption and DFT studies to elucidate NO high-temperature decomposition process and pinpoint the critical role of oxygen vacancy. We have systematically clarified the increasing favorability of NO decomposition on the nano-catalysts (nanospheres and nanorods) at high temperatures is through stable lattice structure, large specific surface areas, high porosity, and active Ba–O–Y bond. Due to the attraction of electrons gathering in vacancies to NO molecules, oxygen vacancies created in situ at high temperatures, as validated by O2-TPD and density functional theory (DFT) calculations, are advantageous for NO adsorption and decomposition. Moreover, N2 formation pathway over Ba-Y2O3(111) structure is revealed by DFT calculations that NO molecules are apt to be caught by active sites, the region of Ba–O–Y, resulting in the production of N2O2 intermediate and its subsequent bond breaking to N2O as well as N2. In situ DRIFTS experiment further confirms the reaction mechanism via the detected adsorbed species, and clarify the significance of NO2− to O2 formation. In a nutshell, the synthetic combustion catalysts are effective in high-temperature environments that contribute to de-NOx combustion, and the insights into the adsorption configurations of reactant and intermediates unlock fundamental understanding for emissions gas chemistry.

Inhibition effect of sulfation on Pt/TiO2 catalysts in methane combustion

Inhibition effect of sulfation on Pt/TiO2 catalysts in methane combustion

Highly Active and Stable Pd/MgAl2O4 Catalysts for Methane Catalytic Combustion

Mesoporous MgAl2O4 is synthesized via a novel sol–gel combustion method and the concentration of oxygen defects on the surface is modulated through varying the calcination temperature (850, 900, 1000, and 1100 °C). Notably, the 1Pd/MgAl2O4‐1000 catalyst exhibits superior catalytic activity and stability. The turnover frequency (TOF) for 1Pd/MgAl2O4‐1000 is 0.079 and 0.058 s−1 under dry conditions (300 °C) and wet conditions (380 °C), respectively. The results of H2 temperature‐programmed reduction and X‐Ray photoelectron spectroscopy reveal that the principal active species within the Pd/MgAl2O4‐y catalyst is PdO. Specifically, the Pd–MgAl2O4‐1000 catalyst exhibits the lowest temperature reduction peak (120 °C) and the highest redox capability. Additionally, O2 temperature‐programmed oxidation further elucidates that PdOx species in the Pd/MgAl2O4‐1000 catalyst is prone to decomposition and the resultant palladium metal is readily reoxidized. Consequently, the rapidity of the redox cycle between PdO and Pd0 emerges as a pivotal factor in CH4 catalytic combustion. Furthermore, a correlation analysis among catalyst particle size, oxygen defect concentration, and TOF is conducted. The findings illustrate a distinct volcano‐shaped curve in the relationship between oxygen defect concentration and TOF for the 1Pd/MgAl2O4−y catalysts. A comparable trend is also evident in the correlation between Pd particle size and TOF.

Efficient catalytic combustion of propane at low temperature based on ignition effect caused by amorphous atomic-layer Pt clusters

Developing highly active catalysts for hydrocarbon combustion at low temperatures is paramount but yet challenging. The crystal form of carrier and the dispersion degree of active species have great influence on propane combustion catalysts, but its internal mechanism is still unclear. In this study, the amorphous atomic-layer Pt clusters (AL) and Pt single atoms (SA) on TiO2 with various crystal phases were prepared and used as propane combustion catalysts, where the as-synthesized Pt/a-TiO2 catalyst with atomic-layer Pt clusters exhibited better catalytic performance. The Pt/a-TiO2-AL could achieve a 90 % propane conversion (T90) at 230 °C, with the highest reaction rate (39.57 × 10−7 mol g−1 s−1) and TOF value (7.72 × 10−2 s−1) at 240 °C. Kinetic studies showed that oxygen had a lower inhibitory effect on Pt/a-TiO2-AL compared to that on the Pt/p-TiO2-AL and Pt/r-TiO2-AL catalysts; simultaneously, the Pt/a-TiO2-AL catalyst presented lower apparent activation energy compared with Pt/a-TiO2-SA. DFT results showed that atomic-layer Pt clusters on TiO2 had the lower formation energy of oxygen vacancy than Pt single atoms due to the synergistic effect between adjacent exposed Pt atoms in the fully exposed atomic-layer Pt clusters, which had a higher activation capacity for oxygen and thus accelerated propane combustion through the ignition effect (rapid activation of oxygen and rapid combustion of propane). Our primary results provide a promising approach for the creation of high-efficiency Pt-based catalysts, specifically tailored for the catalytic combustion of volatile organic compounds (VOCs).

Preparation and properties of nano B/NC/AP@F2602 double-layer energetic fiber

The nano-boron powder (n-B) exhibits remarkable efficacy as a combustion catalyst, making it a prime candidate for use in solid propellant metal burners. Nevertheless, throughout the storage phase, the surface of n-B powder is prone to oxidation and substantial agglomeration, resulting in challenges with ignition and incomplete energy dissipation when utilizing boron powder. In this study, we utilized the coaxial electrospinning technique to produce nanofibers comprised of nano-boron /nitrocellulose/ammonium perchlorate@fluororubber (n-B/NC/AP@F2602), with the nano boron uniformly distributed within the core-shell fibers. In the course of combustion, the fibrous composite of n-B/NC/AP@F2602 undergoes an escalation in the rates of energy output and energy release, owing to the constraints imposed by external F2602((C₂H₂F₂)n and (C₃F₆)n). The n-B/NC/AP@F2602 demonstrates a 1.4-fold increase in peak pressure and a 3.6-fold increase in maximum boost rate when compared to the n-B/NC/AP. The energy performance evaluation results reveal that the mean molecular weight (MC) of combusted products from n-B/NC/AP@F2602 is 29.2 g·mol−1, representing a substantial increase compared to that of n-B/NC/AP. The aforementioned findings exemplify that coaxial electrospinning is an exceedingly efficacious technique for enhancing nanostructures, thereby amplifying the reactivity of energetic particles and offering novel insights into their application in energetic materials.

Nanocrystalline FeMnO3 Powder as Catalyst for Combustion of Volatile Organic Compounds.

The paper shows the obtaining of nanocrystalline iron manganite (FeMnO3) powders and their investigation in terms of catalytic properties for a series of volatile organic compounds. The catalyst properties were tested in the catalytic combustion of air-diluted vapors of ethanol, methanol, toluene and xylene at moderate temperatures (50-550 °C). Catalytic combustion of the alcohols starts at temperatures between 180 °C and 230 °C. In the case of ethanol vapors, the conversion starts at 230 °C and increases rapidly reaching a value of around 97% at 300 °C. For temperatures higher than 300 °C, the degree of conversion is kept at the same value. In the case of methanol vapors, the conversion starts at a slightly lower temperature (180 °C), and the degree of conversion reaches the value of 97% at a higher temperature (440 °C) than in the case of ethanol, and it also remains constant as the temperature increases. Catalytic combustion of the hydrocarbons starts at lower temperatures (around 50 °C), the degree of conversion is generally lower, and it increases proportionally with the temperature, with the exception of toluene, which shows an intermediate behavior, reaching values of over 97% at 430 °C. The studied iron manganite can be recommended to achieve catalysts that operate at moderate temperatures for the combustion of some alcohols and, especially, ethanol. The performance of this catalyst with regard to ethanol is close to that of a catalyst that uses noble metals in its composition.