Catalytic Combustion Performance Research Articles

Effects of Cu2O morphology on the performance of CO self-sustained catalytic combustion

Self-sustained catalytic combustion is a sustainable approach to deal with exhaust gas with high concentration CO, and revealing its reaction process is necessary and challenging. Herein, cube (Cu2O-C), octahedron (Cu2O-O) and dodecahedron (Cu2O-D) exposing different crystal planes were used to explore the catalytic combustion mechanism. The catalytic combustion can be self-sustained on the Cu2O surface and the activities decrease in the order of Cu2O-O > Cu2O-D > Cu2O-C, contributing to the different exposing planes with (1 1 1), (1 1 0) and (1 0 0), respectively. In-situ DRIFTS results prove that the catalytic combustion of CO to CO2 on Cu2O is prone to follow the MvK mechanism. Comparing with Cu2O-D and Cu2O-C, the relatively open surface of Cu2O-O plane composed of unsaturated copper and oxygen atoms facilitates the CO adsorption on Cu (I) and the mobility of lattice oxygen, leading to the highest low temperature reducibility and catalytic activity.

Catalytic combustion of propane over Mg-modified Co1.5Mn1.5O4 spinel catalysts: Boosting C-H cleavage with Lewis acid and oxygen vacancies

Rational modulation of surface electronic structure can optimize the adsorption and activation of reactant molecules on the catalyst surface, which is crucial for catalytic elimination of hydrocarbons. Herein, a facile low-valence Mg doping strategy was applied to synthesize highly active and stable Co-Mn binary oxide (CMO) catalyst. Lewis acid sites and oxygen vacancies were purposefully introduced on CMO through the surface electron deficit caused by the substitution of doped Mg for host metals. For the CMO catalyst modified by appropriate amount of Mg (CMO-Mg0.05), the Co-Mn spinel with lattice expansion is significantly modified through substitution of Co or Mn ions with Mg2+, resulting in generation of abundant higher metal oxidation state species (Co3+, Mn4+) and oxygen vacancies. The best performance for catalytic propane combustion was achieved on CMO-Mg0.05 catalyst, with the T90 at 255 °C under high space velocity (60,000 ml g−1 h−1). Meanwhile, clear improvements on stability and water resistance were also achieved after the modification of Mg in CMO catalyst. Combined with C3H8-TPD, in-situ DRIFTS and various characterizations, it can be revealed that the synergistic effect of Lewis-acid sites and oxygen vacancies would remarkably promote the process of propane dissociative adsorption and mineralization. This work not only gives insight into the Mg dopants in boosting CH activation on CMO catalyst, but also provides a potential strategy for fabricating highly active hydrocarbon combustion catalysts.

Close-Contact Oxygen Vacancies Synthesized by FSP Promote the Supplement of Active Oxygen Species To Improve the Catalytic Combustion Performance of Toluene.

Catalytic combustion is an important means to reduce toluene pollution, and improving the performance of catalytic combustion catalysts is of great significance for practical applications. The study of oxygen vacancies is one of the key steps to improve catalyst performance. Here, two different oxygen vacancy structures were well-defined and controllably synthesized by flame spray pyrolysis (FSP) to evaluate their effect on the catalytic combustion performance of toluene. The closely contacted oxygen vacancies (c-Vo) enhance the oxygen activation capacity of the catalyst, and the temperature of the first oxygen desorption peak and hydrogen reduction peak is 56 and 37 °C lower than the separated oxygen vacancy (s-Vo) sample, respectively. The oxygen activation energy barrier on the c-Vo is calculated to be negligible of only 0.04 eV. Both in situ DRIFT and DFT calculations indicate that the c-Vo structure accelerates the catalytic oxidation of p-toluene molecules. Moreover, due to the unique characteristics of high-temperature synthesis and rapid quenching, FSP brings excellent water resistance and high-temperature stability to the catalyst. In conclusion, utilizing the FSP in situ reduction strategy can create more c-Vo to improve the catalytic combustion performance of toluene.

Hydrothermal aging mechanism of K/CeO2 catalyst in soot catalytic combustion based on the Ostwald ripening mechanism

The thermogravimetric analysis (TGA) experiment of CeO2 and K/CeO2 catalysts prepared with the incipient wetness impregnation method was carried out for the soot catalytic combustion at different K loadings before and after hydrothermal aging. The structure, morphology, and catalytic activity of CeO2 and K/CeO2 catalysts were thoroughly investigated with the means of N2 adsorption/desorption, XRD, XPS, and H2-TPR. The density functional theory (DFT) operation was applied to explain the mechanism of the decrease in catalytic activity of CeO2 and K/CeO2 catalysts after hydrothermal aging. TGA showed that the Tmax of the hydrothermal aging K/CeO2 catalyst was 505 °C, which was higher than CeO2 at 473 °C. After hydrothermal aging, CeO2 catalysts were less agglomerated than K/CeO2, and the ratio of Ce3+/Ce4+ decreases, but the mobile oxygen OII/OI ratio in the lattice were increased compared to CeO2 catalysts. DFT calculations showed that K doping significantly increases the surface energy and decreases the oxygen vacancy formation energy of (1 1 1), (2 0 0), (2 2 0), and (3 1 1) crystal planes, leading to enhanced catalytic combustion performance of the K/CeO2 catalyst soot based on the Mars-Van Krevelen mechanism. Furthermore, K doping decreased the adsorption energy of H2O and the energy barrier of K atoms diffusing near the surface of K/CeO2 catalyst crystals from 5.92 eV to 2.46 eV, which resulted in the loss of the active center number because of migration and coalescence (sintering) caused by crystal plane instability based on the Ostwald ripening mechanism.

Design of hybrid La1-xCexCoO3-δ catalysts for lean methane combustion via creating active Co and Ce species

The catalytic activity of perovskite-typed catalysts depends on both the surface properties and bulk structure. Herein, we report a facile strategy to induce surface reconstruction and lattice distortion of the La1-xCexCoO3-δ catalysts via acid-etching pretreatment, ultimately realizing superior performance for catalytic combustion of lean methane, even in the presence of steam and hydrogen sulfide. The exsolution of small Ce and Co oxides (ca. 5 nm) from the perovskite were found on the surface of the La1-xCexCoO3-δ catalysts to form a hybrid structure after the acid-etching, which interact with the perovskite bulk to create more Co3+ and surface absorbed oxygen as active sites for methane combustion. It is also found that Ce species can be embedded in the crystal lattice and decorated on the surface of the catalysts after the acid-etching, which may enhance the formation of surface absorbed oxygen and the redox ability of Co3+/Co2+ pair. This results in high catalytic activity (T90 = 486 ℃) with a space velocity of 30,000 mL·g−1·h−1. Otherwise, the weak ability of hydroxyl species adsorbed on the surface of acid-etched catalysts restrain further adsorption of water molecules, improving the stability of methane combustion in the presence of water vapour. The increase in CeO2 content on the surface due to acid etching also contributes to the catalyst’s resistance to sulfur poisoning. The present work may provide a new strategy for the synthesis of hybrid perovskite catalysts with excellent catalytic performance, stability and resistance to impurities poisoning.

FSP synthesized core-shell CuOx@SiO2 catalyst with excellent thermal stability for catalytic combustion of ammonia

Ammonia has a great application prospect to reach zero-carbon emissions in the combustion society. However, the poor ignition and combustion performance and NOx emissions of ammonia limit its utilization, and catalytic combustion may be a reliable way to utilize ammonia. In this study, the catalysts were prepared by the flame spray pyrolysis method (FSP), and the catalytic combustion performance of ammonia was investigated in a wide temperature range (100–1000 °C). The results indicated that CuOx and core–shell CuOx@SiO2 had high catalytic activity and N2 selectivity under different equivalence ratios compared with other catalysts (FeOx and MnOx), and the thermal stability of CuOx@SiO2 were more prominent. These two catalysts before and after ammonia catalytic combustion tests were characterized to reveal their acting mechanism. At low temperature (<600 °C), the catalytic ammonia combustion over CuOx followed the internal-selective catalytic reduction (i-SCR) mechanism, while that on CuOx@SiO2 followed the fast i-SCR mechanism, resulting in the outstanding N2 selectivity of CuOx@SiO2. At high temperature (600–1000 °C), CuOx@SiO2 with a better thermal stability hardly sintered. Hydrogen was generated at high temperature and then reacted with oxygen under low equivalence ratio or with the lattice oxygen of the fresh catalyst under high equivalence ratio. The core–shell CuOx@SiO2 catalyst synthesized by the FSP method provides a novel idea on the catalyst design for catalytic ammonia combustion.

Enhanced the combustion performance of DAP-4 with assembled Cu2O nanoclusters

In this work, the catalytic combustion performance of molecular perovskite energetic material DAP-4 with assembled Cu2O nanoclusters added was studied. Results showed that aggregated spherical Cu2O clusters with the size of ∼1 μm were assembled by nano particles with ∼50 nm diameter by the high-temperature reduction method. Assembled Cu2O nanoclusters have intrinsic catalysis combustion characteristics on DAP-4. With 5 wt% Cu2O added, the combustion time of DAP-4 had reduced by ∼70 ms from raw DAP-4 (∼90 ms) to DAP-4/Cu2O (20 ms). The combustion pressurization rate of DAP-4/Cu2O is ∼4 times of DAP-4. The catalysis combustion mechanism of DAP-4 with assembled Cu2O nanoclusters as an additive was proposed. The work offered a new idea to utilize novel catalysts for enhancing the combustion performance of DAP-4.

Rational design of hierarchically micrometer scaled macro-mesoporous ceria-zirconia composites for enhancing diesel soot catalytic combustion performance

Diesel soot particulate is the primary source of urban atmospheric fine particulate matters (PM2.5), catalytic soot elimination on diesel participate filter is invariably an important yet challenging subject, because of the inherently poor solid-solid contact of soot-catalyst. In this study, we report a hierarchically porous ceria-zirconia composite with micrometer scaled macroporous structure, CZ-8, for enhancing catalyst-soot contact efficiency and soot catalytic combustion performance. Scanning electron microscope (SEM), N2 adsorption-desorption and mercury porosimetry results demonstrate that the CZ-8 catalyst has definite micrometer scaled macroporous (0.5–5.0 μm) and interconnected mesoporous (∼20 nm) structure. Raman and X-ray diffraction (XRD) results show that the dominant crystal structure of the CZ-8 is cubic fluorite and the relatively larger crystalline grain contribute to the macroporous structure construction. The filamentous diesel soot particulate (hundreds nanometers or even several micrometers) is difficult to enter the pores of the conventional mesoporous ceria-zirconia catalysts. Nonetheless, it can enter the micrometer scaled pores of the CZ-8 and hence improve the soot-catalyst contact efficiency, and oxygen can efficiently contact with soot-catalyst through the mesopores. Accordingly, the CZ-8 catalyst displays a significantly lower light-off temperature and better soot catalytic combustion performance under loose and tight contact conditions. Thus, this work suggests that enhancing solid(soot)-solid(catalyst)-gas(oxygen) contact efficiency by hierarchically porous structure with micrometer scaled macropores of catalyst is a promising new pathway for improving soot catalytic combustion performance and controlling diesel exhaust particulate emissions.

A facile approach to improve the methane catalytic performance of LaCoO3 perovskite

Some series of LaCoO3 perovskite metal oxide catalysts were modified with different molar amounts of transition metal Co and Fe, namely LaCoO3-xCo and LaCoO3-yFe. They were applied to methane catalytic combustion, and the effects of Co and Fe doping on the defect structure mechanism of LaCoO3 crystal growth and on the performance of methane catalytic combustion were investigated, respectively. The results showed that hydrothermal addition of Co and Fe could both significantly improved the performance of LaCoO3 catalyst for methane catalytic combustion, with the best catalytic methane activity at x=2 and y=7, the T50 was 425 ℃ and 397 ℃, the T90 was 480 ℃ and 457 ℃, respectively. The performance of the hydrothermally modified catalysts were investigated by characterization techniques such as BET, XRD, SEM and XPS, and it turned out that the excellent activity was mainly due to the significantly enhanced oxygen migration rate and the altered LaCoO3 crystal growth mechanism constructing surface defects during the hydrothermal process. In conclusion, this study provides an efficient and simple method for the synthesis of methane combustion catalysts.

L-asparagine Assisted Synthesis of Pt/CeO2 Nanospheres for Toluene Combustion

Pt1/CeO2 nanospheres (Pt/CeO2-NS) were synthesized by the bath oiling method with L-asparagine as a necessary additive. Owing to the morphology control effect and coordination interaction of L-asparagine, CeO2 nanospheres can retain their nanosphere structure and show stronger electronic metal-support interaction with highly dispersed Pt. Moreover, the toluene catalytic combustion performance of Pt/CeO2-NS was investigated. The structure-performance relationship is analyzed according to the coordination state of Pt. The Pt/CeO2-NS catalyst exhibited superior catalytic activity than the commercial CeO2-supported Pt catalyst, which is attributed to its higher oxygen vacancy and Pt4+.

Role of Ni, La impregnation and substitution in Co3O4-ZrO2 catalysts for catalytic hydrogen combustion

Ni and La were substituted and impregnated on Co3O4-ZrO2 (CZ) nanocomposites by solution combustion and wetness impregnation methods for catalytic hydrogen combustion. In this study, our focus is to understand the role of active metals and their interactions with the support CZ in facilitating high oxidation rates. All the impregnated and substituted catalysts showed 100% conversion below 350 °C. The hydrogen combustion is noticeable even at 200 °C due to the activation of hydrogen and oxygen on the active sites. The Ni and La substituted with CZ catalysts showed better catalytic activity than the impregnated catalysts. To explore the mechanistic features and structure-property relations, X-ray photoelectron spectroscopy and TPR studies were carried out for substituted and impregnated catalysts. The regeneration ability was found with the Ni and La substituted catalysts and the redox coupling between Co and La/Ni indicated the possibility of a dual site redox mechanism. Overall, the lattice substitution is found to be desirable and offered high performance for catalytic H2 combustion.

Interactive effects of NOx synergistic and hydrothermal aging on soot catalytic combustion in Ce-based catalysts

The Thermal gravimetric analysis (TGA) with In-situ Fourier transform infrared Spectrometer (In-FTIR) of fresh/hydrothermal aging Ce-based catalysts was carried out for the soot oxidation at different transition metal Mn, alkali metals K, precious metals Ag and rare earth metal Zr doping which used to extend the hydrothermal aging resistance of CeO2 catalysts. The comprehensive combustion index S, combustion stability index Rw and peak temperature Tp from TG-DTG curves were extracted to evaluate the soot catalytic combustion performance, and the NO2/NO ratio during the combustion process was also measured to analyze the NOx synergistic oxidation performance. The effect of metal oxide doping type, doping ratio and hydrothermal aging time on S, Rw, Tp and NO2/NO ratio was evaluated to reveal the change in soot catalytic combustion performance. The result shows that, compared with PU, the NOx synergistic oxidation performance of various metal oxides modified Ce-based catalysts ranked as K > Ag > Mn > Zr. With the metal oxide doping ratio increased, the soot catalytic combustion performance of K and Zr metal oxides modified Ce-based catalysts decreased, Mn and Ag metal oxides modified catalyst increased. After hydrothermal aging treatment, the NOx synergistic oxidation performance of various metal oxides modified Ce-based catalysts ranked as K > Ag > Mn > Zr. This work is helpful to reveal the basic mechanism of hydrothermal aging metal oxide modified Ce-based catalyst and NOx during soot catalytic combustion process.

Construction of a Nanorod Structure-Confined Pt@CeO2 Catalyst by an In-Situ Encapsulation Strategy for Low-Temperature Catalytic Oxidation of Toluene.

In this work, Pt@CeO2 catalysts with a nanorod structure (Pt@CeO2 -R) and a bunch structure (Pt@CeO2 -B) were synthesized through an in-situ encapsulation strategy of Pt species in Ce-MOFs, respectively. It was discovered that the Pt@CeO2 -R catalyst possessed the best catalytic performance for toluene catalytic combustion, and this result was mainly caused by the confinement of Pt nanoparticles in Ce-MOFs, which was related to the chemical state of Pt species, redox ability, and the amount of active oxygen species. The Pt@CeO2 -R catalyst contained more Ce3+ species, rich Pt4+ species, and abundant active oxygen species due to the existence of the confined effect, which was conducive to promote catalytic oxidation of toluene. In addition, the Pt@CeO2 -R catalyst also exhibited more redox ability, which may speed up the catalytic reaction rates. On the contrary, the Pt/CeO2 -R catalyst was synthesized through a simple impregnation method and exhibited the poor activity for toluene catalytic combustion due to poor Pt4+ species and active oxygen species. Therefore, this work provides a feasible experimental basis for the study of different morphologies and encapsulated metal nanoparticles.

Enhancing catalytic performance of Ag-CeO2 catalysts for catalytic CO combustion: Ag-CeO2 interface interaction and Na-promoting action

Ag-CeO2 catalysts were prepared via urea- and activated carbon- assisted pyrolysis to study an improvement strategy for their catalytic performance in catalytic CO combustion. Different synthetic methods induced the change of Ag-CeO2 interface interaction by tuning the surface chemical state of Ag nanoparticles and CeO2 nanoparticles. However, it was completely different to arouse the change degree in the structure and performance of these Ag-CeO2 catalysts. Fabrication of Ag-CeO2 catalysts using a urea pyrolysis induced to create an Ag-CeO2 interface with more metallic Ag species, which improved the reductivity of CeO2 surface and enhanced the Ag-CeO2 catalyst performance. Fabrication of Ag-CeO2 catalysts using an activated carbon pyrolysis method induced to form an Ag-CeO2 interface with more positively charged Ag+ ions and required higher temperature of CO conversion. For the Ag-CeO2 catalysts with more positively charged Ag+ species, the participation of sodium salts could alleviate Ag nanoparticle oxidation and promoted the transformation of Ag-CeO2 interface with more positively charged Ag+ ions into Ag-CeO2 interface with more metallic Ag species, which caused the formation of more Ce3+ cations and the production of more reducible surface oxygen and enhanced the catalyst performance in catalytic CO combustion.

Construction of superhydrophobic layer for enhancing the water-resistant performance of VOCs catalytic combustion

To improve the water-resistance under rich moisture condition of the monolithic Co3O4/NF (Ni-Foam) catalyst for VOCs catalytic combustion, a hydrophobic coating was carefully designed on the monolithic Co3O4/NF catalyst surface. Through the modulation of the thickness of hydrophobic layer with PhTES (phenyltriethoxysilane), we observed that the thickness of hydrophobic layer on these Co3O4/NF-x%Ph catalysts could greatly affect its activity in the wet conditions. More importantly, it is confirmed that the construction of the superhydrophobic surface derived from PhTES hugely inhibited the conformation of hydroxyl groups (OH) on the monolithic Co3O4/NF catalyst, which effectively restrained the adsorption of moisture on monolithic Co3O4/NF catalyst. Thus, the catalytic activity of toluene under wet condition was improved. In addition, this work also provided new ideas and experimental accumulation for future industrial applications of Co-based catalysts. In addition, in-situ DRIFTS results verified that the construction of hydrophobic layer greatly inhibited the adsorption of water molecules on the surface of the Co3O4/NF-25%Ph catalyst.

Effects of Cu2o Morphology on the Performance of Co Self-Sustained Catalytic Combustion

Effects of Cu2o Morphology on the Performance of Co Self-Sustained Catalytic Combustion

Study on catalytic combustion of chlorobenzene over TiO2-supported V-W composite bimetallic catalysts

A series of TiO2-supported V-W bimetallic catalysts were prepared by incipient wetness impregnation method. The effects of V/W ratios on the catalytic combustion performance for chlorobenzene were investigated. The results showed that proper W doping (5V5W-Ti and 3V7W-Ti) improved the catalytic combustion activity of chlorobenzene and the selectivity of HCl. In combination with BET, XRD, XPS, H2-TPR, NH3-TPD and Py-FTIR characterizations, it indicated that higher activity for chlorobenzene oxidation was attributed to the high dispersion of the active species and the abundant surface adsorbed oxygen. In addition, moderate doping of W significantly enhanced the surface acidity of catalysts, especially strong acids and Brønsted acids, and thus improved the selectivity to HCl in the products.

Potassium titanate whiskers on the walls of cordierite honeycomb ceramics for soot catalytic combustion

In this paper, potassium titanate whiskers was prepared via the Molten salt synthesis on the surface of cordierite ceramics for the regeneration of diesel particulate filters (DPFs). SEM, EDS, XRD, FT-IR, TG-DSC and TPO were carried out to characterize the morphology, microstructure, growth mechanism and catalytic performance of the samples. Potassium titanate whiskers with diameter (100–500 nm) and length (about 3 μm) is tightly combined with the cordierite ceramic substrate. The catalyst performance investigation demonstrates that potassium titanate whiskers decrease the soot combustion temperature apparently. The soot combustion process was studied by thermal analysis tests, and the activation energy of the combustion reaction can be calculated using Freeman-Carroll method. The carbon oxidation activation energy is 14.009 kcal/mol, and the activation energy for the catalytic reaction with potassium titanate whiskers is 6.287 kcal/mol, it can be illustrated that potassium titanate whiskers/cordierite catalyst possess excellence performance for carbon catalytic combustion. The coarseness of the interface increased because potassium titanate whiskers grew on the cordierite substrate, and the trapping ability could improve. This unique microstructure has potential application in the DPF field.

Effects analysis on the catalytic combustion and heat transfer performance enhancement of a non-premixed hydrogen/air micro combustor

In this work, a type of non-premixed hydrogen/air micro combustor is designed for the application of micro-thermophotovoltaic (MTPV) systems. The micro combustor is presented with a backward-facing step and unique inlet shape to enhance the mixing performance and flame stabilization. The combustion, flow, and heat transfer characteristics of non-premixed hydrogen/air combustion in micro combustors with/without catalyst segment are numerically investigated. The results indicate that the homogeneous reaction is obviously weakened in the catalytic combustor, but a higher and more uniform outer wall temperature is obtained, and the outer wall temperature difference can be decreased by up to 28%. The flow characteristics of gaseous mixture in the catalytic combustor are better than those in the non-catalytic combustor. When the inlet velocity is 10 m/s, the average flow velocity and pressure loss of the catalytic combustor are decreased by up to 5.6% and 250 Pa, respectively. Furthermore, the heat of reaction and total heat flux at the gas–solid interface of the catalytic combustor are obviously higher and lower than those of the non-catalytic combustor, and the outer wall heat loss ratio is increased by up to 0.59% when the inlet velocity is 10 m/s. All in all, it can be concluded that adopting catalytic combustion to the micro combustor is extremely suitable for the application of MTPV systems.

Boosting the Catalytic Performance of CeO2 in Toluene Combustion via the Ce-Ce Homogeneous Interface.

Catalytic combustion is an advanced technology to eliminate industrial volatile organic compounds such as toluene. In order to replace the expensive noble metal catalysts and avoid the aggregation phenomenon occurring in traditional heterogeneous interfaces, designing homogeneous interfaces can become an emerging methodology to enhance the catalytic combustion performance of metal oxide catalysts. A mesocrystalline CeO2 catalyst with abundant Ce-Ce homogeneous interfaces is synthesized via a self-flaming method which exhibits boosted catalytic performance for toluene combustion compared with traditional CeO2, leading to a ∼40 °C lower T90. The abundant Ce-Ce homogeneous interfaces formed by both highly ordered stacking and small grain size endow the CeO2 mesocrystal with superior redox property and oxygen storage capacity via forming various oxygen vacancies. Surface and bulk oxygen vacancies generate and activate crucial oxygen species, while interfacial oxygen vacancies further promote the reaction behavior of oxygen species (i.e., activation, regeneration, and migration), causing the splitting of redox property toward lower temperature. These properties facilitate aromatic ring decomposition, the important rate-determining step, thus contributing to toluene catalytic degradation to CO2. This work may shed insights into the catalytic effects of homogeneous interfaces in pollutant removal and provide a strategy of interfacial defect engineering for catalyst development.