Low-temperature Catalytic Combustion Research Articles

Investigation of perovskite BaCe1-xMnxO3-δ for methane combustion

The Mn-doped BaCeO3 series composite oxide catalysts were prepared by a sol-gel method. The low-temperature catalytic methane combustion activity test of BaCe1-xMnxO3-δ series composite oxide catalysts at low temperature (200-600 °C) was studied in a fixed bed reactor. The physical properties of the catalyst were characterized by XRD, SEM, particle size analysis and specific surface area measurement, and the conductivity of the sample was measured by AC impedance spectroscopy. Research shows that: the perovskite phase composite oxide catalyst was successfully prepared by the sol-gel method, and the prepared perovskite phase catalyst has good catalytic performance and high temperature stability. The catalytic performance of the catalyst changes with the conductivity, which shows a proportional relationship; when the temperature is lower than 650 °C, Mn doping significantly improves the catalytic activity of the BaCeO3 catalyst for methane combustion. The catalytic activity increases initially and then decreases with the doping amount of Mn. When the doping amount is 0.4 the catalyst has the best catalytic activity, with the ignition temperature of methane at as low as 249.7 °C, and the catalytic methane complete conversion temperature T90 (The corresponding temperature when CH4 conversion rate is 90%) at 423.2 °C. This work is of considerable referential importance in the optimization design of catalysts for CH4 combustion at low temperature.

Platinum Nanoparticles Supported on Hierarchically Porous Aluminosilicate Nanospheres for Low-Temperature Catalytic Combustion of Volatile Organic Compounds

The hierarchically porous silica (NKM-5) and aluminosilicate (Al-NKM-5) supported platinum nanoparticles catalysts were prepared and investigated for the catalytic combustion of toluene and ethanol...

Low temperature catalytic combustion of chlorobenzene over cobalt based mixed oxides derived from layered double hydroxides

Cobalt based mixed oxides were synthesized by a thermal treatment of layered double hydroxides (LDHs) with molar ratio of Co/M = 3 (M = Al, Fe, Cr) and characterized by various techniques such as XRD, N2 sorption, H2-TPR, O2-TPD, NH3-TPD-MS and so on. The results indicated that the mixed oxides derived from LDHs possessed high specific surface area and uniform morphology. Meanwhile, the elements in the mixed oxides were homogenously dispersed. The addition of a second metal (Al, Fe or Cr) enhanced not only the acidity but also the basicity, moreover, Fe and Cr notably improved the reducibility at low temperature and the oxygen mobility of pristine Co3O4. The results of chlorobenzene catalytic combustion showed the addition of Cr or Fe promoted the apparent activity of pristine Co3O4 at low temperature and suppressed the formation of polychlorinated by-products. Among mixed oxides, CoCr catalyst possessed the highest activity and more obvious inhibition of dichlorobenzene formation, which was ascribed to its high redox ability, superior acidity and rapid removal of adsorbed inorganic chlorine species in the form of Cl2. In addition, the CoCr catalyst showed high catalytic stability.

Photoinduced Pt-Decorated Expanded Graphite toward Low-Temperature Benzene Catalytic Combustion

Volatile organic compounds (VOCs) are a great threat to the health of human beings, and developing catalysts with prominent activity and stability to eliminate them are highly desired. In this work...

Facile synthesis of a CuMnOx catalyst based on a mechanochemical redox process for efficient and stable CO oxidation

Low-temperature catalytic combustion of CO is a desirable route for CO removal. We reported the sythesis of highly active CuMnOx catalyst by a mechanochemical redox process.

Simple preparation of uniformly distributed mesoporous Cr/TiO2 microspheres for low-temperature catalytic combustion of chlorobenzene

In this study, novel Cr/TiO2 porous microspheres (h-CrTi) with uniform distribution were successfully prepared by one-step hydrothermal method. For comparative purposes, two other Cr/TiO2 composites were prepared by means of incipient-wetness impregnation (i-CrTi) and co-precipitation (c-CrTi) methods, respectively. The obtained materials were characterized by XRD, BET, XPS, SEM, HRTEM and H2-TPR. The results revealed that h-CrTi0.4 possessed more high valent Cr species and surface-adsorbed oxygen, better crystallinity and Cr species dispersion than i-CrTi0.4 and c-CrTi0.4. These indicated strong interactions between Cr and Ti in h-CrTi0.4 due to better contact. The catalytic activities of the as-obtained materials were tested towards the catalytic combustion of chlorobenzene (CB). The h-CrTi0.4 catalyst possessed not only the best catalytic performance (r = 31.50 × 10−3 μmol·m−2·min−1 at 200 °C at GHSV 15,000 h−1) but also lowest apparent activation energy (55.12 kJ/mol). The TPSR-MS data indicated that h-CrTi0.4 has high ability for removing adsorbed Cl species. h-CrTi0.4 showed stable activity without obvious decrease in CB conversion within 1000 min, which could also degrade dichloromethane (DCM), 1,2-dichloroethane (DCE) and trichloroethylene (TCE) effectively. Therefore, Cr/TiO2 porous microspheres look promising materials for catalytic removal of chlorinated volatile organic pollutants.

Low temperature catalytic combustion of toluene over three-dimensionally ordered La0.8Ce0.2MnO3/cordierite catalysts

Cordierite-supported three-dimensionally ordered macroporous (3DOM) and nanoparticle La0.8Ce0.2MnO3 catalysts were prepared by PMMA-templating and impregnation methods, respectively, to eliminate toluene in low temperature. The catalysts were characterized by BET, SEM, HRTEM, XRD, H2-TPR, NH3-TPD and XPS. The effects of calcination temperature and morphology on the specific surface area, pore volume and size, crystal phase, reduction ability, surface acid distribution and surface property were investigated, and then toluene removal efficiency and apparent active energy were also studied. The results show that the structure and morphology of the active component have a great influence on the specific surface area of the catalyst. At the same calcination temperature of 600 °C, the specific surface area of 3DOM La0.8Ce0.2MnO3/cordierite is 35.3 m2· g−1, which is much larger than that of the nanoparticle La0.8Ce0.2MnO3/cordierite (11.9 m2· g−1). Calcination temperature also can affect the properties of the catalyst and catalytic combustion performance. With different calcination temperatures of 600, 700 and 800 °C, the 3DOM sample calcinated at 600 °C (T50 = 147 °C, T90 = 217 °C, and Ea = 27.01 kJ·mol−1; SV = 6000 h−1) showed the best performances in reduction property, specific surface area, adsorption oxygen concentration, and catalytic combustion performance.

Copper modified manganese oxide with tunnel structure as efficient catalyst for low-temperature catalytic combustion of toluene

Copper-modified manganese oxide catalysts with tunnel, layer, and transitional structure were successfully prepared by a one-step hydrothermal method and investigated for the catalytic oxidation of toluene. The catalysts were characterized by XRD, SEM, TEM, BET, H2-TPR, XPS and ICP-AES techniques. The tunnel-structured catalyst exhibited the best activity among the three Cu-Mn oxide catalysts and excellent water resistance. Abundant surface oxygen species, good low temperature reducibility, low average oxidation state of manganese, and high surface area lead to remarkable catalytic performance of this catalyst. The toluene catalytic combustion over these catalysts was found to follow the Mars-van-Krevelen mechanism and the unique copper states found in the tunnel-structured catalyst play a key role in promoting the cyclic redox process.

Low Temperature Catalytic Combustion Reactors for High Precision Carbon Isotope Measurements in Gas Chromatography Combustion Isotope Ratio Mass Spectrometry

Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution. These modified "ARC" reactors operate with a transition-metal catalyst that requires a flowing O2 gas to enable complete conversion to CO2 at lower temperature (620 °C) with acceptable reactor life, reduced complexity, and improved robustness. Performance of two versions of the ARC reactors with different combustion volumes was characterized by analysis of steroid and alkane isotopic standard materials. Linearity of steroid isotopic standards ranged from 0.02 to 0.60 ‰/V in the range of 25 to 200 ng of each steroid injected. Precisions and accuracies of measurements for steroids and alkanes had average standard deviations of SD(δ13C) less than ±0.18 ‰ and average accuracy of better than 0.19 ‰ δ13CVPDB. Peak width expansion within both devices were similar to that in traditionally used metal oxide reactors. These data demonstrate for the first time that novel combustion schemes enable operation at lower temperatures as an alternative approach comparable to high temperature techniques to yield high precision δ13C data with GCC-IRMS.

Rice Husk Derived Porous Silica as Support for Pd and CeO2 for Low Temperature Catalytic Methane Combustion

The separation of Pd and CeO2 on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly expensive and limits their applicability. In this work, porous silica obtained from acid leached rice husks after calcination (RHS) was used as a sustainable, cheap and broadly available substitute for the above mentioned CPG. RHS-supported Pd-CeO2 with separated CeO2 clusters and Pd nanoparticles was fabricated via subsequent impregnation/calcination of molten cerium nitrate and different amounts of palladium nitrate solution. The Pd/CeO2/RHS catalysts were employed for the catalytic methane combustion in the temperature range of 150–500 °C under methane lean conditions (1000 ppm) in a simulated off-gas consisting of 9.0 vol% O2, and 5.5 vol% CO2 balanced with N2. Additionally, tests with 10.5 vol% H2O as co-feed were carried out. The results revealed that the RHS-supported catalysts reached the performance of the cost intensive benchmark catalyst based on CPG. The incorporation of Pd-CeO2 into RHS additionally improved water-resistance compared to solely Pd/CeO2 lowering the required temperature for methane combustion in presence of 10.5 vol% H2O to values significantly below 500 °C (T90 = 425 °C).

Synthesis and characterization of some nanostructured composite oxides for low temperature catalytic combustion of dilute propane

Five nanosized perovskite and four ferrospinel powders were prepared by sol–gel self-combustion technique. The La0.6Pb0.2Mg0.2MnO3 perovskite was found to exhibit the best catalytic performance with respect to propane combustion at low temperatures.

Estimation of economic efficiency, environmental efficiency and reliability of catalytic heat generators

The statements of developers and manufacturers of catalytic heat generators are analyzed regarding signifi cant advantages of these devices over boilers based on traditional fuel combustion methods: a signifi cant increase in the effi ciency of catalytic boilers, an increased ecological safety of these boilers due to a decrease in the temperature of combustion processes and reduced formation of thermal nitrogen oxides in combustion products, the possibility of signifi cant reduction in the dimensions of catalytic boilers owing to an increase in heat density of heating surfaces in the furnace, as well as increased reliability of catalytic heat generators. The aforesaid statements are demonstrated to be unsubstantiated and inconsistent with the fundamental laws of thermodynamics, physics and chemistry. The results of the experimental studies carried out by the authors of the catalytic boilers are presented. The claims of the creators of catalytic boilers to increase the effi ciency of heat generators due to an increase in the fuel calorifi c value at multi-stage catalytic combustion of fuel are considered. It is theoretically proved that it is impossible to increase the fuel calorifi c value at catalytic combustion, as this assumption of the developers of catalytic boilers contradicts Hess's law, the law of constancy of the sums of the calorifi c values, as well as the laws of Lavoisier and Laplace. The claim of V.N. Parmon on the possibility of increasing the effi ciency of a catalytic heat generator with a factor of 3 – 4, compared to conventional boilers, is shown to be untenable. It is noted that, based on the thermal balance of the boiler, the latter’s thermal effi ciency is not determined by the heat generation method, but, fi rst and foremost, by the extent of cooldown of fuel combustion products. An insuperable theoretical contradiction is shown of the claims of the creators of catalytic boilers on the possibility of low-temperature catalytic combustion of fuel concurrently with an increase in the heat density of the furnace and reduction in the dimensions of the boiler. It is noted that, according to the Stefan-Boltzmann law, the intensity of radiant heat exchange in the furnace is proportional to the absolute temperature of the combustion products to the fourth power. Therefore, in order to provide the necessary intensity of heat exchange in catalytic heat generators, the temperature of the combustion products must be at least as high as that in traditional boilers, and in boilers with an increased heat density of the furnace, even higher. Hence, it follows that the possibility of increasing the ecological safety of these boilers by reducing generation of thermal nitrogen oxides, as declared by the authors and manufacturers of catalytic boilers, is neither theoretically substantiated, nor practically supported. The causes of low reliability of catalytic heat generators are considered. An example is cited of operation of catalytic heat generators in the city of Ulyanovsk, which showed their extremely low reliability. The conclusion is made that it is inexpedient to apply the existing designs of catalytic boilers in domestic heat power engineering.

Low temperature catalytic combustion of ethylene over cobalt oxide supported mesoporous carbon spheres

A novel catalyst has been developed based on cobalt oxide supported mesoporous carbon spheres (MCSs) for the catalytic combustion of ethylene (C2H4). Owing to the unique and well-developed 3D mesoporous structure, the cobalt oxide could be homogenously dispersed on the carbon framework at nanoscale dimensions. The cobalt oxide loaded on MCSs is detected to be in the form of CoO owing to the reduction effect of the carbon support. The MCSs support could facilitate the oxidation ability of CoO, involving more active oxygen species on the catalyst surface. The MCSs supported CoO catalyst could convert 1000ppm C2H4 completely at 185°C, exhibiting a highest catalytic performance among the synthesized catalysts. The reaction order and active energy for C2H4 oxidation are determined to be 0.44 and 79.2kJ/mol, respectively. A GHSV study and a stability test further indicate that the MCSs supported CoO catalyst possesses high catalytic activity and stable catalytic performance for low concentration C2H4, which could benefit for the industrial application of the catalyst in the future.

Effects of ultrasonic impregnation combined with calcination in N2 atmosphere on the property of Co3O4/CeO2 composites for catalytic methane combustion

Co3O4/CeO2 composites with high surface areas and ultrafine crystalline sizes for catalytic combustion of methane were firstly prepared by a new sol-gel method which combined ultrasonic impregnation treatment and calcination in N2 atmosphere. The samples were characterized by various means such as nitrogen adsorption/desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Results showed that the modified catalyst had the mesoporous structure, comparatively higher amount of surface oxygen and larger oxygen vacancies than others. As a result of the structure and surface composition merits, a high methane combustion conversion (50%) could be obtained at a low temperature of 262°C for the modified Co3O4/CeO2 composites catalysts. The experimental results demonstrated that ultrasonic impregnation treatment combined with the N2 thermal treatment prior to calcination in air had a promising application for preparation of Co3O4/CeO2 composites catalysts for low-temperature catalytic combustion of methane.

The Effect of the Presence of Ceria on the Character of TiO2 Mesoporous Films Used as Pt Catalyst Support for Methanol Combustion at Low Temperature

A series of ceria-doped mesoporous TiO2 thin films with anatase phase are synthesized and used as the support of platinum catalysts for low-temperature catalytic combustion of methanol. Since the methanol combustion on the catalysts can usually generate local overheating, which unavoidably leads to the structure destruction and catalytic activity loss, the structure thermal stability of catalytic material is very important. Results show that an appropriate amount of ceria can improve the mesoporous order and especially structure thermal stability of TiO2 thin films. For the TiO2 film (calcined at low temperature of 350°C)-supported Pt catalysts, the catalytic activity of ceria-doped catalysts with ceria dosage of 1–2 mol% is comparable to that of the Pt/TiO2 catalyst without ceria doping and the methanol conversion on these kinds of catalysts is about 70% at room temperature. However, for those TiO2 films calcined at 550°C, under the same reaction condition, methanol conversion on Pt/TiO2 drops to 27% but the conversion on Pt/Ceria-TiO2 with the same small ceria dosage of 1–2 mol% can still be kept as 43%. Moreover, after 72 h reaction at room temperature, the catalytic activity has not changed obviously, which means that the stability of the Pt/Ceria-TiO2 catalyst is very high.

Low temperature catalytic combustion of o-dichlorobenzene over supported Mn–Ce oxides: effect of support and Mn/Ce ratio

Mn9Ce1/cordierite represents the lowest reduction temperature among three supports (cordierite, TiO2and Al2O3) and higher combustion activity foro-DCB due to containing a higher Mn3+species concentration and surface hydroxides.

Platinum nanoparticle modified TiO2 nanorods with enhanced catalytic performances

Low temperature catalytic combustion of methanol to generate electricity has higher energy conversion efficiency than that of conventional combustion process. The performance of the catalyst is one of the key technologies for practical application of methanol used as a fuel for engines. TiO2 modified by platinum nanoparticles were loaded on Al2O3 fibers (Pt–TiO2/Al2O3) by a self-assembly approach. Stable and reproducible catalytic combustion of methanol vapor occurred spontaneously at room temperature with the prepared Pt–TiO2/Al2O3 as a catalyst. The emission spectra for catalytic combustion of methanol vapor were investigated with Pt–TiO2/Al2O3 fibers, Pt–SBA-15/Al2O3 fibers and Pt/Al2O3 fibers as catalysts respectively. The results showed that the catalytic performances of Pt–TiO2/Al2O3 fibers are visiblely better than those of the other two catalysts. Continuous catalytic combustion of ethanol or acetone vapor also occurred with Pt–TiO2/Al2O3 fibers as a catalyst at room temperature. Pt nanoparticles dispersed on the surfaces of TiO2 nanorods significantly improved the catalytic activities of the catalysts. The composite material of Pt–TiO2 nanorods/Al2O3 fibers is a very good catalyst for catalytic combustion of methanol vapor in application of thermoelectric power generation devices.

Low-Temperature Catalytic Combustion of VOCs over MnO<sub>x</sub>–ZnO Mixed Oxides Supported on Cordierite Ceramic

Catalytic combustion of VOCs was investigated over Mn–Zn mixed oxides supported on cordierite ceramic (Cord) and over the promoted Mn-Zn oxides with γ–Al2O3 coating. The properties and performance were characterized by using the XRD, SEM, BET, and TPD techniques. Mn-Zn oxides catalysts with different kinds of γ–Al2O3 sol coating were found to possess a high activity, and the Mn–Zn/γ–Al2O3/Cord (Mn/Zn=2) was identified as the most active that the temperature of complete combustion of toluene was 250°C. Effects of variation of preparation conditions, including molar ratio of Mn and Zn, loading, calcination temperature and different kinds of γ–Al2O3 dipping were investigated.

Si doping influence on the catalytic performance of Pt/TiO2 mesoporous film catalyst for low-temperature methanol combustion

A series of Si-doped mesoporous TiO2 thin films with anatase phase were synthesized and used as the supporters of Pt catalyst for low-temperature catalytic combustion of gaseous methanol. The introduced Pt ions were processed by a simple photo-reduction method. The catalytic performance of thin film catalysts with different Si doping content were measured by gas chromatography method. It was found that the catalytic performance of Pt/TiO2 can be improved a lot by Si doping and the optimized value of Si/Ti ratio is 0.1. At this point, Pt/TiO2 exhibited the best catalytic activity towards methanol combustion reaching up to 92.8% at 100 °C. This conversion rate was 13.2% higher than that of the catalyst without doping. Moreover, the mechanism for Si affecting on the catalytic performance was proposed based on the XRD, FT-IR, SEM, TEM, N2 adsorption–desorption and XPS characterizations.

Low-temperature catalytic combustion of benzene over Ni–Mn/CeO2/cordierite catalysts

The catalytic combustion of benzene over a Ni–Mn mixed oxide supported on cordierite coated with CeO2 was investigated. The catalysts were prepared using a sol–gel method and characterized using BET, H2-TPR, XRD, SEM and TEM. The catalysts calcined at 500°C for 7h with a Ni/Mn molar ratio of 1 exhibited the highest catalytic activity. When the concentration of benzene was 4.8g/m3 and the GHSV was 15,000h−1, the conversion was 94.3% at 300°C. These results were primarily attributed to the catalyst structure and the synergistic activity of the NiMnO3 perovskite and crystalline CeO2.