Complete Combustion Temperature Research Articles

Highly dispersed Pd-based pseudo-single atoms in zeolites for hydrogen generation and pollutant disposal.

Atomically dispersed metal catalysts with excellent activity and stability are highly desired in heterogeneous catalysis. Herein, we synthesized zeolite-encaged Pd-based pseudo-single atoms via a facile and energy-efficient ligand-protected direct H2 reduction method. Cs-corrected scanning transmission electron microscopy, extended X-ray absorption, and pair distribution function measurements reveal that the metal species are close to atomic-level dispersion and completely confined within the intersectional channels of silicalite-1 (S-1) zeolite with the MFI framework. The Pd@S-1-H exhibits excellent activity and stability in methane combustion reactions with a complete combustion temperature of 390 °C, and no deactivation is observed even after 100 h on stream. The optimized bimetallic 0.8Pd0.2Ni(OH)2@S-1-H catalyst exhibits an excellent H2 generation rate from FA decomposition without any additives, affording a superhigh turnover frequency up to 9308 h-1 at 333 K, which represents the top activity among all of the best heterogeneous catalysts under similar conditions. Significantly, zeolite-encaged metal catalysts are first used for Cr(vi) reduction coupled with formic acid (FA) dehydrogenation and show a superhigh turnover number of 2980 mol(Cr2O72-) mol(Pd)-1 at 323 K, surpassing all of the previously reported catalysts. This work demonstrates that zeolite-encaged pseudo-single atom catalysts are promising in efficient hydrogen storage and pollutant disposal applications.

Double perovskite anti-supported rare earth oxide catalyst CeO2/La2CoFeO6 for efficient ventilation air methane combustion

Ventilation air methane is one of available resources with a massive reserve. However, most of ventilation air methane is discharged into the air and pollutes the environment. Catalysts with high temperature resistance (>800 °C) for ventilation air methane are very essential for utilization of the ventilation air methane. We mainly prepared catalysts CeO2/La2CoFeO6 and La2CoFeO6/CeO2 and comparative samples CeO2 and La2CoFeO6 by the simple sol-gel method and calcined them under 900 °C, and tested the catalytic performance of ventilation air methane combustion under the condition of 5 vol% H2O. The experimental results show that the light-off temperature (T10) and complete combustion temperature (T90) of the ventilation air methane combustion reaction of CeO2/La2CoFeO6 catalyst are 417.4 and 587.7 °C, respectively. T10 and T90 of La2CoFeO6/CeO2 only reach 425.5 and 615.8 °C. The T10 and T90 of CeO2/La2CoFeO6 are 417.4 and 587.7 ℃, which are lower than those of La2CoFeO6 (T10 = 452.4 ℃ and T90 = 673.0 ℃) and La2CoFeO6/CeO2 (T10 = 425.5 ℃ and T90 = 615.8 ℃). Therefore, the catalytic performance of the anti-supported rare earth oxide catalyst CeO2/La2CoFeO6 is better than that of La2CoFeO6 and supported catalyst La2CoFeO6/CeO2.

In-situ confinement of ultrasmall palladium nanoparticles in silicalite-1 for methane combustion with excellent activity and hydrothermal stability

Maximizing the use of palladium without compromises in catalytic activity and stability in the combustion of methane is extremely challenging due to the harsh operation conditions. To achieve this goal, a series of core-shell-structured catalysts with different amounts of palladium nanoparticles confined in hydrophobic silicalite-1 (Pd@S-1) was designed. Unexpectedly, a volcanic trend between catalytic activity and palladium loading was found as the loading increased from 0.3 wt% to 1.6 wt%, among which the 0.6 wt%Pd@S-1 exhibited the highest catalytic activity with a complete combustion temperature of 380 °C. Besides, the 0.6 wt%Pd@S-1 showed an ultrahigh stability in the high temperature applications due to the spatial confinement of palladium inside the rigid zeolite matrix. Moreover, owing to the hydrophobicity of the pure silica zeolite, the Pd@S-1 could selectively hinder the diffusion of water vapor into the palladium sites, leading to the outstanding water-resistance ability.

Exhaust emissions of diesel engines with nano-copper additives

The effects of nano-copper additives were investigated through a thermogravimetric (TG) test, diesel engine bench test, and road driving test. The tests demonstrated that the nano-copper additive presented a good catalytic effect on the combustion of soot particles, which reduced the complete combustion temperature from 580 to 520 °C. The diesel engine bench test showed that particulate matter (PM), CO, and HC emissions were reduced by 99.9%, 81.30%, and 33.33%, respectively. The NOx emissions slightly increased due to the lack of carbon as a reducing substance in the exhaust gas. The road driving test with a diesel vehicle demonstrated that more stringent emission standards can be met without any upgrade to the engine.

Enhanced catalytic performance by oxygen vacancy and active interface originated from facile reduction of OMS-2

Manganese oxide octahedral molecular sieves (OMS-2) is a kind of excellent redox catalysts, a key challenge still remains to further increase their catalytic performance. Herein, we report a facile reduction method to enhance the catalytic activity of OMS-2 by producing more oxygen vacancy and creating an active interface between the main phase MnO2 and the minor phase Mn3O4. Compared to the pristine OMS-2, the OMS-2 catalyst reduced in a relatively short time exhibits superior performance for dimethyl ether combustion with a starting-off temperature of 163°C and a complete combustion temperature of 230°C. Such enhanced activity can be ascribed to the higher reducibility, the more oxygen vacancy, and the active heterogeneous interface. These findings open up a new way to design highly efficient catalysts, especially the metal oxides-based catalysts, for redox reactions.

Catalytic combustion of chlorobenzene over core–shell Mn/TiO2 catalysts

Core–shell Mn/TiO2 mixed oxide catalysts (Mn/Ti-cs) were prepared by incipient-wetness impregnation method, and tested in the catalytic combustion of chlorobenzene (CB) as a model of chlorinated aromatics. The obtained catalysts were characterized by XRD, TEM, XPS, BET, and H2-TPR. It was found that Mn/Ti-cs catalysts with different mass ratios of Mn/Ti were found to possess high activity for catalytic combustion of CB. Among these, Mn/Ti20-cs was the most active catalyst, for which the complete combustion temperature (T90) of CB was 296 °C, which was higher than the compared Mn/TiO2 nanoparticles with the same Mn/Ti mass ratio (Mn/Ti20-np). We found that the porous structure and special morphology are the main factors to increase the catalytic activity. Mn/Ti20-cs can provide more reaction and adsorption sites, surface active oxygen species than Mn/Ti20-np on the catalyst surface, which was beneficial to the diffusion and degradation of CB molecule and other intermediate products. By increasing the Mn/Ti mass ratio to 30%, T90 was raised to 400 °C. This is due to the decrease of Mn3+/Mn ratio and specific surface area. Conversion of CB over the MnTi20-cs catalyst was maintained at 90% or more for 900 min, indicating the excellent stability of this catalyst.

Performance of co-doped Mn-Ce catalysts supported on cordierite for low concentration chlorobenzene oxidation

The catalytic activity for low concentration chlorobenzene oxidation was measured with Mn-Ce/cordierite and Mn-Co-Ce/cordierite catalysts with different mole ratios, which were prepared by a sol-gel method and characterized using XRD, BET, SEM Raman, H2-TPR and XPS. The results demonstrated that part of the manganese and cobalt could be incorporated into the lattice of CeO2 to form a solid solution phase. Among all of the catalysts synthesized, Mn8Co1Ce1/cordierite presented the best activity and stability. When the concentration of chlorobenzene was 500ppm, and the GHSV was 15000h−1, the complete combustion temperature (T90%) of chlorobenzene was 325°C. In addition, there was almost no change in the conversion of chlorobenzene during the long-term reaction at 350°C. These results were primarily attributed to the synergistic effect of ceria, manganese and cobalt, which can promote the formation of more lattice defects, more oxygen vacancies and smaller crystallite sizes.

Novel metal loaded KIT-6 catalysts and their applications in the catalytic combustion of chlorobenzene

A series of metal-loaded mesoporous silica catalysts, M/KIT-6 (M = Mn, Cu, Fe, Cr, Sn), were prepared by incipient-wetness impregnation method, and tested in the catalytic combustion of chlorobenzene (CB) as a model of chlorinated aromatics. The effects of metal oxide species and concentration on the textural structure and catalytic properties were studied in detail. It was found that the dispersion, specific surface area and reducibility are the main factors influencing the catalytic activity. On the basis of T50 (temperature at which 50% conversion is attained), the catalytic activity for the CB degradation decreases in the following order: Mn/KIT-6>Cr/KIT-6>Cu/KIT-6>Fe/KIT-6>Sn/KIT-6, correlating with the redox properties of the catalysts. Mn/KIT-6 catalysts having different molar ratios of Mn/Si were found to possess high catalytic activity for catalytic combustion of CB. Among these, Mn3/KIT-6 was the most active catalyst, for which the complete combustion temperature (T90) of chlorobenzene was 210.7°C. By increasing the Mn/Si molar ratio to 1/2, T90 was raised to 238.5°C. This is due to the decrease of pore volume and specific surface area caused by increase in the amount of Mn in the channels of KIT-6, increased agglomeration of Mn, and the lowering of Oads/(Olatt+Oads+Owat) concentration ratio. Conversion of CB over the Mn3/KIT-6 catalyst was maintained at 90% or more for 1000min, indicating the excellent stability of this catalyst.

Study on Combustion and Emission Performance of Oil Shale Mixed with Coal

In this paper, Huadian oil shale from Jilin Province of China was selected as the object of study. Firstly, the ignition temperature, complete combustion temperature, maximum mass loss rate, flammability index C and comprehensive combustion characteristic index S during the separate combustion of oil shale was measured , as well as during the combustion of oil shale mixed with coal, by using the thermo-gravimetric analytical method. Then, the impact of blending ratio on the combustion characteristic parameter was discussed, and conducted modeling for the oil shale blending combustion system was established with the steady-state simulation software program Aspen Plus. Finally, we obtained the exhaust gas temperature, volume flow of gases such as CO, CO2 and SO2, as well as their impacts on the operating conditions of the boiler during the mixing combustion under different excess air coefficients.

Preparation and catalytic performance of OMS-2/Al2O3/cordierite monolithic catalyst

Monolithic catalysts for catalytic combustion of dimethyl ether (DME) were prepared by a dip-coating method using Al2O3/cordierite as support and manganese oxide octahedral molecular sieve (OMS-2) as active component. The effect of different types of organic polymer binder and the coating times of active component on the performance of DME combustion were investigated. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), hydrogen temperature-programmed reduction (H2-TPR) and oxygen temperature-programmed desorption (O2-TPD) techniques. The results showed that the best catalyst was the one using methoxy polyethylene glycol (MPEG) as the coating binder by one-time coating. The active component OMS-2 was in a cluster form and homogeneously dispersed on the surface of the support because of the strong interaction between OMS-2 and Al2O3 coating. The Al2O3 coating could significantly improve the surface area of catalysts, and thus enhance the activity performance. The highest catalytic activity for DME combustion with a complete combustion temperature (t90) of 257°C was obtained.

Enhanced activity and stability of Al2O3-pillared layered manganese oxides for DME combustion

Al2O3-pillared layered manganese oxides (Al2O3–MO), used as catalyst for the catalytic combustion of dimethyl ether (DME), were characterized by XRD, SEM-TEM, N2 adsorption and desorption, O2-TPD and XPS techniques. The Al2O3–MO shows a relative high thermal stability. The layered structure with a basal spacing of 0.67nm could be maintained up to 500°C. The O2-TPD technique showed that all the Al2O3-pillared layered manganese oxides catalysts have large amount of surface oxygen species and the Al2O3 pillars could promote the mobility of the active oxygen. Sample Al2O3–MO (300°C) with large amount of lattice oxygen species and higher oxygen mobility demonstrates excellent activity in the catalytic combustion of DME with a light-off temperature of 140°C and a complete combustion temperature of 149°C. The catalytic activity of the sample Al2O3–MO (300°C) was stable up to 200h. The transient response method was carried out to account for the participation of the lattice oxygen in the catalytic reaction. The results showed that the lattice oxygen of manganese oxide (MnO) was consumed in the combustion reaction and that reduced manganese oxide was reoxidized with O2.

Catalytic Performance of Dimethyl Ether Combustion over La-Ce-Cu/Al<sub>2</sub>O<sub>3</sub> Catalysts

kinds of Al2O3 were synthesized by using aluminum nitrate as the aluminum source, glucose, lactic acid and citric acid as templates respectively. It is showed that all Al2O3 were mesoporous materials due to their BET surface area results. The Al2O3-glu, synthesized by using glucose as a template, demonstrated fine pore shape, larger surface area and pore volume. The Ce0.1Cu0.9O1.1/Al2O3-glu catalyst exhibited good performance for dimethyl ether(DME) Combustion. La-doping can promote its catalytic activity. Over La0.4-Ce0.1Cu0.9O1.1/ Al2O3-glu catalyst, the DME combustion temperature(T10) was 493 K and the complete combustion temperature(T90) was 498 K. The life test result indicated its catalytic activity without any reduce even after 100 h reaction.

Rapid synthesis of cryptomelane-type manganese oxide under ultrasonic process

Cryptomelane-type manganese oxide (OMS-2) was rapidly prepared under ultrasonic irradiation in short time. Characterization results using X-ray powder diffraction (XRD), surface area analyzer, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O 2-TPD) revealed that ultrasonic irradiation has tremendous effect on the surface area, morphology, surface defects, and redox properties of the OMS-2 materials. The OMS-2 prepared via ultrasonic irradiation shows nanoneedle morphology with smaller crystallite size, larger surface area (120.4 m 2/g), more surface defects, and higher oxygen mobility, thus it demonstrates excellent activity in the catalytic combustion of dimethyl ether with a start-off temperature of 160 °C and a complete combustion temperature of 172 °C.

Facile Catalytic Combustion of Rice Husk and Burning Temperature Dependence of the Ashes

In this work, it was discovered and demonstrated that the combustion of rice husk is a catalytic process by the thermoanalytical technique. The catalyst involves the oxides of such transition metals as Mn, Fe, and Cu, which are mainly formed in the initial stage of rice husk combustion and remain in the rice husk ash as an impurity. Mn(2+) ions of various concentrations were reloaded into the HCl-washed husk for cocombustion. As a result, the complete combustion temperature of the husk was decreased exponentially depending on the Mn(2+) concentration. By the facile Mn loading technique using a 0.5 M solution, the combustion temperature can be decreased by approximately 100 degrees C, and the resulting ashes themselves can be a good catalyst in the complete combustion of many other organic compounds. The physicochemical properties and amorphous structure of the ashes from both the raw and HCl-washed husks were found to be strongly dependent on the burning temperature. A decreased complete rice husk combustion temperature can be beneficial in preparing porous amorphous silica with high surface area, high densification, and small Si-O-Si band angles.

Synthesis of hexaaluminate catalysts for methane combustion by reverse microemulsion medium

The aim of this study is to synthesize the catalysts of Fe- and Mn-substituted hexaaluminate by reverse microemulsion medium for methane catalytic combustion application. Pseudo-ternary phase diagrams in quaternary microemulsion systems of cetyltrimethylammonium bromide (CTAB), n-butanol, n-octane, and water [or Al(NO3)3 solution] were presented. The effects of the alcohol chain length, ratio of sur-factant to cosurfactant, and salt concentration on the formation and stability of microemulsion systems were studied. The phase behavior of microemulsion systems was confirmed through the varying of the conductivity with the water content. The performance and structure of the catalysts, La(Mn x /Fe x )Al12−x − O19-δ synthesized with the optimal parameter in the phase diagrams of microemulsions systems were characterized by BET, TG-DTA, and XRD. The micro fix-bed reactor was used to measure the catalytic activities of catalysts to methane combustion. The results showed that this synthesis method could yield non-agglomerated and highly dispersed precursors that would undergo crystallization at the lower temperature of 950°C. When temperature was raised up to 1050°C, the complete crystalline La-hexaaluminate was shaped. The hexaaluminate substituted with Fe had high-catalytic activity and stability at high temperature, while the Mn-substituted had higher catalytic activity at lower temperature. When the cooperation of Fe and Mn occurred, i.e., LaFeMnAl10O19−δ exhibited a high surface area and catalytic activity to CH4 combustion, the CH4 light-off temperature was only 475°C and the complete combustion temperature was 660°C. This was attributed to the synergistic effect between Fe and Mn.

Low-temperature catalytic combustion of chlorobenzene over MnO –CeO2 mixed oxide catalysts

MnOx–CeO2 mixed oxide catalysts prepared by sol–gel method were tested for the catalytic combustion of chlorobenzene (CB), as a model of chlorinated aromatic volatile organic compounds (CVOCs). MnOx–CeO2 catalysts with the different ratio of Mn/Ce + Mn were found to possess high catalytic activity for catalytic combustion of CB, and MnOx(0.86)–CeO2 was the most active catalyst, on which the complete combustion temperature (T90%) of chlorobenzene was 236 °C. The stability of MnOx–CeO2 catalysts in the CB combustion was investigated. MnOx–CeO2 catalysts with high Mn/Ce + Mn ratios present high stable activity, which is related to their high ability to remove Cl species adsorbed and a large amount of active surface oxygen.

Low-temperature catalytic combustion of trichloroethylene over cerium oxide and catalyst deactivation

Cerium oxide catalysts prepared by a thermal decomposition method using the salt nitrate as precursor were tested for the catalytic combustion of trichloroethlyene (TCE), as a model of chlorinated volatile organic compounds (CVOCs). CeO2 catalysts calcined at different temperature were found to possess high catalytic activity for catalytic combustion of TCE, and CeO2 calcined at 550°C was the most active catalyst and the complete combustion temperature (T90%) of TCE was 205°C. Effects of systematic variation of reaction conditions, including space velocity, inlet TCE concentration and water concentration on TCE catalytic combustion were investigated. Additionally, the stability and deactivation of CeO2 catalysts were studied by various characterization methods (such as TG/DTA, EDS, XRD, Raman and XPS) and other assistant experiments.

Mild Thermal Degradation of Pesticides

AbstractPartial degradation of 12 selected analytical grade pesticides was produced by heating the chemicals at temperatures between 100 and 400C. Each pesticide was modified physically and chemically at a temperature at least 300–450C below its complete combustion temperature. At these relatively low temperatures eight of the original nine solids (zineb, picloram, dieldrin, atrazine, bromacil, carbaryl, DNBP, and 2,4‐D) remained solid, while dicamba was converted to a liquid. The three liquids (DBCP, vernolate, and malathion) were all converted to solids. Eight of the original 12 compounds also yielded gray to brown to black residues upon heating. Infrared spectroscopic analyses indicated that the extent of degradation of the heated pesticides ranged from formation of a single degradation product to production of a mixture of compounds. Most pesticides, however, were degraded through loss of one or two substituents of the molecule by processes such as dehalogenation and decarboxylation.