High Temperature Catalytic Combustion Research Articles

ORGANIC MATTER CONTENT AND HUMUS RESERVES IN NATURAL SOILS OF ROSTOV AGGLOMERATION

The research aims to study the content of organic matter in typical chernozem, its distribution in the soil profile under herbaceous and wooden phytocenoses. Organic matter plays a key role in the functioning of soils and their stable performance of ecological functions, including – the protection function. This is particularly relevant in the growing urbanization. The research analysis includes 40 full-profile sections of migration-segregated chernozems (typical carbonate) laid on the upland soil of the Rostov agglomeration. We determined organic matter by high-temperature catalytic combustion on a TOC-L CPN Shimadzu in an SSM-5000A solid sample combustion unit. Based on the data obtained, we calculated the organic carbon reserves. Statistical analysis included the calculation of the Mann-Whitney U-test to consider significant differences in the samples of indicators under wooden and herbaceous phytocenoses and descriptive statistics. The research results showed the influence on the organic carbon content of such a widespread type of anthropogenic impact as planting trees in the steppe zone. Comparison of the total organic carbon content values in similar genetic horizons under herbaceous and wooden phytocenoses indicates the spatial heterogeneity of this indicator, associated primarily with the type of land use. The supply of humus for Rostov chernozems under herbaceous phytocenoses was assessed as low and under wooden phytocenoses – as average. In the one-meter layer of natural chernozems of the Rostov agglomeration, humus reserves are 387 t/ha, which corresponds to the average supply level. Thus, the park and recreational zone, where wooden vegetation grows, plays a special ecological role in the city as a place of accumulation of an increased amount of organic matter of natural origin compared to other soils of the Rostov agglomeration.

Great activity enhancement of Co3O4/γ-Al2O3 catalyst for propane combustion by structural modulation

Co3O4/γ-Al2O3 is a high-active catalyst for VOCs combustion, however large numbers of inactive cobalt species will form easily as a result of strong Co/Al interaction which usually leads to a significant activity reduction of the active cobalt species. Here, a facile reduction-passivation approach has been developed to modulate the Co/Al interaction in 10%Co3O4/γ-Al2O3 catalyst, which produces abundant active cobalt oxides with rather small particle size stabilized on the surface as a core-shell structure. The catalytic activity for the model reaction of propane combustion could be enhanced greatly by this approach. The weak Co-Al interaction and the highly dispersed Co3O4 on the outer-layer of the core-shell structure contribute mainly to the great activity enhancement. Further, the reduction-passivation treated catalyst also exhibits excellent stability and even a moderate activity increase after prolonged or recycling catalytic tests. The present reduction-passivation treatment can be a promising way to improve the catalytic performance of Co-based catalysts for high temperature catalytic combustion.

Synthesis of Nanostructured Catalytic Materials from Microemulsions

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Total Organic Carbon and Total Nitrogen in Sediments and Soils: A Comparison of the Wet Oxidation – Titration Method with the Combustion-infrared Method

Abstract Total organic carbon (TOC) and total nitrogen (TN) are the most important components of sediments and soils as they can be used to distinguish marine and terrestrial sources of organic matter, environmental depositional conditions, pollution indices and soil quality and productivity indicators. In this paper we present datasets of measurements of TOC and TN in sediments applying high temperature (720 C) catalytic combustion (Pt/Al 2 O 3 ) oxidation method, as well as measurements of soil certified references materials (CRM). The detection of TOC and TN was performed using an infrared or a chemiluminescence detector, respectively. We validate the methods studying the range of measurement, the repeatability, reproducibility and precision. TOC results are compared with these measured by the widely used modified Wakley-Black titration method of Gaudette et al. (1974). This comparison indicated that the catalytic combustion method and Wakley-Black titration method have a very good correlation for low total organic carbon content (less than 5%), as well as for high organic carbon content (till 40%), while for sediments with higher organic load the catalytic combustion method is more accurate.

SOME PROBLEMS RESULTING FROM POWERING OF TURBINE ENGINES BY LIQUIFIED PETROLEUM GAS (LPG)

There has been observed for several years a number of attempts to introduce for everyday use small power units which utilize turbine engine as propulsion unit (the U.S., Japan, and Europe). Efficiency increase of such devices is achieved by improving of turbine engine design as well as utilizing of exhaust gas thermal energy to heat the compressed air supplied to combustion chamber and, for example to heat usable water. Significant orientation of turbine engine improvements lead to the modernization of combustion processes by applying of gaseous fuels (such as compressed natural gas) or implementation of high-temperature catalytic combustion. The purpose of these changes reduction of hydrocarbons, carbon monoxide and nitrogen oxides emissions. In Propulsion Department of Aviation Institute a scientific project has been realized, in which the object of study was aircraft turbine engine powered by a liquid propane-butane mixture. The paper presents some results of engine tests carried out, especially concerning feeding system, special fuel system applied LPG pumping systems with the use of sliding-vane pump and by means of pressure reservoir and combustion process of LPG atomized with the use of original GTD-350 vortex injector, adapted for aviation kerosene Jet-A.

Data quality in water analysis: validation of combustion-infrared and combustion-chemiluminescence methods for the simultaneous determination of Total Organic Carbon (TOC) and Total Nitrogen (TN)

Total Organic Carbon (TOC) and Total Nitrogen (TN) were simultaneously determined in water samples, applying the high-temperature (720°C) catalytic combustion (Pt/Al2O3) oxidation method. The detection of TOC and TN was performed using an infrared or a chemiluminescence detector, respectively. Following current law legislations as well as the need to provide accurate and repeatable results, a systematic work has been successfully undertaken for the accreditation according to EN ISO 17025/99. Method characteristics (r ange of measurement, calibration, method detection level, repeatability, reproducibility, precision, accuracy) and measurement uncertainties were determined, while participation in proficiency testing schemes was also implemented. The above methods were tested for the study of water purification from organic pollutants. To this end, organic dyes have been used as model organic pollutants and anionic hydrogels have been used as sorbents. With respect to the colorimetric techniques, TOC-TN characterization is proved to be a reliable tool with significantly lower detection limits of the organic load.

AMnAl1111O19(A=La, Sr, Ba) 및 CeO2/LaAMnAl11O19를 이용한 메탄의 촉매 연소

Mn substituted La, Sr or Ba-hexaaluminate were prepared by co-precipitate method and calcined at for 5 h. Catalysts were characterized by X-ray diffraction and physisorption and scanning electron microscope (SEM). Compared to and , in which La located at mirror plane showed better crystallinity and high surface area, 13 . revealed well developed plate-like structure which is characteristic structure of hexaaluminate. The catalytic activity of methane combustion increased in the following order: > > and was dependent on surface area of catalysts. 60 wt% calcined at showed enhanced methane activity and methane was oxidized completely at low temperature (). It was confirmed that addition of ceria seems to be effective for the low and middle temperature combustion of methane. But, after calcination at high temperature of , it lost the promoting effect of ceria due to increase of ceria particle size and it had a limit to applying to the high temperature catalytic combustion.

Stability of hexaaluminate-based catalysts for high-temperature catalytic combustion of methane

Lanthanum hexaaluminate with a nominal composition of LaAl11O18 was used to support 20wt.% of LaMnO3 and CeO2. LaAl11O18 was prepared through co-precipitation of metal nitrates within the water phase of an isooctane/CTAB/1-butanol microemulsion. The stabilities of the prepared catalysts were assessed by measuring the activities for combustion of methane before and after aging at 1000°C for 100h in air with 10vol.% H2O. The activities were compared with LaMnAl11O19, due to its well-documented stability. It was shown that by using hydrothermal treatment of the microemulsion, a significantly higher surface area was obtained for the LaAl11O18. For LaMnO3, the reference support (Al2O3) was shown to be superior to LaAl11O18 as support, both in terms of activity and stability. Reactions between LaMnO3 and support were observed for all supports included in the study. For CeO2, LaAl11O18 was superior to Al2O3 as support. Deactivations of the CeO2 catalysts were linked to crystal growth of CeO2. LMHA deactivated strongly during aging; LaMnO3 on Al2O3 and several of the catalysts with CeO2 supported on LaAl11O18 showed a much more stable behavior.

Al 18B 4O 33 aluminium borate: A new efficient support for palladium in the high temperature catalytic combustion of methane

Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2.

The effects of transition metal in Sn-based pyrochlores on the methane catalytic combustion

Abstract Lanthanum stannate pyrochlores, La2Sn2O7 and La2SnMO7(M = Mn, Fe, Co, Ni, Cu), were successfully prepared by citric acid method and confirmed by XRD. TG and TPR characterizations showed that the introduction of transitional metals resulted in significant impacts on the structures and redox performances of prochlores. All the selected transitional metals could significantly improve their methane catalytic combustion performance. Among the doped pyrochlores, La2SnCoO7 pyrochlore possessed optimum activities at low temperatures, and Fe-doped pyrochlore showed highest reactivity for high temperature combustion and was proved to be promising materials for high temperature catalytic combustion. The reactivity differences of La2SnMO7 were reasonably attributed to the strong interactions between Sn and transitional metal.

04/02500 Temperature excursions during the transient behaviour of high temperature catalytic combustion monoliths: Di Benedetto, A. et al. Catalysis Today, 2003, 83, (1–4), 171–182

04/02500 Temperature excursions during the transient behaviour of high temperature catalytic combustion monoliths: Di Benedetto, A. et al. Catalysis Today, 2003, 83, (1–4), 171–182

Temperature excursions during the transient behaviour of high temperature catalytic combustion monoliths

Spatio-temporal temperature profiles experimentally observed during the operation of a structured perovskite-based catalytic monolith for the combustion of methane were simulated by means of a transient heterogeneous one-dimensional model which accounts for heat losses to the surroundings and thermal conductivity inside the monolith substrate. In fact it is shown that such thermal phenomena are essential to correctly reproduce the slow warm-up transients and the wrong-way behaviour observed in a low conductivity ceramic monolith. Model simulations reveal that at higher values of solid conductivity the catalyst does not exhibit hot spot both in time and space, but needs higher inlet gas temperatures to reach complete methane conversion. Bifurcation analysis of the catalytic monolith reactor model were carried out to study steady-state multiplicity. We show that the origin of multiplicity is purely thermal as it is mainly ruled by the heat transfer through the external surface.

High temperature catalytic combustion of methane and propane over hexaaluminate catalysts: NO x emission characteristics

Several hexaaluminate-related materials were prepared via hydrolysis of alkoxide and powder mixing method for high temperature combustion of CH 4 and C 3H 8, in order to investigate the effect of the concentration of the fuels, O 2 and H 2O on NO x emission and combustion characteristics. Among the hexaaluminate catalysts, Sr 0.8La 0.2MnAl 11O 19−α prepared by the alkoxide method exhibited the highest activity for methane combustion and low NO x emission capability. NO x emission at 1500 °C was increased linearly with O 2 concentration, whereas water vapor addition decreased NO x emission in CH 4 combustion over the Sr 0.8La 0.2MnAl 11O 19−α catalyst. In the catalytic combustion of C 3H 8 over the Sr 0.8La 0.2MnAl 11O 19−α catalyst, the amount of NO x emitted was raised in the temperature range between 1000 and 1500 °C when the C 3H 8 concentration increased from 1 to 2 vol.%. It was found that NO x emission in this temperature range was reduced effectively by adding water vapor.

The catalytic activity and surface characterization of Ln 2B 2O 7 (Ln=Sm, Eu, Gd and Tb; B=Ti or Zr) with pyrochlore structure as novel CH 4 combustion catalyst

Ln 2B 2O 7 (Ln=Sm, Eu, Gd and Tb; B=Zr or Ti) with pyrochlore structure was prepared by sol–gel method for the high-temperature catalytic combustion. The crystal structure of Ln 2B 2O 7 was identified by XRD and their surface area was about 4 m 2/g after calcinations at 1200 °C. Catalytic activity of methane combustion was observed for Ln 2Zr 2O 7 series and the best catalyst was Sm 2Zr 2O 7. Its relative reaction rate per unit surface area at 600 °C was 2 cm 3/m 2 min, which was twice higher than that of Mn-substituted Sr hexaaluminate. From surface analysis by XPS, the low binding energy of each Ln element of Ln 2Zr 2O 7 compared to that of Ln 2Ti 2O 7, gave the catalytic activity of methane combustion.

Catalytic Total Oxidation of Methane. Part II. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The introduction of solid catalysts into a traditionally non-catalytic free-radical process such as combustion occurred in recent years under the influence of environmental pressures. The major applications of catalytic combustion are two-fold: at low temperatures to eliminate volatile organic compounds (VOCs) and at high temperatures (>1000°C) to reduce NOx emission from gas turbines, jet motors, etc. It is the high temperature application that is reviewed here. Some recent developments in high-temperature catalytic combustion are trend setters in catalysis and hence of particular interest. For instance, novel materials are being developed for catalytic applications above 1000°C for sustained operation longer than one year. Where material/catalyst developments are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid (catalytic + thermal) reactors.

High-Temperature Catalytic Combustion and Its Inhibition of Gas-Phase Ignition

The emissions characteristics of the combustion of fuel-lean mixtures of methane and air were studied in steady-state conditions using two catalytic reactors: a honeycomb monolith burner and a stagnation point flow reactor (SPFR). The investigations showed that the gas-phase fuel/air mixture does not ignite until the catalytic surface is significantly above the ordinary autoignition temperature. This inhibition of gas-phase combustion by the catalytic reactions is desirable, since it extends the range over which clean and stable oxidation conditions persist. The inhibition seen in the monolith burners was observed in more detail in the SPFR experiments. The analysis of the experimental results was assisted by numerical simulations of both reactors using kinetic models consisting of heterogeneous and homogeneous elementary reactions as well as global chemical kinetic mechanisms found in the literature. The measured peak selectivity of the C-containing products was in agreement with the detailed chemical simulations. However, the latter underestimated the temperature range of the inhibition, indicating that the current description of the free radicals formation needs further investigation.

Operational problems related to the preparation of the seawater soluble fraction of crude oil.

Owing to the importance of dissolution and weathering processes following oil spills, this work focused on the operational (quantitative) aspects related to the dissolution of petroleum-derived products, as well as the influence of solar light on both dissolution and the photoproduction of hydrogen peroxide. Four Brazilian crude oil samples were used to study the transfer process of organic compounds from the crude oil film to the aqueous phase (natural seawater) over a period of up to 45 days. Dissolved organic carbon (DOC), measured by non-dispersive infrared spectroscopy followed by high temperature catalytic combustion, was used to follow the partitioning between the two phases. Aqueous DOC values increased as a function of time (up to 15 days) until equilibrium was reached at concentrations ranging from 5 to 45 mg C L(-1). The final DOC concentration as well as the rate of dissolution depends on the nature of the crude oil. When exposed to sunlight, the dissolution was enhanced by up to 67.3%, and inorganic peroxides were generated in the concentration range from 4.5 up to 8.0 micromol L(-1) after 7.3 h irradiation. These results indicate that there is a need for a standard procedure for the production of the WSF in order to generate a more reliable tool to assess the impact of oil spills on the marine environment.

The Merits of the High-temperature Combustion Method for Determining the Amount of Natural Organic Carbon in Surface Freshwater Samples

The merits of the method for the quantitative analysis of carbon of natural organic matter (NOM) in aquatic freshwater samples, using the high-temperature catalytic combustion technique, have to our knowledge not previously been documented. Although a large intercalibration study concerning marine NOM have documented and improved the analytical merits of this technique in marine chemistry, these results cannot directly be adapted to freshwater analysis. This article presents the findings from an intercalibration on the determination of carbon in freshwater NOM, between 25 laboratories participated in using the high-temperature catalytic combustion technique. The laboratories analysed the amount of total- and dissolved organic carbon (i.e. TOC and DOC, respectively) on a set of 10 samples. The samples consisted of fresh surface water, reverse osmosis (RO) isolates of dissolved NOM from natural freshwater locations, as well as synthetic standards. General merits (i.e. accuracy, precision etc.) of the analytical method are presented and problems with detection limits, high blank values, contamination from filters, experience in the use of RO-isolates and analysis of the more refractory (i.e. not readily oxidizable) NOM are discussed. The focus of the study is on the analytical merits achieved on the natural samples compared to the commonly used and possibly readily oxidizable standard material (i.e. potassium hydrogen phthalate). It is demonstrated that the method's merits generated using the readily oxidizable potassium hydrogen phthalate are too optimistic when applied to the analysis of natural aquatic samples.

Preparation, characterisation and catalytic activity of pure and substituted La-hexaaluminate systems for high temperature catalytic combustion

La-Al-O, La-Mg-Al-O, La-Mn-Al-O and La-Mg-Mn-Al-O hexaaluminates have been prepared using the carbonates route previously developed for M-substituted and unsubstituted Ba-β-Al2O3. Starting from amorphous precursors, the formation of a final magnetoplumbite (MP) phase is observed upon calcination at T≥1100°C. In the case of LaMn1Al11O19, the MP phase already forms at 900°C evidencing a promotion effect of Mn ions. Upon calcination at 1300°C, monophasic samples can be obtained only for Mg-substituted samples (LaMg1Al11O19 and LaMg0.5Mn0.5Al11O19), whereas in the other samples the presence of LaAlO3 is always detected. This behaviour is associated with the stabilisation, via a charge compensation mechanism, of the MP phase due to the introduction of Mg2+ ions in the structure. The co-presence of Mg and Mn in the final catalyst has resulted in a higher specific catalytic activity per Mn mol. Such a behaviour is likely associated with the stabilisation of Mn ions at high oxidation state due to the co-presence of Mg2+.

Preparation and characterisation of supported La 0.8Sr 0.2MnO 3+ x

Three supported La 0.8Sr 0.2MnO 3+ x catalysts were prepared, one supported on lanthanum-stabilised alumina and two supported on a NiAl 2O 4 spinel. The catalysts were characterised using X-ray diffraction, transmission electron microscopy and surface area measurements following heat-treatments at temperatures up to 1200°C in air. In the alumina-supported catalyst, a reaction occurred between the active phase and the support at high temperatures, indicating that these materials would be unsuitable for high temperature catalytic combustion. Only in the NiAl 2O 4-supported catalysts were the supported perovskite phases found to be stable at high temperature. These catalysts showed good methane combustion activity.