Povrchová aktivace uspořádaných mezoporézních křemičitých materiálů kobaltem a rhodiem

Import 02/11/2016Import 04/11/2015Three different types of ordered mesoporous silica materials, MCM-41, aluminum incorporated into the silica framework MCM-41 (Al-MCM-41) and SBA-15, were prepared. Apart from elemental composition, they differed in textural and structural properties. Furthermore, aluminum was grafted on the silica surfaces by Molecular Designed Dispersion (MDD) method. Finally, the transition metal (cobalt or rhodium) was applied for the surface activation of the silica supports by MDD technique. Much higher initial concentration of cobalt acetylacetonate complex (3.2 mmolCo(acac)2.gsupport-1) was applied than the concentrations of rhodium acetylacetonate complex (0.2–0.01 mmolRh(acac)3. gsupport-1). The prepared catalysts were characterized by different techniques such as AAS, EPMA, EDX, TGA, N2 physisorption, SEM, XRD, IR and Raman spectroscopy, DR UV-Vis spectroscopy, XPS, TPD-NH3, TPR-H2 and pulse chemisorption of H2 and their catalytic activities were tested for two reactions of environmental application: N2O decomposition (in inert and real conditions and in the presence of the reducing agent) and CO oxidation at low temperatures (below 450 °C). The Co-grafted catalysts showed poor activity (14 %) in catalytic N2O decomposition in the inert condition at 450°C and at GHSV 15648 h-1. This was in agreement with TPR-H2 study as Co-grafted catalysts showed very low hydrogen consumption within the temperature range of catalytic tests of N2O decomposition. The carbon monoxide as the reducing agent can facilitate the reduction of cobalt which was confirmed as the N2O conversion increased up to 26 % at 450°C (at GHSV 15648 h-1). The non-specified oxide CoxOy was detected by DR UV-vis and Raman spectroscopy as well as cobalt spinel phase by XRD analysis in the sample Al-MCM+Co. This catalyst contained both cobalt ions (Co2+ as well as Co3+) as determined by TPR-H2 experiments which seems to be beneficial for the catalytic activity of CO oxidation. On the other hand, a specific ration between Co2+ and Co3+ ions is not definitely required as the most active catalyst in the reaction of CO oxidation was SBA+Co containing tetrahedral Co2+ ions interacting with the support as determined by DR UV-vis analysis. More active sites were distributed on SBA+Co per unit surface area than on other Co-grafted catalysts by expressing the catalytic activity as converted CO molecules per unit BET surface area. Therefore, it is expected that the most important for the catalytic activity is better and higher distribution of cobalt species on the silica support. In the case of Rh-grafted catalysts, the activity of the catalysts with the same initial rhodium loading (0.2 mmolRh(acac)3.gsupport-1) in the reaction of N2O decomposition under the inert and real conditions (the presence of O2, water vapor and NO) was found in the order: Al-MCM+Rh < MCM+Al+Rh < SBA+Rh ≈ MCM+Rh. It was proven experimentally (by TPR-H2 and pulse chemisorption of H2) that aluminum incorporated into the structure of MCM-41 enhanced rhodium dispersion on the support which was beneficial for its catalytic activity in the reaction of N2O decomposition. Nearly the same catalytic activities of MCM+Rh(2.7 %) and SBA+Rh(2.7 %) supports the fact that differences in mesoporous structures of MCM-41 and SBA-15 did not play the key role in the reaction of N2O decomposition within the applied amount of rhodium and experimental conditions of N2O decomposition.Tři různé typy uspořádaných mesoporézních křemičitých materiálů, MCM-41, hliník začleněný do křemičité struktury MCM-41 (Al-MCM-41) a SBA-15, byly připraveny. Kromě elementárního složení se lišily v texturních a strukturních vlastnostech. Kromě toho byl hliník nanesen na povrchu křemičité struktury tzv. metodou Molecular Designed Dispersion (MDD). Nakonec byl použit přechodný kov (kobalt nebo rhodium) pro aktivaci křemičitých nosičů pomocí MDD techniky. Byla použita mnohem vyšší počáteční koncentrace acetylacetonátových komplexů kobaltu (3,2 mmolCo(acac)2.gnosič-1) než byla koncentrace acetylacetonátových komplexů rhodia (0,2–0,01 mmolRh(acac)3.gnosič-1). Připravené katalyzátory byly charakterizovány různými instrumentálními metodami AAS, EPMA, EDX, TGA, N2 fyzisorpce, SEM, RTG difrakce, IČ a Ramanova spektroskopie, DR UV-Vis spektroskopie, XPS, TPD-NH3, TPR-H2 a pulzní chemisorpce vodíku a jejich katalytické aktivity byly testovány na dvou reakcích týkajících se problematiky ochrany životního prostředí: rozklad N2O (v inertních a reálných podmínkách a v přítomnosti redukčního činidla) a oxidaci CO při nízkých teplotách (pod 450 °C). Kobaltové katalyzátory vykazovaly slabou aktivitu (14 %) v reakci katalytického rozkladu N2O v inertních podmínkách. Tento výsledek souhlasí s měřením TPR-H2, kdy kobaltové katalyzátory vykazovaly velmi nízkou spotřebu H2 v rozmezí teplot katalytických testů rozkladu N2O. Bylo potvrzeno, že oxid uhelnatý jako redukční činidlo usnadňuje redukci kobaltu, jelikož konverze N2O se zvýšila na 26 % při 450 °C (při prostorové rychlosti GHSV 15648 h-1). Nespecifikovaný oxid CoxOy byl detekován pomocí DR UV-vis a Ramanovy spektroskopie stejně jako spinel kobaltu pomocí RTG difrakce ve vzorku Al-MCM+Co. Tento katalyzátor obsahoval oba ionty kobaltu (Co2+ a Co3+), což bylo určeno pomocí TPR-H2, a jejich přítomnost se jeví jako prospěšná pro katalytickou aktivitu oxidace CO. Na druhé straně, specifický poměr mezi Co2+ a Co3+ ionty není definitivně nezbytný vzhledem k tomu, že nejaktivnějším katalyzátorem v reakci oxidace CO byl SBA+Co obsahující tetraedrické Co2+ ionty vázané na nosiči podle DR UV-vis analýzy. Více aktivních míst na jednotku plochy bylo rozmístěno na SBA+Co ve srovnání s ostatními kobaltovými katalyzátory vyjádřením katalytické aktivity jako počet zreagovaných molekul CO na jednotku BET plochy. Z tohoto důvodu se předpokládá, že nejdůležitější pro katalytickou aktivitu je lepší a vyšší rozmístění iontů kobaltu na křemičitých nosičích. V případě rhodiových katalyzátorů, aktivita katalyzátorů se stejnou počáteční koncentrací rhodia (0,2 mmolRh(acac)3.gnosič-1) v reakci rozkladu N2O v inertních a reálných podmínkách (přítomnost O2, vodní páry a NO) byla v pořadí: Al-MCM+Rh < MCM+Al+Rh < SBA+Rh ≈ MCM+Rh. Experimentálně bylo prokázáno (pomocí TPR-H2 a pulzní chemisorpce vodíku), že hliník začleněný do struktury MCM-41 zvyšuje disperzi rhodia na nosiči, což zvýšilo aktivitu katalyzátoru v reakci rozkladu N2O. Téměř stejná katalytická aktivita MCM+Rh (2,7 %) a SBA+Rh (2,7 %) podporuje skutečnost, že rozdíly v mezoporézní struktuře MCM-41 a SBA-15 nehrály klíčovou úlohu v reakci rozkladu N2O v rámci použitého množství rhodia a experimentálních podmínek rozkladu N2O.Prezenční9360 - Centrum nanotechnologiívyhově

A comparison of PAH emission sampling methods (cyclone, impactor) in particulate and gaseous phase

Four different domestic heating boilers and four types of fuel (lignite, wet wood, wood pellets and mixed fuel) were tested, and the emissions of the particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) were correlated. Dekati low-pressure impactor (DLPI, Dekati) sorting of the PM fractions into PM0.1, PM1, PM2.5 and PM10 was used to determine the emission factors of the PAHs in a dilution tunnel via isokinetic sampling and was compared with a cyclone (Tecora). The 4 PAHs were mostly detected on the fine particles of PM1 in the DLPI and on the fine particles of PM2.5 in the cyclone, and in some cases, they were mainly detected in polyurethane foam (PUF) used for the collection of the gas phase placed behind the DLPI and cyclone. The effectiveness of DLPI sampling was generally comparable or lower than the cyclone sampling of the range 0.01-1.33 mg kg(-1).Web of Science18485584

Effects of the type of biomass and ashing temperature on the properties of solid fuel ashes

Ashes were prepared by annealing selected types of solid fuels (biomass: corn cobs, sunflower husks, olive pomace, hay pellets and rice husks; coal: lignite and bituminous; and alternative fuel: paper sludge) at different temperatures (550 degrees C, 815 degrees C and 975 degrees C). Based on X-ray fluorescence spectra, the slagging/fouling indexes were used to study the effects of the type of ash and the ashing temperature on the ash fouling and slagging properties. Slagging indexes were compared with the ash fusion temperatures. Ash fusion temperatures were measured by a LECO AF-700. The lowest deformation temperature (below 1000 degrees C) was seen for the ashes prepared from hay pellets and corn cobs. On the other hand, the deformation temperature exceeded 1500 degrees C for ashes prepared from paper sludge, sunflower husks and rice husks. By calculating the different slagging/fouling indexes, all the ashes exhibited slagging/fouling problems of varying degrees.Web of Science212514

Heat energy accumulation construction for bioethanol burner

Commonly sold bioethanol fireplaces can represent significant heat source, however due to their intermittent operation the heat energy output is strongly uneven. The aim of this study was to determine the possibilities of heat energy accumulation by individually built ethanol fireplace intended for commonly sold ethanol burner installation. For the measurements of heat energy output, long term tests of the individually built ethanol fireplace with 1, 2 and 3 consecutive combustion periods in a unique calorific room were performed. Accumulation ethanol fireplace has proven high ratio between accumulated heat energy after the ethanol burner last burn-out reaching from 21.4 to 48.4% according to the number of consecutive fuel doses. By usage of the described ethanol fireplace the time of heat energy releasing was increased from approximately 1.15, 2.35 and 3.55 h in case of ethanol burner usage in a non-accumulation fireplace for 1, 2 and 3 fuel doses to 6.5, 11 and 15 h in case of accumulation ethanol fireplace usage. This was also strongly connected with average heat output ranging between 2.54 to 2.47 kW in the case of ethanol burner usage in a non-accumulation ethanol fireplace and 0.38 to 0.59 kW in the case of accumulation ethanol fireplace usage.Web of Science911410

Influence of fuel mixture and catalyst on the ethanol burner flue gas composition

The aim of this study is to determine the influences of chosen primary (mixing of standard recommended fuel with additives) and secondary (oxidation catalyst) measures on the composition of flue gas, produced by combustion of liquid fuels in a standard ethanol burner. The total amount of emitted NO x was decreased by 63%, after replacing the fuel by pure methanol, while the total amount of emitted CO was the lowest during pure ethanol usage. The implementation of chosen catalyst significantly affected the total amount of emitted CO with high conversion rates (82%-90%). The amount of emitted water vapour was increased by 0%-25% (per 1 kWh of released energy) when additives were used. Overall, applying the mentioned measures together proved to be very beneficial from the total amount of emitted CO and NOx point of view.Web of Science887987

Coagulation contributing to electrostatic precipitation of ultrafine fly ash from small-scale biomass combustions

An electrostatic precipitator (ESP) is an efficient device for removing fly ash from small-scale solid-fuel com-bustion. Under corona discharge, a gaseous medium becomes ionised, and particles become charged by colliding with ions. An electric field forces the movement of charged particles to remove gases and induces the movement of generated ions, causing secondary electrohydrodynamic flow. Thus, particle charge, the presence of neigh-bouring particles, an ESP electric field, and gas flow turbulence can enhance particle coagulation. Therefore, the ultrafine particle concentration in an ESP is expected to evolve under electrostatic removal and enhanced coagulation. In the present study, the contribution of coagulation is explored and confirmed using experimental measurements performed on an ESP used to control emissions from a 160-kW boiler with biomass combustion. The ESP was operated under several modes to obtain different coagulation conditions. Changes in particle concentrations were measured simultaneously using two techniques. It was found that coagulation could be responsible for up to 5% of the total removal efficiency, depending on the ESP operation parameters. The present study can promote a deeper understanding of the processes involved in electrostatic precipitation, and the ob-tained results can be useful for practical ESP engineering.Web of Science16art. no. 10066

Specifics of electrostatic precipitation of fly ash from small-scale fossil fuel combustion

This paper investigates the removal efficiency of a honeycomb electrostatic precipitator (ESP) applied to control particulate matter (PM) emissions from a small-scale boiler with combustion lignite and hard coal. The specifics of the precipitation of emissions from small-scale boilers are discussed, and the design principles for relevant ESPs are presented and used. The ion-induced nucleation of sulfuric acid occurred, causing the drastic penetration of 19 nm particles through the ESP. Despite this, the overall collection efficiency was sufficient to meet the EU’s Ecodesign Directive requirements. Back corona was not detected. The optimal ESP performance is defined with further parameters: a current density of 0.5 mA/m2 at an electric field strength of about 2.7 × 105 V/m; a minimal specific collecting area of ESP (SCA) of 60 m2/(m3/s); and Nt-product of 4.5 × 1014 s/m3 . Such parameters of ESPs should ensure adequate PM emissions control for any type of boiler with similar emissions characteristics. The composition of collected fly ash particles was analysed, and a method for fly ash utilisation was proposed. This research may be helpful for designing ESPs to control PM emissions for small-scale units with fossil fuel combustion.Web of Science113art. no. 80

Long-term neutralization of acidic condensate from gas condensing boilers

The pH of wastewater needs to remain between 6 and 9 to protect water organisms. Condensates from a gas condensing boiler have a pH value of about 3. An optimal way to neutralize the acid condensate is to use cheap material such as dolomite. An old-style neutralization box (NB) was tested with a standard faction of dolomite. However, it did not sufficiently neutralize the condensate. Therefore, several tests were performed involving changes to the construction of the neutralization box, a finer fraction of dolomite and aerating the condensate in the neutralization box. In summary, a new NB technology with partitions, a finer fraction of dolomite and condensate aeration proved sufficient in the neutralization of the pH of the condensate in the short and long terms. It depends on what material the heat exchanger is made of in the condensing boiler. The aluminum content reduces the effectiveness of dolomite in the long run, so aerating the condensate in the NB is recommended, which leads to its more effective neutralization.Web of Science1422art. no. 1501

Škody způsobené korozí materiálů vlivem znečišťování ovzduší

Import 05/05/2008Prezenční616 - Katedra ochrany životního prostředí v průmysluNeuveden

Removal of heavy metals from municipal solid waste fly ash

Import 29/09/2010Popílek ze spalovny komunálního odpadu je řazen mezi nebezpečný odpad. Popílek obsahuje vysoký obsah těžkých kovů, které se mohou uvolnit do životního prostředí. Pro odstanění těžkých kovů (jmenovitě Cd, Pb, Cu, Zn, Ni a Cr), popílek byl tepelně zpracován v souproudém vsádkovém a kontinuálním rotačním reaktoru v laboratorním měřítku při teplotách v rozmezí 950°C až 1100°C. Tomu předcházelo smíchání nebo peletizace popílku s různými přísadami jako např. chlorační činidla (především chlorid vápenatý), písek nebo redukční činidlo jako koks. Sloučeniny těžkých kovů se vypařily v různém množství, maximální odstranění těžkých kovů bylo přitom vyžadováno. Vliv různých přísad v různém množství, vliv teploty nebo různých frakcí popílku podle velikosti zrn bylo studováno. Popílek pocházel ze spalovny komunálního odpadu a teplárny Spittelau ve Vídni, v Rakousku.Fly ash from a municipal solid waste (MSW) incinerator is categorized as a hazardous material. Fly ash contains high amounts of heavy metals which can contaminate the environment. For removal of heavy metals (namely Cd, Pb, Cu, Zn, Ni and Cr), MSW fly ash was treated thermally in co-current batch and continuous mode in a lab-scale indirectly heated rotary reactor at temperature range 950 – 1100°C. Prior to that, fly ash was mixed or pelletized with different additives such as chlorinating agents (mainly calcium chloride), sand or reducing agent as coke. Heavy metal compounds evaporated in different ratios while the maximal removal of heavy metals was required. Influence of different additives in different amounts, influence of temperature or different size fractions of fly ash was studied. MSW fly ash originated from the waste-to-energy plant Fernwärme Wien / Spittelau in Vienna, Austria.619 - Katedra fyzikální chemie a teorie technologických pochodůvýborn