Magnetically modified nanogold-biosilica composite as an effective catalyst for CO oxidation

The temperature-dependent biosynthesis of gold nanoparticles (AuNP) using diatom cells of Diadesmis gallica was successfully performed. The resulting biosynthesis product was a bio-nanocomposite containing AuNP (app. 20 nm) subsequently anchored on the silica surface of diatomaceous frustules. As-prepared nanogold-biosilica composite was tested as catalyst in the oxidation of carbon monoxide using gas chromatograph with thermal conductivity detector. For catalytic activity enhancement, bionanocomposite was magnetically modified by ferrofluid using two different methods, i.e., with and without the use of methanol. The oxidation of CO at 300 degrees C was 58-60% in the presence of nanogold-biosilica composites. CO conversion at 300 degrees C was only 15% over magnetically responsive sample modified in the presence of methanol. On the other hand, complete CO conversion was reached over direct (without methanol) magnetically modified nanogold-biosilica composite at 330 degrees C (GHSV = 60 l g(-1) h(-1)). Our results show, that the type of magnetic modification can influence the catalytic activity of bionanocomposite. The best catalytic effect in CO conversion established direct magnetically modified nanogold-biosilica composite.Web of Science1271158114

Catalysts with low content of active species for dinitrogen monoxide decomposition

Import 04/07/2011Diplomová práce se zabývá testováním katalytické aktivity vzorků katalyzátorů při rozkladu oxidu dusného. Oxid dusný se vyznačuje nízkou reaktivitou, a proto nebyl dlouho považován za významný polutant, který by měl být monitorován. V posledních desetiletích se však ukázalo, že N2O je plyn, který se významně podílí na skleníkovém efektu a úbytku stratosférického ozónu. Z možností, jak snížit koncentraci N2O v odpadních plynech, je nejvhodnější katalytický rozklad, neboť při něm vznikají pouze přirozené složky ovzduší N2 a O2. Pro praktickou aplikaci této metody je nutné nalezení vhodného katalyzátoru. V rámci této diplomové práce byla testována katalytická aktivita oxidických práškových i tvarovaných katalyzátorů s nízkým obsahem aktivních složek Co a Mn pro rozklad N2O.This diploma thesis deals with the testing of catalytic activity of catalysts samples in the decomposition of nitrous oxide. Nitrous oxide is characterized by low reactivity, hence for a long time not be considered as an important environmental pollutant. During last decade it turned out, that N2O is an important greenhouse gas, as well as a contributor decay of stratospheric ozone. N2O catalytic decomposition is the best possibility for decreasing of N2O concentration in waste gases, because natural components N2 and O2 arise. Retrieval of the suitable catalyst is fundamental for practical application of this process. In this diploma thesis, catalytic activities of mixed oxide powdered and shaped catalysts with low content of active species Co and Mn were tested for nitrous oxide decomposition.617 - Katedra chemievelmi dobř

Preparing of Carbon Sorbens for the Gas Separation

Import 01/09/2009Prezenční617 - Katedra chemievýborn

Optimization of cesium content in cobalt mixed oxides for N2O catalytic decomposition

Import 11/02/2016Import 02/11/2016Tato disertační práce se zabývá katalytickým rozkladem N2O na směsných oxidech s obsahem aktivních složek – kobaltu a manganu, které byly modifikovány cesiovým promotorem. Série směsných oxidů Co4MnAlOx modifikovaných cesiem v koncentračním rozmezí 0,6 – 4,5 hm. % byla připravena kalcinací prekurzoru se strukturou hydrotalcitu s molárním poměrem Co:Mn:Al = 4:1:1. Vzniklý směsný oxid byl následně impregnován cesiem pomocí metody zaplňování pórů za použití dvou solí – Cs2CO3 a CsNO3. Připravené vzorky katalyzátorů byly charakterizovány několika analytickými metodami – AAS, XRD, SBET, TPR-H2, TPD-CO2, TPD-NH3, XPS, a TAD. Experimentální měření katalytického rozkladu N2O bylo provedeno v laboratorním nerezovém trubkovém průtočném reaktoru s integrální vrstvou katalyzátoru v teplotním rozmezí 210 – 450 °C. Specifický povrch směsného oxidu Co4MnAlOx byl roven 92 m2/g a modifikací cesiem k jeho významné změně nedošlo. XRD analýzou byla ve vzorcích katalyzátorů identifikována spinelová fáze. Se stoupajícím množstvím cesia stoupala i bazicita jednotlivých vzorků. Vzorky modifikované cesiem za použití CsNO3 vykazovaly poněkud horší redukovatelnost než vzorky modifikované cesiem za použití Cs2CO3. Termální alkalická desorpce ukázala, že cesium je na povrchu katalyzátoru stabilní až do teploty 550 °C. Aktivita katalyzátorů stoupala se zvyšujícím se množství cesia ve vzorku. Nejvyšší katalytickou aktivitu vykazovaly katalyzátory s množstvím cesia v rozmezí 3 – 4 hm. % bez ohledu na použitou cesiovou sůl, a to i v podmínkách simulujících odpadní plyn z výroby kyseliny dusičné. Na základě laboratorních výsledků katalytických testů byl zvolen optimální obsah cesia 3,4 hm. % pro výrobu poloprovozního katalyzátoru označeného AST3. Katalyzátor AST3 byl testován pro snížení emisí N2O v odpadním plynu v poloprovozním reaktoru připojeném na koncový plyn z výroby kyseliny dusičné ve společnosti BorsodChem MCHZ Ostrava. Při prostorové rychlosti 11 130 l.llože-1.h-1 a teplotě 450 °C bylo dosaženo vysoké konverze N2O v rozmezí 64 – 94 %, jejíž hodnota byla závislá na proměnlivém složení reakční směsi. Po 142 dnech provozu nebyla pozorována deaktivace. Bylo zjištěno, že cesium funguje jako elektronový promotor, umožňuje snadnější štěpení molekuly N2O na rozhraní Cs–Co. Posun teplotních maxim redukčních píků do nižších teplot se stoupajícím množstvím cesia ukazuje na snadnější redukci Co3+, což souvisí s oslabením vazby Co–O, čímž dochází ke snížení doby zdržení kyslíku na povrchu katalyzátoru. Testy TPD-O2 potvrdily, že optimální množství cesia napomáhá rychlejší desorpci kyslíku z povrchu katalyzátoru, což je rychlost určující krok katalytického rozkladu N2O.This dissertation deals with N2O catalytic decomposition over mixed oxides containing active species – cobalt and manganese, which were modified with cesium promoter. A series of Co4MnAlOx mixed oxides modified by cesium in concentration range of 0.6 – 4.5 wt. % was prepared by calcination of hydrotalcite-like precursor with molar ratio Co:Mn:Al = 4:1:1. Subsequently formed mixed oxide was impregnated with cesium by pore filling method. Two different salts (Cs2CO3 a CsNO3) were used for impregnation. Samples was characterized by several analytical methods – AAS, XRD, SBET, TPR-H2, TPD-CO2, TPD-NH3, XPS and TAD. Experimental measurements of N2O catalytic decomposition was carried out in an integral fixed bed stainless steel reactor in temperature range of 210 – 450 °C. The specific surface area of Co4MnAlOx mixed oxide was 92 m2/g and no significant changes were observed after cesium modification. Spinel phase was identified by XRD analysis in catalyst samples. The sample basicity increased with increasing amount of cesium. Samples modified by cesium using CsNO3 exhibited relatively worse reducibility than ones modified by cesium using Cs2CO3. Thermal alkali desorption showed that cesium on the catalyst surface is stable until 550 °C. The catalyst activity increased with increasing cesium amount. The highest catalytic activity was achieved over catalysts with cesium amount in concentration range of 3 – 4 wt. % at conditions simulating the waste gas from nitric acid plant. Used impregnation salt had no influence on catalytic activity. Based on these laboratory results, optimal cesium amount of 3.4 wt. %. was chosen for preparing of pilot plant catalyst designated as AST3. AST3 catalyst was tested for N2O emission reduction in the waste gas in pilot plant reactor connected to tail gas from nitric acid production in BorsodChem MCHZ Ostrava. The high N2O conversion value of 64 – 94 % was achieved at space velocity 11 130 l.lbed-1.h-1 and 450 °C. These values were dependent on variable reaction mixture composition. No deactivation was observed after 142 days of operation. It was found that cesium acts as electron promoter. Small amount of cesium promotes easier scission of N2O molecule on Cs–Co interface. The shift of temperature maxima of TPR-H2 peaks to lower temperatures with increasing cesium amount confirmed easier Co3+ reduction which is related to weakening Co–O bond which leads to lowering of oxygen residence time on the catalyst surface. TPD-O2 tests confirmed that optimal amount of cesium promotes faster oxygen desorption from the catalyst surface, which is a crucial step for N2O catalytic decomposition.Prezenční619 - Katedra fyzikální chemie a teorie technologických pochodůvyhově

N2O catalytic decomposition - From laboratory experiment to industry reactor

Paper deals with design of pilot reactor for low temperature N2O decomposition in off-gases from HNO3 production. Pseudo-homogeneous one-dimensional model of an ideal plug flow reactor was used for modeling of N2O decomposition in a laboratory fixed bed reactor filled with grains or pellets of a Co–Mn–Al mixed oxide catalyst. Increase in inlet pressure up to 0.6 MPa did not influence the effective diffusion coefficient, but improved the achieved N2O conversion. Based on the laboratory data of N2O decomposition over Co–Mn–Al mixed oxide pellets, catalyst bed of 3400 kg was estimated for target 90% N2O conversion (30 000 m3 h−1 of exhaust gases from HNO3 plant containing 0.1 molar% N2O, 0.01 molar% NO, 0.01 molar% NO2, 3 molar% H2O, 5 molar% O2) at 420 °C and 600 kPa inlet pressure.Web of Science191112011

Optimization of Cs content in Co-Mn-Al mixed oxide as catalyst for N2ON_2O decomposition

A series of Co–Mn–Al mixed oxide catalysts with different Cs contents (0.5–4.6 wt%) was prepared by calcination of Co–Mn–Al hydrotalcite (Co:Mn:Al = 4:1:1), followed by impregnation by cesium salt (CsNO3, Cs2CO3) using the pore filling method. Chemical analysis, N2 sorption, temperature programmed reduction (TPR)-H2, temperature programmed desorption (TPD)-CO2 and TPD-NH3 and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. All prepared catalysts were tested for N2O catalytic decomposition in inert gas and in the presence of oxygen, water vapor and nitric oxide. The influence of Cs salts used for catalyst preparation and cesium content on catalyst activity were studied. A significant increase in catalytic activity with increasing amount of cesium promoter was observed without respect to the Cs precursor. The strong promotional effect of cesium is electronic in nature and is discussed in term of changes in surface composition and catalyst reducibility.Web of Science41129332931

A comparative study of TiO2-supported and bulk Co-Mn-Al catalysts for N2O decomposition

A series of Co–Mn–Al/TiO2 catalysts with different Co + Mn loading (5–24 wt.%) was prepared by impregnation of TiO2 support. Bulk Co–Mn–Al mixed oxides were prepared by different methods. The prepared catalysts were characterized by chemical analysis, surface area measurement, temperature programmed techniques (TPR, TPD) and tested for N2O catalytic decomposition. TiO2 acted only as a catalytic support and did not contribute to the catalytic activity. The N2O conversion over TiO2-supported Co–Mn–Al catalysts was increasing with Co + Mn loading, and was proportional to the amount of easily reducible components. Comparing the catalysts with identical amount of active components, the highest catalytic activity was achieved on the calcined precursors having carbonates in their molecules (layered double hydroxides Co–Mn–Al-HT-ex and Co–Mn–Al-carb), the lowest one on the calcined Co–Mn–Al nitrates due to the lower surface area, less advantageous porous structure and worse reducibility.Web of Science191111511

On the stability of alkali metal promoters in Co mixed oxides during direct NO catalytic decomposition

Co-Mn-Al mixed oxide and Co3O4 catalysts with alkali metal promoters (K, Cs) were tested for direct NO decomposition with the aim to determine their activity and stability. The catalysts were prepared by coprecipitation with subsequent impregnation by alkali metal salts and characterized by AAS, MP-AES, XRD, N-2 physisorption and species-resolved thermal alkali desorption (SR-TAD). Long-term experiments of NO catalytic decomposition performed above the temperature of alkali metal desorption showed slow deactivation which has not yet been reported by other authors, since only short laboratory tests of NO catalytic decomposition have been presented. The reason for the observed deactivation was identified as volatilization of alkali metal promoters from the catalyst surface, which was revealed by SR-TAD and chemical analysis of alkali metals. Measurements conducted below the temperature of alkali metal desorption yielded an increase in NO conversion during the initial period of measurement, which can be explained by rearrangement of surface species.Web of Science428403

K-doped Co-Mn-Al mixed oxide catalyst for N2O abatement from nitric acid plant waste gases: pilot plant studies

The K-doped Co-Mn-Al mixed oxide deN2O catalyst was prepared by calcination of Co-Mn-Al layered double hydroxide, subsequent impregnation with KNO3, and shaping into tablets of 5 mm × 5 mm. Tablets were tested for N2O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NOx/NH3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical-chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N2O conversion of 90 ± 6% at 450 °C was kept (GHSV = 11 000 m3 mbed-3 h-1). The obtained kinetic data were applied in modeling of a full-scale reactor for the N2O emissions abatement and can be used for estimation of the amount of the catalyst necessary for obtaining required N2O conversion in the target plant.Web of Science55267084707

Effect of precursor synthesis on catalytic activity of Co3O4Co_3O_4 in N2ON_2O decomposition

Series of precursors was prepared by precipitation of cobalt nitrate in aqueous solutions using various precipitation agents (NH3·H2O, NaOH, Na2CO3) and reactions conditions (OH/Co molar ratio, aging time). Powder XRD showed different phase composition of the obtained precursors, in which β-Co(OH)2, CoII–CoIII layered double hydroxide, and basic cobalt carbonate were identified. Only Co3O4 spinel-like oxide was found in products after heating at 500 °C in air but different N2O conversions were observed over the examined oxide catalysts. Especially the catalysts obtained from β-Co(OH)2 precursors showed high catalytic activity in N2O decomposition. The correlation between methods of preparation, phase composition of precursors, catalytic properties of the related oxide catalysts, and the role of the cobalt ions as catalytic active sites is discussed