Sol-derived AuNi/MgAl2O4catalysts: Formation, structure and activityin dry reforming of methane

Ni nanoparticles doped with different amount of gold were supported on MgAl2O4by deposition fromaqueous metal sol producing a series of catalysts with different Au content. The sol procedure was allowedto obtain dispersed metal particles with different composition. The particle size and the particle compo-sition of the sol were maintained even after being deposited on the support. The catalysts, characterizedby several techniques such as TPR, XPS, XRD, TEM, HRTEM and EELS at the different stages of their lifeexhibited significant structural modification. In particular, thermal treatments in reducing and oxidizingenvironment produced NiAu alloy phases and NiO surface segregation, respectively. When testing formethane dry reforming with CO2in temperature ramped reaction, the monometallic nickel catalyst wasmore active at lower temperature whereas the bimetallic catalysts were more active at higher temper-ature. The presence of gold slightly affected the CO/H2ratio due to the occurrence of parallel reactionssuch as the reverse water gas shift reaction (RWGS). Both types of catalysts, monometallic and bimetallicones, deactivated a little with time but the degree of activity loss was not in straightforward relation withAu content due to the different effect of gold on the stability and on the amount of carbon formation.© 2013 Elsevier B.V. All rights reserved

Metán aktiválás új módszere: nemes fémmel promoveált Ga-HZSM-5 katalizátor alkalmazása N2O jelenlétében = Novel method in methane activation: noble metal modified Ga-HZSM-5 in the presence of N2O

H-ZSM-5 zeolitból kiindulva gallium ioncserével Ga/H-ZSM-5, valamint második fém (M- Fe, Co, Mo, Ag, Au) vegyületéből impregnálással egyfémes M/H-ZSM-5 és kétfémes M/Ga/H-ZSM-5 katalizátor sorozatot állítottunk elő. A mintákat XRF, XRD, XPS, TPR, TPD, TPSR, TPReact, NH3 lépcsőzetes termo-deszorpció (STD-NH3), Mössbauer spektroszkópia (Fe tartalmú minták esetén), TEM, valamint kinetikus módszerekkel vizsgáltuk. A Ga bevitel növeli a H-ZSM-5 savas centrumainak erejét és számát, a második fém hatására pedig a Ga/H-ZSM-5 erős savas centrumai pedig a M/Ga/H-ZSM-5 minták oxidációs centrumaivá generálódnak. A M/Ga/H-ZSM-5 katalizátorcsalád legjobb mintáin az N2O bontás, valamint a CH4+N2O reakció reaktánsainak 50 %-os konverziójának hőmérséklete 70-160 K-nel csökken a folyamat közismerten legjobb katalizátorához viszonyítva. N2O bomlásakor az erős redox centrumokon nitrogén és oxigén keletkezik. Az oxigén atomok kisebb hányada beépül a zeolit felületbe (Oa), nagyobbik része pedig rövid életű köztes állapotú atomi oxigén (nascent oxygen) formájában reagál a metánnal. Az N2O és CH4 közötti reakció összetett oxigén átviteli mechanizmus alapján megy végbe, amely szerint a N2O nem közvetlenül reoxidálja a katalitikusan aktív centrumokat, hanem MGa-OCH3 összetételű szpecieszekkel reagálva. A katalizátor szerkezetbe beépült Oa oxigén biztosítja a M/Ga/H-ZSM-5 minták kis hőmérsékletű (323-373 K) extra aktivitásának alapját. | Monometallic M/H-ZSM-5 and bimetallic M/Ga/H-ZSM-5 (M- Fe, Mo, Co, Ag, Au) catalysts were prepared by impregnation of H-ZSM-5 and H-ZSM-5 modified by Ga ion exchange, respectively, with M-precursor. The samples were investigated by XRF, XRD, XPS, TPR, TPD, TPSR, TPReact, stepped NH3 desorption (STD-NH3), Mössbauer spectroscopy (in case of Fe containing samples), TEM and kinetic methods. Introduction of Ga increases the strength and number of acidic sites in H-ZSM-5, on the effect of the second metal addition the strong acid centres of Ga/H-ZSM-5 transform into the strong redox sites of M/Ga/H-ZSM-5. On the best performing samples of the M/Ga/H-ZSM-5 catalyst family the temperature of the 50% conversion (T50) in N2O decomposition and CH4+N2O reaction is lower by 70 and 160 K, respectively, than that on the catalysts regarded recently as the most active in these processes. N2O decomposition on the strong redox sites produces nitrogen and oxygen. A smaller part of atomic oxygen is accommodated on the zeolite surface, the larger part of short life time transient atomic oxygen reacts with methane producing MGa-OCH3 species. The reaction between N2O and CH4 takes place via complex oxygen transfer mechanism. N2O does not reoxidize the reduced active sites directly, but reacting with the MGa-OCH3 species. The oxygen accommodated on the catalyst surface plays key role in the low-temperature (323-373 K) extra activity of M/Ga/H-ZSM-5

Thermodynamic equilibrium analysis of CO2 reforming of methane: elimination of carbon deposition and adjustment of H2/CO ratio

Dry (CO2) reforming of methane (DRM) is considered as a promising technique to produce syngas. In this study, to optimise the operating conditions for elimination of carbon deposition, thermodynamic calculations were carried out to understand the effect of various temperatures (550-1200 ̊C), pressures (0.05-5 MPa) and CH4/CO2 mole ratios (0.5-2) on the product of H2/CO ratio as well as the formation of carbon deposition. The suggested DRM operating conditions for carbon free regime are at a temperature greater than 1000 ̊C with CH4/CO2 mole ratio = 1 and pressure P = 0.1 MPa. The operating temperature of carbon free regime could be switched to lower temperature by either lowering the CH4/CO2 mole ratio or decreasing the reaction pressure. The results illustrated that the temperature range for severe carbon formation was between 546 ̊C and 703 ̊C. CH4 decomposition and CO disassociation reaction are considered as the major reactions contributing to carbon formation. The former was promoted at operating conditions of P ≤ 0.1 MPa and 550 ̊C ≤ T ≤ 1000 ̊C, while the latter was enhanced at operating conditions of P ≥ 0.1 MPa and T ≤ 700 ̊C. The syngas produced from optimised carbon free regime operating conditions, could be used to synthesis olefin, heavy hydrocarbons and oxygenated compounds. H2 /CO ratio could be adjusted by the changing CH4 /CO2 mole ratio and/or pressure to satisfy F-T process for different application. Since the latter is only effective when operating temperature is lower than 900 ̊C, the former is proposed as a more efficient method to adjust H2/CO ratio. When the operating temperature of DRM is over 700 ̊C, H2/CO ratio obtained at CH4/CO2 mole ratio of DRM ≤ 1 and P = 0.1 MPa is more preferable to be used for the synthesis of olefin, heavy hydrocarbons and oxygenated compounds. Otherwise the syngas is more suitable for producing alkane (C1 –C5)

Molekuláris klaszter és fémszol prekurzorokból előállított nanorészecskék mezopórusos hordozóban: kialakulásuk, szerkezetük, stabilitásuk és katalitikus jellemzőik vizsgálata = Molecular cluster and metal sol derived nanoparticles in mesoporous supports: study of their genesis, structure, stability and catalytic properties

CO oxidációban katalitikusan aktív Au-redukálható fémoxid nanoszerkezeteket hoztunk létre és stabilizáltunk mezopórusos szilícium-oxid hordozón. Au szolok kontrollált méretű nanorészecskéit adszorpcióval helyeztük a hordozóra, a redukálható Ti-, Ce- és Mn-oxidokat szervetlen vagy fémorganikus prekurzorokkal vittük a rendszerbe. Az inert hordozón stabilizált nagy diszperzitású oxiddal az Au aktívabb határfelületet képez, mint a jól kristályosodott, hordozóként alkalmazott aktív oxidokkal. Nagy aktivitáshoz az Au-redukálható oxid határfelület preferált kialakítása szükséges. A preparálás során a komponensek között fellépő elektrosztatikus kölcsönhatások meghatározó jelentőségűek a határfelületek kialakulásában, amit a kolloid stabilizátorának, az oxidprekurzornak (töltés, ligandum), a pH-nak megfelelő megválasztásával szabályozhatunk. A szilícium-oxid hordozós, aktív oxiddal módosított Au méretstabilitása nagyobb az aktív oxid hordozós aranyénál. A mezopórusos SBA-15 hordozó alkalmazásával ez a stabilitás még nagyobb. CO oxidációban, CO hidrogénben végzett preferenciális oxidációjában (PROX) és propén teljes oxidációjában a redukálható oxidokkal promoveált Au rendszerek az aktívabbak a SiO2 hordozós aranyhoz képest, de a redukálható oxidok minőségének és a morfológiájának hatása eltérő a 3 folyamatban. A glükóz szelektív oxidációjában ellentétes hatást tapasztaltunk, az Au/SiO2 módosítása redukálható oxidokkal csökkentette az aktivitást. | Au-reducible oxid nanostructures catalytically active in CO oxidation have been prepared and stabilised on mesoporous silica support. Controlled size nanoparticles of Au colloids were adsorbed on the support, the reducible Ti, Ce- and Mn-oxides were introduced by inorganic or metal organic precursors. The highly dispersed reducible oxides stabilised on the inert support forms more active interface with Au, than the well crystallised active oxide applied as support. For high activity the preferential formation of the Au-reducible oxid interface is required. The electrostatic interactions between the components during the preparation are decisive in formation of the interfaces, which can be controlled by the proper choice of the colloid stabiliser, the oxide precursor (charge, ligand), the pH. In SiO2 supported, reducible oxide modified Au catalysts the size stability of gold increased compared to the active oxide supported Au. The stability increased further by application of mesoporous SBA-15. In CO oxidation, preferential CO oxidation in hydrogen (PROX) and total oxidation of propene the reducible oxide promoted systems were more active, than the inert SiO2 supported Au, but the effect of the type and morphology of the reducible oxides were different in these 3 reactions. In the selective glucose oxidation opposite trend was experienced, the modification of Au/SiO2 by reducible oxides decreased the activity

Környezetvédelmileg ártalmas anyagok csökkentése arany és ezüst katalizátorral: a szerkezetfüggés modellezése = Gold and silver catalysts for abatement of environmentally harmful materials: modelling the structure dependency

A gépkocsik kipufogó gázaiban nagy mennyiségű NOx, CO és szénhidrogén-származék található, amelyek ártalmasak az emberi szervezetre. Ezek a komponensek drasztikusan csökkenthetők a háromutas katalizátor alkalmazásával. A napjainkban alkalmazott háromutas katalizátorokban Pt, Pd és Rh található cirkónium-oxid stabilizált cérium-oxid, cirkónium-oxid és α-alumínium-oxid hordozón. A jelen munka célja volt Au és Ag alapú katalizátor család fejlesztése a drága Pt és Rh helyettesítésére. Au-Ag kétfémes és az egyfémes Au és Ag mintákat SiO2, TiO2 és CeO2 hordozón állítottunk elő szol adszorpciós módszerrel, hogy vizsgáljuk a két fém egymásra hatását az ötvözet fázisban, és a hordozó hatást. Au/ és Ag/redukálható fémoxid határfelületek hatását különböző jól definiált szerkezetű modell katalizátorokon vizsgáltuk. Ezért Au és Ag nanorészecskéket és rétegeket párologtattunk kontrolált körülmények között a natív SiO2-vel borított Si(100) felületekre különböző módszerekkel (PLD, MBE, magnetron porlasztás). Redukálható oxid (pl. TiO2 FeOx és CeO2) Au-val és Ag-vel alkotott határfelületét többféle szerkezettel hoztuk létre, különböző sorrendben építve egymásra a részecskés vagy a vékonyréteg szerkezetű komponenseket. A minták jellemzését különböző módszerekkel végeztük (XPS, AFM, TEM, XRD, SIMS), valamint vizsgáltuk őket CO oxidációban és NOx redukciójában, valamint kiegészítésként glükóz szelektív oxidációjában. | Automotive exhaust gas contains high concentrations of NOx, CO, and hydrocarbons, which are harmful to human health. These components can be reduced drastically by the use of a three-way catalyst. All commercial three way catalysts in use at present are based on Pt, Pd, and Rh on a support comprised of zirconia-stabilized ceria, zirconia and α-alumina. The present project was aimed at developing a novel family of catalysts, based on Au and Ag, the most promising alternative candidates, to replace the more expensive Pt and Rh. We produced SiO2, TiO2 and CeO2 supported bimetallic Au-Ag and monometallic Au and Ag particles using sol preparation and adsorption method to clarify the cooperation of the two metals in the alloyed phase, and the support effect. The effect of the Au/, Ag/reducible metal oxide interface was studied with model catalysts of well defined various structures produced by different techniques. For this purpose Au and Ag nanoparticles and layers were evaporated in controlled ways onto Si(100) wafers using different new techniques (PLD, MBE, magnetron sputtering). Interface of gold and different oxides like TiO2, FeOx and CeO2 were created in different morphology fabricating of the layers or particles of the two components and changing of the order of the deposition. The samples were characterized by different techniques (XPS, AFM, TEM, XRD, SIMS), and studied in CO oxidation and NOx reduction as well as additionally in glucose selective oxidation

Advanced reactor engineering with 3D printing for the continuous-flow synthesis of silver nanoparticles

The implementation of advanced reactor engineering concepts employing additive manufacturing is demonstrated. The design and manufacturing of miniaturised continuous flow oscillatory baffled reactors (mCOBR) employing low cost stereolithography based 3D printing is reported for the first time. Residence time distribution experiments have been employed to demonstrate that these small scale reactors offer improved mixing conditions at a millimetre scale, when compared to tubular reactors. Nearly monodisperse silver nanoparticles have been synthesised employing mCOBR, showing higher temporal stability and superior control over particle size distribution than tubular flow reactors

Low-temperature coupling of methane

Methane is the main component of natural gas and its utilization amounts to ca. 1.7 109 tons of oil equivalent per year [1]. Since the present reserve of methane is located in remote places, its transportation is a major problem. Methane coupling to form C2+ hydrocarbons is, therefore, of a primary importance because before transportation methane should be converted into hydrocarbons with higher boiling points, such as ethane, propane, etc. The catalytic conversion of methane can be carried out in several ways which have excellently been reviewed in Refs. 1 and 2. Basically, three routes exist: (i) the indirect route in which methane is first converted into syngas in presence of water (steam reforming), CO2 (carbon dioxide reforming), or oxygen (partial oxidation) and the resultant syngas can be utilized in the traditional way; (ii) direct coupling in the presence of oxygen (oxidative coupling of methane, OCM) or hydrogen (two-step polymerization); and (iii) direct conversion in the presence of oxygen to oxygenates (CH3OH, HCOH), in the presence of Cl2, HCI to methane chlorides, in the presence of ammonia to HCN, etc

ON CORRELATION BETWEEN SURFACE STRUCTURE AND CATALYTIC ACTIVITY OF AMORPHOUS ALLOYS

The present paper is a review summarizing our results gained in the field of catalysis over amorphous alloys. The route leading to the formation of the catalytically active phase is presented and the factors which may play a decisive role in this process is discussed. Following the surface characterization of amorphous alloys led to the constructions of a surface model its modifying effects are described. Their catalytic properties are further influenced by the structure and the morphology. These parameters are crucial to the formation of the active metal ensembles and to the behaviour of reactants over the surface. These factors are discussed in detail for the utilization of amorphous alloys, primarily as catalyst precursors