Adszorpciós és katalitikus vizsgálatok DRIFT spektroszkópiai módszerrel = Studies of adsorption and catalysis using the DRIFT spectroscopic method

Tanulmányoztuk az N2 és O2 adszorpció dinamikáját és egyensúlyát természetes és szintetikus zeolitokon. A kutatás eredményeire alapozva 1 m3/óra kapacitással 95 %-os tisztaságú oxigén előállítására alkalmas PSA oxigén generátort terveztünk és építettünk. A munka kapcsán kidolgoztuk az N2 és O2 adszorpció tanulmányozására alkalmas nagynyomású DRIFT spektroszkópiai módszert. A nagynyomású DRIFT spektroszkópiai módszerrel tanulmányoztuk a gyenge bázis nitrogén és a zeolitok savas alakulatainak kölcsönhatását. A vizsgálatok alapján következtetni tudtunk néhány H- és Pt,H-zeolit katalizátor Br?nsted savas helyeinek belső saverősségére. Rámutattunk, hogy a nagy Si/Al arányú H-zeolitok fajlagos (TOF) alkán konverziós alktivitásának különbözőséget nem a belső saverősség különbözősége okozza, hanem elsősorban az adszorpciós környezet zeolitszerkezetből és összetételből fakadó különbözősége. Pontosabb leírást adtunk a Pt,H-zeolit bifunkciós katalizátorok aktív alakulatairól, a hidrogén és az alkánok aktiválódásának lehetséges módjáról ezeken a katalizátorokon. Rámutattunk a Co- és Co,Pt- mordenit katalizátorok metános NOx-SCR reakcióban mutatott aktivitásvesztésének egy lehetséges okára.Operando DRIFT-MS módszerrel kimutattuk, hogy a metános NOx-SCR reakcióban a nitrogénképződés legfontosabb intermedierjei a nitrozóniumion (NO+) és az adszorbeált ammónia (NH3, NH4+). | The dynamics and the equilibrium of the N2 and O2 adsorption were studied on natural and synthetic zeolites. Based on the research results a PSA type O2 generator, having a capacity of 1 m3/h at an oxygen purity of 95 %, was designed and built . In relation to this work the DRIFTS spectroscopic method of high- pressure N2 and O2 adsorption was developed. Using the High-pressure DRIFTS method the interaction of the weak base nitrogen and the acid sites of zeolites was studied. Conclusions could be drawn about the intrinsic acid strength of Brönsted sites in some H- and Pt,H-zeolites. It was pointed out that the different site specific alkane conversion activities (TOFs) of zeolites, having high Si/Al ratio, result primarily from the differences in the adsorption environment that is related with the differences in the zeolite structure and composition, and not from differences in the intrinsic acid strength of the sites. A more precise description was given for the active centers of Pt,H-zeolite bifunctional catalysts and for the activation mechanism of hydrogen and alkane over these catalysts. We pointed out a possible reason for the activity loss of Co- and Co,Pt-mordenite catalysts during the NOx-SCR with methane. Using operando DRIFTS-MS technique we have shown that the most important intermediates of N2 formation in the NOx-SCR with methane are the nitrosonium ion (NO+) and the adsorbed ammonia (NH3,NH4+)

In situ és operando vizsgálatok az NOx szelektív katalitikus átalakításában = In situ and operando studies of the selective catalytic conversion of NOx

A projektben a metánnal végzett szelektív katalitikus NO redukció (NO-SCR) mechanizmusának alaposabb megértését és ezáltal a reakcióban hatékonyabb katalizátor kifejlesztésének megalapozását tűztük ki célul. Vizsgálataink elsősorban a reakcióhoz legígéretesebb Co-, In-, és Pd-, valamint Co,In-, és Pd,In-zeolitokra irányultak. A katalitikus kísérletekben a reduktív szilárdfázisú ioncserével (RSSIE) előállított, promoveált In-zeolitok bizonyultak a legaktívabb és legszelektívebb katalizátoroknak. Rámutattunk arra, hogy az RSSIE folyamat illékony InOH köztitermék keletkezésén és annak a savas helyekkel lejátszódó reakcióján keresztül megy végbe. Megvizsgáltuk, hogy a katalizátorban hogyan és milyen aktív helyek alakulnak ki. Operando DRIFT spektroszkópiai módszerrel tanulmányoztuk az NO-SCR reakció körülményei között kialakuló felületi képződményeket és reaktivitásukat. Az eredményekből a katalizátorszerkezet és aktivitás közötti összefüggésekre, valamint az NO-SCR reakció mechanizmusára következtettünk. Kimutattuk, hogy az NO-SCR reakció körülményei között az aktív centrumokon NO+/NO3- képződmények alakulnak ki. A metán az NO3- képződménnyel reagálva aktiválódik, míg az NO+ a keletkezett aktív intermedierrel a nitrogén képződéséhez vezető lépésben vesz részt. Az NO+/NO3- képződmények kialakulásához NO2, ill. annak képződését katalizáló katalitikus funkció szükséges. A Co és Pd promótor az NO oxidációját gyorsítja fel oxigénnel NO2-vé, ami nagyobb felületi NO+/NO3- koncentrációhoz, s végül nagyobb NO-SCR aktivitáshoz vezet. | The present project concerns the understanding of the mechanism of selective catalytic reduction of NO (NO-SCR) with methane and, thereby, to provide better scientific bases for the development of a more effective catalyst for the reaction. The investigation was focused on the most promising Co-, In-, Pd-, Co,In-, and Pd,In-zeolites. The results of the study revealed that promoted In-zeolites prepared by reductive solid state ion-exchange (RSSI) method were the most active and selective catalysts. It was shown that the RSSIE process proceeded via volatile InOH intermediate and its reaction with the Br?nsted acidic sites of the zeolite. We studied the relation between the method of catalyst preparation and catalytic properties. The surface species formed under reaction conditions in the NO-SCR reaction and their reactivity were investigated by operando DRIFT spectroscopy. The results obtained allowed us to verify the relationship between the catalyst structure and activity and outline a plausible reaction mechanism. It was shown that under conditions of the NO-SCR reaction NO+/NO3- species were formed on the active sites. Methane was activated in reaction with NO3- species, whereas NO+ took part in the reaction with the thus obtained active intermediate leading to the formation of N2. A catalytic function was necessary to obtain NO2 that was needed for the formation of NO+/NO3- species. The Co and Pd promoters accelerated the oxidation of NO to NO2 with O2, which resulted in a higher NO+/NO3- concentration and finally in a higher NO-SCR activity

Hordozós zeolitmembránok előállítása, fizikai-kémiai jellemzése és katalitikus alkalmazása = Preparation and characterization of supported zeolite membranes

Újfajta módon, gőzfázisú anyagtranszport eljárással alakítottunk ki vékony, részben orientált MFI zeolitréteget makropórusos hordozón, magadiit Si prekurzorból. Továbbá szintetizáltunk nagy áteresztőképességű, termikusan stabil, nagy szelektivitású zeolitmembránt in-situ eljárással és un. másodlagos növesztéssel amorf Si-forrásból kiindulva. Az ecetsav etanolos észterezésében sikerült az egyensúlyt az etilacetát képződés irányába eltolni a víz folyamatos pervaporációs eltávolításával [Fe]MFI (Si/Fe=100) zeolit membránon keresztül. Ebben a kísérletben a zeolitmembrán inert szeparátorként funkcionált. Bórral izomorfan szubsztituált MFI membrán az 1-butén izomerizációjában katalizátorként és szeparátorként működött. Rámutattunk, hogy a vázszerkezetbe beépült bórhoz kapcsolódó hidroxilcsoportok gyenge Brönsted-savas centrumok, amit a termékeloszlás (transz-2-butén, cisz-2-butén) is igazolt. A permeát oldali, termodinamikai egyensúlyi koncentrációnál magasabb transz-2-butén koncentráció oka, hogy a zeolit csatornáiban transz-2-butén diffúziója gyorsabb. A katalitikus módszert alkalmasnak tartjuk a membránt alkotó zeolitkristályok saverősségének jellemzésére, a zeolit vázszerkezetben az izomorf szubsztitúció bizonyítására, a membránréteg irreverzibilis károsodása nélkül. Anyagtudományi ismereteink bővülésén, kutatási infrastruktúránk javulásán túl a projekt lehetőséget nyújtott Kollár Márton PhD hallgató felkészült szakemberré válásához. | Thin, oriented zeolite layer was synthesized on macroporous alfa-Al2O3 support by vapor-phase transport method applying sheet silicate as Si precursor. High-throughput and high selectivity zeolite membranes, having high thermal and chemical stability were also prepared by in-situ and secondary growth techniques. In the esterification of acetic acid with ethanol the equilibrium was shifted to the formation of ethyl acetate by removing the formed water through the [Fe]MFI (Si/Fe=100) zeolite membrane by pervaporation. In this experiment zeolite membrane worked as inert separator. However, in the reaction of 1-butene isomerization the studied boron substituted MFI membrane had the dual role of the catalyst and the permselective layer. It was proved that double-bond shift occurred, thus cis- and trans-2-butenes were formed. The catalytic selectivity is due to the low acid strength of the Bronsted-sites generated by the framework boron. The ratio of the trans/cis-2-butenes in the permeate stream was higher than the equilibrium value, which was attributed to the permeation selectivity of the membrane for the trans-2-butene. The catalytic method can be applied as acidity characterization technique for the zeolite crystals that build the continuous membrane layer, without irreversible damage of the zeolite film. The project gave opportunity for Márton Kollár Phd student to be trained in membrane techniques and gain experience in this research areas and obtain PhD degree

Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts

Results of X-ray photoelectron spectroscopic (XPS) examination and temperatureprogrammed reduction measurements by H2 (H2-TPR) showed that the Co-zeolite catalysts, which were found most active in the selective catalytic reduction of NO by methane to N2 in the presence of excess O2 (NO-SCR), contain both Co2+/[Co-OH]+/H+ exchange cations, Cooxo species and cobalt oxide clusters. Using operando Diffuse Reflectance Infrared Fourier Transform Spectroscopic method (DRIFTS method) the NO-SCR reaction was shown to proceed in consecutive steps via bifunctional mechanism over active sites (i) promoting the oxidation of NO by O2 to NO2 (NO-COX reaction), and sites (ii) whereon disproportionation and charge separation of 2NO2 generates activated surface intermediate NO3 -/NO+ ion pair. Latter process was found to require Co2+ zeolite cations. The NO-COX reaction was shown to proceed over Co-oxo species and cobalt oxide, if present, and also over Brønsted acid sites but at a significantly lower rate. In the reaction of methane and the NO3 -/NO+ ion pair CO2, H2O, and N2 was formed and the active Co2+ sites were recovered (CH4/NO-SCR reaction). The surface concentration of the NO3 -/NO+ ion pair must have been controlled by the relative magnitude of the apparent rate constants of the consecutive NO-COX and CH4/NO-SCR reactions. Below about 700 K reaction temperature latter reaction governed the rate of the consecutive NO reduction process. Above about 700 K combustion became the main reaction of methane. Because of the low equilibrium NO2 concentration at these high temperatures the NO-COX reaction took over the control over the rate of the NO-SCR process. Under steady state reaction conditions a temperature-dependent fraction of the Co2+ active sites was always poisoned by adsorbed H2O formed in the CH4 oxidation reaction

Selective hydroconversion of levulinic acid to γ-valerolactone or 2 methyltetrahydrofuran over silica-supported cobalt catalyst

Solvent-free hydroconversion of levulinic acid (LA) was studied over Co/silica catalysts applying flow-through fixed-bed microreactor. Consecutive hydrogenation/hydrogenolysis and dehydration reactions proceeded over the catalyst having Co0 metal and CoOx Lewis acid active sites. As a first step, LA was dehydrated to form angelica lactone (AL) intermediate. Because dehydration of LA is a facile reaction, the selectivity was controlled by the hydrogenation/hydrogenolysis activity of the catalyst. At 200 °C and 30 bar total pressure in the steady state, the catalyst could only saturate the double bond of AL ring. Thus, γ-valerolactone (GVL) was obtained with 98 mol% yield at full LA conversion. However, at temperature 225 °C the hydrogenation activity was high enough to cleave the GVL ring and obtain 2-methyltetrahydrofuran (2-MTHF) with a stable yield of about 70 mol %. FT-IR spectroscopic examination of the adsorbed LA showed the formation of H-bound LA and also surface carboxylate. 4-Hydroxy-3-pentenoate and 4-hydroxypentanoate were substantiated as surface intermediates of lactone formation by dehydration

Texture and morphology-directed activity of magnesia-silica mixed oxide catalysts of ethanol-to-butadiene reaction

Magnesia-silica mixed oxide catalysts of different texture and morphology were prepared for the ethanolto-butadiene (ETB) reaction. Magnesia of low and high specific surface area (SSA) were made by thermal decomposition of magnesium nitrate. High-SSA MgO was prepared using hard-templating (HT) method. Mesoporous carbon, obtained by carbonizing a resorcinol-formaldehyde polymer was used as template. The carbon pores were saturated by Mg(NO3 )2 solution and calcined then in order to decompose the nitrate and combust the carbon to get high-SSA MgO. The processes induced by latter calcination were followed by Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) method. To obtain MgO-SiO2 catalysts both magnesia samples were wet-kneaded (WK) with a silica aerogel and a structured mesoporous SBA-15 silica material, having lower and higher SSA, respectively. Morphological and textural properties of these mixed oxide catalysts were characterized by means of N2 physisorption, X-ray powder diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Energy Dispersive X-ray Spectroscopy (EDX). Ranking the catalysts was attempted according to their acidity and basicity, i. e., by the concentration and strength of their acidic and basic sites. Therefore, the samples were characterized by their adsorption interaction with molecules, having either basic or acidic character. The adsorption of CO2 and NH3 was studied by Temperature-Programmed Desorption (TPD) method, whereas that of the pyridine and CDCl3 by Fourier Transform Infrared Spectroscopy (FT-IR). The WK changed the structure of the parent oxides, generated Mg-O-Si bonds, acidity, and basicity. The XPS and EDX results showed that the surface Mg content of the mixed oxide samples made from the low-SSA MgO was higher than that of the bulk phase, while that of the samples made of the high-SSA MgO was lower. This demon- strates that MgO prepared by use of a carbon template proved to be more reactive in the WK process and generated more Mg-O-Si bonds. The mixed oxide catalysts containing high-SSA MgO showed always higher activity and butadiene (BD) selectivity than the corresponding catalyst containing low-SSA MgO. The higher BD selectivity of these catalysts is related to their subtle acidity-basicity balance. Neverthe- less, the measured selectivities did not show correlation with any of the parameters characterizing the acid-base properties of the catalysts. The highest BD yield was obtained at 425 °C achieving 75% ethanol conversion level and 50% BD selectivity