Hidrogén előállításának új lehetőségei kis szénatom számú vegyületek reakcióiban = New route for hydrogen production in the conversion of C1-C2-compounds

Az alternatív energiaforrások iránt megnövekedett igény fordította a figyelmet az etanol reformálása felé. Ideális esetben a reakció terméke H2 és CO2 lenne. E pályázat keretében részletesen vizsgáltuk a H2 előállításának lehetőségeit bioetanolból. Az etanol + víz reakciójában Al2O3 hordozós nemesfém katalizátorokon a H2 képződés sebessége időben csökken, míg az etilén szelektivitása nő közel állandó konverzió mellett. A legnagyobb mértékű változást a Pt katalizátorok esetében észleltük, mely a katalizátor Pt tartalmának, a víz koncentrációjának növelésével és a reakció hőmérsékletének az emelésével jelentősen csökkenthető. Részletesen vizsgáltuk az etanol és az etanol + víz elegy kölcsönhatását Al2O3 és CeO2 hordozós nemesfém katalizátorokon FTIR, TPD és TPR módszerekkel. Megállapítottuk, hogy a hőmérséklettől függően az adszorbeált etanol mellett, különböző etoxi csoportok, CO, acetaldehid, valamint acetát csoportok kimutathatók a katalizátorok felületén. A felületi acetát még 700 K körüli is detektálható. Az adszorbeált etanol TPD görbéjén egy magas hőmérsékletű deszorpciós formát is találtunk, melyet a hordozók esetében nem észleltünk. Ezt az eredményt a felületi acetát formák képződésével és bomlásával értelmeztük A katalizátorok szelektivitásának megváltozását az etanol + víz reakcióban az acetát csoportok képződésének tulajdonítottuk, melyek gátolják a fémen lejátszódó reakciót annak ellenére, hogy ezek a formák a hordozókhoz kötődnek. | The increasing demand for alternative energy sources turned the attention towards the reforming of ethanol. In an ideal case, the products would be H2 and CO2. In the frame of this project we studied the H2 production from ethanol that itself can be produced by biotechnological methods. In the reaction of ethanol and H2O over the Al2O3 supported noble metal catalysts the formation rate of H2 decreased and that of C2H4 increased in time, while the conversion was almost constant. The highest change in the products selectivity was observed on the Pt sample. This trend was attenuated by increasing: the H2O concentration, the metal loading and the reaction temperature. We have studied the interaction of ethanol and the ethanol - H2O mixture over Al2O3 and CeO2 supported noble metal catalysts by FTIR, TPD and TPR methods. It was proved that depending on the temperature, adsorbed ethanol, different ethoxy species, CO, acetaldehyde, and acetate species are present on the surfaces. The acetate is stable even above 700 K. On the TPD curves of the adsorbed ethanol a high temperature desorption stage was observed which did not occur in the case of the pure supports. This result was explained by the formation and decomposition of the acetate species. It was assumed that the selectivity change in the ethanol + H2O reaction can be attributed to the formation of surface acetate groups which hindered the reaction on the metal, although these species were located rather on the support

Rapid-Scan Operando Infrared Spectroscopy

Novel methodology, referred to as rapid-scan operando, has been demonstrated to be a highly powerful tool for studying reaction mechanisms in heterogeneous catalysis, because it combines rapid scan for IR monitoring in the milliseconds time frame and operando methodology. As proof of concept, the NOx–CO and NOx–H2 reactions were studied as model catalyzed reactions with practical interest for removal of NOx in diesel exhausts. Rapid-scan operando experiments confirmed state-of-the-art knowledge concerning the reaction mechanisms and, more importantly, allowed us to elucidate, for the first time, the different roles of the surface hydroxy groups depending on the reductant used (CO or H2). Moreover, this new tool was used to distinguish the behavior of carbonates and nitrites under reaction conditions that could not be monitored by conventional IR spectroscopy approaches owing to overlap of their absorbance bands.Financial support from Generalitat Valenciana (Project PROMETEOII/2014/010 and grant BEST/2014/250), Spanish Ministry of Economy and Competitiveness (Projects CTQ2012–30703 and MAT2014–61992-EXP, and grant PRX14/00249), and the European Union (FEDER funding)

Effects of Ba loading and calcination temperature on BaAl2O4 formation for BaO/Al2O3 NOx storage and reduction catalysts

The effect of thermal treatment on the structure and chemical properties of Ba-oxide-based NOx storage/reduction catalysts with different Ba loadings was investigated using BET, TEM, EDS, TPD and FT-IR techniques. On the basis of the present and previously reported results, we propose that moderate ( 8 wt.% BaO), small (similar to 5 nm) particles of 'bulk' BaO are present on top of the one ML BaO/Al2O3 surface. We did not observe any detectable morphological changes upon higher temperature thermal treatment of 2 and 8 wt.% BaO/Al2O3 samples, while dramatic changes occurred for the 20 wt.% sample. In this latter case, the transformations included BaAl2O4 formation at the expense of the bulk BaO phase. In particular, we conclude that the surface (ML) BaO phase is quite stable against thermal treatment, while the bulk phase provides the source of Ba for BaAl2O4 formation. (c) 2006 Elsevier B.V. All rights reservedclose526

Reduction of stored NOx on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts with H-2 and CO

in situ Fourier transform infrared spectroscopy, coupled with mass spectrometry a the efficiency of nitrate reduction with CO and H-2 on Pt/Al-2-O-3 and Pt/BaO/Al2O3 NOx storage reduction (NSR) catalysts. Surface nitrates NO2 adsorption. and their reduction efficiencies were examined oil the catalysts together with the analysis of the gas-phase were generated by NO2 composition in the presence of the two different reductants. H-2 was found to be a more effective reducing agent than CO. In particular, the reduction of surface nitrates proceeds very efficiently with H-2 even at low temperatures (similar to 420 K). During reduction with CO2 isocyanates form and adsorb on the oxide components of the catalyst; however, these surface isocyanates readily react with water to form CO2 and ammonia. The NH3 at higher temperatures (> 473 K) to produce N-2. In the absence of H2O the NCO species are stable to high temperatures and are removed from the catalyst only when they react with NOx thermal decomposition products to form N-2 and CO2 The results of this study point to a complex reaction mechanism involving tile removal of Surface oxygen atoms from Pt particles by either H-2 or CO2 the direct reduction of stored NOx with H-2 (low-temperature NOx reduction), the formation and subsequent hydrolysis of NCO species, and the direct reaction of NCO with decomposing NOx (high-temperature NOx reduction). (c) 2006 Elsevier Inc. All rights reservedclose11011

Changing morphology of BaO/Al2O3 during NO2 uptake and release

The changes in the morphology of Ba-oxide-based NOx storage/reduction catalysts were investigated using time-resolved X-ray diffraction, transmission electron microscopy, and energy dispersed spectroscopy. Large Ba(NO3)(2) crystallites form on the alumina support when the catalyst is prepared by the incipient wetness method using an aqueous Ba(NO3)(2) solution. Heating the sample to 873 K in a He flow results in the decomposition of the Ba(NO3)(2) phase and the formation of both a inonolayer BaO film strongly interacting with the alumina support and nanocrystalline BaO particles. Upon NO exposure of these BaO phases at room temperature, small (nanosized) Ba(NO3)(2) crystals and a monolayer of surface nitrate form. Heating this sample in NO2 results in the coalescence of the nanocrystalline Ba(NO3)(2) particles into large crystals. The average crystal size in the reformed Ba(NO3)(2) layer is significantly smaller than that measured after the catalyst preparation. Evidence is also presented for the existence of a monolayer Ba(NO3)(2) phase after thermal treatment in NO2, in addition to these large crystals. These results clearly demonstrate the dynamic nature of the Ba-containing phases that are active in the NOx storage/reduction process. The proposed morphology cycle may contribute to the understanding of the changes observed in the performances of these catalysts during actual operating conditionsclose656

Effect of barium loading on the desulfation of Pt-BaO/Al2O3 studied by H-2 TPRX, TEM, sulfur K-edge XANES, and in situ TR-XRD

Desulfation processes were investigated over sulfated Pt-BaO/Al2O3 with different barium loading (8 and 20 wt%) by using H-2 temperature programmed reaction (TPRX), transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and in situ time-resolved X-ray diffraction (TR-XRD) techniques. Both sulfated samples (8 and 20 wt%) form sulfate species (primarily BaSO4) as evidenced by S K-edge XANES and in situ TR-XRD. However, the desulfation behavior is strongly dependent on the barium loading. Sulfated Pt-BaO(8)/Al2O3,consisting predominantly of surface BaO/BaCO3 species, displays more facile desulfation by H-2 at lower temperatures than sulfated Pt-BaO(20)/Al2O3, a material containing primarily bulk BaO/BaCO3 species. Therefore, after desulfation with H-2 up to 1073 K, the amount of the remaining sulfur species on the former, mostly as BaS, is much less than that on the latter. This suggests that the initial morphology differences between the two samples play a crucial role in determining the extent of desulfation and the temperature at which it occurs. It is concluded that the removal of sulfur is significantly easier at lower barium loading. This finding can potentially be important in developing more sulfur resistant LNT catalyst systemsclose272