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1.
M. Santhosh Kumar J. Prez-Ramírez M.N. Debbagh B. Smarsly U. Bentrup A. Brückner 《Applied catalysis. B, Environmental》2006,62(3-4):244-254
Fe-silicalite and Fe-SBA-15 with similar iron content have been characterized by N2 adsorption, small angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM), high-resolution transmission electron micrographs (HRTEM), UV–vis–DRS and EPR, and tested in direct N2O decomposition, N2O reduction by CO and N2O-mediated propane oxidative dehydrogenation. Both catalysts contain almost exclusively isolated Fe3+ sites of similar concentration and structure, which are, however, stabilized in markedly different pore geometries (intersecting channels of ca. 0.55 nm diameter in Fe-silicalite versus parallel linear pores of ca. 7.5 nm diameter in Fe-SBA-15). This aspect is of vital importance in order to exclusively ascribe different catalytic performances to the environment where the iron species are stabilized. Fe-silicalite revealed to be much more active than Fe-SBA-15 in all reactions studied. This clearly illustrates that the confinement of the iron species in pores of suitable geometry (structure and size) is essential to originate their remarkable catalytic properties. The large pores in ordered mesoporous materials apparently do not generate the required intimate contact between potentially active Fe sites and reactant molecules. 相似文献
2.
The adsorption and reaction of toluene on vanadyl pyrophosphate catalysts was studied by in situ infrared spectroscopy. Strongly adsorbed benzaldehyde and physically adsorbed cyclic anhydride species were observed at temperatures above 523 K. Water formed during reaction generates acid hydroxyl groups which cause a stronger adsorption of benzaldehyde and consecutive oxidation reactions. By co-adsorption of pyridine the acid sites are blocked and the deeper oxidation is suppressed. This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Ursula Bentrup Jörg Radnik Udo Armbruster Andreas Martin Jork Leiterer Franziska Emmerling Angelika Brückner 《Topics in Catalysis》2009,52(10):1350-1359
A new setup is presented which enables simultaneous wide- and small-angle X-ray scattering (WAXS/SAXS) and Raman spectroscopic
experiments during the synthesis of Mo-based mixed oxide catalyst precursors at the μ-spot beamline at the Berliner Elektronenspeicherring-Gesellschaft
für Synchrotronstrahlung (BESSY). Furthermore, we report about the separate monitoring of the same reactions under comparable
conditions by simultaneous combined ATR/UV–vis/Raman spectroscopic measurements. For testing the performance of both experimental
setups two syntheses were described comprising the precipitation of metal molybdates by mixing solutions of metal nitrates
and ammonium heptamolybdate. Additionally, the effect of H3PO4 admixture on precipitation was investigated. The combined evaluation of spectroscopic and WAXS/SAXS data allows the discrimination
between different molybdate species appearing in solution and precipitate. Furthermore, these molybdate species could be assigned
to separate phases of different crystallinity. 相似文献
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5.
M. Stoyanova U. Rodemerck U. Bentrup U. Dingerdissen D. Linke R.-W. Mayer H.G.J. Lansink Rotgerink T. Tacke 《Applied Catalysis A: General》2008,340(2):242-249
High-throughput (HT) experimentation in heterogeneous catalysis exemplifies a multidisciplinary approach to address in an efficient manner different aspects of catalyst development – from synthesis to testing and characterization. The present work reports on preparation systems for rapid parallel synthesis of well defined heterogeneous catalysts and catalyst screening in olefin metathesis. Metathesis of ethene and but-2-ene to propene was chosen as a test reaction. The influences of various parameters such as rhenium oxide loading, catalyst calcination conditions, catalyst pre-treatment, as well as the reaction temperature and contact time on the catalytic performance are discussed. Sample characterization by UV–vis and FT-IR gave an evidence for the formation of active surface perrhenate species, very sensitive to humidity and pre-treatment conditions applied. 相似文献
6.
Catalytic performance of vanadyl pyrophosphate in the partial oxidation of toluene to benzaldehyde 总被引:1,自引:0,他引:1
Vanadyl pyrophosphate catalysts were generated by dehydrating VOHPO4·(1/2)H2O at different temperatures and duration of the dehydration procedure. The as-synthesised materials were characterised by
X-ray diffractometry, FTIR spectroscopy and temperature-programmed reduction. The prolongation of the formation period at
higher temperatures led to improved crystallinity and lower BET surface areas of the vanadyl pyrophosphate specimens and,
additionally, a significantly impeded reducibility of the vanadyl sites was observed. The catalytic performance of the samples
was tested in the partial oxidation of toluene to benzaldehyde. The obtained results revealed an increasing benzaldehyde selectivity
with improved catalyst crystallinity. In situ FTIR and ESR spectroscopy were used to throw more light on the interaction of
the toluene–air feed with the surface of the catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
8.
C. Janke M. Schneider U. Bentrup J. Radnik A. Martin G. Scholz A. Brückner 《Journal of Catalysis》2011,277(2):196-207
Novel P-containing oxynitrides VZrPON were tested besides their VZrPO oxide precursors in the ammoxidation of 3-picoline and compared with P-free VZrON catalysts for analysing the influence of both incorporated P and N on the catalytic performance. Results of XRD, XPS, 31P and 51V MAS NMR as well as of simultaneous in situ-EPR/UV–vis/Raman studies during nitridation have shown that the incorporation of phosphorus enhances the V dispersion, reduces vanadium partially even down to V3+ and leads to the formation of a crystalline ZrV2?xPxO7 phase for Zr/V ? 0.5 with V sites surrounded by four O atoms only. N is preferentially incorporated in the vicinity of P, thus, suppressing the formation of VN moieties. These facts may be a reason why the incorporation of P does not markedly improve the catalytic performance of VZrPON catalysts. 相似文献
9.
K. V. Narayana A. Martin U. Bentrup B. Lücke J. Sans 《Applied Catalysis A: General》2004,270(1-2):57-64
The present contribution is a brief account of investigations carried out on the ammoxidation of o-xylene over a few VPO and V2O5 based catalysts. The desired reaction product is phthalonitrile, however, phthalimide is the main product in most cases besides carbon oxides. The product distribution between nitrile and imide mainly depends on the reaction conditions and the nature of catalyst used. Influence of various reaction parameters such as effects of (i) reaction temperature, (ii) water vapour addition in the feed gas, (iii) NH3/o-xylene mole ratio and (iv) space velocity were studied. It is interesting to note that the removal of water vapour from the feed gas has a highly pronounced promotional effect on the selectivity of phthalonitrile. The nitrile selectivity increased from 2.1 to 34% at the expense of phthalimide (decreased from 53 to 9%) with the complete removal of water vapour in the reactant feed mixture. This observation gives an indication that phthalonitrile being formed in the reaction is further getting hydrolysed to phthalimide via amide intermediate in presence of water vapour. Another interesting aspect of the present investigation is that the titania supported catalysts always gave significantly higher selectivities of phthalimide compared to phthalonitrile. Phthalimide yields up to 80% were reached on a VPO/TiO2 catalyst. 相似文献
10.
V.A. Kondratenko U. Bentrup M. Richter T.W. Hansen E.V. Kondratenko 《Applied catalysis. B, Environmental》2008,84(3-4):497-504
A mechanistic scheme of N2O and N2 formation in the selective catalytic reduction of NO with NH3 over a Ag/Al2O3 catalyst in the presence and absence of H2 and O2 was developed by applying a combination of different techniques: transient experiments with isotopic tracers in the temporal analysis of products reactor, HRTEM, in situ UV/vis and in situ FTIR spectroscopy. Based on the results of transient isotopic analysis and in situ IR experiments, it is suggested that N2 and N2O are formed via direct or oxygen-induced decomposition of surface NH2NO species. These intermediates originate from NO and surface NH2 fragments. The latter NH2 species are formed upon stripping of hydrogen from ammonia by adsorbed oxygen species, which are produced over reduced silver species from NO, N2O and O2. The latter is the dominant supplier of active oxygen species. Lattice oxygen in oxidized AgOx particles is less active than adsorbed oxygen species particularly below 623 K. The previously reported significant diminishing of N2O production in the presence of H2 is ascribed to hydrogen-induced generation of metallic silver sites, which are responsible for N2O decomposition. 相似文献