Special Issue “Selected Papers from the 5nd Edition of Global Conference on Catalysis, Chemical Engineering and Technology (CAT 2019)”

The present Special Issue concerns the papers which have been presented at the fifth edition of the Global Conference on Catalysis, Chemical Engineering & Technology (CAT 2019) that promote linkage of the catalytic science, engineering and technology [...

What Do Tantalum Framework Sites Look Like in Zeolites? A Combined Theoretical and Experimental Investigation

Times Cited: 1 Article English Cited References Count: 61 600rcAb initio periodic DFT calculations on the structural and energy properties of different model tantalum framework sites in tantalum-substituted socialite cavities are presented and related to experimental FTIR measurements on Ta-containing SiBEA zeolites. The tantalum framework sites are characterized by their calculated geometrical parameters, vibrational frequencies, and (de)protonation energies. Ta(V) is stabilized in the zeolite framework as a pentacoordinated site possessing one hydroxyl group. The Ta(V)-OH group is not acidic. It is found that hydration of this site is easier than dehydration. This site is found to be only slightly hydrophilic. Dehydration of the site leads to the formation of Lewis acidic and Lewis basic sites. These results are in agreement with experimental data and allow determining the molecular structure of tantalum sites in the zeolite framework

What Do the Niobium Framework Sites Look Like in Redox Zeolites? A Combined Theoretical and Experimental Investigation

Times Cited: 3 Article English Cited References Count: 61 556gqAb initio periodic DFT calculations oil the structural and energy properties of different model niobium framework sites ill niobium-substituted zeolites containing sodalite cavities are presented and related to experimental FTIR measurements oil Nb containing SiBEA zeolite. The niobium framework sites are characterized by their calculated geometrical parameters, vibrational frequencies, and (de)protonation energies. Niobium(V) is stabilized ill the zeolite framework Lis a penta-coordinated site possessing one hydroxyl group. The Nb-OH group is not acidic. It Was found that hydration of this site was easier than dehydration, although the relative low hydrophylicity of the site. Dehydration of the site leads to the formation of Lewis acidic and Lewis basic sites as it was found in mesoporous niobium doped silica materials. These results are fully consistent with experimental data and allow the identification of the molecular structure of niobium sites in a zeolite framework

Preparation of two series of VxSiBeta zeolite catalysts with V centres in framework and extra-framework positions and their application in selective oxidation of methanol

International audienceTwo series of V-containing Beta zeolites have been prepared by contacting of the aqueous NH 4 VO 3 solution with two SiBeta zeolites at pH = 2.5 and 6, respectively. Because of the presence in NH 4 VO 3 solution at pH = 2.5 mainly monomeric VO 2 + ions, vanadium have been easily incorporated into framework of SiBeta zeolite as pseudo-tetrahedral non hydroxylated (SiO) 3 V = O and hydroxylated (SiO) 2 (OH)V = O species. The moderate nucleophilicity of the basic vanadyl oxygen of the latter species play important role in methanol oxidation toward formaldehyde. The selectivity toward formaldehyde on this series of V x SiBeta(I) increases with the amount of pseudo-tetrahedral hydroxylated (SiO) 2 (HO)V = O species, which act as either redox or acidic and basic centres. In contrast at pH = 6, the aqueous NH 4 VO 3 solution is expected to contain both mononuclear and polynuclear V ions, thus it is more difficult to incorporate V species in SiBeta at this condition as shown by FT-IR and NMR data. The absence of pseudo-tetrahedral V species in framework position of V 0.6 SiBeta(II) is probably responsible for lack of activity of this catalyst in methanol oxidation. The appearance of this species in the series of V x SiBeta(II) zeolites for high V content leads to their activity in methanol oxidation toward formaldehyde

Identification of iron species in FeSiBEA by DR UV–vis, XPS and Mössbauer spectroscopy : influence of Fe content

International audienceThe nature of iron in FeSiBEA zeolite was identified using DR UV-vis, XPS and Mössbauer spectroscopy. Various FexSiBEA zeolites (x = 3.8, 8.2 and 15 wt.%) were prepared by a two-step post synthesis method, which consisted in the creation of vacant T-atom sites by dealumination of tetraethylammonium BEA zeolite with nitric acid and then impregnation of resulting SiBEA with an aqueous solution of Fe(NO3)3. The incorporation of iron into the framework of SiBEA was evidenced by XRD. In Fe3.8SiBEA with low Fe content mainly framework tetrahedral Fe(III) species is present, in contrast, with high Fe content additional octahedral FeOx oligomers (Fe8.2SiBEA) and iron oxides (Fe15SiBEA) occur. The presence of iron in its 3+ oxidation state as isolated tetrahedral Fe(III) species for low metal content was demonstrated by DR UV-vis, XPS and Mössbauer spectroscopy. Moreover, the presence of Fe(III) species in two different tetrahedral environments was evidenced by Mössbauer results. For high iron content, diffuse reflectance UV-vis and Mössbauer spectra revealed additional presence of extra-framework FeOx oligomers. After calcination and rehydration significant amounts of oxide phases are formed, which were evidenced by DR UV-vis, Mössbauer spectroscopy and XPS

Catalytic properties of AgAlBEA and AgSiBEA zeolites in H2-promoted selective reduction of NO with ethanol

International audiencePhysicochemical properties of AgAlBEA and AgSiBEA zeolites were investigated by IR spectroscopy with pyridine, H2-TPR, XPS and diffuse reflectance UV–vis spectroscopy. Their catalytic properties were studied in the process of selective reduction of NO with ethanol and in the presence of hydrogen in reaction mixture. AgAlBEA catalysts show wider temperature range of NO-to-N2 conversion in the process of SCR with ethanol than AgSiBEA. Promoting H2-effect on the SCR of NO with ethanol is observed in the presence of AgAlBEA catalysts, whereas it is almost absent for AgSiBEA. A key factor for better performance of AgAlBEA than AgSiBEA is the presence of silver nanoclusters in close proximity of strong Lewis acidic sites