Geopolymerization of meta-kaolins with different morphologies

The reactivity of two commercial meta-kaolins with similar composition and specific surface areas but different morphologies was tested during geopolymerization with potassium silicate alkaline solution. Manual and short term mechanical stirrings were used to not complete geopolymerization and to emphasize the powders surface reactivity. Moreover, radiation, infra red, micro waves heating were used during curing. The degree of geopolymerization was checked by SEM and N2 adsorption (BET), FTIR and 27Al MAS NMR spectroscopies. The meta-kaolin powder with rounded agglomerates was the less reactive, but it was the more sensitive to the various geopolymerization conditions. The fine dispersed lamellar powder was more reactive and it was mainly affected by mixing. The addition to the potassium silicate alkaline solution of a small alkaline cation such as lithium favoured the dissolution stage during geopolymerization, but decreased the melting temperatur

Reduction catalytique sélective de NO par NH3 sur Fe-ZSM-5

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Oxidative dehydrogenation of propane over Fe-BEA catalysts

Conférence du 02 au 06 septembre 2008International audienc

Nízkoteplotní selektivní oxidace metanu na vzdálených binukleárních kationtových centrech zeolitů

Highly active oxygen capable to selectively oxidize methane to methanol at low temperature can be prepared in transition-metal cation exchanged zeolites. Here we show that the alpha-oxygen stabilized by the negative charges of two framework aluminum atoms can be prepared by the dissociation of nitrous oxide over distant binuclear cation structures (M(II) ... M (II), M = cobalt, nickel, and iron) accommodated in two adjacent 6-rings forming cationic sites in the ferrierite zeolite. This alpha-oxygen species is analogous to that known only for iron exchanged zeolites. In contrast to divalent iron cations, only binuclear divalent cobalt cationic structures and not isolated divalent cobalt cations are active. Created methoxy moieties are easily protonated to yield methanol, formaldehyde, and formic acid which are desorbed to the gas phase without the aid of water vapor while previous studies showed that highly stable methoxy groups were formed on isolated iron cations in iron exchanged ZSM-5 zeolites.Vysoce aktivní kyslík dostupný pro selektivní oxidaci metanu na metanol při nízkých teplotách může být připraven iontovou výměnou v zeolitech

Effect of the Al Siting on the Structure of Co(II) and Cu(II) Cationic Sites in Ferrierite. A Periodic DFT Molecular Dynamics and FTIR Study

Periodic DFT molecular dynamics and FTIR spectroscopy were used to investigate the cationic sites of ferrierite exchanged with Co­(II) and Cu­(II) and their complexes with NO. Particular attention was paid to the effect of the Al siting in six-membered rings forming the cationic sites on the structure of these sites and the corresponding binding energies of Me­(II) (Me = Co and Cu). Our calculations show that both the cations upon binding to cationic sites induce a rearrangement of the local structure of the zeolite framework. The rearrangement is significant for the α and β-2 sites while it is minor for the β-1 site. Comparison of the observed and theoretical NO stretching frequencies of ferrierite Co­(II) and Cu­(II) complexes with a NO molecule permitted the assignment of IR bands to the individual types of cationic sites. For NO-Co-ferrierite, the IR bands found at 1956, 1941, and 1935 cm^–1 can be assigned to NO-Co complexes with Co­(II) located in the α, β-1, and β-2 sites, respectively. Similarly for NO-Cu-ferrierite, the frequencies of 1864, 1912, 1904, and 1892 cm^–1 belong to NO-Cu complexes having Cu­(II) accommodated in the α, β-1, β-2 (conformer 1), and β-2 (conformer 2) sites, respectively. The calculated adsorption energies are systematically higher for Co­(II) than for Cu­(II) for all the three sites and are in the order α > β-2 > β-1 for both the cations. Our computational results further reveal that upon binding Me­(II) both the local structure of the zeolite framework as well as the binding energies of Me­(II) strongly depend on the Al siting in the rings forming the cationic sites. The calculated relative binding energies of Me­(II) are in the order β-1 > β-2 > α for both the cations. The general tendency of Me­(II) accommodated in a cationic site to react is inversely proportional to the corresponding binding energies. We also showed that FTIR spectroscopy of complexes of NO and Me­(II)-exchanged ferrierite can serve to identify the Al siting in the six-membered rings forming cationic sites