Synthesis and Characterization of Al-MCM-41 and Al-MCM-48 Mesoporous Materials

A novel route in the synthesis of Al-MCM-41 and Al-MCM-48, using tetraethoxysilane (TEOS) and sodium aluminate (NaAlO₂) as Si and Al source has been obtained. The effect of surfactant nature and the synthesis conditions such as surfactant/Si ratio and hydrothermal treatment time on the formed mesostructure regularity has been studied. Different methods of template removal have also been evaluated. The samples were characterized by X-ray diffraction, nitrogen physisorption, FT-IR, and solid-state MAS NMR spectroscopy.     

Synthesis and characterization of Pt‐CMK‐3 hybrid nanocomposite for hydrogen storage

The nanometric carbon CMK‐3 modified with Pt was synthesized and applied as a reservoir for hydrogen uptake. We found that the newly synthesized hybrid composites exhibited significantly enhanced H₂ storage. The approach that we have followed includes synthesis of nanostructures with the experimental study of its adsorption capacity and storage properties. In summary, we have shown that CMK‐3 ordered porous carbon modified with Pt nanoclusters is a promising material for hydrogen uptake. The samples were characterized by X‐ray diffraction, N₂ isotherms, X‐ray photoelectron spectra and transmission electron microscopy. The nanoparticles of Pt (~1.7 nm) incorporated onto the nanostructured carbon CMK‐3 showed higher hydrogen uptake at low and high pressures (3.3 wt% of H₂ sorption at 10 bar and 77 K) than CMK‐3. Copyright © 2014 John Wiley & Sons, Ltd.     

Methane Transformation using Light Gasoline as Co-Reactant over Zn/H-ZSM11

The catalytic conversion of methane (C1) to aromatic hydrocarbons (AH) such as benzene, toluene and xylenes (BTX) over a Zn/H-ZSM-11 catalyst using Light Gasoline (C5+C6) as co-reactant was studied. AH yields were as high as 30 %mol at 500 °C, w/f = 40 g h mol⁻¹ at C1 molar fraction = 0.20. The contact time and time-on-stream effects on the product distribution, were analyzed in detail in order to obtain information about the evolution of different species. The C1 conversion reached 36 mol% C using Zn/HZSM-11 with content of 2.13 mol of Zn²⁺ per cell unit.     

Studies on the synthesis of diacetyl over oxidation zeolite catalysts

Diacetyl (2,3-butanedione) synthesis from methyl ethyl ketone over oxidation zeolites using O₂ as oxidant was studied. Various zeolites with Fe, V and Ti as active sites were employed. VS-1, Ti-NCL, Ti-MCM-41 and FeBEA type materials were synthesized and characterized by BET, FTIR, XRD, pyridine adsorption and template desorption. The detailed study of the effect of reaction temperature, the effect of concentration of oxygen and the addition of water was realized. The most active catalyst was zeolites with V as oxidation center.     

Nature of the active sites in H-ZSM-11 zeolite modified with Zn(2+) and Ga(3+)

H-ZSM-11 zeolite modified with zinc and gallium by ion exchange was investigated using XRD, IR and TPD of ammonia. The modification of the material by zinc produced a lowering of the strong Brønsted acidic sites generating new and strong Lewis sites. Unlike zinc-zeolites, the gallium is localized preferentially on the outer surface of microcrystallites blocking a few Brønsted centers.     

Methane transformation into aromatic hydrocarbons by activation with LPG over Zn‐ZSM‐11 zeolite

Methane (C₁) can be activated by interaction with liquefied petroleum gas (LPG) even at very high C₁ molar fractions in the feed (C₁/(C₁ + LPG)=0.85) at temperatures of 450–550°C, GHSV(LPG)=2240 and 810 ml/g h, over Zn‐ZSM‐11 (molar fraction Zn²⁺/(Zn²⁺H⁺=0.86) and total pressure of 1 atm. The isobutane (i‐C₄) of LPG could be the main responsible of this interaction. Aromatic hydrocarbons were the main products in the whole range of C₁ molar fractions (0.4–0.85) studied, reaching excellent levels of 10–45%. This revised version was published online in July 2006 with corrections to the Cover Date.     

In-containing H-ZSM5 zeolites with various Si/Al ratios for the NO SCR in the presence of CH4 and O2. PAC, TPAD and FTIR studies

A series of In-loaded ZSM5 catalysts with Si/Al ratios of 17, 27 and 50 was studied. The catalytic activity for the NO reduction followed the 27 > 17 = 50 order. The acid properties were investigated by FTIR of pyridine as probe molecule desorbed in vacuum at different temperatures and by Temperature-Programmed Ammonium Desorption (TPAD) of NH₄–In–ZSM5. The nature of the In-species was determined by the Perturbed Angular Correlation (PAC) technique using ¹¹¹In as a probe. The contribution of indium to the acidity nature of the samples seems to be important taking into account that the number of Brönsted acid sites was reduced after the In exchange. In the same way new and strong electron-donor acceptor sites were generated. The PAC results indicate that there exists an important fraction of the indium present in the active sample coordinated as in the In₂O₃ case, while another one corresponding to a non-well defined near-In-neighborhood, is present too in a small fraction.     

Zn-ZSM-11 zeolite catalyst for LPG aromatization

LPG transformation into aromatic hydrocarbons using Zn²⁺ modified pentasil zeolites has been studied at 450–540 °C and 10–58 g h/mol. The conversion and selectivity to aromatics obtained over Zn-H-ZSM-11 catalysts with different degree of exchange suggest, the primary role of the Zn²⁺ species is in C-H activation and the transformation of the intermediates into aromatic hydrocarbons.     

Nature and Reactivity of the Active Species Formed After NO Adsorption and NO + O2 Coadsorption on an Fe-Containing Zeolite

Reactivity of the NO adspecies on Fe-ZSM-11 was studied by FTIR in situ. The effect of Fe content and the oxidation state of Fe in the samples were correlated with the catalytic activity. The relation between the adsorbed species, the Brønsted sites and catalytic activity in the SCR of NO_x to N₂ was also investigated. Moreover, FTIR allowed us to identify the active sites and the adsorption complexes present in FeMFI. Samples prepared by the sol–gel method with different Fe content displaying vastly different activity and selectivity in the reduction of NO to N₂ with isobutane in excess of O₂. Thus, in contact with pure nitric oxide, NO ions, mononitrosyl groups, nitro groups and nitrate ions have been identified. Feⁿ⁺ active sites are the most probable centers for NO oxidation to NO₂ and its further conversion to adsorbed nitro groups and nitrate ions, steps that are crucial for NO reduction. The concerted action of Feⁿ⁺ and H⁺ sites of the catalysts over the NO conversion to N₂ and isobutane conversion was analyzed.