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Abstract: Nanometric Fe2O3 particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica when Fe(III) chelates (EDTA, gluconate and citrate) were used as impregnating precursors. Fe(III) nitrate preferentially yields 8nm uniformly sized Fe2O3 clusters that selectively plug the SBA-15 channels through a geometric confinement effect. An oxidative degradation of Fe-chelate precursors yielded Fe(III) oxidic particles of various sizes and dispersion, depending on the nature and geometry of chelate anion. Fe(EDTA) precursors specifically generated Fe2O3 nanoparticles that selectively migrate towards two types of positions where the silica surface exhibits a high curvature. In samples involving low Fe loadings, Fe2O3 particles first creep towards the silica micropore mouths (nests), in which they are readily confined and stabilized. For higher Fe loadings, when most of the micropore nests were filled, oxidic particles eventually settle as a superficial film on the mesopore walls and undergo stabilization onto the surface roughness that can also favors their confinement, as theoretically predicted by Derouane and co-workers. Upon further reduction, as selectively followed by combined cyclic voltammetry and TPR, Fe2O3 readily yield FeO nanoslabs that remain even more efficiently confined within their respective nest positions through a further acid–base type stabilization. [Copyright &y& Elsevier]

Abstract: Hydrothermally synthesized Ni-containing 1:1 and 2:1 phyllosilicates (PS) were used as catalyst precursors for the CO2 reforming of CH4 to synthesis gas. The textural properties of the reduced and unreduced Ni-based PS were determined by N2 sorption analyses. In situ X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) experiments were used to characterize the generated Ni0 nanoparticles after reduction of the Ni-containing PS under various conditions such as H2 concentration and temperature. In the case of thermally stable PS (2:1 type), the reduction of structural nickel led to the formation of nanometric Ni0 particles over the surface of the remaining unreduced PS, while for Ni 1:1 PS phases nickel particles were supported on silica only. All catalysts were also investigated in the reverse water gas shift (RWGS) reaction to elucidate the effect of RWGS on the reforming reaction. The catalytic results obtained over reduced Ni-containing 1:1 and 2:1 PS confirmed that CH4 conversion was favored by very small Ni0 particles size, whereas CO2 conversion was catalyst support dependent. Our study demonstrated that a number of side reactions can compete with CO2 reforming of CH4 over Ni-containing phyllosilicates. However, by choosing the suitable phyllosilicate structure as catalyst precursor, as well as appropriate reduction conditions and reaction temperature, it may be possible to suppress the parallel reactions to some extent, thereby increasing the selectivity towards the products of the reforming reaction (H2 and CO). Reduced Ni-containing 2:1 PS proved to be stable even at high temperature. Highly dispersed homogeneously sized supported nanometric Ni0 particles over the remaining unreduced 2:1 PS structure are the key factors for high catalytic activity in CO2 reforming of CH4. [ABSTRACT FROM AUTHOR]

Abstract: CO2 reforming of CH4 to synthesis gas was investigated on new grounds using Ni-containing phyllosilicates (PS) as catalyst precursors. Ni-containing 1:1 PS and 2:1 PS were synthesized hydrothermally from a gel containing sodium silicate and nickel chloride, then they were reduced under H2 flow before being used as catalysts. Several complementary techniques including XRD, TG-DTA, FTIR, and TPR were used to evaluate the structural, thermal, spectroscopic and redox properties of the samples, respectively. Ni 2:1 PS were found to be more thermally stable and catalytically active than Ni 1:1 PS. Well crystallized Ni 1:1 PS thermally treated at 700°C resulted in a transitional 2:1 PS phase. The reduction of structural nickel in thermally stable PS led to the formation of nanometric Ni0 particles over the surface of the remaining unreduced PS as well as on silica. The unreduced PS structure with surface OH groups appeared as one of the best supports for Ni0 nanoparticles, resulting in less coke formation, and thereby leading to a high catalytic stability. [ABSTRACT FROM AUTHOR]

Starting from an as-synthesized Na-bearing MCM-41 sample with Si/Al=20, several Cs or K exchanged samples have been obtained. All samples, both washed after exchange to remove the excess alkali–metal salt and unwashed, were characterized by studying in the IR the adsorption of CO at a nominal temperature of 77 K, and of CO2 at room temperature.On unwashed samples, after thermal treatment at 500 °C, a basic alkali-oxide phase and a surface silicate were detected. In contrast, washed samples did not exhibit basic character and only Lewis acidic cationic centers were detected, the strength of which is close to that of alkali-cation exchanged ZSM-5 systems. Unwashed samples were inactive in the isomerization of 1-butene. Washed samples converted 1-butene to cis/trans-2-butene, with a ratio close to one (the presence of isobutene was negligible), as typical of mildly acidic Brønsted centers, which are probably present even after exchange: indeed, a sample of Al-MCM-41 in the protonic form, tested as reference, gave the same reaction with highest activity. [Copyright &y& Elsevier]