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The conversion of methane or natural gas into turquoise H2 and carbon represents a promising pathway towards decarbonised energy. The pyrolysis of biogas (mainly a mixture of methane and CO2) is considered to be a negative carbon-emission technology, as the carbon source comes from biomass and the carbon is captured in solid form. In addition, the presence of CO2 in the gas mixture enables the dry reforming of methane into syngas. In this study, we show that direct biogas conversion in a fluidised catalytic reactor can produce a syngas whose composition meets the requirements for methanol synthesis or for liquid hydrocarbon production via the Fischer-Tropsch process. Confirmed by thermodynamic analysis, we show that the reaction proceeds at temperatures above 900 1C to produce carbon materials, whereas at lower temperatures the carbon is converted to CO by the Boudouard reaction. At 950 1C, very high methane and CO2 conversions are achieved (490% and 99%, respectively), accompanied by high hydrogen yield (490%) and the sequestration of carbon into a turbostratic structure. We believe that the direct catalytic reforming of biogas in a fluidised bed, when combined in series with an FTS process, could allow the production of liquid fuels with no need for costly gas separation units, in particular those implemented for CO2 capture. [ABSTRACT FROM AUTHOR]

The characterization of acid sites on solid catalysts is a key to understanding reaction mechanisms at the molecular level. This is generally done indirectly using a model probe molecule able to coordinate or be protonated on surface acid sites. For instance, Temperature Programmed Desorption (TPD) of the pyridine probe molecule followed by IR spectroscopy has become a standard method for the quantification and identification of Brønsted and Lewis acid sites found in zeolites. On the other hand, there is a lack of molecules able to be protonated on very weak Brønsted acid sites. In this work 2,6-ditert- butylpyridine is shown to be a suitable probe for characterizing weak Brønsted acidity. The proof of concept is performed on a series of Pt catalysts supported on a chlorinated alumina support (Pt--γ-Al2O3--Cl) generally used in the reforming process. In particular, we show that the area of the 1617 cm-1 vibration band is correlated to the concentration of Cl introduced into the catalyst. We also underline the relative insensitivity of pyridine as an IR probe molecule and the inadequacy of NH3 TPD for the characterization of acid sites of reforming catalysts, making 2,6-di-tert-butylpyridine a particularly important and specific probe molecule. [ABSTRACT FROM AUTHOR]

A set of 15 metal–organic frameworks (MIL-53, MIL-68, MIL-125, UiO-66, ZIF) exhibiting different pore size, morphology, and surface chemistry is used to unravel the numerous behaviors of water adsorption at room temperature in this class of materials. Outstanding “S”-shaped (type V) adsorption isotherms are observed for MIL-68 type solids. We show that the underlying mechanism of water adsorption can be rationalized using a simple set of three parameters: the Henry constant (i.e. the slope of the adsorption pressure in the low pressure range), the pressure at which pore filling occurs, and the maximum water adsorption capacity. While the Henry constant and pore filling pressure mostly depend on the affinity of water for the surface chemistry and on pore size, respectively, these two parameters are correlated as they both reflect different aspects of the hydrophobicity–hydrophilicity of the material. For a given type of porous structure, the functionalization of the material by hydrophilic moieties such as hydrogen bonding groups (amine or aldehyde) systematically leads to an increase in the Henry constant concomitantly with a decrease in the pore filling pressure. As for the adsorption mechanism, we show that, for a given temperature, there is a critical diameter (Dc∼ 20 Å for water at room temperature) above which pore filling occurs through irreversible capillary condensation accompanied by capillary hysteresis loops. Below this critical diameter, pore filling is continuous and reversible unless the material exhibits some adsorption-induced flexibility. [ABSTRACT FROM AUTHOR]

A key to address advanced MOF materials suitable for more sophisticated applications is to add functionalities of greater complexity in a controlled manner. We report a generic and original post-synthetic modification method starting from amino derived MOFs. The first step consists in converting the amino group into azide (N3). Without isolation nor purification, the desired functionalized material is obtained by grafting the corresponding alkyne using “Click Chemistry”. This work reports for the first time the synthesis of a two-dimensional combinatorial library of 24 functionalized MOFs. We also show that the grafting yield can be controlled from 10 to 100%. Finally, we compare the effect of the grafting yield on the porous volume of (1D) and (3D)MOF porous structures. [ABSTRACT FROM AUTHOR]

The zinc benzimidazolate coordination polymer (ZIF-7) shows a reversible gate-opening effect upon variation of partial pressure of CO2or temperature. This phenomenon, which is unique for a MOF with sodalite topology, arises from a phase-to-phase transformation upon guest adsorption–desorption. [ABSTRACT FROM AUTHOR]