Alternative energy technologies are greatly hindered by significant limitations in materials science. From low activity to poor stability, and from mineral scarcity to high cost, the current materials are not able to cope with the significant challenges of clean energy technologies. However, recent advances in the preparation of nanomaterials, porous solids, and nanostructured solids are providing hope in the race for a better, cleaner energy production. The present contribution critically reviews the development and role of mesoporosity in a wide range of technologies, as this provides for critical improvements in accessibility, the dispersion of the active phase and a higher surface area. Relevant examples of the development of mesoporosity by a wide range of techniques are provided, including the preparation of hierarchical structures with pore systems in different scale ranges. Mesoporosity plays a significant role in catalysis, especially in the most challenging processes where bulky molecules, like those obtained from biomass or highly unreactive species, such as CO2 should be transformed into most valuable products. Furthermore, mesoporous materials also play a significant role as electrodes in fuel and solar cells and in thermoelectric devices, technologies which are benefiting from improved accessibility and a better dispersion of materials with controlled porosity.

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A series of carbide-derived carbons (CDC) have been prepared starting from TiC and using different chlorine treatment temperatures (500ºC-1200ºC). Contrary to N 2 adsorption measurements at -196ºC, CO 2 adsorption measurements at room temperature and high pressure (up to 1 MPa) together with immersion calorimetry measurements into dichloromethane suggest that the synthesized CDC exhibit a similar porous structure, in terms of narrow pore volume, independently of the temperature of the reactive extraction treatment used (samples synthesized below 1000ºC). Apparently, these carbide-derived carbons exhibit narrow constrictions were CO 2 adsorption under standard conditions (0ºC and atmospheric pressure) is kinetically restricted. The same accounts for a slightly larger molecule as N 2 at a lower adsorption temperature (-196ºC), i.e. textural parameters obtained from N 2 adsorption measurements on CDC 2 must be underestimated. Furthermore, here we show experimentally that nitrogen exhibits an unusual behavior, poor affinity, on these carbide-derived carbons. CH 4 with a slightly larger diameter (0.39 nm) is able to partially access the inner porous structure whereas N 2 , with a slightly smaller diameter (0.36 nm), does not. Consequently, these CDC can be envisaged as excellent sorbent for selective CO 2 capture in flue-gas streams.

The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

Highlights Desilication of TS-1 using NaOH gives rise to hierarchical zeolites.  Desilicated TS-1 exhibits a large BET surface area together with a well-developed mesoporosity.  Hierarchical TS-1 remains the activity of the original TS-1 for oxidation of small molecule.  Hierarchical TS-1 shows a significant improvement compared to original TS-1 for the oxidation of bulky molecules. AbstractA series of hierarchical TS-1 zeolites have been produced by desilication of the original TS-1 (4 wt.% Ti) using a chemical treatment with NaOH. Desilicated TS-1 zeolites exhibit a large BET surface area together with a well-developed mesoporosity. The hierarchical samples show good catalytic activity for the oxidation of small molecules while significantly higher activity for the oxidation of bulky molecules.

Hysteresis phenomena are usually observed in the characterization of porous solids using gas adsorption of polar and nonpolar probe molecules. Commonly, hysteresis phenomena take place at high relative pressures due to the presence of metastable states associated with the capillary condensation of the probe molecule on mesopores. However, low-pressure hysteresis phenomena have also been reported for porous solids such as ordered mesoporous silicas, zeolites, and activated carbons. Unfortunately, the reason behind these processes taking place at low pressure is still unclear. Here we prove that the low-pressure hysteresis is rather an artifact associated with the lack of equilibrium in the adsorption isotherm and/or the lack of proper outgassing, mainly found in porous solids where narrow pore constrictions are expected.

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