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.

Novel insights into the surfactant-templating process leading to the formation of tailored intracrystalline mesoporosity in USY zeolite are presented in the light of the changes in the textural, morphological, and chemical properties of this zeolite produced during its treatment in a basic solution of cetyltrimethylammonium bromide (CTAB). The inability of analogous surfactants with bulkier heads to produce mesoporosity suggests that individual CTAB molecules can actually enter the zeolite through its microporosity. Once inside, the surfactant molecules self-assemble to produce the micelles responsible for the formation of mesoporosity causing the expansion of the zeolite crystals, as evidenced by He pycnometry measurements. The analysis of ultramicrotomed samples by transmission electron microscopy evidenced the formation of uniform intracrystalline mesoporosity throughout the entire crystals. In order to investigate an alternative method, namely, the dissolution and reassembly of zeolites, this was performed in USY leading to the formation of composite materials, which are distinctly different from the zeolite with intracrystalline mesoporosity obtained by surfactant-templating. Finally, it was proved that the presence of mesoporosity in the initial zeolite is not needed for the surfactant-templating to occur. This was verified by surfactant-templating of a NaY zeolite, which does not present the large mesopores found in USY.

The development of intracrystalline mesoporosity within zeolites has been a long-standing goal in catalysis as it greatly contributes to alleviating the diffusion limitations of these widely used microporous materials. The combination of in situ synchrotron X-ray diffraction and liquid-cell transmission electron microscopy enabled the first in situ observation of the development of intracrystalline mesoporosity in zeolites and provided structural and kinetic information on the changes produced in zeolites to accommodate the mesoporosity. The interpretation of the time-resolved diffractograms together with computational simulations evidenced the formation of short-range hexagonally ordered mesoporosity within the zeolite framework, and the in situ electron microscopy studies allowed the direct observation of structural changes in the zeolite during the process. The evidence for the templating and protective role of the surfactant and the rearrangement of the zeolite crystal to accommodate intracrystalline mesoporosity opens new and exciting opportunities for the production of tailored hierarchical zeolites.

Mesoporous silica, which shows well-defined pore systems, tunable pore diameters (2-30 nm), narrow pore size distributions and high surface areas (>600 m(2) g(-1)), is frequently modified using different methodologies (including in situ and post-synthetic strategies) to introduce various chemical functionalities useful in applications like catalysis, separation, drug delivery, and sensing. This contribution aims to provide a critical overview of the various strategies to incorporate chemical functionalities in mesoporous silica highlighting the advantages of the in situ methods based on the bottom-up construction of mesoporous silica containing various chemical functionalities in its structure.

Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro‐ and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already‐measured raw adsorption isotherms were provided to sixty‐one labs, who were asked to calculate the corresponding BET areas. This round‐robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well‐known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Pd nanoparticles are immobilized by a green procedure onto unconventional dual porosity titania monoliths. The material is used in catalytic continuous-flow hydrogenation reactions showing excellent efficiency, selectivity, and durability. C ontinuous-flow catalytic processes represent a convenient alternative to heterogeneous phase batch systems in terms of efficiency, safety, waste emission, purification, automation, space and energy consumption, 1−3 thus providing a considerable contribution to the sustainability of long-term production of chemical compounds, particularly fine-chemicals. 4,5 To this purpose, different types of microfluidic flow reactors have been developed so far. 6−10 Monolith-based reactors have attracted increasing interest in recent years 11 because of their significant advantages compared to conventional packed-bed systems, including better heat and mass transfer, lower pressure drop, narrow residence time distribution, which ultimately result in higher productivities. 12 Polymeric materials were the first to demonstrate the utility of monoliths in the catalytic fine-chemicals production under flow. 13−16 However, despite their unquestionable interest, polymer-based monoliths may present some drawbacks from an engineering point of view, such as volume and porosity changes with swelling, thermal, mechanical, and chemical stability, shrinking phenomena, back pressure evolution at high flow rate due to limited porosity, which adversely affect their performance as catalyst supports. 17−19 To avoid these problems different types of inorganic monoliths have been synthesized, including conventional ceramic monoliths obtained by extrusion, that are largely employed in conversion of raw materials, pollutant abatement, and automotive exhaust gas treatment. 20,21 Only two types of unconventional inorganic monolith materials were reported for continuous flow operations in fine chemical synthesis, and both based on silica. One was obtained by emulsion templating synthesis and featured a disordered macropores network for transesterification reactions; 22 the other one, showing a well-defined hierarchical porosity network of flow-through macropores (2−10 μm) and diffusive mesopores within the struts (2−20 nm), was obtained by a combination of spinodal decomposition and sol−gel transition, and it was used for diverse organic catalysis. 23 These latter materials can be particularly useful in the synthesis of fine chemicals, being able to address the need of both efficient processing (within small pores) and fast diffusion (by macropores). 24,25 Despite these favorable features, this type of monoliths have never been explored in highly selective transition-metal catalyzed reactions, for example, in hydrogenation reactions. Selective hydrogenation of hydrocarbons with multiple CC and/or CC bonds to achieve partial hydrogenation products is a highly desired and challenging process in the pharmaceutical, agrochemical, and petrochemical industries. 26,27 Particularly, the stereo-and chemo-selective hydrogen...

Water soluble, monodispersed Pd nanoparticles with a narrow particle size distribution have been successfully synthesized by controlled reduction of [PdCl 4 ] 2À . The resulting aqueous colloids are stable over extended periods of time and can be prepared at high nanoparticle loading (20 g/L of Pd) with no agglomeration. The size of the nanoparticles can be reduced from the nanometer (ca. 3.5 nm) to the sub-nanometer size range (ca. 0.9 nm). Detailed magnetic characterization indicated that the larger, 3.5 nm nanoparticles show ferromagnetic properties at room temperature, while the sub-nanometric ones lose this magnetic behavior.

The assembly and structural evolution of amorphous precursors during zeolite crystallization is an important area of interest owing to their putative roles in the nucleation and growth of aluminosilicate microporous materials. Precursors range in complexity from oligomeric molecules and colloidal particles to gels comprised of heterogeneous silica and alumina domains. The physical state of precursors in most zeolite syntheses is generally not well understood; however, it is evident that the physicochemical properties of precursors depend on a wide range of conditions that include (but are not limited to) the selection of reagents, the composition of growth mixtures, the methods of preparation, and the use of inorganic and/or organic structure-directing agents. The fact that precursors evolve in size, shape, and/or microstructure during the course of nucleation and potentially throughout crystallization leads to questions pertaining to their mode of action in the formation of zeolites. This also highlights the diversity of species that are present in growth media, thus rendering the topic of zeolite synthesis essentially a black box to those attempting to better understand the fundamental role(s) of precursors. In this Article, we discuss the wide variety of precursors encountered in the synthesis of various framework types, emphasizing their complex physical states and the thermodynamic and kinetic factors that govern their heterogeneity. E lucidating the mechanisms of zeolite crystallization is complex owing in large part to the vast number of species present in synthesis mixtures. 1,2 This is a contributing factor to the challenges associated with zeolite crystal engineering where it is difficult to design materials with predetermined physicochemical properties without sufficient knowledge of how synthesis variables can be tailored to mediate crystal growth. 3 The ubiquitous presence of amorphous precursors throughout nucleation and growth make zeolites quintessential examples of materials that grow via nonclassical pathways, which include crystallization by particle attachment. 4−7 This rapidly emerging area is garnering considerable attention owing to the expanding list of materials that show evidence of growth via multifaceted pathways. 8−13 Knowledge of nonclassical mechanisms, however, is rather limited due to inadequate analytical techniques available to observe dynamic processes of growth in situ with sufficient spatiotemporal resolution. In this perspective Article, we highlight the various routes leading to the assembly and evolution of amorphous precursors in zeolite synthesis wherein it is recognized that changes in conditions, most notably the selection of silica/alumina sources and room temperature aging protocols, can significantly influence polymorphism, crystallization kinetics, and the properties of zeolites, among other factors. Here, we address the physical state 51 of precursors with an emphasis on the appropriate use of the 52 word "gel" to properly convey the heterogeneity of these species...