Ferdi Schüth

Chemical and Physical Solutions for Hydrogen Storage

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.

Ordered mesoporous materials

About six years after the first publication, ordered mesoporous oxides can be prepared by a variety of procedures and over a wide range of compositions using various different surfactant templates. The mechanisms of formation, although still a matter of discussion, are understood in principle, and the macroscopic morphology as well as the orientation of the pores can be controlled in fortunate cases. However, still lacking are groundbreaking developments in the field of applications, either in catalysis or other areas. The state-of-the-art in the synthesis, characterization and application of ordered mesoporous oxides will be covered in this review.

Handbook of porous solids

INTRODUCTION. Historical Aspects. Definitions, Terminology and Classification of Pore Structures. GENERIC METHODS FOR THE CHARACTERIZATION OF POROUS MATERIALS. Modelling of Ideal Pore Structure. Fractal Analysis. Microscopy and Stereology. Scattering and Diffraction Methods. Adsorption from Gas Phase. Adsorption from Liquid Phase. Capillarity and Fluid Displacement. Mercury Porosimetry. Fluid Flow. Thermoporometry. Surface Hydrophobicity/Hydrophilicity. Surface Acidity. NMR Techniques. Positron Annihilation Spectroscopy. GENERAL PRINCIPLES FOR SYNTHESIS AND MODIFICATION OF POROURS MATERIALS. CLASSES OF MATERIALS. Clathrates and Inclusion Compounds. Crystalline Microporous Solids. Porous Metal Organic Frameworks. Layered Structures and Pillared Layered Structures. Ordered Mesoporous Oxides. Porous Glasses. Other Oxides. Carbons. Porous Polymers and Resins. Aerogels. Macroporous Solids. Miscellaneous. MASS TRANSFER IN POROUS MATERIALS. Diffusion and Adsorption in Porous Media. Transport Phenomena and Reaction in Porous Media. TECHNOLOGICAL ASPECTS. Technical Adsorption of Gases. Membrane Technology. Drying Processes. Liquid Separation. Gas Liquid Chromatography. Environmental Protection. Water Treatment. Respiratory Protection. Catalysis. Pharmaceutical Application. Cements. Optically and Electronically Functional Materials. Miscellaneous and Novel Applications.

Oil-Water Interface Templating of Mesoporous Macroscale Structures

Ordered mesostructured porous silicas that are also macroscopically structured were created by control of the interface on two different length scales simultaneously. Micellar arrays controlled the nanometer-scale assembly, and at the static boundary between an aqueous phase and an organic phase, control was achieved on the micrometer to centimeter scale. Acid-prepared mesostructures of silica were made with the p6, Pm3n, and the P63/mmc structures in the form of porous fibers 50 to 1000 micrometers in length, hollow spheres with diameters of 1 to 100 micrometers, and thin sheets up to 10 centimeters in diameter and about 10 to 500 micrometers in thickness. These results might have implications for technical applications, such as slow drug-release systems or membranes, and in biomineralization, where many processes are also interface-controlled.

Acid Hydrolysis of Cellulose as the Entry Point into Biorefinery Schemes

Cellulose is a major source of glucose because it is readily available, renewable, and does not compete with the food supply. Hydrolysis of cellulose is experiencing a new research and development cycle in which this reaction is carried out over solid catalysts and coupled to other reactions for increased efficiency. Cellulose is typically not soluble in conventional solvents and very resistant to chemical and biological transformations. This Review focuses on aspects related to the hydrolysis of cellulose as this process is a significant entry point into the biorefinery scheme based on carbohydrates for the production of biofuels and biochemicals. Structural features of cellulose, conventional acid-catalyzed reactions, and the use of solid acid catalysts for hydrolysis are discussed. The longterm success of the biorefinery concept depends on the development of energetically efficient processes to convert cellulose directly or indirectly into biofuels and chemicals.

Structurally Designed Synthesis of Mechanically Stable Poly(benzoxazine-co-resol)-Based Porous Carbon Monoliths and Their Application as High-Performance CO2 Capture Sorbents

Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO(2) capture and separation capacities, high selectivity, and facile regeneration at room temperature. At ~1 bar, the equilibrium capacities of the monoliths are in the range of 3.3-4.9 mmol g(-1) at 0 °C and of 2.6-3.3 mmol g(-1) at 25 °C, while the dynamic capacities are in the range of 2.7-4.1 wt % at 25 °C using 14% (v/v) CO(2) in N(2). The carbon monoliths exhibit high selectivity for the capture of CO(2) over N(2) from a CO(2)/N(2) mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO(2) release in an argon stream at 25 °C, indicating a good regeneration capacity.

Calcination behavior of different surfactant-templated mesostructured silica materials

Abstract The removal of the template by calcination from mesostructured M41S and SBA-type silica materials was studied by combining high temperature X-ray diffraction, thermogravimetry–differential thermal analysis and mass spectrometry, allowing detailed in situ investigations during the thermal treatment. A comparison was made between materials with different mesoscopic structures, resulting from different synthesis routes and chemical treatment. The in situ XRD studies showed a strong increase in scattering contrast observed for the low angle reflections occurring when the template is removed from the inside of the pores, irrespective of the type of mesostructure. In agreement with the XRD investigations, the TG–DTA/MS experiments proved that the removal of the surfactant is a stepwise mechanism. Marked differences in the scattering contrast variations and chemical reactions were observed depending on the synthesis conditions and the type of surfactant, which highlight the role of the silica–surfactant interfaces. MCM-41 and MCM-48 materials synthesized in the presence of alkyltrimethylammonium surfactant under alkaline conditions showed a template removal mechanism based on an Hofmann degradation at low temperatures, followed by oxidation and combustion reactions above 250 °C. On the other hand, acidic conditions employed for the synthesis of SBA-3 type materials seems to favor reactions of oxidations after the evaporation of water and hydrochloric acid at low temperature. In that case, large contraction of the hexagonal unit cell was usually observed. Most of the block-copolymer template is removed from SBA-15 at lower temperatures, in a single oxidation step. The SBA-15 framework possibly catalyzes the oxidation of the block copolymer template species. In addition, the presence of framework porosity or pore connectivities seems to be responsible for the strong scattering contrast variations observed below 250 °C. Residual carbonaceous species and water are removed from the structure upon heating from 300 °C up to 550 °C. During this subsequent process a large contraction of the hexagonal unit cell is observed, possibly due to further framework condensation. In addition, a brief survey of the previous investigations reported in the literature related to the decomposition of structure-directing agents is given.

Comparison of an ordered mesoporous aluminosilicate, silica, alumina, titania and zirconia in normal-phase high-performance liquid chromatography

This paper investigates the behaviour of silica, alumina, titania, zirconia and the novel mesoporous aluminosilicate MCM-41 in normal-phase high-performance liquid chromatography under comparable conditions. The physicochemical properties of the oxides and MCM-41 are described. MCM-41 is an ordered mesoporous material with a regular pore structure composed of an assembly of hexagonal tubes with a pore diameter of 4 nm. In chromatography MCM-41 exhibits acid and basic properties and proves to be suitable for the separation of acid, neutral and basic compounds.

Ammonia as a possible element in an energy infrastructure: catalysts for ammonia decomposition

The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered.

Spatially and Size Selective Synthesis of Fe-Based Nanoparticles on Ordered Mesoporous Supports as Highly Active and Stable Catalysts for Ammonia Decomposition

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.