Alfons Baiker

Bio: Alfons Baiker is an academic researcher from ETH Zurich. The author has contributed to research in topics: Catalysis & Enantioselective synthesis. The author has an hindex of 83, co-authored 978 publications receiving 42903 citations. Previous affiliations of Alfons Baiker include University of Vienna & Paul Scherrer Institute.

Mixed-Linker Metal-Organic Frameworks as Catalysts for the Synthesis of Propylene Carbonate from Propylene Oxide and CO2

Abstract: A series of mixed-linker metal-organic frameworks(MIXMOFs) of the general formula Zn4O(BDC)x(ABDC)3–x has been synthesized and tested as catalyst in the reaction of propylene oxide (PO) and carbon dioxide. Based on MOF-5 a new synthetic route was developed which allows the partial substitution of benzene-1,4-dicarboxylate (BDC) linkers in the material by functionalized 2-aminobenzene-1,4-dicarboxylate. In that way the number of catalytically active amino groups can be tuned using the desired BDC/ABDC ratio. The presence of MIXMOFs (instead of a mechanical mixture of MOF-5 and IRMOF-3) was proven by high-resolution X-ray diffraction and DTG. XRD and TG/MS analysis revealed that pure MIXMOF materials can be obtained up to an ABDC loading of 40 %. The thermal stability in air is decreasing with increasing ABDC content from 450 °C for pure MOF-5 (0 % ABDC) to ca. 350 °C for the 40 % MIXMOF Zn4O(BDC)1.8(ABDC)1.2. Consequently, MIXMOF materials represent a promising class of materials for catalytic applications in the temperature range at least up to 300 °C which is proven using the synthesis of propylene carbonate (PC) from propylene oxide and carbon dioxide as a test reaction. The catalytic results indicate that solid MIXMOF catalysts in combination with tetraalkylammonium halides (NR4X) as promoters are as active as the corresponding homogeneously dissolved reference compounds (H2ABDC, H2BDC and Zn salts) and that they can be recycled with only moderate loss in activity. A comparison of MIXMOFs from 0 to 40 % of ABDC revealed a dependence of activity on the number of amino groups. Due to the fact that even pure MOF-5 catalyzed the reaction to some extent, surface Zn centers with free coordination sites might also contribute to substrate activation. Using optimized reaction conditions, a PC yield of up to 63 % can be obtained after 3 h in the presence of low catalyst concentration (0.045 mol-% of 40 % MIXMOF, containing 0.05 mol-% of NH2 groups).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Aerogels in catalysis

Abstract: Introduction Aerogels offer interesting opportunities for catalysis due to their unique morphological and chemical properties. These properties originate from their wet-chemical preparation by the solution-sol-gel (SSG) method and their subsequent liberation from the solvent via critical-point drying or supercritical (or hypercritical) drying (SCD). Due to the “structure-preserving” ability of SCD, the usually oxidic (or metallic) aerogels are solids of high porosity and specific surface area.

X-ray absorption spectroscopy under reaction conditions: suitability of different reaction cells for combined catalyst characterization and time-resolved studies

Abstract: Structure–activity correlations of solid catalysts and time-resolved studies generally require that the structure within a solid catalyst is probed simultaneously and at the same location where the catalysis and the structural changes occur These requirements lead to a compromise between the spectroscopic arrangement and the optimum design for an in situ reactor cell Opportunities and limitations of in situ and time-resolved X-ray absorption spectroscopy (XAS) combined with gas analysis are critically analysed with the help of two different cell designs, an in situ EXAFS cell designed for solids in the form of pressed wafers and a capillary cell where the catalyst is packed similarly to a plug flow reactor On the basis of three examples, the reduction of CuO/ZnO, the reduction of PdO/ZrO2 and methane oxidation over PdOx/ZrO2, criteria are developed which allow to judge the appropriate cell design in solid–fluid reactions The prerequisites for the design of an in situ cell including the catalyst shape strongly depend on the time resolution required Important issues embrace the type of reaction to be investigated (slow vs fast), the reaction medium, and the porosity of the catalyst material Criteria for assessing the role of pore and film diffusion in in situ studies are of paramount importance for a proper experimental design

A new hydrosol of gold clusters

Abstract: Reduction of gold(III) ions by tetrakis(hydroxymethyl)phosphonium chloride gives a hydrosol of gold clusters with mean diameter 1.5 nm (average nuclearity about Au170) and smaller.

Metallic glasses in heterogeneous catalysis

Abstract: Metallic glasses exhibit some unique properties which make them interesting materials in catalysis. Recently their use as catalyst precursors has been advanced and several efficient catalysts have been prepared by various pretreatments of the metallic glasses. An understanding of the solid-state reactions occurring during the transition of the amorphous precursor to the active catalyst was found to be crucial for successful application of these materials. This paper describes the present knowledge and discusses principal possibilities and problems involved in the application of metallic glasses in catalysis.

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

The Chemistry and Applications of Metal-Organic Frameworks

Abstract: Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.