Catalysis Science & Technology Blog

Membranes are versatile supports for the immobilisation of catalysts; they allow the use of different manufacturing materials and their properties such as pore size, morphology, flexibility, chemical and thermal stability can be finely tuned. These polymeric membranes have successfully been used to support chiral complexes of ruthenium-Binap and manganese-Salen in enantioselective epoxidation and hydrogenation reactions. Although versatile and ideal for industrial scale applications, their major drawback proved to be metal leeching, which reduced their efficiency and contaminated the products.

Research groups lead by Barbaro recently developed a series of organic/inorganic polymeric membranes incorporating rhodium complexes of chiral diphosphino ligands that proved nearly immune to metal leeching and provided clean, enantioselective hydrogenation of methyl-2-acetoamidoacrylate with enantiomeric excesses comparable with their homogeneous analogues. The novelty of the approach resided in the incorporation of the metal occurring on the preformed membrane, thus avoiding derivatisation steps and chemical modifications.

The reaction times proved to be considerably longer than the homogeneous catalyst with yields exceeding 90 % only after 17 hours, but enantioselectivities of up to 98 % could be achieved without any loss of activity after five cycles using methanol as the solvent. A screening of several other substrates and solvents proved the versatility of the system. Remarkably, the most performing membranes presented a metal leeching of less than 1 ppm even after 25 hours of use in methanol, outperforming existing catalytic membranes. The stability of the membrane-complex adduct is thought to reside in the interaction between the metal and tungsten oxide (WO3) or sulphite anions in the membrane structure.

Find more about the article here.

Enantioselective hydrogenation of prochiral substrates in catalytic membrane reactors
Pierluigi Barbaro, Claudio Bianchini, Francesca Liguori, Claudio Pirovano and Haruo Sawa
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C0CY00030B, Communication

The BBC radio series Discovery – Can Chemistry Save the World? presents an episode on Green Chemistry, well worth a listen:

http://www.bbc.co.uk/i/p00dtz7p/

All TAP micro-reactors have inert particles which are used so that the catalyst zone can be maintained under isothermal conditions. Even on “inert” particles adsorption will occur to some degree; however, the extent to which this occurs has a critical influence on the analysis of the TAP data.

In their recent paper, Chris Hardacre and co-workers, from Queen’s University, Belfast, UK, discuss the development of a function which accounts for the adsorption over the inert material, so that the TAP data analysis can be accurately determined. They also demonstrate this analysis method using the selective reduction of oxygen in a hydrogen rich ethylene feed over silver catalysts as a case study. Find out how they got on by reading their Catalysis Science & Technology Hot Article.

Correction for a possible reversible adsorption over an “inert” material
Alexandre Goguet, Christopher Hardacre, Burapat Inceesungvorn, Kevin Morgan and Sergiy O. Shekhtman
Catal. Sci. Technol., 2011, DOI: 10.1039/C0CY00075B, Paper

Zeolite synthesis, has been vigorously explored and developed for more than half a century and yet most zeolites known to date have not been synthesized without templating with an appropriate organic molecule. But the discovery of zeolite MCM-22 promises to change all that. The MCM-22 framework was found to form by two pathways and unlike conventional 3D zeolites the layered precursor could be structurally modified after synthesis. With 2D zeolites adsorption and catalysis occur almost exclusively on the surface of these materials and not inside the zeolite pores as in conventional zeolites.
This PERSPECTIVE aims to provide an up-to-date knowledge and challenges associated with “two-dimensional zeolites (2D zeolites)”.

Two-dimensional zeolites

Read more at:

Wieslaw J. Roth and Jiří Čejka, Catal.  Sci. Technol., 2011, Advance Article DOI: 10.1039/C0CY00027B, Perspective

In one of the very first published papers in Catalysis Science & Technology, Graham Hutchings and co-workers investigate how changing the metal ratio and heating affects the structure and activity of copper gold catalysts. Find out the results here.

Understanding the effect of thermal treatments on the structure of CuAu/SiO2 catalysts and their performance in propene oxidation 
Charlotte L. Bracey, Albert F. Carley, Jennifer K. Edwards, Peter R. Ellis and Graham J. Hutchings
Catal. Sci. Technol., 2011, Advance Article   DOI: 10.1039/C0CY00003E, Paper

Read this Catalysis Science & Technology communication for FREE!

Ferdi Schüth and colleagues have found that gold nanoparticles encapsulated in a zirconia shell show significantly enhanced catalytic activity for carbon monoxide oxidation when doped with small amounts of TiO₂.

The titania promotes high activity at low temperature while the zirconia shell acts as a structural support, providing stability against sintering.

These characteristics are important for potential applications in air purification for long-duration space travel and vehicle exhaust gas catalysis.

Activity improvement of gold yolk–shell catalysts for CO oxidation by doping with TiO₂
Robert Güttel, Michael Paul and Ferdi Schüth
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C0CY00026D, Communication