Catalysis Science & Technology Blog

Whenever dangerous nitrogen oxides are generated after a fuel-combustion process, a selective catalytic reduction (SCR) step is implemented in the process to catalyse their conversion into less harmful molecular nitrogen and water. Large diesel engines, industrial boilers and furnaces are an example of the areas in which this technology plays a fundamental role in keeping the fumes emission clean.

Most catalysts for SCR are consist of metal oxides absorbed on porous supports as alumina, zirconia, titanium oxide and zeolites that, in synergy with a reducing agent like ammonia or urea efficiently decompose nitrogen oxides at relatively low temperatures. The understanding of the interactions between the metal oxides and the supports is of key importance in the development of increasingly efficient catalysts.

After working on copper-containing catalysts for the ammonia-catalysed SCR with low toxic profile, the Chinese group of Duan Weng, presented a comprehensive characterisation of their most effective CuOx-WOx-zirconia systems and highlighted the importance of tungsten oxides for the efficacy of the catalyst. The samples where studied by X-ray diffraction, photoelectron spectroscopy (XPS), Raman spectroscopy and other techniques.

The group concluded that the increased activity of their tungsten-containing catalysts might be attributed to the higher dispersion of copper oxides obtained in the presence of tungsten clusters, directly linked to an increased Lewis and Bronsted acidity that allow for higher adsorption of ammonia and inhibits its oxidation on the catalyst.

Read the full article for free.

Synergistic effects between copper and tungsten on the structural and acidic properties of CuOx/WOx–ZrO2 catalyst
Zhichun Si, Duan Weng, Xiaodong Wu, Yang Jiang and Bin Wang
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C0CY00086H, Paper

A Catalysis Science & Technology article has appeared in the society magazine Chemistry World. The paper, by Colin P. Horwitz, Terrence J. Collins and colleagues from Carnegie Mellon University, Pittsburgh, has recently been published as an Advance Article, read the original manuscript:

Fe-TAML/hydrogen peroxide degradation of concentrated solutions of the commercial azo dye tartrazine
Evan S. Beach, Ryan T. Malecky, Roberto R. Gil, Colin P. Horwitz and Terrence J. Collins
Catal. Sci. Technol. , 2011, Advance Article
DOI: 10.1039/C0CY00070A, Paper

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Real-world treatment for dye-contaminated effluents

US scientists have found that a dye oxidation process using low levels of an iron catalyst could be used to degrade highly contaminated wastewater under ambient conditions.

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