Catalysis Science & Technology Blog

Hydrogen is undoubtedly one of the most appealing candidates as a replacement for fossil fuels in the automotive sector. Despite the logistical difficulties connected to storage and transportation, hydrogen still remains the most environmentally friendly and sustainable fuel available.

The most common source of hydrogen is steam reforming of hydrocarbons, but intensive research has been devoted to more sustainable production processes such as the thermochemical and photochemical splitting of water into its components.

Several titanium, niobium and tantalum based materials have been employed in the preparation of suitable catalysts for the photochemical splitting of water, often suffering from weaknesses such as limited absorbtion of light in the visible region, chemical instability and other issues related to the materials` morphology.

A recent study by Jiang et al. on doped titania addresses the latter concerns; the group investigated the effect of molibdenum doping (which increases the photonic efficiency of the catalyst) and thermal treatments in the layer-by-layer fabrication of catalytic films.

The study highlights how the concentration of molibdenum affects the temperature of the transitions between different morphologies and the effect of the thermal tratments conducted on the material. A detailed characterisation of the catalysts by TEM, XPS, XRD as well as their photochemical activity shows that the presence of opportune amounts of molibdenum allow for an easier control of the morphology in the fabrication of the material and that higher concentrations of dopant result in a higher photocatalytic actvity.

For more details, please find the full communication here.

Structural and morphological control of Mo doped titania films
Chunxiang Li, Zhongping Yao, Guangmei Wu, Zhaohua Jiang and Fangzhou Jia
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C1CY00024A, Communication

Enzymes are by far the most active and selective catalysts known to chemistry but although progress has been made to incorporate them into industrial use (i.e. in batch reactors, fixed bed immobilised enzyme reactors), their intrinsic biological nature makes them too substrate-specific and limits them to a reduced range of operational conditions.

In an attempt to bypass these limitations, scientists developed bio-inspired catalysts: structures designed upon the active sites of enzymes but lacking the organic framework that characterise them, making them easier to heterogenise, recover and more resilient to harsh conditions than their natural counterpart.

To reintroduce the selectivity given by the enzyme`s structure, these catalysts can be incorporated into micro- or mesoporous supports such as silica and zeolites exploiting ionic interactions between metal and support or different anchoring techniques.The selectivity is mostly size-driven, dictated by the dimension of the pores in the material, or induced by the presence of chiral ligands on the catalyst.

In addition to metal complexes, natural and modified aminoacids can also be chemically bound to porous supports, resulting in efficient catalysis of a wide range of reactions. The characterisation of the active sites, though, is made more difficult by the lack of appropriate techniques that clearly discriminate the catalytic species from the support.

In-depth coverage of the topic and future perspectives can be found here.

Design strategies for engineering selectivity in bio-inspired heterogeneous catalysts
David J. Xuereb and Robert Raja
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C0CY00088D, Perspective

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