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Nanoconfinement leads to increased catalytic stability

Steam reforming, where hydrogen gas is produced from hydrocarbon fuels such as natural gas, is an important industrial catalytic process.  Nickel is the catalyst of choice due to its low cost and high C-C bond rupture activity, and zirconia (ZrO2) is widely used as the catalytic support due to its thermal and chemical stability, moderate acidity and surface oxygen mobility.  The same supported Ni/ZrO2 catalyst is a promising candidate for ethanol steam reforming (ESR), but its deactivation caused by sintering and coke deposition remains a problem.

Jinlong Gong and researchers from Tianjin University used a surfactant-assisted method to prepare a nanocomposite Ni@ZrO2 catalyst made up of nickel nanoparticles distributed evenly throughout a similarly sized zirconia matrix.  The new catalyst demonstrated higher activity and selectivity for the conversion of ethanol into CO2 and H2.  Almost complete conversion of ethanol over a 50 hour period was observed, while the activity of the traditional Ni/ZrO2 catalyst decreased continually after just six hours.

The even distribution of metal nanoparticles throughout the matrix allows the pore structure of the solid to be maintained while increasing the accessibility of the catalytically active nickel.  The larger metal-oxide interface promotes the removal of carbon deposits while the “confinement effect” prevents the nickel metal from sintering.  As highlighted in a recent C&EN article, these promising catalytic properties suggest that the synthetic methodology may be useful for the design of metal catalysts for other processes, such as dehydrogenation, that encounter similar problems.

Read this HOT Chem Comm article today (free to access until the 27th December):

A Ni@ZrO2 nanocomposite for ethanol steam reforming: enhanced stability via a strong metal-oxide interaction
Shuirong Li, Chengxi Zhang, Zhiqi Huang, Gaowei Wu and Jinlong Gong
Chem Commun., 2013, Advance Article
DOI: 10.1039/C2CC37109J

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Flexible post-synthetic approach to functionalised MOFs

Metal-organic frameworks (MOFs), formed from the assembly of metal ions and organic bridging ligands, often have large pores and high surface areas.  Such properties are attractive for various potential applications from gas storage to catalysis.  The diverse structures and properties of MOFs can be extended by incorportaing functional groups onto the organic linker after MOF formation through post-synthetic modification.

MIL-101(Cr), a MOF first reported by Ferey et al. in 2005, exhibits mesoporous cages with accessible metal sites as well as high chemical and hydrothermal stability.  Amine functionalisation of the framework’s benzene dicarboxylate ligands has been reported for analagous iron and aluminium frameworks, but has so far proven elusive for MIL-101(Cr).

Burrows et al. from the University of Bath have synthesised MIL-101(Cr)-NH2 using a hydrothermal method, and found that the resultant framework is stable up to 250 °C and, most interestingly, is stable to acids.  This unusual stability has allowed them to post-synthetically transform the amine group into an arenediazonium salt which they used in situ to generate a variety of functional groups.  MIL-101(Cr)-azo, in particular, showed excellent CO2 selectivity at low pressure.

This new approach to post-synthetic modification has provided a flexible route to functionalised MIL-101 materials, with further studies concentrating on selected frameworks already underway.

Read this HOT Chem Comm article today (free to access until the  7th of December 2012):

Synthesis and post-synthetic modification of MIL-101(Cr-NH2) via a tandem diazotisation process

Dongmei Jiang, Luke L. Keenan, Andrew D. Burrows and Karen J. Edler
Chem. Commun., 2012, Advance Article
DOI: 10.1039/c2cc36344e

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