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[交流] 【分享】New catalyst for methane to methanol

【新甲烷制甲醇催化剂】New catalyst for methane to methanol

Chemists in Germany have invented a new solid catalyst forconverting methane to methanol. The system could eventually provide asmaller-scale alternative to current commercial methods for methanolproduction from natural gas, which rely on big, expensive industrialfacilities for steam reforming of methane to syngas - typicallyso-called 'megamethanol' plants where there is a large supply ofnatural gas.

However, natural gas is often found in smallerquantities in remote locations where its transportation cannot bejustified economically. Here, smaller-scale conversion to methanolcould be the answer. For many years people have searched for new waysto convert methane to methanol. One promising technique used aplatinum-based catalyst developed by Periana and colleagues,1in which platinum is co-ordinated to a bipyrimidine. This is thendissolved in fuming sulfuric acid - oleum - to carry out the oxidation,which involves sulfur trioxide. However, the expensive platinum proveddifficult to recover from solution.

Now, a team led by FerdiSchüth at the Max-Planck-Institut für Kohlenforschung in Mülheim havecreated what is in effect a solid Periana catalyst which appears to berecyclable with no loss of platinum.2

'Colleagues ofours created a highly porous carbon-nitrogen polymer, which we realisedhad very similar structural motifs to the Periana catalyst,' Schüth says, 'so we wondered if we could incorporate platinum into thestructure.'

The process proved surprisingly simple. The polymeris created by trimerising the aromatic nitrile 2,6-dicyanopyridine inmolten zinc chloride. This trimer is then polymerised by heating toform an amorphous, highly porous 'triazine-based framework polymer'.'Simply by dropping the platinum precursor and the polymer into theoleum, the catalyst forms in situ,' says Schüth.

Thereaction used a solid catalyst in a covalent triazine-based framework.The material possesses bipyridine units as coordination sites forplatinum. It shows high activity and can be separated easily from thereaction mixture and recycled several times without significant loss ofactivity.

© Angew. Chem. Int. Ed

Ifthe mixture is then pressurised in an autoclave with methane, themethane is consumed and methanol formed at conversion rates comparableto Periana-based systems but with the solid catalyst easily recoverableat the end of the reaction.

'We are now looking at ways toimprove the activity of the system,' Schüth says. 'We would like tomove the process from batch to continuous, and ultimately find a way ofcarrying out the conversion in the gas phase.'

Justin Hargreaves,a catalyst expert at the University of Glasgow in the UK, says that theGerman researchers have produced 'a very interesting study.'

'Toheterogenise a homogeneous system provides a significant advantage,'Hargreaves adds. 'Whilst the reaction is undertaken at lowtemperatures, which potentially provides selectivity advantages with respect to direct partial oxidation with oxygen, regeneration of sulfurtrioxide by oxidation of sulfur dioxide and the use of concentratedsulfuric acid are required.'

References1. R A Periana et al, Science, 1998, 280, 560-564
2. R Palkovits et. al, Angew. Chem. Int. Ed., 2009, DOI: 10.1002/anie.200902009

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