Heterogeneous Acid Catalysis in Nonasymmetric Synthesis

Green Chemistiy Centre of Excellence, Department of Chemistry, 

University of York, Heslington York YOlO 5DD, UK Email duncan.macquarrie york.ac.uk 

Sustainable Catalysis Without Metals or Other Endangered Elements, Part 1 

In the area of heterogeneous acid catalysis, zeolites (microporous, crystalline aluminosilicates) have had a massive impact on the conversion of small molecules, usually at high temperatures, and their role in the conversion of crude oil to smaller, typically unsaturated molecules has been a cornerstone of chemistry for almost half a century. This relies on a combination of tunable (and potentially very strong) acidity, shape selectivity due to small and very uniform pores, and exceptional thermal stability, which allows regeneration to be carried out by burning off heavy byproducts. 

While the zeolites have the remarkable property of shape selectivity (allowing, e.g., PET to be produced with the enormous regioselective control required - 99.9% para is necessary for high-quality plastic to be obtained) this is also one of their weaknesses. Only small molecules can enter and leave the pores and therefore the vast majority of chemical reactions are not catalysed by zeolites. Larger pore materials are thus required, and many have been evaluated. 

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