With the recent boom in shale gas availability around the world, the industry increasingly uses natural gas in place of oil as a chemical feedstock. Whereas oil mainly consists of long molecules containing carbon and hydrogen (hydrocarbons), natural gas is a mixture of small hydrocarbon molecules. The key components in the chemical industry are medium-sized hydrocarbons; two of these are butadiene and propene, used to produce rubber and plastics. These compounds are made from oil by cutting the long hydrocarbons into smaller pieces in a process called cracking.
However, when starting from the small hydrocarbons from natural gas one has to stitch the molecules into medium-length hydrocarbons in a process called oligomerisation. Current industrial processes achieve oligomerisation in catalytic reactions using toxic solvents.
The OLIGOM project aims to do oligomerisation of ethene, obtained from natural gas, to butadiene and propene in a catalytic process that does not use a solvent. The process uses porous metal-containing zeolites and metal-organic frameworks as catalysts; the gas phase ethene molecules stick to the metal atoms inside the materials, react and form the products. The metal atoms are called the active sites. In OLIGOM we seek to understand the details of the catalytic cycle; which bonds form and break at the active site in the course of transforming the reactants to the products. We use this understanding to develop a rational strategy for tailoring materials with improved active sites and hence higher catalytic activity for ethene oligomerisation. Such catalysts could ultimately replace the industrial catalysts, increase catalyst recyclability and avoid the use of toxic solvents.
The materials are subjected to catalytic tests to measure their activity and to spectroscopic characterization to elucidate the nature of the active site and molecules adsorbed on it. In parallel, we model the oligomerisation reaction and active sites by atom-scale methods based on quantum mechanics. Thanks to this tight interplay between theory and experiment we are currently moving towards a detailed understanding of the catalytic cycle with nickel atoms as active sites. The next step is to identify the properties that determine the activity of the catalyst; this allows us to accelerate our search for materials with high catalytic activity for ethene oligomerisation.
