Ethene oligomerisation and metathesis (OLIGOM)

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 and co-catalyst. The OLIGOM project aimed 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 seeked 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 used 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 and co-catalyst. The materials were 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 modelled 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. More precisely, experiments show that a high ethene pressure is required in order to obtain ethene oligomerization in microporous zeolites (0.5-0.8 nm pore size) compared to macroporous alumina or metal-organic framework structures (1-2 nm pore size). Theory suggests that this is due to stabilization of long-chain products in the sub-nm micropores, leading to product poisoning of the active sites. Moreover, theory suggests that activation of the Ni/zeolite catalyst proceeds by hydrogen transfer from an ethene molecule adsorbed on the Ni site, to a nearby basic site which thereby acts as an internal co-catalyst. Further experimental work, using MOF-based catalysts, is in progress in another on-going porject, CONFINE (FriPro Toppforsk) to confirm this prediction and use it to develop superior catalysts.

Light alkenes (ethene, propene, and butadiene) serve as feedstock for polymer production. Currently, the petrochemical industry is experiencing a shift in raw material, from oil to natural gas. Thus, traditional naphtha crackers are being replaced by etha ne crackers, resulting in an increased production of ethene, but leaving propene and butadiene in short supply. The OLIGOM project proposal addresses this issue. We propose to develop new catalytic systems for selective production of propene and butadiene from ethene. These catalysts will be based on alkali metal or transition metal active sites deposited on a new class of nanostructured acidic zeolites. We apply for two 3-year grants for post doctoral candidates or researchers. The fundamental challeng es are to maximize product selectivity and to minimize catalyst deactivation by coking. To address these issues, the OLIGOM project will place strong emphasis on three key areas: 1. Synthesis of diffusion resistance free, unit cell thick sheets of zeolite supports using surfactants as morphology modifiers. 2. Measurements of catalyst performance and mechanistic investigations employing traditional microreactors, pulse reactors facilitating transient studies, and high pressure reactors operated at industri ally relevant conditions. 3. Extensive catalyst characterization with surface sensitive infra red spectroscopy and X-ray absorption spectroscopy to investigate the local environment of metal based active sites. The OLIGOM project team comprises particip ants from the inGAP Center of Research Based Innovation at the University of Oslo (project management, catalyst synthesis, testing, and characterization); the Department of Process, Energy, and environmental Technology at Telemark University College (cata lyst synthesis and testing); the NIS Center of Excellence at the University of Torino (spectroscopic characterization); and global supplier of catalysts and technology Haldor Topsøe (high pressure catalyst performan