Periodic Reporting for period 2 - TAILORCAT (Towards the selective hydrodeoxygenation and hydrogenation of levoglucosenone using base metal heterogeneous catalysts modified by atomic layer deposition)
Berichtszeitraum: 2019-06-15 bis 2020-06-14
The TAILORCAT project was concerned with the development of catalytically active and non-leaching heterogeneous base metal catalysts (e.g. copper, iron, nickel), which could be used in an aqueous reaction medium. This was a challenging objective as base metals tend to leach (disappear) easily during any aqueous phase reaction therewith rendering the catalyst inactive. To achieve this aim, it was proposed to stabilize or even encapsulate the supported base metal nanoparticles with oxides or oxide layers. This was expected to contain the base metal leaching but also to enhance the activity & selectivity of the catalysts. The ability to use base metal catalysts over noble metal catalysts is important to society while noble metals (e.g. platinum, palladium) are becoming ever scarcer. The scarcity of noble metals reflects itself already in ever increasing raw material prices. Generally spoken base metals are significantly cheaper and much more abundantly available.
In a first instance the TAILORCAT project focused on the use of copper as a hydrogenation catalyst, while copper is one of the cheapest base metals and readily available in large quantities. After a first general screening process, copper supported on layered double hydroxide (a type of clay also known as hydrotalcite) was found to hold the best cards in terms of catalytic activity. Gratifyingly, this catalyst was found free of copper leaching and this without the application of protective oxide layers onto the supported copper nanoparticles. Equally surprising this catalyst displayed markedly different activity levels in flow and batch reactors. This was found to relate to an inherent and unexpected acidity of the starting reaction mixture. As a result, a continuous loss of very small amounts of magnesium from the supporting clay material was observed. This work was published in the journal of Green Chemistry and bestowed hot article status: Green Chem., 2019, 21, 5000-5007 (DOI: 10.1039/C9GC00564A). Finally, using a combination of XRD and in situ UV-VIS, it could be shown that Cu(I) species play an important role.
With the discovery of a non-copper leaching heterogeneous catalyst capable of doing hydrogenation reactions in water, the TAILORCAT project has ventured into uncharted territory. Indeed, to date no real non-copper-leaching heterogeneous catalyst exists that can operate in aqueous medium. It is further also noteworthy that the invented copper catalyst can operate at temperatures as low as 333 K which is very unusual. Presently the TAILORCAT project has been focusing on the making of levoglucosanol. The latter compound is of significant importance while it can be further transformed into (bio-derived) 1,2,6-hexanetriol and 1,6-hexanediol – two very important commodity chemicals! With a view on the future, it is expected that the application range of this catalyst will increase further as we gain more knowledge on the why and how of the non-leaching character of the copper metal.