(79b) Deactivation of Zeolite Catalysts during Hydrodeoxygenation of Aromatic Oxygenates

Pyrolysis and liquefaction are promising processes for converting biomass into liquid bio-oils. However, upgrading of these bio-oils is typically needed to obtain properties that are compatible with processes for the production of chemicals and fungible gasoline additives. Hydrodeoxygenation (HDO) is an attractive approach for achieving this goal by replacing oxygen containing functional groups with hydrogen. In principle, water is formed as the only by-product. The process provides oils with reduced reactivity and corrosiveness and increases the energy density of the oil. Noble metal containing zeolite catalysts show considerable HDO activity, but deactivation remains an issue. In most studies, coking is assumed to be the primary cause of deactivation.

Here, we show that additional deactivation paths need to be considered. Bifunctional aromatics, like catechol and guaiacol, can strongly adsorb on Lewis acid sites and form rigid surface species, so-called roadblocks, that prevent access to active sites [1]. Roadblocks can drastically reduce the activity of zeolite catalysts even when only a fraction of the pore space and external surface area are occupied. In addition, dealumination processes during HDO will be discussed. The same deactivation phenomena occur during the conversion of pyrolysis vapors from pine indicating that model compound studies allow for accurate prediction of deactivation phenomena of zeolites in HDO reactions [2]. Based on these results, strategies for improving the design of HDO catalysts and processes will be discussed.

References:

[1] Foo, G. S.; Rogers, A. K.; Yung, M. M.; Sievers, C. ACS Catalysis 2016, 6, 1292–1307.

[2] Yung, M.M., Foo, G.S., Sievers, C. Catal. Today, accepted.