RESUMO
Invited for this month's cover is the group of Pieter Bruijnincx from Utrecht University. The image shows an imaginary police line-up of two molecules suspected to be involved as intermediates in the catalytic ketonization reaction. Based on the evidence collected, depicted on the pinboard on the wall, the scientist discusses the impact of all this with somebody interested in catalysis that converts waste, wastewater-derived volatile fatty acids in this case, to value-added circular chemicals. The Full Paper itself is available at 10.1002/cssc.202100721.
RESUMO
The choice of TiO2 crystal phase (i. e., anatase, rutile, or brookite) greatly influences catalyst performance in the gas-phase ketonization of small volatile fatty acids, such as acetic acid and propionic acid. Rutile TiO2 was found to perform best, combining superior activity, as exemplified by an exceptional reaction rate of 141.8â mmol h-1 gcat -1 (at 425 °C and 24â h-1 ) with excellent ketone selectivity when propionic acid was used. Brookite, to the best of our knowledge never reported before as a viable ketonization catalyst, was found to outperform the well-studied anatase phase, but not rutile. Operando Fourier-transform IR spectroscopy measurements combined with on-line mass spectrometry showed that bidentate carboxylates were the most abundant surface species on the rutile and brookite surfaces, while on anatase both monodentate and bidentate carboxylates co-existed. The bidendate carboxylates were thought to be precursors to the active ketonization species, likely monodentate intermediates more prone to C-C coupling. Ketonization activity did not directly correlate with acidity; the observed, strong crystal phase effect did suggest that ketonization activity is influenced strongly by geometrical factors that determine the ease of formation of the relevant surface intermediates.
