Skeletal isomerisation of oleic acid over ferrierite in the presence and absence of triphenylphosphine: Pore mouth catalysis and related deactivation mechanisms

Skeletal isomerisation of oleic acid over ferrierite: Influence of acid site number, accessibility and strength on activity and selectivity

“…Protonated ferrierite undergoes a rapid and severe deactivation during the alkyl isomerisation reaction with OA as feedstock, resulting from two different mechanisms [20]. The rapid loss of internal surface area is due to pore blockage, which occurs even before the reaction temperature is reached.…”

“…The external surface areas show a large variation, with the S E of catalyst 1 (52 m 2 /g) being $50% larger than for 2 or 5 (both 32 m 2 /g). As OA isomerisation is thought to occur mostly via pore-mouth catalysis [20], this parameter should be taken into account when studying the differences in activity. In addition, there is a significant variation in total pore volume ($20%), while the micropore volume remains largely unchanged (<2%).…”

“…We chose to use pyridine as probe instead (Py, kinetic diameter of 0.6 nm), in order to focus on the acid sites located in the 10-MR channels, and those accessible from these channels [5]. As a result of the pore-mouth catalysis, only (part of) these channels are believed to take part in the isomerisation of the long-chain OA molecules [20]. Fig.…”

“…9). The use of TPP specifically is based on results from catalytic testing, in which it has been shown to enhance selectivity of H-Fer-catalysed alkyl isomerisation of OA by preventing unwanted oligomerisation reactions [19,20]. The spectra recorded for catalysts 2 and 4 after reaction with TPP show 3 distinctive bands: an intense one at 226 nm and two smaller ones at 267 and 274 nm, all originating from TPP cations.…”

“…The deactivation has been shown to proceed via two mechanisms: Firstly, pore blockage occurs from a very early stage in the reaction, with dodecylbenzene and its precursors having been identified as the major coke constituents. Secondly, activity is further reduced due to acid site poisoning, caused by strong adsorption of polyenylic species formed by hydrogen transfer reactions [20]. These modes of deactivation imply that from the very early stages of reaction, only the pore mouth is participating in catalysis.…”