Mapping the coke formation within a zeolite catalyst extrudate in space and time by operando computed X-ray diffraction tomography

Real-time regeneration of a working zeolite monitored via operando X-ray diffraction and crystallographic imaging: how coke flees the MFI framework

“…Recently Rojo-Gama et al [32] demonstrated that this apparent symmetry is a metric coincidence and appears in some H-ZSM-5 samples. However, the difference in length of the a-and b-axes can be used as a global descriptor for the deactivation of the H-ZSM-5 zeolite catalyst, referred to as the a minus b parameter, or simply (a-b) [32,33,45].…”

“…However, the difference in length of the a - and b - axes can be used as a global descriptor for the deactivation of the H-ZSM-5 zeolite catalyst, referred to as the a minus b parameter, or simply ( a − b ). 32,33,45…”

“…However, the difference in length of the a-and b-axes can be used as a global descriptor for the deactivation of the H-ZSM-5 zeolite catalyst, referred to as the a minus b parameter, or simply (a − b). 32,33,45 Thus, we have previously shown that during the MTG reaction, (a − b) is proportional to the amount of coke and consecutively to the degree of the H-ZSM-5 catalyst deactivation. 32,33 As the coke level increases, it starts occupying preferential sites within the MFI framework, equalizing the a and b-axes length from 20.17 Å and 20.01 Å, respectively, to 20.04 Å.…”

A review of recent developments for the in situ/operando characterization of nanoporous materials

“…18). [106] They could show that during the catalytic conversion of methanol to hydrocarbons, the activation starts at the external layers of the extrudates and progresses into the bulk. Through the operando monitoring of the deactivation process in both time and space, it was possible to obtain a kinetic model for the coking, providing crucial insight which allows improvement of the catalyst and process design.…”

Direct analysis at temporal and molecular level of deactivating coke species formed on zeolite catalysts with diverse pore topologies

“…19,20 The lack of precise analyses of coke composition has grown at the same rate we have developed a picture of coke as a highly aromatic structure given its very low H/C ratios. 21 In-situ techniques, from spectroscopy 22,23 to microscopic-tomographic 24,25 techniques, have contributed substantially to the understanding of the coke formation mechanisms. To date, in-situ techniques cannot resolve the molecular-level characterization, and ex-situ techniques, such as disaggregation and extraction 26 or extraction alone, 27,28 are widely used instead.…”