Microwaves effectively examine the extent and type of coking over acid zeolite catalysts

Abstract

Coking leads to the deactivation of solid acid catalyst. This phenomenon is a ubiquitous problem in the modern petrochemical and energy transformation industries. Here, we show a method based on microwave cavity perturbation analysis for an effective examination of both the amount and the chemical composition of cokes formed over acid zeolite catalysts. The employed microwave cavity can rapidly and non-intrusively measure the catalytically coked zeolites with sample full body penetration. The overall coke amount is reflected by the obtained dielectric loss (ε″) value, where different coke compositions lead to dramatically different absorption efficiencies (ε″/cokes’ wt%). The deeper-dehydrogenated coke compounds (e.g., polyaromatics) lead to an apparently higher ε″/wt% value thus can be effectively separated from lightly coked compounds. The measurement is based on the nature of coke formation during catalytic reactions, from saturated status (e.g., aliphatic) to graphitized status (e.g., polyaromatics), with more delocalized electrons obtained for enhanced Maxwell–Wagner polarization.

Threshold catalytic onset of carbon formation on CeO2during CO2electrolysis: mechanism and inhibition

“…5,6 However, carbon poisoning, or "coking", due to carbon deposition on the catalyst surface during operation, is an important issue for processes involving carbon-containing species. 7,8 This coking process can lead to irreversible catalyst deactivation and cause mechanical degradation. 9 One major type of carbon poisoning is from CO, [10][11][12][13][14] which has been reported as either CO dissociation 15,16 (CO / C + O) or the Boudouard disproportionation [17][18][19] (2CO / CO 2 + C).…”

Rapid, non-invasive characterization of the dispersity of emulsionsviamicrowaves

“…The cavity excitation is provided by two open-circuit SMA connectors coupled into the electric field at a frequency of 2.5 GHz. The TM 010 mode is employed to establish a highly uniform E-field near the axis, resulting in a minimal depolarization of the sample in the measurement 23. The electric field distribution in this cavity simulated by COMSOL Multiphysics is shown in Fig.…”

Overcoming Stability Problems in Microwave-Assisted Heterogeneous Catalytic Processes Affected by Catalyst Coking

“…Specifically, the dielectric loss of the coked 6% Mo/ZSM-5 sample at 700 • C is δ spent-700 • C = 7.6 × 10 −2 , whereas that of the fresh one with the same metal loading is δ fresh-700 • C = 4.3 × 10 −2 . This behavior is attributed to the excellent microwave absorption ability of the carbonaceous materials given by the displacement of the delocalized π electrons in the presence of an electromagnetic field (δ CNT-700 • C = 1.59), thus converting MW energy into heat [1,15]. Therefore, the results shown in Figure 1 suggest that the dielectric properties of the catalyst will be affected not only by changes in temperature but also by the chemical reaction.…”

“…Carbon species are excellent MW-susceptors and their presence may promote the formation of hot spots and temperature gradients along the catalytic sample, which further impact both operational controllability and experimental reproducibility [10]. Under certain conditions, coke deposits may disturb the electromagnetic field within the resonator leading to cavity uncoupling and causing the instantaneous decrease of the catalytic sample temperature, thus, extinguishing the catalytic process [15,16].…”