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A clue to exploration of the pathway of coke formation on Mo/HZSM-5 catalyst in the non-oxidative methane dehydroaromatization at 1073 K

Paper ID Volume ID Publish Year Pages File Format Full-Text
39623 45828 2014 10 PDF Available
Title
A clue to exploration of the pathway of coke formation on Mo/HZSM-5 catalyst in the non-oxidative methane dehydroaromatization at 1073 K
Abstract

•Investigation on the lifetime performance and coking behavior of Mo/HZSM-5 catalyst.•Three stages catalyst deactivation with rapid decrease in benzene selectivity in the last stage.•Continuous increase in C2H4 formation rate over the whole second and part of last stage.•The average coke formation rate is higher in the last than second deactivation stage.•C2H4 is the dominating source of coke formation in the last stage of catalyst deactivation.

Experimental investigation on the lifetime performance and coking behavior of a 6 wt% Mo/HZSM-5 catalyst in the non-oxidative methane dehydroaromatization was conducted in a three layers fixed-bed mode and at 1073 K and a space velocity of 5000 mL/g/h. Characterization of the coke in all spent samples recovered after different periods of the reaction was performed using TG, XPS and TPO techniques. The time-dependence of the catalytic performance revealed that the test catalyst undergoes three stages deactivation over its lifetime, the benzene selectivity remains high and constant in the second deactivation stage and then decreases very rapidly from 64 to 18% in the last stage, and the C2H4 formation rate keeps increasing in a wide region covering the whole second stage and the first one third of the last stage. On the other hand, quantification of the coke contents of the spent samples and their characterization revealed that the average coke formation rate in the last deactivation is obviously higher than that recorded over the second stage and the formation of the aromatic type of coke inside the zeolite channels is primarily accelerated in the last stage. Thus, both observations together lead to a conclusion that C2H4, which has a smaller molecular diameter than benzene and is allowed to form inside the narrowed zeolite channels, is the main source of coke formation in the last stage of catalyst deactivation. C2H4 has been well recognized to form throughout the whole course of the reaction, and therefore the present observations are expected to provide a clue to exploration of the pathway that dominates the coke formation in the period of the benzene selectivity remaining constant (the second stage of catalyst deactivation) as well.

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Keywords
Methane dehydroaromatization; Mo/HZSM-5; Coke type; Coking pathways; Coke distribution
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A clue to exploration of the pathway of coke formation on Mo/HZSM-5 catalyst in the non-oxidative methane dehydroaromatization at 1073 K
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 482, 22 July 2014, Pages 387–396
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us