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Oxidation of isobutene to methacrolein using bismuth molybdate catalysts: Comparison of operation in periodic and continuous feed mode

Song, N., Rhodes, C., Bartley, Jonathan Keith, Taylor, Stuart Hamilton, Chadwick, D. and Hutchings, Graham John 2005. Oxidation of isobutene to methacrolein using bismuth molybdate catalysts: Comparison of operation in periodic and continuous feed mode. Journal of Catalysis 236 (2) , pp. 282-291. 10.1016/j.jcat.2005.10.008

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Abstract

A series of bismuth molybdate catalysts were compared using a continuous feed of isobutene in air or a cyclic/pulse or gas-gas periodic flow mode, in which the oxide is first treated with air at the reaction temperature, followed by reaction of isobutene in nitrogen or argon in the absence of oxygen. For nonpromoted catalysts, in the continuous-feed mode, relatively low selectivities for methacrolein are observed and significant amounts of byproduct CO 2 are formed. In contrast, in the pulse mode, no CO2 and almost 100 selectivity to methacrolein can be observed with nonpromoted BiMoOx, especially for the initial reaction period. At realistic reaction temperatures, no carbon or carbon-containing product depositions are observed during the pulse mode, indicating that the very high selectivity observed is realistic for the nonpromoted catalyst under pulse conditions. The effect of Co and Fe as promoters on the catalytic performance was also investigated. The addition of Co and Fe leads to the observation of CO 2 also in the pulse mode along with some carbon deposition, although the selectivity to methacrolein remains significantly higher than that observed in the continuous-feed mode. Investigation of a more complex promoted catalyst representative of a commercial formulation BiMo12Fe 2NiCo7MgSb0.9Ti0.1Te 0.02Cs0.4Ox also shows that CO2 is observed in the pulse mode but, at much lower levels than observed with the less complex catalysts. However, in subsequent operation in the gas-gas periodic flow, the catalytic performance for this catalyst is almost identical in the continuous and pulse operations. It is concluded that, for pulse-mode operation, the best results, including almost total selectivity to methacrolein, are observed with the relatively simple nonpromoted binary oxides. In general, the first pulse-mode operation of these catalysts gives the highest yield of methacrolein and subsequent oxidation/reaction cycles gives lower yields. The origin of this effect was investigated using cyclic TPO/TPR and TPR/TPO analysis, revealing that the first TPR/TPO cycles are significantly different than subsequent cycles, likely due to the initial state of the catalyst surface. © 2005 Elsevier Inc. All rights reserved.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Uncontrolled Keywords: Bismuth; Byproducts; Catalyst selectivity; Catalysts; Oxidation; Reaction kinetics; Temperature programmed desorption, Bismuth molybdate catalysts; Continuous flow; Isobutene; Methacrolein; Oxidation cycle; Periodic flow; Reduction/oxidation; Selective oxidation; TPO cycle, Butenes
Additional Information: cited By (since 1996) 9
Publisher: Academic Press
ISSN: 00219517
Last Modified: 04 Jun 2017 02:10
URI: http://orca.cf.ac.uk/id/eprint/10274

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