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Title: Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5

Abstract

In this paper, we present a new class of catalysts, InMo-ZSM- 5, which can be prepared by indium impregnation of Mo-ZSM- 5. The incorporation of indium dramatically decreases coke formation during methane dehydroaromatization. The benzene and C 2 hydrocarbons selectivity among total hydrocarbons over InMo-ZSM- 5 remains comparable to that of Mo-ZSM- 5 despite reduced methane conversion due to decreased coke formation. We found 1 wt% indium to be optimal loading for reducing coke selectivity to half that of Mo-ZSM- 5. Characterization methods were not helpful in discerning the interaction of In with Mo but experiments with bimetallic 1In2Mo-ZSM- 5 and mechanical mixture 1In+2Mo-ZSM- 5 suggest that In and Mo need to be in close proximity to suppress coke formation. Finally, this is supported by temperature programmed reduction experiments which show that In incorporation leads to lower Mo reduction temperature in In2Mo-ZMS- 5.

Authors:
 [1];  [2];  [1];  [1];  [2];  [2];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1302883
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Catalysis Letters
Additional Journal Information:
Journal Name: Catalysis Letters; Journal ID: ISSN 1011-372X
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; methane to benzene; methane dehydroaromatization; coking suppression; heterobimetallic zeolites; InMo-ZSM-5

Citation Formats

Zhang, Yang, Kidder, Michelle, Ruther, Rose E., Nanda, Jagjit, Foo, Guo Shiou, Wu, Zili, and Narula, Chaitanya K. Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5. United States: N. p., 2016. Web. doi:10.1007/s10562-016-1831-5.
Zhang, Yang, Kidder, Michelle, Ruther, Rose E., Nanda, Jagjit, Foo, Guo Shiou, Wu, Zili, & Narula, Chaitanya K. Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5. United States. doi:10.1007/s10562-016-1831-5.
Zhang, Yang, Kidder, Michelle, Ruther, Rose E., Nanda, Jagjit, Foo, Guo Shiou, Wu, Zili, and Narula, Chaitanya K. 2016. "Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5". United States. doi:10.1007/s10562-016-1831-5. https://www.osti.gov/servlets/purl/1302883.
@article{osti_1302883,
title = {Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5},
author = {Zhang, Yang and Kidder, Michelle and Ruther, Rose E. and Nanda, Jagjit and Foo, Guo Shiou and Wu, Zili and Narula, Chaitanya K.},
abstractNote = {In this paper, we present a new class of catalysts, InMo-ZSM-5, which can be prepared by indium impregnation of Mo-ZSM-5. The incorporation of indium dramatically decreases coke formation during methane dehydroaromatization. The benzene and C2 hydrocarbons selectivity among total hydrocarbons over InMo-ZSM-5 remains comparable to that of Mo-ZSM-5 despite reduced methane conversion due to decreased coke formation. We found 1 wt% indium to be optimal loading for reducing coke selectivity to half that of Mo-ZSM-5. Characterization methods were not helpful in discerning the interaction of In with Mo but experiments with bimetallic 1In2Mo-ZSM-5 and mechanical mixture 1In+2Mo-ZSM-5 suggest that In and Mo need to be in close proximity to suppress coke formation. Finally, this is supported by temperature programmed reduction experiments which show that In incorporation leads to lower Mo reduction temperature in In2Mo-ZMS-5.},
doi = {10.1007/s10562-016-1831-5},
journal = {Catalysis Letters},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
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  • Kinetic isotope effects (KIEs) during the oxidative coupling of methane over a Li[sup +]/MgO catalyst at 700[degrees]C have been determined using several different experimental methods and by a reaction model that includes both heterogeneous and homogeneous reactions. By maintaining a constant partial pressure of methane of 190 Torr and changing the partial pressure of oxygen, a variation in the H/D KIE, based on differing rates of CH[sub 4] and CD[sub 4] conversion, was observed. In addition, a similar variation in KIE was found from the isotopic distribution of H and D in the ethane product when CH[sub 4] and CD[submore » 4] were co-fed into the reactor. The decrease in KIE with increasing methane-to-oxygen reactant ratio is evidence that a unique rate-limiting step does not exist; rather, the rates of methane activation and of oxygen incorporation, as individual steps, are comparable. Other factors, such as the absolute partial pressures of the reagents may become even more important than the methane-to-oxygen ratio under some conditions. When N[sub 2]O was used as the oxidant instead of O[sub 2] and normal catalytic conditions were employed, the observed KIE was unity, even though the N[sub 2]O was present in excess. In this case, a unique rate-limiting step was operative, viz., the incorporation of oxygen into the lattice. The KIE was also determined separately for the production of methyl radicals, but these experiments were carried out at much lower reagent partial pressures (<1 Torr). With O[sub 2] as the oxidant, KIEs of 1.5 [+-] 0.2 were observed, although the methane-to-oxygen ratios were large (>40). This result confirms that there is a KIE associated with the activation of methane on the surface but that this is not necessarily a unique rate-limiting step. With N[sub 2]O as the oxidant, it was possible to vary the methane-to-nitrous oxide ratio over a large range (from 0.29 to 44). 29 refs., 4 figs., 5 tabs.« less
  • The kinetic isotope effect for CH{sub 4} compared to that for CD{sub 4} has been measured for the oxidative coupling reaction of methane over Li/MgO, SrCO{sub 3}, and Sm{sub 2}O{sub 3} catalysts in a flow reactor. Each catalyst gave results consistent with C-H bond breaking being the slow step. For temperatures between 680-780 C over Li/MgO, k{sub H}/k{sub D} decreased slightly with temperature. The isotope effect for ethane production was more sensitive to the level of conversion and declined from 1.8 at low conversion to near unity under conditions where the ethylene to ethane ratio was high ({approximately}1). Selectivities tomore » hydrocarbons were lower with CD{sub 4} and did not change with decreased flow rates, implying that either CO{sub x} and C{sub 2} products arise by totally separate slow steps or, if a common step with CH{sub 3} radicals is involved, then CO{sub x} formation occurs on the catalyst. Experiments with CH{sub 4}/CD{sub 4} mixtures showed that CH{sub 3}CD{sub 3} and CH{sub 2}CD{sub 2} were the dominant mixed products. The distribution of the ethanes always reflected the relative concentrations of CH{sub 3} and CD{sub 3} determined by the kinetic isotope effect. At low ethylene to total C{sub 2} ratios ({approximately}0.2) this was also true for ethylene; but at higher ratios substantial exchange to produce ethylenes other than C{sub 2}H{sub 4}, CH{sub 2}CD{sub 2}, and C{sub 2}D{sub 4} occurred. The concentration of the exchanged methanes correlated with total methane conversion but was dependent on the surface. Exchange in the ethylenes also correlated with exchange in the methanes and purely gas phase processes appear at least partially responsible. H{sub 2}:HD:D{sub 2} ratios are always at equilibrium and exchange also occurs between CD{sub 4} and H{sub 2}.« less
  • The effects of adding H{sub 2}O to the gas feed on the oxidative coupling of methane over Li/MgO catalyst at different partial pressures of H{sub 2}O and temperatures and in the presence of cofed CO{sub 2} have been studied. Results indicated that H{sub 2}O enhanced the deactivation rate. The deactivation rate increased with increasing partial pressure of the steam in the feed as well as with increasing temperature. The deactivation rate is decreased by adding small amounts of CO{sub 2} to the reaction mixture. The effects of injecting different amounts of liquid water into the catalyst bed under different reactionmore » conditions have also been investigated. Results showed that under the conditions of the experiments water significantly enhanced the activity of the catalyst. The methane conversion increased by 86%--124% while the C{sub 2} selectivity remained relatively unchanged. The liquid water treatment significantly increased the product C{sub 2}H{sub 4}: C{sub 2}H{sub 6} ratio. The catalyst lithium content decreased and the BET surface area increased due to the water treatment. Some of the lithium lost from the catalyst was deposited on the walls of the reactor; however, this lithium was not responsible for the enhanced activity.« less
  • The effects of CO[sub 2] partial pressure on oxidative methane coupling over a Li/MgO catalyst were studied under low conversion conditions in a flow reactor. Methane to oxygen ratios from 0.5 to 35 and temperatures from 973 to 1073 K were used in the experiments and modeling. Varying flow rates of CO[sub 2] were mixed with the methane and oxygen prior to the reaction. Results indicate that CO[sub 2] has a poisoning effect on both carbon oxides (CO and CO[sub 2]) and C[sub 2] hydrocarbon (C[sub 2]H[sub 4] and C[sub 2]H[sub 6]) formation rates, while selectivity to the C[sub 2]more » hydrocarbon was not significantly affected. The apparent activation energy increased with CO[sub 2] partial pressure in the feed. Results also indicate that a small amount of methane reacts with carbon dioxide to produce carbon monoxide. Empirical rate expressions and rate expressions rigorously derived from proposed mechanisms were obtained. The rate expressions agree well with the measured rates and also predict the observed trend in apparent activation energy.« less
  • A simple liquid water treatment applied to fresh and thermally aged Pt(2wt%)-BaO(20wt%)/Al2O3 lean NOx trap catalysts at room temperature induces morphological and structural changes in the barium species as followed by XRD and TEM analysis. During the water treatment, liquid water sufficient to fill the catalyst pore volume is brought into contact with the samples. It was found that irrespective of the original barium chemical state (highly dispersed BaO or crystalline BaAl2O4), exposing the sample to this liquid water treatment promotes the formation of BaCO3 crystallites (about 15 – 25 nm of its size) without changing the Pt particle size.more » Such transformations of the barium species are found to significantly promote NOx uptake from 250 °C to 450 °C. The increase in the NOx uptake for the water-treated samples can be attributed to an enhanced Pt-Ba interaction through the redistribution of barium species. These results provide useful information for the regeneration of aged lean NOx trap catalysts since water is plentiful in the exhaust of diesel or lean-burn engines.« less