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Title: Methane Conversion to Ethylene and Aromatics on PtSn Catalysts

Abstract

Pt and PtSn catalysts supported on SiO 2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO 2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO 2:Al 2O 3 = 280 in comparison to those over PtSn(3:1)/SiO 2. H-ZSM-5-supported catalysts were also active for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)).more » Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO 2-supported catalysts, as a possible source of their high activity. As a result, a microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.« less

Authors:
 [1];  [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Research Org.:
Univ. of Wisconsin-Madison, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Org.:
DoD High Performance Computing Modernization Program (US Ai Force Research Laboratory); DoD Supercomputing Resource Center (AFRL DSRC); the US Army Engineer Research and Development Center (ERDC), Navy DoD Supercomputing Resource Center (Navy DSRC); UW Materials Research Science and Engineering Center; UW Nanoscale Science and Engineering Center; UW-Madison Soft Materials Laboratory
OSTI Identifier:
1395572
Grant/Contract Number:
FC02-07ER64494
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 7; Journal Issue: 3; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; aromatics; ethylene; H-ZSM-5; methane conversion; microkinetic model; particle size; platinum; tin

Citation Formats

Gerceker, Duygu, Motagamwala, Ali Hussain, Rivera-Dones, Keishla R., Miller, James B., Huber, George W., Mavrikakis, Manos, and Dumesic, James A. Methane Conversion to Ethylene and Aromatics on PtSn Catalysts. United States: N. p., 2017. Web. doi:10.1021/acscatal.6b02724.
Gerceker, Duygu, Motagamwala, Ali Hussain, Rivera-Dones, Keishla R., Miller, James B., Huber, George W., Mavrikakis, Manos, & Dumesic, James A. Methane Conversion to Ethylene and Aromatics on PtSn Catalysts. United States. doi:10.1021/acscatal.6b02724.
Gerceker, Duygu, Motagamwala, Ali Hussain, Rivera-Dones, Keishla R., Miller, James B., Huber, George W., Mavrikakis, Manos, and Dumesic, James A. Fri . "Methane Conversion to Ethylene and Aromatics on PtSn Catalysts". United States. doi:10.1021/acscatal.6b02724. https://www.osti.gov/servlets/purl/1395572.
@article{osti_1395572,
title = {Methane Conversion to Ethylene and Aromatics on PtSn Catalysts},
author = {Gerceker, Duygu and Motagamwala, Ali Hussain and Rivera-Dones, Keishla R. and Miller, James B. and Huber, George W. and Mavrikakis, Manos and Dumesic, James A.},
abstractNote = {Pt and PtSn catalysts supported on SiO2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO2:Al2O3 = 280 in comparison to those over PtSn(3:1)/SiO2. H-ZSM-5-supported catalysts were also active for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)). Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO2-supported catalysts, as a possible source of their high activity. As a result, a microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.},
doi = {10.1021/acscatal.6b02724},
journal = {ACS Catalysis},
number = 3,
volume = 7,
place = {United States},
year = {Fri Feb 03 00:00:00 EST 2017},
month = {Fri Feb 03 00:00:00 EST 2017}
}

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  • No abstract prepared.
  • The structure and density of Mo species in Mo/H-ZSM5 during catalytic CH4 reactions was investigated using in-situ X-ray absorption spectroscopy (XAS), temperature-programmed oxidation after reaction, and the isotopic exchange of D2 with OH groups in H-ZSM5 before and after CH4 reactions. These methods reveal that CH4 reactions cause exchanged Mo2O52+ dimers, formed from physical mixtures of MoO3 and H-ZSM5, to reduce and carburize to form small (0.6-1 nm) MoCx clusters with the concurrent regeneration of the bridging OH groups that were initially replaced by Mo oxo dimers during exchange. In this manner, catalytically inactive Mo oxo species activate in contactmore » with CH4 to form the two sites required for the conversion of CH4 to aromatics: MoCx for C-H bond activation and initial C-C bond formation and acid sites for oligomerization and cyclization of C2+ hydrocarbons to form stable aromatics. These MoCx clusters resist agglomeration during methane reactions at 950 K for > 10 h. The Bronsted acid sites formed during carburization and oligomerization of MoCx species ultimately become covered with hydrogen-deficient reaction intermediates (H/C{sup X} 0.2) or unreactive deposits. The highly dispersed nature of the MoCx clusters was confirmed by detailed simulations of the XAS radial structure function and by the low temperatures required for the complete oxidation of these MoCx species compared with bulk Mo2C. Initial CH4 reactions with MoOx precursors are stoichiometric and lead first to the removal of oxygen as CO, CO2, and H2O and to the introduction of carbidic carbons into the reduced structures. As carbidic carbon passivates the surface, C-H bond activation reactions become catalytic by the coupling of this activation step with the removal of the resulting CHx species to form C2 hydrocarbons, which desorb to re-form the MoCx sites required for C-H bond activation steps.« less
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