Title: Methane and Ethane Steam Reforming over MgAl₂O₄-Supported Rh and Ir Catalysts: Catalytic Implications for Natural Gas Reforming Application

Abstract

Solar concentrators employed in conjunction with highly efficient micro- and meso-channel reactors offer the potential for cost-effective upgrading of the energy content of natural gas, providing a near-term path towards a future solar-fuel economy with reduced carbon dioxide emissions. To fully exploit the heat and mass transfer advantages offered by micro- and meso-channel reactors, highly active and stable natural gas steam reforming catalysts are required. In this paper, we report the catalytic performance of MgAl₂O₄-supported Rh (5 wt.%), Ir (5 wt.%), and Ni (15 wt.%) catalysts used for steam reforming of natural gas. Both Rh- and Ir-based catalysts are known to be more active and durable than conventional Ni-based formulations, and recently Ir has been reported to be more active than Rh for methane steam reforming on a turnover basis. Thus, the effectiveness of all three metals to perform natural gas steam reforming was evaluated in this study. Here, the Rh- and Ir-supported catalysts both exhibited higher activity than Ni for steam methane reforming. However, using simulated natural gas feedstock (94.5% methane, 4.0% ethane, 1.0% propane, and 0.5% butane), the Ir catalyst was the least active (on a turnover basis) for steam reforming of higher hydrocarbons (C2+) contained in themore » feedstock when operated at <750 °C. To further investigate the role of higher hydrocarbons, we used an ethane feed and found that hydrogenolysis precedes the steam reforming reaction and that C–C bond scission over Ir is kinetically slow compared to Rh. Catalyst durability studies revealed the Rh catalyst to be stable under steam methane reforming conditions, as evidenced by two 100-hour duration experiments performed at 850 and 900 °C (steam to carbon [S/C] molar feed ratio = 2.0 mol). However, with the natural gas simulant feed, the Rh catalyst exhibited catalyst deactivation, which we attribute to coking deposits derived from higher hydrocarbons contained in the feedstock. Increasing the S/C molar feed ratio from 1.5 to 2.0 reduced the deactivation rate and stable catalytic performance was demonstrated for 120 h when operated at 850 °C. However, catalytic deactivation was observed when operating at 900 °C. While improvements in steam reforming performance can be achieved through choice of catalyst composition, this study also highlights the importance of considering the effect of higher hydrocarbons contained in natural gas, operating conditions (e.g., temperature, S/C feed ratio), and their effect on catalyst stability. The results of this study conclude that a Rh-supported catalyst was developed that enables very high activities and excellent catalytic stability for both the steam reforming of methane and other higher hydrocarbons contained in natural gas, and under conditions of operation that are amendable to solar thermochemical operations.« less

Authors:

Lopez, Johnny Saavedra  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-7542-5826"

Dagle, Vanessa Lebarbier ^[1]; Deshmane, Chinmay A. ^[1]; Kovarik, Libor ^[1]; Wegeng, Robert S. ^[1]; Dagle, Robert A.  ^[1]

• Search DOE PAGES for author "Dagle, Robert A."
• Search DOE PAGES for ORCID "0000-0002-8208-2163"

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Publication Date:

Wed Sep 25 00:00:00 EDT 2019

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1573015

Report Number(s):

PNNL-SA-146376
Journal ID: ISSN 2073-4344; CATACJ

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Catalysts

Additional Journal Information:

Journal Volume: 9; Journal Issue: 10; Journal ID: ISSN 2073-4344

Publisher:

MDPI

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 03 NATURAL GAS; catalyst; steam reforming; methane; natural gas; hydrogen