Synthesis Gas Conversion over Rh/Mo Catalysts Prepared by Atomic Layer Deposition

Journal Article · Wed Jan 16 00:00:00 EST 2019 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.8b04649· OSTI ID:1542657

Zhang, Lifeng ^[1]; Ball, Madelyn R. ^[1]; Liu, Yifei ^[1]; Kuech, Thomas F. ^[1]; Huber, George W. ^[1]; Mavrikakis, Manos ^[1]; Hermans, Ive  ^[1]; Dumesic, James A.  ^[1]

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1. Univ. of Wisconsin-Madison, Madison, WI (United States)

Conversion of synthesis gas into value-added products, including oxygenates and C₂₊ hydrocarbons, was studied at 523 K, 580 psi, and a 1/1 CO/H₂ ratio over Rh catalysts on catalyst supports prepared by atomic layer deposition (ALD) of molybdenum and tungsten species on silica. The reactivity measurements showed that coating the silica support with molybdenum and tungsten species helped to suppress the methane selectivity and promote the overall conversion rate. When the silica support was coated with five cycles of β-Mo₂C, the methane selectivity decreased from 32% (1% Rh/SiO₂) to 13% (1% Rh/5c-Mo₂C/SiO₂), and the overall product rate increased 33 times from 0.4 to 12.7 mmol min^–1 (g of Rh)^–1. CO-FTIR results showed that supporting Rh on silica led to the formation of Rh(211) facets, which favored the formation of methane and had a higher CO conversion rate. Rh on a MoO₃/SiO₂ support prepared by ALD was found to be the most active catalyst while maintaining the suppression of methane selectivity, showing an overall rate ~60 times higher than that of 1% Rh/SiO₂. A reaction pathway is proposed, in which hydrogenation steps are promoted most significantly by Mo and W species, followed by promotion of CO insertion steps for ethanol synthesis and C–C coupling steps for hydrocarbon formation. CO-FTIR results showed that 1% Rh/MoO₃/SiO₂ has the highest proportion of gem-dicarbonyl adsorption sites and the lowest proportion of bridge-bonded CO adsorption sites. As a result, the rate of methanol formation shows a positive correlation with the number of sites that form gem-dicarbonyl species.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0014058
• OSTI ID: 1542657
• Journal Information: ACS Catalysis, Vol. 9, Issue 3; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
synthesis gas conversion
rhodium
molybdenum
atomic layer deposition (ALD)
metal carbides