In Situ Spectroscopic Investigation into the Active Sites for Crotonaldehyde Hydrogenation at the Pt Nanoparticle–Co₃O₄ Interface

Journal Article · Sat Sep 17 00:00:00 EDT 2016 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.6b01640· OSTI ID:1393085

Kennedy, Griffin ^[1]; Melaet, Gérôme ^[1]; Han, Hui-Ling ^[1]; Ralston, Walter T. ^[1]; Somorjai, Gabor A. ^[1]

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1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

The hydrogenation of crotonaldehyde by platinum nanoparticles supported on cobalt oxide was used as a reaction to probe the effect of the interface between the two materials on the activity and selectivity of the catalyst. Four potential products can be formed by this reaction: propylene, butyraldehyde, crotyl alcohol, and butanol. When Pt nanoparticles are supported on SiO₂, an inert support, only propylene and butyraldehyde are formed. However, when Pt is supported on cobalt oxide, the alcohols make up roughly 40% of the total activity, indicating that cobalt oxide plays a pivotal role in the reaction, much like other active supports such as TiO₂. To elucidate the mechanism of alcohol formation, in situ sum frequency generation vibrational spectroscopy (SFG) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were utilized to probe the reactant adsorption and intermediate formation and the chemical state of the materials under working catalytic conditions. The SFG data indicate that crotonaldehyde adsorbs on the oxide surface, likely through the aldehyde oxygen as well as on the Pt surface through the alkene group. AP-XPS results show that the surface of the Co₃O₄ support becomes partially reduced under the reaction conditions and Pt exists in its metallic state. Taking these results together, we propose in this paper that the crotonaldehyde adsorbs at reduced oxide surface sites and that this adsorption mode is responsible for the production of alcohol products. A platinum nanoparticle density dependence study was also undertaken to change the abundance of interface sites and study their effect on the reaction. The selectivity between the two alcohol products was altered as a function of the Pt nanoparticle density: higher selectivity toward butanol and lower selectivity toward crotyl alcohol was obtained with increasing density, while propylene and butyraldehyde selectivities were constant with respect to density. Finally, on the basis of the data presented, we propose that butanol is preferentially formed at the metal–oxide interface, while crotyl alcohol is formed at oxide surface sites by reaction with spillover hydrogen.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1393085
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 10 Vol. 6; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ambient-pressure XPS
cobalt oxide
hydrogenation
in situ characterization
sum frequency generation
support effects