(750c) Measurement of the Concentration and Intrinsic Catalytic Activity of Monometallic and Interfacial Sites

Title: Measurement of the concentration and intrinsic catalytic activity of monometallic and interfacial sites

Insoo Ro^a, Yifei Liu^a, Isaias B. Aragao^b, Madelyn R. Ball^a, Joseph P. Chada^a, Canan Sener^a, Daniela Zanchet^b, James A. Dumesic^a, and George W. Huber^a

^a Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI

^b Institute of Chemistry, University of Campinas, Campinas, SP, Brazil

Many previous studies have proposed that several types of catalytic reactions occur at the interface between a metal and metal oxide or an “interfacial catalytic site”. However, the measurement of the intrinsic activity of an interfacial catalytic site has not previously been possible. This is primarily because the synthesis of catalysts by traditional methods produces a wide distribution of metal particle sizes and compositions which results in a distribution of interfacial sites. We have developed synthetic routes to prepare a series of metal-metal oxide catalysts (including Au-MoO_x, Pt-MoO_x, Cu-ZrO₂, and Pt-FeO_x all supported on SiO₂) with well-defined concentrations of interfacial sites using an approach called controlled surface reactions (CSR). We were able to quantify the concentrations of monometallic and interfacial sites using a combination of sub-ambient CO Fourier transform infrared spectroscopy (FT-IR), CO chemisorption, reactive N₂O chemisorption, and scanning transmission electron microcopy (STEM)/energy dispersive X-ray spectroscopy (EDS). We then measured the intrinsic activity in the reverse water gas shift reaction (RWGS), methanol synthesis reaction, hydrogenation of carbonyls, CO oxidation, and ethanol conversion into ethyl acetate [1-4]. The intrinsic reaction rate at these interfacial sites was 8 to 700 times higher than the intrinsic reaction rate on monometallic sites. In this presentation we will attempt to develop a relationship between the structure of the interfacial site and the catalytic activity in different reactions. We will discuss how we can control the catalyst activity by changing the concentration and types of interfacial sites. We will illustrate how this approach can be used to design improved catalysts by maximizing the concentration of interfacial sites.

Reference

[1] Ro et al. Role of the Cu-ZrO₂ Interfacial Sites for Conversion of Ethanol to Ethyl Acetate and Synthesis of Methanol from CO₂ and H₂, ACS Catalysis, 6 (2016) 7040

[2] Ro et al. Measurement of intrinsic catalytic activity of Pt monometallic and Pt-MoO_x interfacial sites over visible light enhanced PtMoO_x/SiO₂ catalyst in reverse water gas shift reaction, Journal of Catalysis, 344 (2016) 784

[3] Carrasquillo-Flores and Ro et al. Reverse water-gas shift on interfacial sites formed by deposition of oxidized molybdenum moieties onto gold nanoparticles, Journal of the American Chemical Society 137 (2015) 10317

[4] Ro et al. Intrinsic kinetics of plasmon-enhanced reverse water gas shift on Au and Au–Mo interfacial sites supported on silica, Applied Catalysis A: General, 521 (2016) 182