Direct ethanol synthesis from syngas provides a promising pathway to convert biomass and organic waste into valuable fuel. However, the applicability of this reaction is still limited by the lack of a satisfactory catalyst. Rhodium (Rh) nanoparticles with appropriate oxide supports or promoters have shown high ethanol production among different candidates. However, previous studies showed that Rh alone is not very selective to ethanol. The activity and selectivity of Rh nanoparticles, therefore, largely depend on the metal oxide supports and promoters. Although many different metal oxides have been demonstrated to be effective in improving ethanol production, the role of metal oxides in this reaction is still controversial and not fully understood. In this work, we investigate the function of metal oxide supports on the overall reaction rate and product distribution through a series of experiments in which we modify the identity, position and thickness of the surrounding metal oxides (MOx). Atomic layer deposition (ALD) is applied to deposit ultrathin metal oxide layers in order to change the surface composition and Rh-MOx interface structure of the catalysts. ALD has the unique capability to achieve uniform coating on high surface area substrates and complex nanostructures. Compared to traditional co-impregnation method, ALD allows versatile manipulation of the structure of these catalysts and accurate control of the surface metal oxide composition. Both conventional and inverse catalysts are synthesized. Rh nanoparticles are deposited on silica gel substrates (Rh/SiO2) by incipient wetness impregnation. Titanium oxide, manganese oxide and zinc oxide layers of different thickness are deposited by ALD. The resulting catalysts (Rh/MOx/SiO2, MOx/Rh/SiO2) are characterized by scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature programmed reduction (TPR). The catalytic behavior is tested by syngas conversion reaction, and the activity and selectivity of the ALD-modified catalysts will be presented.

Understanding metal oxide effects in syngas conversion catalysts through interface modification by atomic layer deposition

248th National Meeting (2014)

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