CO2 is one of the primary causes of global warming; therefore, it is vital to control the emissions. Even when long-term CO2 storage (sequestration) is possible, it is more desirable to use catalysts to convert CO2 into value-added chemicals and fuels. One of the most interesting products that can be obtained from CO2 is methanol, as this can be used as (1) fuel for DMFC, (2) a hydrogen storage medium, and (3) a convenient chemical feedstock to produce countless products. However, the hydrogenation of CO2 to methanol is not straightforward since it competes with the methanation reaction. Thus, it is necessary to use catalysts that can adsorb and activate CO2 without breaking both C-O bonds in the molecule. Cu-ceria interfaces have been reported to be very active in the hydrogenation of CO2 to methanol due to the formation of an unstable carboxylate intermediate that is readily converted. However, the number of active sites has been limited due to the large size of the CeO2 nanoparticles deposited onto the copper surface. To address this limitation, we developed a series of inverse CeOx-Cu/SiO2 catalysts with different CeOx loadings to generate a high number of interfacial sites for an improved hydrogenation rate. First, a monometallic Cu/SiO2 catalyst was synthesized by strong electrostatic adsorption (SEA). Then, after the addition of CeOx by controlled surface reactions (CSR), these inverse catalysts were characterized by temperature-programmed reduction, inductively coupled plasma optical emission spectroscopy, N2O chemisorption, X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM). While the XPS results showed 100% Ce(III) at low CeOx loadings, which is attributed to the small size of the CeOx nanoislands, this value decreased at higher CeOx contents. The larger size of the CeOx nanoclusters at higher CeOx loadings was also confirmed by STEM, which revealed the presence of ceria nanorods due to the non-selective deposition of CeOx onto the Cu nanoparticles. Unexpectedly, when studied in the hydrogenation of CO2, these catalysts provided not only methanol but also higher alcohols.

Inverse CeOx-Cu/SiO2 catalysts for the hydrogenation of CO2

ACS Spring Meeting 2021

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