Unraveling the structure sensitivity in methanol conversion on CeO2: A DFT+U study

Abstract

Highlights:-Structure sensitivity correlates with the surface oxygen content in the methanol decomposition on ceria.-Methanol selectively converts to formaldehyde on ceria (111) and (110) facets.-The CeO 2 (100) facet traps formaldehyde and ultimately enables its oxidation to produce CO+H 2 .-Hydrogen evolution is permitted on (100) due to its ability to stabilize a hydrogen precursor.-Formaldehyde can easily exchange its oxygen with the lattice in all facets. 2 ABSTRACTMethanol decomposes on oxides, in particular CeO 2 , producing either formaldehyde or CO as main products. This reaction presents structure sensitivity to the point that the major product obtained depends on the facet exposed in the ceria nanostructures. Our Density Functional Theory (DFT) calculations illustrate how the control of the surface facet and its inherent stoichiometry determine the sole formation of formaldehyde on the closed surfaces or the more degraded byproducts on the open facets (CO and hydrogen). In addition, we found that the regular (100) termination is the only one that allows hydrogen evolution via a hydride-hydroxyl precursor. The fundamental insights presented for the differential catalytic reactivity of the different facets agree with the structure sensitivity found for ceria catalysts in several reactions and provide a better understanding on the need of shape control in selective processes.3

Descriptor Analysis in Methanol Conversion on Doped CeO2(111): Guidelines for Selectivity Tuning

“…65,78 The resulting chemisorbed HCHO binds rather strongly, 1.23 eV, therefore allowing an eventual subsequent conversion to CO.…”

“…This process is 0.32 eV more demanding than formaldehyde desorption, and this fact is the ultimate responsible for the experimentally observed formaldehyde selectivity. 65 Then, the energy required for the second C-H stripping is 1. Therefore, the use of dopants (Zr, Hf) allows modifying the selectivity of the most stable facet of ceria for the particular process of methanol conversion.…”

Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

“…121 The decomposition of methanol on CeO 2 films involves the formation of formaldehyde, CO, and oxygen vacancies. [122][123][124] Therefore, the reduction of Pt 2+ species is observed as a consequence of the formation of oxygen vacancies regardless of the Pt loading (see Fig. 23).…”

“…The nearly linear increase of the RER on the Pt-free CeO 2 film indicates the formation of oxygen vacancies resulting from desorption of formaldehyde, CO, and water that involves partial removal of lattice oxygen from ceria. [122][123][124] In the presence of metallic Pt particles, however, a second channel opens that involves reverse hydrogen spillover followed by desorption of molecular hydrogen. 118 This process is accompanied by re-oxidation of ceria.…”

The Active Molybdenum Oxide Phase in the Methanol Oxidation to Formaldehyde (Formox Process): A DFT Study

“…As we have seen in the analysisofthe pure compounds, the activity of a-MoO 3 is poor as ar esult of aw eak trapping of methanol andt he overall activity is controlled by the easy formation of the vacancy on the surface, which is the highest point in the energy profile presented in Figure 2. [40] The most stable adsorption of formaldehydei nvolves av acancy site (bound to the Oa tom) and an oxygen atom from the lattice that formsaC ÀObond in adioxirane configuration (Figure 3, CH 2 O*). In addition, to reachs electivity,t he adsorption of formaldehyde needs to be smaller than that of methanol (thermodynamic competitive selectivity) [39] and smaller than the HÀCa ctivation in H 2 CO, as discussed earlier for CeO 2 .…”