(718a) Production of Formaldehyde On Transition Metal Catalysts Via the Anhydrous Dehydrogenation of Methanol

A
simple web-based application called "CatApp" has recently been made available to the public, which
provides access to the adsorption and transition state energies of different
molecules on transition metal surfaces. This paper illustrates the utility of
such a database for predicting trends in the activities and selectivities of materials
for a given reaction. In this case, the anhydrous dehydrogenation of methanol
to formaldehyde is used as a test reaction, but the methods presented here are
widely applicable to a broad range of reactions.

The
DFT-calculated adsorption and transition state energies of the relevant
intermediates were accessed via CatApp
for the stepped (211) surfaces of Ag, Cu, Pd, Pt, and Rh. As described in the
literature, the binding energies for these intermediates on a given surface can
be scaled with the binding energies of carbon and oxygen. Likewise, the
energies of a given transition state species can be scaled with the energies of
the reaction products. By combining these scaling relations with a microkinetic
modeling technique, we calculated the turnover frequencies for CH₂O
and CO production (the desired and undesired reaction products, respectively)
for a range of carbon and oxygen binding energies (Figure 1).

The
results of these calculations are consistent with findings from the literature,
which indicate that there are no transition metal catalysts that are active and
selective for the production of formaldehyde. Importantly, our analysis also
predicts that materials with a carbon binding energy similar to that of Cu or
Zn, but with higher oxygen binding energies, would be highly active and
selective for formaldehyde production.

Figure
1 - Calculated turnover
frequencies (TOFs) for CH₂O and CO production as a function of
carbon and oxygen binding energies. The carbon and oxygen binding energies for
the stepped (211) surfaces of selected transition metals are depicted. The
error bars indicate an estimated error of 0.2 eV for E_C and E_O.
Reaction conditions are 823 K and 1 bar with a gas composition of 95% CH₃OH,
1% CH₂O, 1% CO, and 3% H₂.