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.