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The production of formaldehyde is of great importance because of its role as platform reagent and wide application in industry. The current industrial method is a three-step process, which is energy extensive and has separation problem. However, the direct hydrogenation of CO to formaldehyde is challenging because it’s thermodynamically unfavorable¹. Our previous work has shown that MOFs functionalized with Lewis pairs (LPs) have the potential to be effective catalysts for the conversion of CO₂ to formic acid through direct hydrogenation^2-4. Herein, we proposed a new approach to directly synthesize formaldehyde from CO and H₂, by using Lewis pairs functionalized MOFs as the heterogeneous catalyst, to address the sluggish reaction kinetic and the thermodynamic limitations.

We have computed the overall reaction pathways in gas phase, inside the functionalized UiO-67, and on the LP cluster analog using the density functional theory (DFT), in addition to more advanced methods. The activation barrier of the rate-limiting step for CO hydrogenation is reduced to 1.67 eV from 3.54 eV for uncatalyzed gaseous reaction. We also did GCMC simulations to calculate adsorption isotherms for CO and H₂, which show enhanced pressures for CO and H₂ inside the MOF pores. Our results indicate that LPs functionalized MOF, UiO-67-NBF₂, is a promising catalyst for gas-phase synthesis of formaldehyde from CO and H₂, with enhanced rate and conversion, and the ease of product separation.

References:

1. Bahmanpour, A. M.; Hoadley, A.; Tanksale, A., Critical review and exergy analysis of formaldehyde production processes. Rev Chem Eng 2014, 30 (6), 583-604.
2. Ye, J. Y.; Johnson, J. K., Screening Lewis Pair Moieties for Catalytic Hydrogenation of CO2 in Functionalized UiO-66. Acs Catalysis 2015, 5 (10), 6219-6229.
3. Ye, J. Y.; Johnson, J. K., Design of Lewis Pair-Functionalized Metal Organic Frameworks for CO2 Hydrogenation. Acs Catalysis 2015, 5 (5), 2921-2928.
4. Ye, J. Y.; Johnson, J. K., Catalytic hydrogenation of CO2 to methanol in a Lewis pair functionalized MOF. Catal. Sci. Technol. 2016, 6 (24), 8392-8405.