Computational Mechanism of Methyl Levulinate Conversion to γ-Valerolactone on UiO-66 Metal Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) are gaining importance in the field of biomass conversion and valorization due to their porosity, well-defined active sites, and broad tunability. But for a proper catalyst design, we first need detailed insight of the system at the atomic level. Herein, we present the reaction mechanism of methyl levulinate to γ-valerolactone on Zr-based UiO-66 by means of periodic density functional theory (DFT). We demonstrate the role of Zr-based nodes in the catalytic transfer hydrogenation (CTH) and cyclization steps. From there, we perform a computational screening to reveal key catalyst modifications to improve the process, such as node doping and linker exchange.

Scheme 1. Conversion of Methyl Levulinate (ML) into γ-Valerolactone (GVL) via Catalytic Transfer Hydrogenation

Figure 1

Representation of Zr-based nodes. Zr = dark green, O = red, H = white.

Figure 2

Computed structure 1 at defective UiO-66 MOF. The periodic structure was cropped for better visualization. The black square indicates a Zr vacant site. Zr = dark green, O = red, H = white.

Figure 3

Reaction mechanism of ML to GVL at defective UiO-66 with relative Gibbs energies (in eV). R = (CH₂)₂CO₂Me.

Figure 4

Gibbs energy reaction profile (in eV) at defective UiO-66 with relative barriers for each step.

Figure 5

DFT-optimized TS structures. Relevant atoms are display in ball-and-stick format, the rest of them in tube format. Selected distances are shown in Å.

Figure 6

(a) Hf-, Ti-, and Ce-doped nodes and (b) relative Gibbs energy barriers (in eV) for selected models. Barriers are computed from the transition state to the previous most stable intermediate.

Figure 7

(a) Linker-modified nodes and (b) relative Gibbs energy barriers (in eV) for selected models. Barriers are computed from the transition state to the previous most stable intermediate.