Furfural to Furfuryl Alcohol: Computational Study of the Hydrogen Transfer on Lewis Acidic BEA Zeolites and Effects of Cation Exchange and Tetravalent Metal Substitution

Abstract

The hydrogen transfer of furfural to furfuryl alcohol with i-propanol as the hydrogen source over cation-exchanged Lewis acidic BEA zeolite has been investigated by means of density functional calculations. The reaction proceeds in three steps. First the O-H bond of i-propanol is broken to form a propoxide intermediate. After that, the furylmethoxy intermediate is formed via hydrogen transfer process, and finally furylmethoxy abstracts the proton to form the furfuryl alcohol product. The second step is rate-determining by requiring the highest activation energy (23.8 kcal/mol) if the reaction takes place on Li-Sn-BEA zeolite. We find that the catalytic activity of various cation-exchanged Sn-BEA zeolites is in the order Li-Sn-BEA > Na-Sn-BEA > K-Sn-BEA. The lower activation energy for Li-Sn-BEA compared to Na-Sn-BEA and K-Sn-BEA can be explained by the larger charge transfer from the carbonyl bond to the catalyst, leading to its activation and to the attraction of the hydrogen being transferred. The larger charge transfer in turn is due to the smaller gap between the energies of furfural HOMO and the zeolite LUMO in Li-Sn-BEA, compared to both Na-Sn-BEA and K-Sn-BEA. In a similar way, we also compare the catalytic activity of tetravalent metal centers (Sn, Zr, and Hf) substituted into BEA and find in the order Zr ≥ Hf > Sn, based on activation energies. Finally we investigate statistically which property of the reactants is a suitable descriptor for an approximative prediction of the reaction rate in order to be able to quickly screen promising catalytic materials for this reaction.

Density Functional Investigation of the Conversion of Furfural to Furfuryl Alcohol by Reaction with i-Propanol over UiO-66 Metal–Organic Framework

“…This activation energy is in the range of the energies reported for the corresponding reaction of Meerwein–Ponndorf–Verley–Oppenauer on Sn- and Zr-BEA . However, the barrier is lower than the energies found for the reaction of cations exchanged with Lewis acidic BEA zeolites . The interaction energy of this complex is −9.1 kcal/mol.…”

“…One imaginary frequency at 849.2 i cm –1 is found for this transition state. The activation energy of this process is 14.9 kcal/mol, which is again lower than that of the reaction occurring on cations exchanged with Lewis acidic BEA zeolites . Then, the transition state proceeds to a furfurylmethoxy intermediate formation, acetone and water molecules (Int_2) adsorbed together on the active site of UiO-66.…”

Porous SiO2 Nanospheres Modified with ZrO2 and Their Use in One-Pot Catalytic Processes to Obtain Value-Added Chemicals from Furfural

“…Although the CTH process is relatively novel for the synthesis of FOL, this was discovered nearly 100 years ago by Meerwein, Ponndorf, and Verley. − The first studies were carried out through homogeneous catalysis, using some metal complexes and/or alkoxides, which act as Lewis acid sites. , Nevertheless, heterogeneous catalysts have progressively appeared as a greener alternative to the traditional homogeneous ones, because they are easily separable and can be reused. Several solid Lewis acid, or basic, catalysts, such as ZrO 2 , − Al 2 O 3 , ,, Fe 2 O 3 , , MgO, ,− Zr-, − Hf-, , or Sn-zeolites ,,, and Zr-, − Ru-modified zirconium hydroxide, Ni- and Ni–W/active carbon, or Hf- MOFs − have been proposed for the CTH of FUR.…”

Recyclable Zr/Hf-Containing Acid-Base Bifunctional Catalysts for Hydrogen Transfer Upgrading of Biofuranics: A Review

“…For the CTH conversion of FF to FA. 2-PrOH as the H-donor over cation-exchanged Lewis acidic BEA zeolite was calculated by DFT (Prasertsab et al, 2018). The catalytic activity of tetravalent metal centers (Sn, Zr, and Hf) substituted into BEA.…”