Support Effect of Metal-Organic Frameworks on Ethanol Production through Acetic Acid Hydrogenation.

Shotaro Yoshimaru,Masaaki Sadakiyo,Jenny Pirillo,Nobutaka Maeda,Yuh Hijikata,Miho Yamauchi,Kenichi Kato

doi:10.1021/acsami.1c01100

Abstract

We present a systematic study on the support effect of metal–organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH2, UiO-66-NH2, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH2 and MIL-125-NH2) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH2 showed a remarkably high EtOH yield (31% at 200 °C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO2, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH2 support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH.

Highlights

Heterogeneous catalysis with metal catalysts loaded on support materials has greatly contributed to our industry for various chemical conversions such as the Haber−Bosch process[1,2] and H2 production from methane.[3]
We chose 13 thermally stable Metal−organic frameworks (MOFs), having various functional groups (e.g., −COOH, −NH2, and open metal sites) on the framework, as candidates for support materials, as listed in Table S1.23−29,40−44 In particular, we aimed at introducing basic sites, such as −NH2, on the framework because they have a strong affinity for acidic molecules
A systematic study on catalysis with metal NPs loaded on MOFs is not easy because various parameters, such as the NP particle size, loading amount, and protecting reagents on NPs, modulate the catalytic properties.[19]

Summary

■ INTRODUCTION

Heterogeneous catalysis with metal catalysts loaded on support materials has greatly contributed to our industry for various chemical conversions such as the Haber−Bosch process[1,2] and H2 production from methane.[3]. The support effect regarding substrate adsorption in this reaction was reported by Rachmady et al.[7] They found that the Pt NPs loaded on TiO2 that is expected to show a strong affinity for carboxylic acid exhibited the best catalytic activity and EtOH selectivity, whereas other oxide supports such as SiO2, Al2O3, and Fe2O3 showed low activity and selectivity. In the case of XRPD measurements under AcOH conditions, all Pt/ MOFs put inside a glass capillary were preliminarily heated at 150 °C under vacuum overnight to remove water molecules in their pores. Before the TPD-MS measurements, each sample was put inside a glass tube and was exposed to AcOH vapor (P/P0 = 1) for 6 h at room temperature after complete dehydration overnight under vacuum at 150 °C. Egas is the energy of the gas in an enough large supercell

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES