Active Sites on ZnxZr1–xO2–x Solid Solution Catalysts for CO2-to-Methanol Hydrogenation

Authors
Shohei Tada, Nagomu Ochiai, Hiroka Kinoshita, Mitsuhiro Yoshida, Natsumi Shimada, Tatsuya Joutsuka, Masahiko Nishijima, Tetsuo Honma, Noriko Yamauchi, Yoshio Kobayashi, Kenta Iyoki

Abstract
Recently, Zn_xZr_1–xO_2–x catalysts have attracted attention as next-generation CO₂-to-methanol hydrogenation catalysts. In this study, we examined the effect of the Zn content on CO₂-to-methanol hydrogenation over Zn_xZr_1–xO_2–x catalysts and determined the active-site structure through both calculations and experiments. When the Zn content was low, Zn_xZr_1–xO_2–x contained Zn clusters (isolated [ZnO_a] clusters and [Zn_bO_c] oligomers). The presence of clusters indicates the formation of Zn–O–Zr sites. Interestingly, our calculations revealed that the Zn species in the clusters are easily exposed on the Zn_xZr_1–xO_2–x surface. This result is in line with the experimental results, suggesting that Zn species were unevenly distributed on the Zn_xZr_1–xO_2–x surface and deposited near the surface. The addition of excess Zn to ZrO₂ led to the formation of both Zn-containing clusters and ZnO nanoparticles. During the reactions, the Zn–O–Zr sites derived from the clusters showed specific activity for CO₂-to-methanol hydrogenation. Understanding the active-site structure will lead to the future development of Zn_xZr_1–xO_2–x catalysts.

ACS Catalysis: https://pubs.acs.org/doi/10.1021/acscatal.2c01996