Highly Dispersed Zn Sites on ZrO 2 by Flame Spray Pyrolysis for CO 2 Hydrogenation to Methanol

In this study, we synthesized x ZnO–ZrO 2 ( x = 14–40 at%) by flame spray pyrolysis under a lean-fuel condition. The optimal ZnO content was investigated to obtain a ZnO–ZrO 2 solid solution with high specific surface area for CO 2 -to-methanol hydrogenation. The Zn species in ZnO–ZrO 2 were highly dispersed and hexagonal ZnO was not detected by X-ray diffraction (XRD). After heating the particles in Ar at 400 °C for 3 h, hexagonal ZnO particles were observed at x = 40 at%, while below x = 28 at%, the Zn species remained high dispersion state. A fraction of the Zn species was substituted into the bulk of the ZrO 2 particles, as evidenced by the shift of the ZrO 2 (101) peak in the XRD patterns. The elemental mapping of Zn and Zr in 28 at% ZnO–ZrO 2 showed that the Zn species on the surface were uniformly distributed. The presence of partially reduced Zr δ+ state (δ < 4) was confirmed by X-ray photoelectron spectroscopy. The Zr δ+ state in the ZnO–ZrO 2 particles was prominent when ZnO content was below 28 at%. The catalytic activity of 28 at% ZnO–ZrO 2 for CO 2 -to-methanol hydrogenation was higher than that of 40 at% ZnO–ZrO 2 . At 300 °C and 1.0 MPa, the CO 2 conversion and the selectivity to methanol over 28 at% ZnO–ZrO 2 were 9 and 48%, respectively, resulting in the high yield of methanol (4.3%). Graphical abstract