Mechanistic Insights into Near Ambient Pressure Activity of Intermetallic NiZn/TiO₂ Catalyst for CO₂ Conversion to Methanol

Abstract

NiÀ Zn pair is predicted through descriptor-based studies to be conducive for CO 2 hydrogenation. In this study, NiZn (1 : 1) intermetallics supported on TiO 2 is identified as a potential candidate for near ambient pressure activity. The effect of reduction temperature on the catalyst textural properties as well as on CO 2 to methanol reduction are explored. Structural and microscopic studies provide clear evidence of phase evolution of NiZn alloy with increasing reduction temperatures, along with phase variations of Zn based oxides. Interface between NiZn intermetallics and ZnO nanoparticles observed at reduction temperature of 550 °C, seems to play a crucial role in making this system most active and selective to methanol. In addition, in-situ IR studies provide mechanistic insights and indicates the formation of methanolic species even at ambient pressure.

Application of Intermetallic Compounds as Catalysts for the Selective Hydrogenation of CO2 to Methanol

“…Interestingly, the formation of methanolic species was observed by in‐situ IR characterization suggested that methanol formation from CO 2 could be possible in the reaction carried out at atmospheric pressure. It was concluded that ZnNi intermetallics could be the active phase for methanol formation at low pressures, which is corroborated by in situ IR studies, where methoxy species were detected even at ambient pressure [149] . However, with regard to ZnNi intermetallic compound, since this compound is not stable under MSR conditions, [151] it is very unlikely that ZnNi intermetallics could be stable under MeOH synthesis conditions.…”

“…[148] The efficiency of the ZnNi (1 : 1) intermetallic catalysts supported on TiO 2 was studied by Dongapure et al [149] The TiO 2 support was commercial P25 TiO 2 material consisting of rutile and anatase, which is known for activating CO 2 through formate pathway. [149] In comparison with ZnPd intermetallic catalyst supported on TiO 2 anatase phase, [70] the formation of the ZnNi intermetallics occurred at much higher temperature of 550 °C, as it was confirmed by XRD and HAADF-STEM microscopic studies. [149] Since the ZnNi intermetallic particles were found to be in close proximity to ZnO NPs, it was concluded that the reaction might occur at interphase between ZnNi and ZnO.…”

“…It was concluded that ZnNi intermetallics could be the active phase for methanol formation at low pressures, which is corroborated by in situ IR studies, where methoxy species were detected even at ambient pressure. [149] However, with regard to ZnNi intermetallic compound, since this compound is not stable under MSR conditions, [151] it is very unlikely that ZnNi intermetallics could be stable under MeOH synthesis conditions. Thus, in view of the findings of Friedrich et al, the catalytic properties cannot be attributed to the intermetallic compound, but are more likely due to a mixture of the decomposition products.…”

“…The efficiency of the ZnNi (1 : 1) intermetallic catalysts supported on TiO 2 was studied by Dongapure et al [149] . The TiO 2 support was commercial P25 TiO 2 material consisting of rutile and anatase, which is known for activating CO 2 through formate pathway [149] .…”

“…The TiO 2 support was commercial P25 TiO 2 material consisting of rutile and anatase, which is known for activating CO 2 through formate pathway [149] . In comparison with ZnPd intermetallic catalyst supported on TiO 2 anatase phase, [70] the formation of the ZnNi intermetallics occurred at much higher temperature of 550 °C, as it was confirmed by XRD and HAADF‐STEM microscopic studies [149] . Since the ZnNi intermetallic particles were found to be in close proximity to ZnO NPs, it was concluded that the reaction might occur at interphase between ZnNi and ZnO.…”