Abstract
CO2 hydrogenation to methanol is one of the main and valuable catalytic reactions applied on Cu/ZnO-based catalysts; the interface formed through Zn migration from ZnO support to the surface of Cu nanoparticle (ZnOx-Cu NP-ZnO) has been reported to account for methanol synthesis from CO2 hydrogenation. However, the accompanied reverse water gas shift (RWGS) reaction significantly decreases methanol selectivity and deactivates catalysts soon. Inhibition of RWGS is thus of great importance to afford high yield of methanol. The clear understanding of the reactivity of RWGS reaction on both the direct contact Cu-ZnO interface and ZnOx-Cu NP-ZnO interface is essential to reveal the low methanol selectivity in CO2 hydrogenation to methanol and look for efficient catalysts for RWGS reaction. Cu doped plate ZnO (ZnO:XCu) model catalysts were prepared through a hydrothermal method to simulate direct contact Cu-ZnO interface and plate ZnO supported 1 wt % Cu (1Cu/ZnO) catalyst was prepared by wet impregnation for comparison in RWGS reaction. Electron paramagnetic resonance (EPR), XRD, SEM, Raman, hydrogen temperature-programmed reduction (H2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) were employed to characterize these catalysts. The characterization results confirmed that Cu incorporated into ZnO lattice and finally formed direct contact Cu-ZnO interface after H2 reduction. The catalytic performance revealed that direct contact Cu-ZnO interface displays inferior RWGS reaction reactivity at reaction temperature lower than 500 °C, compared with the ZnOx-Cu NP-ZnO interface; however, it is more stable at reaction temperature higher than 500 °C, enables ZnO:XCu model catalysts superior catalytic activity to that of 1Cu/ZnO. This finding will facilitate the designing of robust and efficient catalysts for both CO2 hydrogenation to methanol and RWGS reactions.
Highlights
IntroductionClimate change and ocean acidification resulting from the emission of greenhouse gases have received widespread attention in the environmental and energy fields [1,2,3]
In the recent years, climate change and ocean acidification resulting from the emission of greenhouse gases have received widespread attention in the environmental and energy fields [1,2,3].the utilization and conversion of CO2 to valuable chemicals have been proposed to alleviate CO2 emission [4,5]
CO2 hydrogenation to methanol is a promising way to Catalysts 2020, 10, 533; doi:10.3390/catal10050533
Summary
Climate change and ocean acidification resulting from the emission of greenhouse gases have received widespread attention in the environmental and energy fields [1,2,3]. The utilization and conversion of CO2 to valuable chemicals have been proposed to alleviate CO2 emission [4,5]. CO2 hydrogenation to methanol is a promising way to Catalysts 2020, 10, 533; doi:10.3390/catal10050533 www.mdpi.com/journal/catalysts. Catalysts 2020, 10, 533 reduce the emission and make the utilization of CO2. Methanol is an excellent commodity chemical, served as an alternative fuel and feedstock in the chemical industry [6]. Considering the sources of hydrogen, it can be produced through renewable energies, such as solar energy, wind power, hydropower and biomass. Methanol formation always accompanies with CO formation, known as the reverse water gas shift (RWGS) reaction, which significantly decreases methanol selectivity
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