Syngas Production Through H2O/CO2 Thermochemical Splitting Over Doped Ceria-Zirconia Materials

Giuseppina Luciani,Gianluca Landi,Almerinda Di Benedetto

doi:10.3389/fenrg.2020.00204

Giuseppina Luciani, Gianluca Landi + Show 1 more

Open Access

https://doi.org/10.3389/fenrg.2020.00204

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Abstract

Ceria-zirconia (CeZr) catalysts co-doped with K+ and either Cu2+ or Fe3+ cations were studied in the co-splitting of water and carbon dioxide. Both materials are able to separately split CO2 and H2O into CO and H2 respectively. Co-splitting tests were carried out. On K-Cu-CeZr catalyst water reacts faster and negligible CO production is detected. In the case of K-Fe-CeZr catalyst, two peaks are found: at low temperature, only H2 is produced while at high temperature, CO is preferentially produced. A kinetic model was developed to get insights into the reason for the observed selectivity toward H2 at low temperature and CO at higher temperature. Different reaction orders of CO2 and H2O reactions with respect to the site fraction were found highlighting that H2 production requires a larger number of adjacent reduced sites than CO production. From the model, three regimes were identified: Regime I- H2O driven regime @T≤650 °C; Regime II- mixed regime @ 560 700 °C. These results may drive the choose of the appropriate conditions for getting the desired H2/CO selectivity, depending on the type of feed.

Highlights

The transformation of solar energy into synthetic fuels holds huge promise for sustainable approaches to harvesting renewable energy (Nguyen and Blum, 2015; Chuayboon and Abanades, 2020; Mao et al, 2020)
Results by Landi (2019) showed that K-addition to bare ceria-zirconia and materials doped with transition metals (KFe-CeZr and K-Cu-CeZr) significantly enhance the evolved oxygen amount and lower the reduction onset temperature
Ceria-zirconia was co-doped with transition metal (Cu2+, Fe3+) and potassium cations

Summary

Introduction

The transformation of solar energy into synthetic fuels holds huge promise for sustainable approaches to harvesting renewable energy (Nguyen and Blum, 2015; Chuayboon and Abanades, 2020; Mao et al, 2020). Thermochemical splitting cycles have been proposed as a promising sustainable option, as this approach uses concentrated solar energy to convert H2O and CO2 into H2 and CO (Costa Oliveira et al, 2018; Bhosale et al, 2019; Takalkar et al, 2019). These building blocks can be further reacted into gaseous and liquid fuels. The thermochemical cycle can be schematically defined as follows: CeO2 → CeO(2−δ) + δ/2 O2

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