Dataset Information

K-doped CeO₂-ZrO₂ for CO₂ thermochemical catalytic splitting.

ABSTRACT: Green syngas production is a sustainable energy-development goal. Thermochemical H₂O/CO₂ splitting is a very promising sustainable technology allowing the production of H₂ and CO with only oxygen as the by-product. CeO₂-ZrO₂ systems are well known thermochemical splitting catalysts, since they combine stability at high temperature with rapid kinetics and redox cyclability. However, redox performances of these materials must be improved to allow their use in large scale plants. K-doped systems show good redox properties and repeatable performances. In this work, we studied the effect of potassium content on the performances of ceria-zirconia for CO₂ splitting. A kinetic model was developed to get insight into the nature of the catalytic sites. Fitting results confirmed the hypothesis about the existence of two types of redox sites in the investigated catalytic systems and their role at different K contents. Moreover, the model was used to predict the influence of key parameters, such as the process conditions.

SUBMITTER: Portarapillo M

PROVIDER: S-EPMC9044484 | biostudies-literature | 2021 Dec

REPOSITORIES: biostudies-literature

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K-doped CeO2-ZrO2 for CO2 thermochemical catalytic splitting.

Portarapillo Maria M Russo Danilo D Landi Gianluca G Luciani Giuseppina G Di Benedetto Almerinda A

RSC advances 20211212 62

Green syngas production is a sustainable energy-development goal. Thermochemical H2O/CO2 splitting is a very promising sustainable technology allowing the production of H2 and CO with only oxygen as the by-product. CeO2-ZrO2 systems are well known thermochemical splitting catalysts, since they combine stability at high temperature with rapid kinetics and redox cyclability. However, redox performances of these materials must be improved to al ...[more]

PMID: 35492484

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Project description:CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol-gel synthesis to improve catalyst's performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M-Ce-O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s-1) follows the order Cu-Ce-O > Ce-Co-O > Ni-Ce-O > Mn-Ce-O > Fe-Ce-O > Ce-Zn-O > CeO2. Participation of mobile lattice oxygen species in the CO/O2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18O-labeled experiments involving 16O/18O exchange followed by step-gas CO/Ar or CO/O2/Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars-van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the Olattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order αCu > αCo> αMn > αZn. Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO2 surface is more favorable (-16.63 eV), followed by Co, Mn, Zn (-14.46, -4.90, and -4.24 eV, respectively), and pure CeO2 (-0.63 eV). Also, copper compensates almost three times more charge (0.37e-) compared to Co and Mn, ca. 0.13e- and 0.10e-, respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom-ceria surface interaction (Oa species) of different extents and of different populations of Oa species.

Project description:In this paper, a series of tungsten-zirconium mixed binary oxides (denoted as W m ZrO x ) were synthesized via co-precipitation as supports to prepare Ce0.4/W m ZrO x catalysts through an impregnation method. The promoting effect of W doping in ZrO2 on selective catalytic reduction (SCR) performance of Ce0.4/ZrO2 catalysts was investigated. The results demonstrated that addition of W in ZrO2 could remarkably enhance the catalytic performance of Ce0.4/ZrO2 catalysts in a broad temperature range. Especially when the W/Zr molar ratio was 0.1, the Ce0.4/W0.1ZrO x catalyst exhibited the widest active temperature window of 226-446 °C (NO x conversion rate > 80%) and its N2 selectivity was almost 100% in the temperature of 150-450 °C. Moreover, the Ce0.4/W0.1ZrO x catalyst also exhibited good SO2 tolerance, which could maintain more than 94% of NO x conversion efficiency after being exposed to a 100 ppm SO2 atmosphere for 18 h. Various characterization results manifested that a proper amount of W doping in ZrO2 was not only beneficial to enlarge the specific surface area of the catalyst, but also inhibited the growth of fluorite structure CeO2, which were in favor of CeO2 dispersion on the support. The presence of W was conducive to the growth of a stable tetragonal phase crystal of ZrO2 support, and a part of W and Zr combined to form W-Zr-O x solid super acid. Both of them resulted in abundant Lewis acid sites and Brønsted acid sites, enhancing the total surface acidity, thus significantly improving NH3 species adsorption on the surface of the Ce0.4/W0.1ZrO x catalyst. Furthermore, the promoting effect of adding W on SCR performance was also related to the improved redox capability, higher Ce3+/(Ce3+ + Ce4+) ratio and abundant surface chemisorbed oxygen species. The in situ DRIFTS results indicated that nitrate species adsorbed on the surface of the Ce0.4/W0.1ZrO x catalyst could react with NH3 due to the activation of W. Therefore, the reaction pathway over the Ce0.4/W0.1ZrO x catalyst followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms at 250 °C.

Dataset Information

K-doped CeO₂-ZrO₂ for CO₂ thermochemical catalytic splitting.

Publications

K-doped CeO<sub>2</sub>-ZrO<sub>2</sub> for CO<sub>2</sub> thermochemical catalytic splitting.

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