CO2 Hydrogenation over Nanoceria-Supported Transition Metal Catalysts: Role of Ceria Morphology (Nanorods versus Nanocubes) and Active Phase Nature (Co versus Cu)

In this work we report on the combined impact of active phase nature (M: Co or Cu) and ceria nanoparticles support morphology (nanorods (NR) or nanocubes (NC)) on the physicochemical characteristics and CO2 hydrogenation performance of M/CeO2 composites at atmospheric pressure. It was found that CO2 conversion followed the order: Co/CeO2 > Cu/CeO2 > CeO2, independently of the support morphology. Co/CeO2 catalysts demonstrated the highest CO2 conversion (92% at 450 °C), accompanied by 93% CH4 selectivity. On the other hand, Cu/CeO2 samples were very selective for CO production, exhibiting 52% CO2 conversion and 95% CO selectivity at 380 °C. The results obtained in a wide range of H2:CO2 ratios (1–9) and temperatures (200–500 °C) are reaching in both cases the corresponding thermodynamic equilibrium conversions, revealing the superiority of Co- and Cu-based samples in methanation and reverse water-gas shift (rWGS) reactions, respectively. Moreover, samples supported on ceria nanocubes exhibited higher specific activity (µmol CO2·m−2·s−1) compared to samples of rod-like shape, disclosing the significant role of support morphology, besides that of metal nature (Co or Cu). Results are interpreted on the basis of different textural and redox properties of as-prepared samples in conjunction to the different impact of metal entity (Co or Cu) on CO2 hydrogenation process

Erratum: Effect of alkali (Cs) doping on the surface chemistry and CO2hydrogenation performance of CuO/CeO2catalysts [Journal of CO2 Utilization (2021) 44 (101408) DOI: 10.1016/j.jcou.2020.101408)

The publisher regrets that the printed version of the above article contained a number of typo errors inserted during proofing process. The publisher would like to apologise for any inconvenience caused. In particular: • The units throughout the text must be in the form A/B instead of A/ B-1, i.e., cm3/min, °C/min, μmol/g, gcat/m3, mol/m3, m2/s instead of cm3/min-1, °C/min-1, μmol/g-1, gcat/m-3, mol/m-3, m2/s-1, respectively. • In the definition of turnover frequency (Eq. (6)) the term B must be defined as the total CO2uptake in μmol/g, i.e. "⋯derived by the total CO2uptake in μmol/g (B) calculated by CO2-TPD measurements" instead of "⋯derived by the total CO2uptake in 40 μmol/g (B) calculated by CO2-TPD measurements". • The y-axis in Figure 7 must be dimensionless, i.e., ln(TOF) instead of ln(TOF) (s-1).publishersversionpublishe

Remarkable efficiency of Ni supported on hydrothermally synthesized CeO2 nanorods for low-temperature CO2 hydrogenation to methane

project code: T1EDK-00094 IF/01381/2013/CP1160/CT0007 UIDB/50020/2020 UIDB/50006/2020Nickel particles deposited on hydrothermally synthesized ceria nanorods (CeO2-NR) were found to be highly active and stable for CO2 methanation. A CO2-to-CH4 yield of 92% was achieved at 300 °C. The impact of various operational parameters was explored in conjunction with a thermodynamic analysis. The superior performance of Ni/CeO2-NR was demonstrated through a comparison with i) CeO2 and Ni/CeO2 commercial products, ii) various M/CeO2-NR lab-synthesized catalysts (M = Cu, Co, Fe), and iii) state-of-the-art literature catalysts. The results revealed that a unique combination of Ni with ceria nanorods is required for boosting the reducibility and in turn the methanation efficiency.authorsversionpublishe

Catalytic decomposition of N2O on inorganic oxides: effect of doping with Au nanoparticles

Summarization: The aim of this work is to explore the influence of the support (MxOy: Al2O3, CeO2, Fe2O3, TiO2 and ZnO) on the physicochemical characteristics and the N2O decomposition (deN2O) performance of supported gold nanoparticles (Au/MxOy). Both the bare oxides and the Au/oxide catalysts were characterized by several methods (BET, XRD, SEM, HR-TEM, XPS and H2-TPR) and comparatively evaluated in order to gain insight into the structure-property relationships. A close correlation between the catalytic performance and the redox properties (reducibility and oxygen mobility) of oxide carriers was revealed on the basis of a redox type mechanism, resulting in the following deN2O activity order: Fe2O3 >> CeO2 > ZnO > TiO2 > Al2O3. In contrast, no significant effect of textural/structural characteristics on the deN2O performance was found. Addition of gold to the oxides facilitates the surface oxygen reduction and, consequently, the deN2O performance, without, however, affecting the activity order. When oxygen is in excess in the feed stream (N2O + O2) a slight inhibition was observed for all samples, due to the competitive adsorption of both reactants on the catalyst surface. On the basis of a kinetic analysis the superior performance of Fe2O3-based samples can be attributed to the optimum compromise between the activation energy and the pre-exponential factor under the present conditions.Presented on: Molecular Catalysi

Effect of alkali (Cs) doping on the surface chemistry and CO2 hydrogenation performance of CuO/CeO2 catalysts

Summarization: The reaction of captured carbon dioxide with renewable hydrogen towards the eventual indirect production of liquid hydrocarbons via CO2 reduction to CO (reverse water-gas shift reaction, rWGS) is a promising pathway in the general scheme of worldwide CO2 valorization. Copper-ceria oxides have been largely employed as rWGS catalysts owing to their unique properties linked to copper-ceria interactions. Here, we report on the fine-tuning of CuO/CeO2 composites by means of alkali promotion. In particular, this work aims at exploring the effect of cesium doping (0–4 atoms Cs per nm2) on co-precipitated CuO/CeO2 catalysts under CO2 hydrogenation conditions. The as-prepared samples were characterized by N2 physisorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), CO2-temperature programmed desorption (CO2-TPD), Fourier-transform infrared spectroscopy (FTIR) of pyridine adsorption and CO-diffuse reflectance Fourier-transform infrared spectroscopy (CO-DRIFTS). The results demonstrated that a low amount of Cs exerted a beneficial effect on CO selectivity, inhibiting, however, CO2 conversion. Specifically, a doping of 2 atoms Cs per nm2 offers > 96 % CO selectivity and equilibrium CO2 conversion at temperatures as low as 430 °C, whereas further increase in cesium loading had no additional impact. The present findings can be mainly interpreted on a basis of the alkali effect on the textural and acid/base properties; Cs doping results in a significant reduction of the surface area and thus to a lower population of active sites for CO2 conversion, whereas it enhances the formation of basic sites and the stabilization of partially reduced Cu+ species, favoring CO selectivity.Presented on: Journal of Co2 Utilizatio

Erratum to “Effect of alkali (Cs) doping on the surface chemistry and CO2 hydrogenation performance of CuO/CeO2 catalysts” [J. CO2 Util. 44 (2021) 101408]

Summarization: Correction to "Effect of alkali (Cs) doping on the surface chemistry and CO2 hydrogenation performance of CuO/CeO2 catalysts" article, published at Journal of CO2 Utilization, vol 44, February 2021.Presented on

Co2 hydrogenation over nanoceria-supported transition metal catalysts: Role of ceria morphology (nanorods versus nanocubes) and active phase nature (co versus cu)

Summarization: In this work we report on the combined impact of active phase nature (M: Co or Cu) and ceria nanoparticles support morphology (nanorods (NR) or nanocubes (NC)) on the physicochemical characteristics and CO2 hydrogenation performance of M/CeO2 composites at atmospheric pressure. It was found that CO2 conversion followed the order: Co/CeO2 > Cu/CeO2 > CeO2, independently of the support morphology. Co/CeO2 catalysts demonstrated the highest CO2 conversion (92% at 450◦ C), accompanied by 93% CH4 selectivity. On the other hand, Cu/CeO2 samples were very selective for CO production, exhibiting 52% CO2 conversion and 95% CO selectivity at 380◦ C. The results obtained in a wide range of H2:CO2 ratios (1–9) and temperatures (200–500◦ C) are reaching in both cases the corresponding thermodynamic equilibrium conversions, revealing the superiority of Co-and Cu-based samples in methanation and reverse water-gas shift (rWGS) reactions, respectively. Moreover, samples supported on ceria nanocubes exhibited higher specific activity (µmol CO2·m−2·s−1 ) compared to samples of rod-like shape, disclosing the significant role of support morphology, besides that of metal nature (Co or Cu). Results are interpreted on the basis of different textural and redox properties of as-prepared samples in conjunction to the different impact of metal entity (Co or Cu) on CO2 hydrogenation process.Παρουσιάστηκε στο: Nanomaterial

Nitrous oxide decomposition over Al2O3 supported noble metals (Pt, Pd, Ir): Effect of metal loading and feed composition

Δημοσίευση σε επιστημονικό περιοδικόSummarization: The N2O decomposition (de-N2O) performance of Al2O3 supported, low content (0.25, 0.5 and 1.0 wt.%) noble metal (Pt, Pd, Ir) catalysts, is comparatively explored in the present study. The effect of metal content, operation temperature and feed composition on de-N2O performance is investigated. Characterization studies involving BET, XRD, TEM and H2-TPR were also carried out to reveal the impact of metal entity and content on the structural, morphological and redox characteristics of the catalysts. The catalytic results imply that the de-N2O performance is in general increased upon increasing metal loading, a fact being more intense over Ir-based catalysts. Under oxygen deficient conditions, N2O conversions as high as ∼100% and ∼80% are reached at 600 °C over Ir- and Pd-based catalysts, respectively, instead of only ∼30%, achieved over Pt-based catalysts. A moderate degradation in oxygen excess conditions is observed with Ir and Pd catalysts, while Pt-based catalysts are almost fully depressed. The superior de-N2O performance of Ir-, Pd-based catalysts can be mainly interpreted by taking into account the formation of metal oxide phases, not easily susceptible to oxygen poisoning. For Ir-based catalysts the active phase seems to be mainly the metal oxide phase (IrO2), as revealed by H2-TPR, XRD and TEM experiments. In the case of palladium catalysts two different metal phases, i.e. PdO and metallic Pd0 were detected. On the other hand, platinum catalysts presented only metallic Pt0 species, which are prone to poisoning by strongly adsorbed oxygen atoms.Παρουσιάστηκε στο: Journal of Environmental Chemical Engineerin

Effect of alkali promoters (K) on nitrous oxide abatement over Ir/Al2O3 catalysts

Summarization: The promoting impact of potassium (0–1 wt% K) on nitrous oxide (N2O) catalytic decomposition over Ir/Al2O3 is investigated under both oxygen deficient and oxygen excess conditions. All samples were characterized by means of X-ray powder diffraction (XRD), temperature-programmed reduction (H2-TPR), ammonia desorption (NH3-TPD) and Fourier Transform Infrared Spectroscopy of pyridine adsorption (FTIR-Pyridine). The results reveal that the K-free Ir/Al2O3 catalyst consists mainly of the IrO2 phase, exhibiting also significant Lewis acidity, which is gradually eliminated by the addition of K. Catalytic performance results showed that the deN2O performance in the absence of O2 in the feed mixture is negatively affected upon increasing potassium loading. However, under oxygen excess conditions, a pronounced effect of K is observed. Although the catalytic performance of the un-doped catalyst is drastically hindered by the presence of O2, the K-promotion notably prohibits the oxygen poisoning. The optimum deN2O performance under oxygen excess conditions is obtained with potassium loading of 0.5 wt% K, which offers complete conversion of N2O at 580 °C, instead of the corresponding 50 % N2O conversion achieved with the un-modified sample. On the basis of characterization results, it was concluded that alkali-doping in combination with oxygen excess conditions are required towards the formation of active Ir entities.Presented on: Topics in Catalysi