Sónia Carabineiro got her Ph.D. degree in 2001 in Chemical Engineering (Catalysis) at the NOVA University of Lisbon, Portugal. Then she was a post doc at the University of Leiden, Netherlands (2001-2003), and the University of Lisbon (2004-2007). She was Assistant Researcher (2008-2013) and Principal Researcher (2013-2018) at Porto University. Since 2016, she is a Collaborator Researcher of Center of Structural Chemistry of the University of Lisbon. Her current research interests deal with catalysis by gold nanoparticles, mixed metal oxides, nanostructured carbon materials, oxidation and hydrogenation reactions, degradation and adsorption of air and water pollutants, and heterogenisation of homogenous metal complexes. She is currently one of the top female reviewers in the world.
Journal of Chemical Technology & Biotechnology , 2018
The aim of this study is to test different supports on which to deposit Au nanoparticles and to d... more The aim of this study is to test different supports on which to deposit Au nanoparticles and to determine the most suitable for Orange II (OII) dye degradation by a photo‐assisted wet peroxidation (PWPO) process. The catalysts used (Au‐Fe2O3, Au‐TiO2, Au‐ZnO and Au‐Al2O3) were prepared by the deposition–precipitation method; a reference catalyst from the World Gold Council, hereafter denoted as Au‐Fe2O3*, was also used for comparison. The catalysts were characterized in terms of surface area (SBET), gold nanoparticles size, Au loading and Au oxidation state using several techniques (namely, nitrogen adsorption at −196°C, X‐ray photoelectron spectroscopy – XPS, and high resolution transmission electron microscopy – HR‐TEM). Several runs were carried out for each material, to evaluate its efficiency in OII dye degradation by the PWPO process.
It is easier to optimize reactions when the mechanism is well understood. Nowadays, catalytic car... more It is easier to optimize reactions when the mechanism is well understood. Nowadays, catalytic carbon gasification is an area of industrial importance. The mechanism based on C-bulk diffusion has been recently updated. The relevance of the Tammann temperature to get efficient carbon/catalyst nanoparticle contact is now better understood. However, the interaction between kinetics and thermodynamics still needs some clarification. Rate jump is a kinetic phenomenon observed in some cases in catalytic carbon gasification by air or oxygen following a minor increase in temperature (v.g. ΔT = 5 °C). This occurrence has been reported, but the phenomenon is not well understood. In this short review, we show that the rate jumps can be consistently explained by the “carbon-worm” mechanism due to a jump in the temperature of the moving nanocatalyst particles. The carbon bulk diffusion step is then much faster and the external film mass transfer becomes the rate-limiting step. The reaction order changes from zero to one. The nature and role of catalyst‑carbon contact in catalytic carbon gasification is discussed.
Pristine nanodiamonds (NDs) obtained by detonation, or functionalized by different treatments, na... more Pristine nanodiamonds (NDs) obtained by detonation, or functionalized by different treatments, namely oxidation, hydrogenation and amination, were used to synthesize composites by insertion in TiO2 matrixes. The different treatments of the NDs lead to materials containing diverse texture properties and surface chemistry functionalities, particularly concerning the insertion of nitrogen and oxygen groups. The photocatalytic activity of the prepared composites was evaluated for the oxidative degradation of two water soluble pharmaceuticals – diphenhydramine and amoxicillin – under near-UV/Vis irradiation. The most active photocatalyst in what concerns both pollutants degradation under near-UV/Vis irradiation was the composite containing pristine NDs (NDDT). The photocatalytic performances were dependent on the specific surface area and on the amount of functional groups incorporated over the NDs. The influence of ND in the composites activity is well correlated with the observed photoluminescence quenching of TiO2, which corresponds to a delay in the recombination rate of charge carriers that benefices the photocatalytic reaction. Scavenging of photogenerated holes and radicals by employing sacrificial hole and radical agents revealed that the holes played the main role on both pollutants degradation under UV/Vis irradiation. Reutilization experiments proved that the ND composites have good stability and reusability.
M. Lykaki, E. Papista, S.A.C. Carabineiro, P.B. Tavares, M. Konsolakis* (2018), “”, (Royal Socie... more M. Lykaki, E. Papista, S.A.C. Carabineiro, P.B. Tavares, M. Konsolakis* (2018), “”, (Royal Society of Chemistry), 8, 2312-2322 (DOI: ).
The C‐scorpionate iron(II) complex [FeCl2(Tpm)] [Tpm=κ3‐HC(C3H3N2)3] (1) was immobilized on five ... more The C‐scorpionate iron(II) complex [FeCl2(Tpm)] [Tpm=κ3‐HC(C3H3N2)3] (1) was immobilized on five different nanostructured carbon materials (nanodiamonds, graphene nanoplatelets, graphene oxide, reduced graphene oxide, and nanohorns) to produce active, selective, and recyclable catalysts for alkane and alcohol oxidations. The heterogenized systems (including the first ever reported complexes supported on carbon nanohorns) exhibited good activity concomitant with rather high selectivity to the formation of ketone alcohol (KA) oil (cyclohexanol and cyclohexanone mixture, yields up to 29 %) from microwave‐assisted oxidation of cyclohexane, and allowed their easy recovery and reuse, at least for five consecutive cycles maintaining 90.3 % of the initial activity. Moreover, the functionalized nanodiamond supports (used for the first time as supports for iron complexes) were also able to effectively (yields up to 97 %) catalyze the microwave‐induced oxidation of 1‐ and 2‐phenylethanol to acetophenone and 2‐phenylacetaldehyde, respectively, and could be reused for seven consecutive cycles without losing catalytic activity.
Strategies are presented for single‐pot efficient oxidative functionalization of cyclohexane and ... more Strategies are presented for single‐pot efficient oxidative functionalization of cyclohexane and alcohols, under mild conditions, catalysed by Au(I) or Au(III) compounds supported on different carbon materials with three different surface treatments. The obtained materials were tested for the oxidation of cyclohexane under mild conditions (room temperature and atmospheric pressure), using an environmentally friendly oxidant (tert‐butyl hydroperoxide, TBHP, 70 % aqueous solution). All materials were very selective to the production of cyclohexanol and cyclohexanone with no trace of by‐products detected. The catalysts were also tested in the selective oxidation of methyl benzyl alcohol, cyclohexanol, and 2‐octanol with TBHP, under microwave irradiation, to the corresponding aldehydes or ketones. In general, better results are obtained for the heterogenised complexes and that the most efficient support is CNT‐ox‐Na. This is the first report on the oxidation of C−H bonds using the mononuclear gold complexes used; only the oxidation of unsaturated units had been reported previously. The sp3‐C−H activation is much more difficult than the oxidation of unsaturated molecules with molecular oxidants.
M. Lykaki, E. Pachatouridou, S.A.C. Carabineiro, E. Iliopoulou, C. Andriopoulou, N. Kallithrakas-... more M. Lykaki, E. Pachatouridou, S.A.C. Carabineiro, E. Iliopoulou, C. Andriopoulou, N. Kallithrakas-Kontos, S. Boghosian, M. Konsolakis* (2018), “Ceria Nanoparticles Shape Effects on the Structural Defects and Surface Chemistry: Implications in CO oxidation by CuO/CeO2 oxides”, Applied Catalysis B: Environmental (Elsevier) 230, 18-28 (DOI: 10.1016/j.apcatb.2018.02.035).
Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.
Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by ... more Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by solution casting, were studied their chemical, mechanical, electrical and electro-mechanical properties evaluated. Few-layer graphene (FLG) nanoplatelets (G-NPL), graphene oxide (GO) and reduced graphene oxide (rGO) and single-walled carbon nanohorns (SWCNH)) were found to have a strong influence in the overall properties of the composites prepared with up to 5 wt% nanofiller contents. The mechanical strain of carbonaceous nanofillers/PVDF composites decreases from 15% to near 5% of maximum strain. The electrical percolation threshold depends on the nanofiller type, being below 1 wt% for rGO and near 2 wt% for the remaining nanofillers. The electrical conductivity shows a maximum increase of nine orders of magnitude, from s z 5 Â 10 À11 S/m of pure PVDF to s z 1 Â 10 À2 S/m for rGO/PVDF composites with 5 wt% nanofillers. The conduction mechanism being related to hopping between the carbonaceous nanofillers for concentrations higher than the percolation threshold. Furthermore, the composites show electro-mechanical properties, except for G-NPL materials, with rGO/PVDF composites with 5 wt% nanofiller content showing higher Gauge factor (GF) values, reaching GFz 11 for deformations between 0.5 and 2 mm in 4-point bending experiments. These results demonstrate the suitability of the composites for strain sensing applications.
A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catal... more A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catalysts for the alkane hydro-carboxylation reaction. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid was carried out in the presence of CO and water, peroxodisulfate, in water/acetonitrile medium, at ca. 50 °C, with gold nanoparticles deposited by a colloidal method on carbon nanotubes and activated carbon with three different surface che-mistries: in their original forms (CNT or AC, respectively), oxidized with HNO 3 (ox) or oxidized with HNO 3 and subsequently treated with NaOH (ox -Na). Au/CNT-ox-Na was the best catalyst, yielding cyclohexanecarboxylic acid up to 88.2% yield, with excellent recyclability (97.5% of the initial activity was maintained after five consecutive catalytic cycles).
The cycloaddition of CO 2 and epoxides to yield cyclic carbonate under solvent-free conditions is... more The cycloaddition of CO 2 and epoxides to yield cyclic carbonate under solvent-free conditions is an eco-friendly way to utilize CO 2 in environmental science and green chemistry. In this paper, we report that boron doped carbon nitride (BCN) is highly active and selective for such reactions. BCN, especially if supported on mesoporous silica SBA-15 (i.e., B 0.1 CN/SBA-15), shows above 95% conversion and selectivity for cycloaddition of CO 2 and styrene oxide (SO) to yield styrene carbonate (SC), even under solvent-free conditions. That is mainly due to the acid-base duality induced by B doping, which enables the co-activation of CO 2 and epoxide. A mechanism based on acid-base duality is proposed, where CO 2 is activated on the basic >NH sites and SO is on the acidic −B(OH) 2 sites through a hydrogen bonding. The co-activated CO 2 and SO react with each other to yield the SC. Density functional theory (DFT) calculations were conducted to support the mechanism, which show that the co-adsorption of CO 2 and SO on BCN is energetically favorable and the reaction follows the Langmuir-Hinshelwood mechanism. The BCN with acid-base duality provides an option for cheap, green and efficient catalysts for CO 2 utilization.
C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1);... more C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1); x = 1, R = CH 2 OH (2)o r CH 2 OSO 2 Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m-o rp-xylene, with TBHP (70 %a queous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably,ap-toluic acid yield of 43 %(73 %s electivi-ty,T ON = 1.34 10 3)w as obtained with 2@CNT in as imple microwave-assisted mild oxidation procedure, using av ery low catalyst charge(3.2 10 À2 mol % vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of ag reener and more sustainable process for oxidation of xylenes. Moreover,r euse of catalysts with preservation of their activity was found for up to six consecutive cycles. Thee ffects of reaction parameters , such as reaction time, temperature, amount of catalyst or type of heating source,o nt he performance of the above catalytic systems are reported and discussed.
Photocatalysis promotes the degradation of contaminants in water, transforming them into by-produ... more Photocatalysis promotes the degradation of contaminants in water, transforming them into by-products with lower or no toxicity. The photocatalysts can be applied in suspension or immobilized onto a support. The aim of using the immobilized form against the suspension form is that the costly extra final filtration process can be avoided, which is particularly important in water decontamination. This work reports on reusable Fe3O4/SiO2/TiO2 particles and the assessment of their photocatalytic activity on the degradation of methylene blue (MB), ciprofloxacin (CIP), norfloxacin (NOR) and ibuprofen (IBP). To achieve the most efficient photocatalyst it is necessary to determine the optimal thermal treatment parameters therefore, the Fe3O4/SiO2/TiO2 particles were calcined at different temperatures (500 °C and 600 °C) and times (30 min and 60 min). Higher degradation rates were achieved with calcination at 600 °C, reaching a total degradation of CIP, NOR, and MB, and half of IBP. The reuse of the magnetic particles is an economic and eco-friendly way to treat polluted water. The produced Fe3O4/SiO2/TiO2 particles showed a remarkable photocatalytic degradation of recalcitrant micropollutants, without significant efficiency loss after five uses. In addition, no other works reporting on the degradation of recalcitrant micropollutants using similar magnetic particles were found in the literature.
Nowadays, gold is used in (nano-)medicine, usually in the form of nanoparticles, due to the solid... more Nowadays, gold is used in (nano-)medicine, usually in the form of nanoparticles, due to the solid proofs given of its therapeutic effects on several diseases. Gold also plays an important role in the vaccine field as an adjuvant and a carrier, reducing toxicity, enhancing immunogenic activity, and providing stability in storage. An even brighter golden future is expected for gold applications in this area
Au nanoparticles (2.2 nm) deposited on TiO2 by the deposition-precipitation method were found to ... more Au nanoparticles (2.2 nm) deposited on TiO2 by the deposition-precipitation method were found to be extremely active and stable for CO2 hydrogenation to CO. A CO2 to CO yield up to 50% was achieved at temperatures as low as 400 °C for at least 60 h. Under identical reaction conditions, both bare TiO2 and Au/Al2O3 were practically inactive for CO2 reduction. The unique combination of the Au nanoparticles and TiO2 support – linked to a peculiar synergistic effect – is essential to the enhanced CO2 reduction activity.
The present work aims to explore the impact of the support (MxOy: Al2O3, TiO2, Fe2O3, CeO2, ZnO) ... more The present work aims to explore the impact of the support (MxOy: Al2O3, TiO2, Fe2O3, CeO2, ZnO) on the CO2 hydrogenation activity of supported gold nanoparticles (Au/MxOy) at atmospheric pressure. The textural, redox and surface properties of Au/MxOy catalysts were evaluated by various characterisation methods, namely N2 adsorption-desorption at −196 °C, temperature-programmed reduction in H2, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results revealed a strong influence of the support both on CO2 conversion and on products distribution. Gold nanoparticles supported on ZnO and CeO2 were highly selective towards methanol. TiO2- and Fe2O3-based samples demonstrated high CO2 conversion, leading, however, almost exclusively to CO and/or CH4. Au/Al2O3 was practically inactive in the investigated temperature range (200–350 °C). The following activity order, in terms of methanol formation rate, was obtained: Au/CeO2 > Au/ZnO > Au/Fe2O3 > Au/TiO2 > Au/Al2O3. Au/CeO2 exhibited a methanol formation rate of 4.1 × 10−6 mol s−1 gAu−1 at 250 °C, which is amongst the highest reported at ambient pressure, in spite of the chemical inertness of bare ceria. In view of the characterisation results, the superiority of the Au/CeO2 sample could be mainly ascribed to a synergistic effect linked to the Au-ceria interactions.
The aim of this work is to explore the influence of the support (MxOy: Al2O3, CeO2, Fe2O3, TiO2 a... more 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.
A readily accessible route to obtain solid-supported nitrogen acyclic carbene (SNAC) complexes of... more A readily accessible route to obtain solid-supported nitrogen acyclic carbene (SNAC) complexes of gold was designed using flow chemistry, and an analogous homogeneous gold complex was synthesized for comparison. Both were screened for counter ions in order to perform the Hashmi phenol synthesis. A recyclability study was performed on the SNAC complex, which showed the high stability of this catalyst, with no observed leaching or gold nanoparticle formation. XPS analysis was employed to confirm the presence of gold and its oxidation state.
The efficient single-pot oxidative functionalisation of alkanes and alcohols under mild condition... more The efficient single-pot oxidative functionalisation of alkanes and alcohols under mild conditions was catalysed by Au nanoparticles supported on Al2O3, Fe2O3, ZnO and TiO2. The obtained materials were tested for cyclohexane oxidation under mild conditions (60 °C, atmospheric pressure) using an environmentally friendly oxidant (H2O2). The materials were also tested in the oxidation of benzyl alcohol and methylbenzyl alcohol in the presence of tert-butylhydroperoxide as the oxidant under microwave irradiation. With regard to cyclohexane oxidation, all materials were highly selective towards the formation of cyclohexanol and cyclohexanone. No traces of byproducts were detected under the optimised conditions. Au on Fe2O3 led to the best results (13.5 % yield). This system showed an interesting almost exclusive formation of cyclohexanol at 4 h reaction time. Catalyst recycling was tested in up to five cycles, and the catalyst maintained almost the original level of activity after three cycles with no significant leaching. With regard to oxidation of benzyl alcohol and methylbenzyl alcohol, all materials were highly selective towards the formation of benzaldehyde or acetophenone, respectively. No traces of byproducts were detected. Addition of Au increased alcohol conversion from 5 (TiO2) to 91 % (Au/TiO2). The recycling of Au/TiO2 was tested in up to 10 cycles, and the catalytic activity remained high in the first four cycles.
The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cycloh... more The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid (up to 55% yield) with CO, water, and peroxodisulfate in a water/acetonitrile medium at circa 50 °C has been achieved in the presence of gold nanoparticles deposited by a colloidal method on a carbon xerogel in its original form (CX), after oxidation with HNO3 (-ox), or after oxidation with HNO3 and subsequent treatment with NaOH (-ox-Na). Au/CX-ox-Na behaves as re-usable catalyst maintaining its initial activity and selectivity for at least seven consecutive cycles. Green metric values of atom economy or carbon efficiency also attest to the improvement brought by this novel catalytic system to the hydrocarboxylation of cyclohexane.
Journal of Chemical Technology & Biotechnology , 2018
The aim of this study is to test different supports on which to deposit Au nanoparticles and to d... more The aim of this study is to test different supports on which to deposit Au nanoparticles and to determine the most suitable for Orange II (OII) dye degradation by a photo‐assisted wet peroxidation (PWPO) process. The catalysts used (Au‐Fe2O3, Au‐TiO2, Au‐ZnO and Au‐Al2O3) were prepared by the deposition–precipitation method; a reference catalyst from the World Gold Council, hereafter denoted as Au‐Fe2O3*, was also used for comparison. The catalysts were characterized in terms of surface area (SBET), gold nanoparticles size, Au loading and Au oxidation state using several techniques (namely, nitrogen adsorption at −196°C, X‐ray photoelectron spectroscopy – XPS, and high resolution transmission electron microscopy – HR‐TEM). Several runs were carried out for each material, to evaluate its efficiency in OII dye degradation by the PWPO process.
It is easier to optimize reactions when the mechanism is well understood. Nowadays, catalytic car... more It is easier to optimize reactions when the mechanism is well understood. Nowadays, catalytic carbon gasification is an area of industrial importance. The mechanism based on C-bulk diffusion has been recently updated. The relevance of the Tammann temperature to get efficient carbon/catalyst nanoparticle contact is now better understood. However, the interaction between kinetics and thermodynamics still needs some clarification. Rate jump is a kinetic phenomenon observed in some cases in catalytic carbon gasification by air or oxygen following a minor increase in temperature (v.g. ΔT = 5 °C). This occurrence has been reported, but the phenomenon is not well understood. In this short review, we show that the rate jumps can be consistently explained by the “carbon-worm” mechanism due to a jump in the temperature of the moving nanocatalyst particles. The carbon bulk diffusion step is then much faster and the external film mass transfer becomes the rate-limiting step. The reaction order changes from zero to one. The nature and role of catalyst‑carbon contact in catalytic carbon gasification is discussed.
Pristine nanodiamonds (NDs) obtained by detonation, or functionalized by different treatments, na... more Pristine nanodiamonds (NDs) obtained by detonation, or functionalized by different treatments, namely oxidation, hydrogenation and amination, were used to synthesize composites by insertion in TiO2 matrixes. The different treatments of the NDs lead to materials containing diverse texture properties and surface chemistry functionalities, particularly concerning the insertion of nitrogen and oxygen groups. The photocatalytic activity of the prepared composites was evaluated for the oxidative degradation of two water soluble pharmaceuticals – diphenhydramine and amoxicillin – under near-UV/Vis irradiation. The most active photocatalyst in what concerns both pollutants degradation under near-UV/Vis irradiation was the composite containing pristine NDs (NDDT). The photocatalytic performances were dependent on the specific surface area and on the amount of functional groups incorporated over the NDs. The influence of ND in the composites activity is well correlated with the observed photoluminescence quenching of TiO2, which corresponds to a delay in the recombination rate of charge carriers that benefices the photocatalytic reaction. Scavenging of photogenerated holes and radicals by employing sacrificial hole and radical agents revealed that the holes played the main role on both pollutants degradation under UV/Vis irradiation. Reutilization experiments proved that the ND composites have good stability and reusability.
M. Lykaki, E. Papista, S.A.C. Carabineiro, P.B. Tavares, M. Konsolakis* (2018), “”, (Royal Socie... more M. Lykaki, E. Papista, S.A.C. Carabineiro, P.B. Tavares, M. Konsolakis* (2018), “”, (Royal Society of Chemistry), 8, 2312-2322 (DOI: ).
The C‐scorpionate iron(II) complex [FeCl2(Tpm)] [Tpm=κ3‐HC(C3H3N2)3] (1) was immobilized on five ... more The C‐scorpionate iron(II) complex [FeCl2(Tpm)] [Tpm=κ3‐HC(C3H3N2)3] (1) was immobilized on five different nanostructured carbon materials (nanodiamonds, graphene nanoplatelets, graphene oxide, reduced graphene oxide, and nanohorns) to produce active, selective, and recyclable catalysts for alkane and alcohol oxidations. The heterogenized systems (including the first ever reported complexes supported on carbon nanohorns) exhibited good activity concomitant with rather high selectivity to the formation of ketone alcohol (KA) oil (cyclohexanol and cyclohexanone mixture, yields up to 29 %) from microwave‐assisted oxidation of cyclohexane, and allowed their easy recovery and reuse, at least for five consecutive cycles maintaining 90.3 % of the initial activity. Moreover, the functionalized nanodiamond supports (used for the first time as supports for iron complexes) were also able to effectively (yields up to 97 %) catalyze the microwave‐induced oxidation of 1‐ and 2‐phenylethanol to acetophenone and 2‐phenylacetaldehyde, respectively, and could be reused for seven consecutive cycles without losing catalytic activity.
Strategies are presented for single‐pot efficient oxidative functionalization of cyclohexane and ... more Strategies are presented for single‐pot efficient oxidative functionalization of cyclohexane and alcohols, under mild conditions, catalysed by Au(I) or Au(III) compounds supported on different carbon materials with three different surface treatments. The obtained materials were tested for the oxidation of cyclohexane under mild conditions (room temperature and atmospheric pressure), using an environmentally friendly oxidant (tert‐butyl hydroperoxide, TBHP, 70 % aqueous solution). All materials were very selective to the production of cyclohexanol and cyclohexanone with no trace of by‐products detected. The catalysts were also tested in the selective oxidation of methyl benzyl alcohol, cyclohexanol, and 2‐octanol with TBHP, under microwave irradiation, to the corresponding aldehydes or ketones. In general, better results are obtained for the heterogenised complexes and that the most efficient support is CNT‐ox‐Na. This is the first report on the oxidation of C−H bonds using the mononuclear gold complexes used; only the oxidation of unsaturated units had been reported previously. The sp3‐C−H activation is much more difficult than the oxidation of unsaturated molecules with molecular oxidants.
M. Lykaki, E. Pachatouridou, S.A.C. Carabineiro, E. Iliopoulou, C. Andriopoulou, N. Kallithrakas-... more M. Lykaki, E. Pachatouridou, S.A.C. Carabineiro, E. Iliopoulou, C. Andriopoulou, N. Kallithrakas-Kontos, S. Boghosian, M. Konsolakis* (2018), “Ceria Nanoparticles Shape Effects on the Structural Defects and Surface Chemistry: Implications in CO oxidation by CuO/CeO2 oxides”, Applied Catalysis B: Environmental (Elsevier) 230, 18-28 (DOI: 10.1016/j.apcatb.2018.02.035).
Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.
Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by ... more Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by solution casting, were studied their chemical, mechanical, electrical and electro-mechanical properties evaluated. Few-layer graphene (FLG) nanoplatelets (G-NPL), graphene oxide (GO) and reduced graphene oxide (rGO) and single-walled carbon nanohorns (SWCNH)) were found to have a strong influence in the overall properties of the composites prepared with up to 5 wt% nanofiller contents. The mechanical strain of carbonaceous nanofillers/PVDF composites decreases from 15% to near 5% of maximum strain. The electrical percolation threshold depends on the nanofiller type, being below 1 wt% for rGO and near 2 wt% for the remaining nanofillers. The electrical conductivity shows a maximum increase of nine orders of magnitude, from s z 5 Â 10 À11 S/m of pure PVDF to s z 1 Â 10 À2 S/m for rGO/PVDF composites with 5 wt% nanofillers. The conduction mechanism being related to hopping between the carbonaceous nanofillers for concentrations higher than the percolation threshold. Furthermore, the composites show electro-mechanical properties, except for G-NPL materials, with rGO/PVDF composites with 5 wt% nanofiller content showing higher Gauge factor (GF) values, reaching GFz 11 for deformations between 0.5 and 2 mm in 4-point bending experiments. These results demonstrate the suitability of the composites for strain sensing applications.
A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catal... more A B S T R A C T Gold nanoparticles were deposited on different carbon materials and used as catalysts for the alkane hydro-carboxylation reaction. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid was carried out in the presence of CO and water, peroxodisulfate, in water/acetonitrile medium, at ca. 50 °C, with gold nanoparticles deposited by a colloidal method on carbon nanotubes and activated carbon with three different surface che-mistries: in their original forms (CNT or AC, respectively), oxidized with HNO 3 (ox) or oxidized with HNO 3 and subsequently treated with NaOH (ox -Na). Au/CNT-ox-Na was the best catalyst, yielding cyclohexanecarboxylic acid up to 88.2% yield, with excellent recyclability (97.5% of the initial activity was maintained after five consecutive catalytic cycles).
The cycloaddition of CO 2 and epoxides to yield cyclic carbonate under solvent-free conditions is... more The cycloaddition of CO 2 and epoxides to yield cyclic carbonate under solvent-free conditions is an eco-friendly way to utilize CO 2 in environmental science and green chemistry. In this paper, we report that boron doped carbon nitride (BCN) is highly active and selective for such reactions. BCN, especially if supported on mesoporous silica SBA-15 (i.e., B 0.1 CN/SBA-15), shows above 95% conversion and selectivity for cycloaddition of CO 2 and styrene oxide (SO) to yield styrene carbonate (SC), even under solvent-free conditions. That is mainly due to the acid-base duality induced by B doping, which enables the co-activation of CO 2 and epoxide. A mechanism based on acid-base duality is proposed, where CO 2 is activated on the basic >NH sites and SO is on the acidic −B(OH) 2 sites through a hydrogen bonding. The co-activated CO 2 and SO react with each other to yield the SC. Density functional theory (DFT) calculations were conducted to support the mechanism, which show that the co-adsorption of CO 2 and SO on BCN is energetically favorable and the reaction follows the Langmuir-Hinshelwood mechanism. The BCN with acid-base duality provides an option for cheap, green and efficient catalysts for CO 2 utilization.
C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1);... more C-Scorpionate vanadium(IV) [VO x Cl 3Àx {k 3-RC(pz) 3 }] [pz = pyrazol-1-yl; x = 0, R = SO 3 (1); x = 1, R = CH 2 OH (2)o r CH 2 OSO 2 Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m-o rp-xylene, with TBHP (70 %a queous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably,ap-toluic acid yield of 43 %(73 %s electivi-ty,T ON = 1.34 10 3)w as obtained with 2@CNT in as imple microwave-assisted mild oxidation procedure, using av ery low catalyst charge(3.2 10 À2 mol % vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of ag reener and more sustainable process for oxidation of xylenes. Moreover,r euse of catalysts with preservation of their activity was found for up to six consecutive cycles. Thee ffects of reaction parameters , such as reaction time, temperature, amount of catalyst or type of heating source,o nt he performance of the above catalytic systems are reported and discussed.
Photocatalysis promotes the degradation of contaminants in water, transforming them into by-produ... more Photocatalysis promotes the degradation of contaminants in water, transforming them into by-products with lower or no toxicity. The photocatalysts can be applied in suspension or immobilized onto a support. The aim of using the immobilized form against the suspension form is that the costly extra final filtration process can be avoided, which is particularly important in water decontamination. This work reports on reusable Fe3O4/SiO2/TiO2 particles and the assessment of their photocatalytic activity on the degradation of methylene blue (MB), ciprofloxacin (CIP), norfloxacin (NOR) and ibuprofen (IBP). To achieve the most efficient photocatalyst it is necessary to determine the optimal thermal treatment parameters therefore, the Fe3O4/SiO2/TiO2 particles were calcined at different temperatures (500 °C and 600 °C) and times (30 min and 60 min). Higher degradation rates were achieved with calcination at 600 °C, reaching a total degradation of CIP, NOR, and MB, and half of IBP. The reuse of the magnetic particles is an economic and eco-friendly way to treat polluted water. The produced Fe3O4/SiO2/TiO2 particles showed a remarkable photocatalytic degradation of recalcitrant micropollutants, without significant efficiency loss after five uses. In addition, no other works reporting on the degradation of recalcitrant micropollutants using similar magnetic particles were found in the literature.
Nowadays, gold is used in (nano-)medicine, usually in the form of nanoparticles, due to the solid... more Nowadays, gold is used in (nano-)medicine, usually in the form of nanoparticles, due to the solid proofs given of its therapeutic effects on several diseases. Gold also plays an important role in the vaccine field as an adjuvant and a carrier, reducing toxicity, enhancing immunogenic activity, and providing stability in storage. An even brighter golden future is expected for gold applications in this area
Au nanoparticles (2.2 nm) deposited on TiO2 by the deposition-precipitation method were found to ... more Au nanoparticles (2.2 nm) deposited on TiO2 by the deposition-precipitation method were found to be extremely active and stable for CO2 hydrogenation to CO. A CO2 to CO yield up to 50% was achieved at temperatures as low as 400 °C for at least 60 h. Under identical reaction conditions, both bare TiO2 and Au/Al2O3 were practically inactive for CO2 reduction. The unique combination of the Au nanoparticles and TiO2 support – linked to a peculiar synergistic effect – is essential to the enhanced CO2 reduction activity.
The present work aims to explore the impact of the support (MxOy: Al2O3, TiO2, Fe2O3, CeO2, ZnO) ... more The present work aims to explore the impact of the support (MxOy: Al2O3, TiO2, Fe2O3, CeO2, ZnO) on the CO2 hydrogenation activity of supported gold nanoparticles (Au/MxOy) at atmospheric pressure. The textural, redox and surface properties of Au/MxOy catalysts were evaluated by various characterisation methods, namely N2 adsorption-desorption at −196 °C, temperature-programmed reduction in H2, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results revealed a strong influence of the support both on CO2 conversion and on products distribution. Gold nanoparticles supported on ZnO and CeO2 were highly selective towards methanol. TiO2- and Fe2O3-based samples demonstrated high CO2 conversion, leading, however, almost exclusively to CO and/or CH4. Au/Al2O3 was practically inactive in the investigated temperature range (200–350 °C). The following activity order, in terms of methanol formation rate, was obtained: Au/CeO2 > Au/ZnO > Au/Fe2O3 > Au/TiO2 > Au/Al2O3. Au/CeO2 exhibited a methanol formation rate of 4.1 × 10−6 mol s−1 gAu−1 at 250 °C, which is amongst the highest reported at ambient pressure, in spite of the chemical inertness of bare ceria. In view of the characterisation results, the superiority of the Au/CeO2 sample could be mainly ascribed to a synergistic effect linked to the Au-ceria interactions.
The aim of this work is to explore the influence of the support (MxOy: Al2O3, CeO2, Fe2O3, TiO2 a... more 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.
A readily accessible route to obtain solid-supported nitrogen acyclic carbene (SNAC) complexes of... more A readily accessible route to obtain solid-supported nitrogen acyclic carbene (SNAC) complexes of gold was designed using flow chemistry, and an analogous homogeneous gold complex was synthesized for comparison. Both were screened for counter ions in order to perform the Hashmi phenol synthesis. A recyclability study was performed on the SNAC complex, which showed the high stability of this catalyst, with no observed leaching or gold nanoparticle formation. XPS analysis was employed to confirm the presence of gold and its oxidation state.
The efficient single-pot oxidative functionalisation of alkanes and alcohols under mild condition... more The efficient single-pot oxidative functionalisation of alkanes and alcohols under mild conditions was catalysed by Au nanoparticles supported on Al2O3, Fe2O3, ZnO and TiO2. The obtained materials were tested for cyclohexane oxidation under mild conditions (60 °C, atmospheric pressure) using an environmentally friendly oxidant (H2O2). The materials were also tested in the oxidation of benzyl alcohol and methylbenzyl alcohol in the presence of tert-butylhydroperoxide as the oxidant under microwave irradiation. With regard to cyclohexane oxidation, all materials were highly selective towards the formation of cyclohexanol and cyclohexanone. No traces of byproducts were detected under the optimised conditions. Au on Fe2O3 led to the best results (13.5 % yield). This system showed an interesting almost exclusive formation of cyclohexanol at 4 h reaction time. Catalyst recycling was tested in up to five cycles, and the catalyst maintained almost the original level of activity after three cycles with no significant leaching. With regard to oxidation of benzyl alcohol and methylbenzyl alcohol, all materials were highly selective towards the formation of benzaldehyde or acetophenone, respectively. No traces of byproducts were detected. Addition of Au increased alcohol conversion from 5 (TiO2) to 91 % (Au/TiO2). The recycling of Au/TiO2 was tested in up to 10 cycles, and the catalytic activity remained high in the first four cycles.
The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cycloh... more The use of gold as a promotor of alkane hydrocarboxylation is reported for the first time. Cyclohexane hydrocarboxylation to cyclohexanecarboxylic acid (up to 55% yield) with CO, water, and peroxodisulfate in a water/acetonitrile medium at circa 50 °C has been achieved in the presence of gold nanoparticles deposited by a colloidal method on a carbon xerogel in its original form (CX), after oxidation with HNO3 (-ox), or after oxidation with HNO3 and subsequent treatment with NaOH (-ox-Na). Au/CX-ox-Na behaves as re-usable catalyst maintaining its initial activity and selectivity for at least seven consecutive cycles. Green metric values of atom economy or carbon efficiency also attest to the improvement brought by this novel catalytic system to the hydrocarboxylation of cyclohexane.
The efficiency of Au/TiO2 based catalysts in 1-phenylethanol oxidation was investigated. The role... more The efficiency of Au/TiO2 based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La2O3 or CeO2), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O2, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O2-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La2O3, regardless of the alcohol and the type of oxidant. When O2 was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active ca...
Photocatalysis has become an attractive process to treat wastewater since it allows a rapid and e... more Photocatalysis has become an attractive process to treat wastewater since it allows a rapid and efficient degradation of micropollutants in water. A solution of ciprofloxacin (CIP) was photocatalytically treated by ultraviolet A light (UVA) and titanium dioxide (TiO2) or zinc oxide (ZnO) nanoparticles. Toxicity of CIP and of the treated CIP solutions, as well as the toxicity of TiO2 and ZnO irradiated nanoparticles, was evaluated towards Vibrio fischeri. The lowest concentration of CIP tested, 10 μg L−1, leads to 50% of luminescence inhibition. Regarding irradiated nanoparticles, ZnO presented higher bacteria luminescence inhibition than TiO2, 97 and 38%, respectively. Due to high toxicity of ZnO, it was only possible to evaluate the CIP solution treated by UVA/TiO2. Initially, the toxicity decreased with the time of the process, but after 15 min the toxicity increased significantly (55%) and after 45 min of treatment, was 70%. High-performance liquid chromatography (HPLC) and Fourier transform infrared spectroscopy (FTIR) analysis proved that the initial decrease of toxicity was caused by CIP adsorption on catalyst surface, which latter increased due to the generation of by-products and toxicity contribution of soluble nanoparticles. Ten by-products were identified by liquid chromatography-mass spectrometry (LC-MS) and the mechanism of CIP photocatalytic degradation was proposed.
Page 1. VANADIUM MIXTURES FOR NO CONVERSION Sónia A. Carabineiro 1 , F. Brás Fernandes 2 , Joaqui... more Page 1. VANADIUM MIXTURES FOR NO CONVERSION Sónia A. Carabineiro 1 , F. Brás Fernandes 2 , Joaquim S. Vital 1 , Ana M. Ramos 1 , Isabel F. Fonseca* 1 ... Catalysis Today 2000; 57 (3-4): 305-312. [8] McKee DW. Chemistry and Physics of Carbon. Vol. ...
Using synchrotron radiation x-ray photoelectron spectroscopy we have determined the surface compo... more Using synchrotron radiation x-ray photoelectron spectroscopy we have determined the surface composition during the reduction reactions of nitric oxide with hydrogen and carbon monoxide on Pt(100). It is found that NO dissociates readily on this surface and that the dissociation product oxygen is only partially removed by reducing agents H2 and CO. Two oxygen species have been identified after NO dissociation, and they appear to react with H2 and CO at different rates. With increasing total pressures in the NO–H2 reaction, new N-containing surface species are observed. Some preliminary results are presented concerning the reduction of NO in the presence of both CO and H2. For this system partially hydrogenated CO molecules are found in addition to partially hydrogenated N-species.
Abstract Cerium-containing mixed oxides (Ce–Cu, Ce–Ni and Ce–Co) were synthesized by exotemplatin... more Abstract Cerium-containing mixed oxides (Ce–Cu, Ce–Ni and Ce–Co) were synthesized by exotemplating and evaporation methods. A carbon xerogel was used as template in the exotemplating procedure. The evaporation method was based on thermal decomposition of oxalates. Samples were characterized by thermogravimetry and differential scanning calorimetry, N2 adsorption at −196 °C, temperature programmed reduction, scanning electron microscopy and X-ray diffraction. The materials obtained were tested as catalysts for ethyl acetate oxidation, as a model volatile organic compound. In general, materials with larger surface areas were achieved by exotemplating. Apart from the Ce–Cu oxides, the samples with a molar ratio of 1:2 had larger surface areas than the corresponding 1:1 materials. Smaller crystallite sizes were obtained with calcinations at lower temperatures. Materials prepared by evaporation were more active than those prepared by exotemplating and the 1:1 ratio was more favourable than 1:2. Full conversion of ethyl acetate was achieved at much lower temperatures with the mixed metal oxides, in comparison to single oxides. The most active materials were Ce–Co and Ce–Cu oxides. Ce–Ni oxide samples were the least active. Catalytic activity seems to be related not only with surface area, but also with the amount of Ce contained in the samples, calcination temperature (which influenced the particle size) and the reducibility of the catalysts.
A novel method to prepare supported metal catalysts is described. A microwave frequency plasma to... more A novel method to prepare supported metal catalysts is described. A microwave frequency plasma torch was employed to create supported metal catalysts from physical mixtures of a metal (palladium, particles or molecular precursor) and a traditional support material ( ...
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Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.
Copper-ceria binary oxides have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction to their lower cost as compared to noble metal-based systems. However, various parameters related to different counterparts characteristics, such as particle size and morphology, can exert a profound influence on the structural/redox properties of binary oxides and, consequently, on their catalytic performance. Here, we report on ceria nanoparticles shape effects: nanorods (NR), nanopolyhedra (NP) and nanocubes (NC) on the solid state properties of copper-ceria binary oxides. A thorough characterization study by both ex situ (surface area determination, X-ray diffraction, X-ray fluorescence, H2-temperature programmed reduction, transmission electron microscopy, X-ray photoelectron spectroscopy) and in situ (Raman spectroscopy) techniques was undertaken to gain insight into the impact of the support morphology on the surface, structural and redox properties. A novel approach based on sequential in situ Raman spectra obtained under alternating oxidizing and reducing atmospheres was employed to reveal the impact of ceria exposed facets on the structural defects. CO oxidation was employed as a probe reaction to disclose structure-property relationships. The results clearly revealed the key role of ceria morphology rather than structural/textural characteristics on the reducibility and oxygen mobility, following the sequence: NR > NP > NC. The latter seems to have a profound influence on copper-ceria interactions towards the stabilization of Cu+ species, via Ce4+/Ce3+ and Cu2+/Cu+ redox equilibrium. Interestingly, CuO incorporation in different ceria carriers boosts the catalytic activity without, however, affecting the order observed for bare ceria, i.e., CeO2-NR > CeO2-NP > CeO2-NC, implying the key role of support. The Cu/CeO2 sample with the rod-like morphology exhibited the highest catalytic performance, offering almost complete CO elimination at temperatures as low as 100 °C. A perfect relationship between the catalytic performance and the following parameters was disclosed, on the basis of a Mars-van Krevelen mechanism: i) abundance of weakly bound oxygen species, ii) relative population of Cu+/Ce3+ redox pairs, iii) relative abundance of defects and oxygen vacancies.