Effect of CO2, H2O and SO2 in the ceria-catalyzed combustion of soot under simulated diesel exhaust conditions

The effect of CO2, H2O and SO2 in the Ce0.73Zr0.27O2 and Ce0.64Zr0.27Nd0.09O2 catalyzed combustion of soot with NOx + O2 has been studied. Combustion experiments performed in a fix-bed reactor with soot-catalyst mixtures prepared in loose contact mode showed that CO2, H2O and SO2 lower the activity of both catalysts, and the inhibiting effect follows the trend SO2 > H2O > CO2. Regardless the gas mixture composition, the catalytic activity for soot combustion of Ce0.64Zr0.27Nd0.09O2 is equal or higher to that of Ce0.73Zr0.27O2 because Nd3+ doping seems to promote the participation of the active oxygen mechanism together with the NO2-assisted mechanism in the catalytic combustion of soot. The maximum soot combustion rate achieved during a Ce0.64Zr0.27Nd0.09O2-catalyzed reaction in NOx/O2/CO2/H2O/N2 is about three times higher than that of the uncatalyzed combustion, and this catalyst also improves the CO2 selectivity. In situ DRIFTS experiments showed that CO2, H2O and SO2 compete with NOx for the adsorption sites on the catalysts’ surface. CO2 partially impedes the catalytic oxidation of NO to NO2, affecting much more to the Nd3+-containing catalyst; however, the contribution of the active oxygen mechanism seems to remain relevant in this case. H2O also hinders the catalytic oxidation of NO to NO2 on both catalysts, and therefore the catalytic combustion of soot, because delays the formation of nitrogen reaction intermediates on the catalysts’ surface and favors the formation of more stable nitrogen surface species than in a H2O-free gas stream. For both catalysts, SO2 chemisorption (with sulfate formation) is even able to remove nitrogen surface groups previously formed by NOx chemisorption, which significantly inhibits the catalytic oxidation of NO to NO2 and the catalytic combustion of soot.Financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the UE (FEDER funding)

CuO/cryptomelane catalyst for preferential oxidation of CO in the presence of H2: deactivation and regeneration

Cryptomelane and CuO/cryptomelane catalysts have been tested in the preferential oxidation of CO in the presence of H2 (CO-PROX reaction), paying special attention to deactivation and regeneration issues. Cryptomelane was stable during the CO-PROX reactions in ramp experiments until 200 °C and in a long-term isothermal experiment (10 h). Changes neither in the H2 reducibility and porosity nor in the crystalline phases detected by XRD were observed. On the contrary, CuO/cryptomelane was partially deactivated during the consecutive CO-PROX reaction cycles performed until 200 °C, and the catalytic activity was partially restored by reoxidising the catalyst at 200 °C or 400 °C, the latter temperature being more effective. In spite of the CuO/cryptomelane partial deactivation, the CO-PROX activity of this catalyst was higher than that of cryptomelane once a stable behaviour was achieved. The partial deactivation of CuO/cryptomelane was attributed to the segregation of crystalline phases (hausmannite (Mn3O4) and/or hopcalite (CuMn2O4)), with the segregation of potassium to the surface and decrease in the copper cations' reducibility. The potential contribution to deactivation of the changes in the porous texture of CuO/cryptomelane was ruled out.The authors are thankful for the financial support from Generalitat Valenciana (Project PROMETEOII/2014/010), the Spanish Ministry of Economy and Competitiveness (Project MAT2014-61992-EXP and CTQ2015-67597-C2-2-R), the Spanish Ministry of Education, Culture and Sports (grant FPU14/01178), the Spanish Catalysis Society (SECAT TFM 2015), and the UE (FEDER funding)

On the soot combustion mechanism using 3DOM ceria catalysts

CeO2 catalysts have been prepared with conventional (Ref) and three dimensionally order macroporous (3DOM) structures, and the effect of the structure on the soot combustion mechanism has been studied in detail. Isotopic exchange experiments showed that the CeO2-3DOM catalyst produces more active oxygen upon O2 chemisorption than the counterpart CeO2-Ref catalyst, and this active oxygen is transferred more efficiently to soot due to the macroporous structure. CeO2-3DOM and CeO2-Ref also accelerate the oxidation of NO to NO2, and their activity is equal. However, CeO2-3DOM utilizes NO2 more efficiently than CeO2-Ref for soot combustion. NO2 has two roles in the soot combustion mechanism: i) reacts with soot and ii) is chemisorbed on ceria and produces active oxygen, which is more oxidizing than NO2. In ceria catalysts with a conventional structure, the main role of NO2 is the direct oxidation of soot, because active oxygen has restrictions to be transferred from catalyst to soot due to the poor soot-catalyst solid-solid contact. However, the 3DOM structure improves the transfer of active oxygen, and therefore, an additional benefit is obtained from NO2, that is, NO2 contributes to active oxygen production and the 3DOM structure allows its efficient transference to soot.The authors thank the financial support of Generalitat Valenciana (Project PROMETEOII/2014/010), the Spanish Ministry of Economy and Competitiveness (Project CTQ2015-67597-C2-2-R), the Spanish Ministry of Education, Culture and Sports (grant FPU14/01178) and the UE (FEDER funding)

Design and fabrication of integral carbon monoliths combining 3D printing and sol-gel polymerization: effect of the channels morphology on the CO-PROX reaction

The authors acknowledge the financial support from the Spanish Ministry of Science and Innovation (PID2019-105960RB-C22), the University of Alicante (Project GRE18-01A), the Generalitat Valenciana (Projects PROMETEO/2018/076 and GV2020-075, PhD grant GRISOLIAP/2017/177 and contract APOSTD/2019/030), the Junta de Andalucia (Project P18-RTJ-2974) and the UE (FEDER funding).A new method to synthesize integral carbon monoliths with a controlled channel morphology has been developed in this work by combining 3D-printing technology and sol–gel polymerization. By this method, robust and consistent carbon monoliths were obtained with a perfect replica of the channel architecture at a microscale range. As a proof of concept, a carbon monolith with tortuous channels that split and join successively along the monolith length has been designed, fabricated and tested as a CuO/CeO2 support for the preferential oxidation of CO in the presence of H2 (CO-PrOx), which is a topic of ongoing research for H2 purification in fuel cells. The behavior of this novel carbon monolith catalyst has been compared with that of a counterpart catalyst prepared with a conventional honeycomb design. Results shown that the wide macroporosity of the carbon network favors the anchoring and dispersion of the active phase both in the channel surface and the carbon network. The channel architecture affects the gas diffusion both through the channel and the carbon network and consequently, affects the active phase accessibility and activity. T50 (the temperature to achieve 50% CO conversion) decreases by almost 13 °C at 240 mL min−1 in the carbon monolith with tortuous channels (T50 = 79.7 °C) compared to the honeycomb monolith (T50 = 93.1 °C). The turbulent path created by the tortuous channels favours the active phase–gas contact and even the gas diffusion inside the macropores of the carbon skeleton improving the catalytic performance of the active phase compared to that by the conventional honeycomb design. Thus, this work demonstrates the potential of 3D printing to improve the catalytic supports currently available.Spanish Government PID2019-105960RB-C22University of Alicante GRE18-01AGeneralitat ValencianaEuropean CommissionGeneral Electric PROMETEO/2018/076 GV2020-075 GRISOLIAP/2017/177 APOSTD/2019/030Junta de Andalucia P18-RTJ-2974UE (FEDER funding

Asymmetric hybrid capacitors based on activated carbon and activated carbon fibre–PANI electrodes

Composites consisting of polyaniline (PANI) coatings inside the microporosity of an activated carbon fibre (ACF) were prepared by electrochemical and chemical methods. Electrochemical characterization of both composites points out that the electrodes with polyaniline show a higher capacitance than the pristine porous carbon electrode. These materials have been used to develop an asymmetric capacitor based on activated carbon (AC) as negative electrode and an ACF–PANI composite as positive electrode in H2SO4 solution as electrolyte. The presence of a thin layer of polyaniline inside the porosity of the activated carbon fibres avoids the oxidation of the carbon material and the oxygen evolution reaction is produced at more positive potentials. This capacitor was tested in a maximum cell voltage of 1.6 V and exhibited high energy densities, calculated for the unpackaged active materials, with values of 20 W h kg−1 and power densities of 2.1 kW kg−1 with excellent cycle lifetime (90% during the first 1000 cycles) and high coulombic efficiency.Financial support by the Ministerio de Ciencia e Innovación (MAT2010-15273 and CTQ2009-10813) and Generalitat Valenciana and FEDER (PROMETEO/2009/047 and ACOMP/2012/133) projects are gratefully acknowledged. J.M.S. thanks Ministerio de Educación (SB2010-132). D.S.T. thanks Ministerio de Ciencia e Innovación (BES-2010-035238)

Role of Hydroxyl Groups in the Preferential Oxidation of CO over Copper Oxide–Cerium Oxide Catalysts

Model CuO/Ce0.8X0.2Oδ catalysts (with X = Ce, Zr, La, Pr, or Nd) have been prepared in order to obtain CuO/ceria materials with different chemical features and have been characterized by X-ray diffraction, Raman spectroscopy, N2 adsorption, and H2 temperature-programmed reduction. CO-PROX experiments have been performed in a fixed-bed reactor and in an operando DRIFTS cell coupled to a mass spectrometer. The CO oxidation rate over CuO/ceria catalysts correlates with the formation of the Cu+–CO carbonyl above a critical temperature (90 °C for the experimental conditions in this study) because copper–carbonyl formation is the rate-limiting step. Above this temperature, CO oxidation capacity depends on the redox properties of the catalyst. However, decomposition of adsorbed intermediates is the slowest step below this threshold temperature. The hydroxyl groups on the catalyst surface play a key role in determining the nature of the carbon-based intermediates formed upon CO chemisorption and oxidation. Hydroxyls favor the formation of bicarbonates with respect to carbonates, and catalysts forming more bicarbonates produce faster CO oxidation rates than those which favor carbonates.The authors thank the financial support of Generalitat Valenciana (Project PROMETEOII/2014/010 and Grant BEST/2014/250), the Spanish Ministry of Economy and Competitiveness (Projects CTQ2012-30703, CTQ2012-31762, MAT2014-61992-EXP, and Grant PRX14/00249), and the UE (FEDER funding)

Investigation of Pd nanoparticles supported on zeolites for hydrogen production from formic acid dehydrogenation

Catalysts based on palladium nanoparticles supported on different zeolites (BETA, ZSM-5 and Y) were prepared and their catalytic performance in formic acid dehydrogenation was studied. The effects of the zeolite structure and porous texture on the catalytic activity were investigated by comparing the behavior of these samples. The results revealed that the samples based on BETA zeolite are promising catalysts for this application.The authors would like to acknowledge the Ministerio de Economía y Competitividad, GV and FEDER (CTQ2012/31762 and PROMETEOII/2014/010) for the financial support. Miriam Navlani-García thanks the University of Alicante for the PhD studentship. Martin Martis thanks the Japan Society for the Promotion of Science (JSPS) for the fellowship

Effect of Ru loading on Ru/CeO2 catalysts for CO2 methanation

The conversion of CO2 towards added valuable products is considered as a potential alternative to achieve the increase of the petrochemical industry while reducing the CO2 emissions. In the present work, the effect of Ru loading on CeO2 supports has been studied for the CO2 methanation reaction, and catalysts with different Ru loading in the 1–5 wt. % range have been prepared, characterized, and tested. The optimum Ru loading has been found to be 2.5 wt. %. Ruthenium cations are reduced at the lowest temperature for this optimum loading according to H2-TPR experiments (even at room temperature), and the highest proportion of ruthenium cations with strong interaction with ceria is achieved, as deduced from XPS. XRD characterization suggests partial insertion of ruthenium cations into the ceria lattice. In situ DRIFTS experiments evidenced that the balance between formation upon CO2 chemisorption and further hydrogenation of surface carbon intermediates is optimum for 2.5 wt. % Ru/CeO2. For low metal contents, the CO2 chemisorption is limited and no relevant, while as the metal content is increased, the hydrogenation of carbon species is less favourable. The 2.5 wt.% Ru/CeO2 catalyst comprises a balance between surface-carbon groups formation and further hydrogenation.Generalitat Valenciana (PROMETEO/2018/0765); MICINN (PID2019-105960RB-C22); Junta de Andalucía (Project P18-RTJ-2974); European Union's Horizon 2020 research and innovation program (Marie Skłodowska-Curie grant agreement No 713567); Science Foundation Ireland Research Centre (award 12/RC/2278_P2)

Carbon sorbents for the retention of thermodecomposition compounds from microplastics

Carbon sorbents have been tested in this study to improve the retention of microplastics thermodecomposition compounds in Thermoextraction-Desorption Gas Chromatography-Mass Spectrometry (TED-GC-MS) technique and has been demonstrated an optimal behavior for this application, highlighting two main advantages with regard to conventional PDMS sorbents; On the one hand, carbons present slit-type pores, being optimal for retaining the aromatic compounds released from most polymers. In addition, those materials have shown to have a greater retention capacity than PDMS being between 1.25 and 25 times more efficient. Combination of PDMS+Carbon sorbents increases retention of the most representative compounds for each polymer up to 1.7 times with regard to only carbon, increasing sensitivity, but with an experimental procedure more complicated, because two desorption process must be done. On the other hand, carbon materials can retain the chlorinated compounds released by thermodecomposition of PVC, while conventional PDMS sorbent is not effective for these compounds.Authors thank the funding from Vice-Rector for Research and Knowledge Transfer of the University of Alicante (Project UAIND19-02), Labaqua and Interlab for funding the Industrial Doctorate

Mineral Manganese Oxides as Oxidation Catalysts: Capabilities in the CO-PROX Reaction

Cryptomelane is an abundant mineral manganese oxide with unique physicochemical features. This work investigates the real capabilities of cryptomelane as an oxidation catalyst. In particular, the preferential CO oxidation (CO-PROX), has been studied as a simple reaction model. When doped with copper, the cryptomelane-based material has revealed a great potential, displaying a comparable activity to the high-performance CuO/CeO2. Despite stability concerns that compromise the primary catalyst reusability, CuO/cryptomelane is particularly robust in the presence of CO2 and H2O, typical components of realistic CO-PROX streams. The CO-PROX reaction mechanism has been assessed by means of isotopic oxygen pulse experiments. Altogether, CuO/CeO2 shows a greater oxygen lability, which facilitates lattice oxygen enrolment in the CO-PROX mechanism. In the case of CuO/cryptomelane, in spite of its lower oxygen mobility, the intrinsic structural water co-assists as active oxygen species involved in CO-PROX. Thus, the presence of moisture in the reaction stream turns out to be beneficial for the stability of the cryptomelane structure, besides aiding into the active oxygen restitution in the catalyst. Overall, this study proves that CuO/cryptomelane is a promising competitor to CuO/CeO2 in CO-PROX technology, whose implementation can bring the CO-PROX technology and H2 purification processes a more sustainable nature.The authors thank the financial support of the Spanish Ministry of Economy and Competitiveness (Project CTQ2015-67597-C2-2-R and grant FJCI-2015-23769), the Spanish Ministry of Science and Innovation (PID2019-105960RB-C22), Spanish Ministry of Education (FPU14/01178), Generalitat Valenciana (Project PROMETEO/2018/076), and the EU (FEDER funding)