Miriam Navlani-García

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 behaviour of these samples. The results revealed that the samples based on BETA zeolite are promising catalysts for this application.

Palladium nanoparticles supported on titanium doped graphitic carbon nitride for formic acid dehydrogenation

Pd nanoparticles (NPs) supported on Ti-doped graphitic carbon nitride (g-C3 N4 ) were synthesized by a deposition-precipitation route and a subsequent reduction with NaBH4 . The features of the NPs were studied by XRD, TEM, FTIR, XPS, EXAFS and N2 -physisorption measurements. It was found that the NPs had an average size of 2.9 nm and presented a high dispersion on the surface of Ti-doped g-C3 N4 . Compared to Pd loaded on pristine g-C3 N4 , the Pd NPs supported on Ti-doped g-C3 N4 exhibited a high catalytic activity in formic acid dehydrogenation in water at room temperature. The enhanced activity could be attributed to the small Pd NPs size, as well as the strong interaction between Pd NPs and Ti-doped g-C3 N4 .

Optimizing the performance of catalytic traps for hydrocarbon abatement during the cold-start of a gasoline engine

A key target to reduce current hydrocarbon emissions from vehicular exhaust is to improve their abatement under cold-start conditions. Herein, we demonstrate the potential of factorial analysis to design a highly efficient catalytic trap. The impact of the synthesis conditions on the preparation of copper-loaded ZSM-5 is clearly revealed by XRD, N2 sorption, FTIR, NH3-TPD, SEM and TEM. A high concentration of copper nitrate precursor in the synthesis improves the removal of hydrocarbons, providing both strong adsorption sites for hydrocarbon retention at low temperature and copper oxide nanoparticles for full hydrocarbon catalytic combustion at high temperature. The use of copper acetate precursor leads to a more homogeneous dispersion of copper oxide nanoparticles also providing enough catalytic sites for the total oxidation of hydrocarbons released from the adsorption sites, although lower copper loadings are achieved. Thus, synthesis conditions leading to high copper loadings jointly with highly dispersed copper oxide nanoparticles would result in an exceptional catalytic trap able to reach superior hydrocarbon abatement under highly demanding operational conditions.

CuH-ZSM-5 as Hydrocarbon Trap under Cold Start Conditions

Cold start tests are carried out to evaluate the performance of copper-exchanged zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the role of copper in the performance of these zeolites. It is concluded that the partial substitution of the protons in the parent H-ZSM-5 zeolite is highly beneficial for hydrocarbon trapping due to the formation of selective adsorption sites with specific affinity for the different exhaust components. However, it is also observed that uncontrolled exchanging process conditions could lead to the presence of CuO nanoparticles in the zeolite surface, which seem to block the pore structure of the zeolite, decreasing the hydrocarbon trap efficiency. Among all the zeolites studied, the results point out that a CuH-ZSM-5 with a partial substitution of extra-framework protons by copper cations and without any detectable surface CuO nanoparticles is the zeolite that showed the best performance under simulated cold start conditions due to both the high stability and the hydrocarbon retaining capacity of this sample during the consecutive cycles.

Pd/zeolite-based catalysts for the preferential CO oxidation reaction: ion-exchange, Si/Al and structure effect

A screening of Pd/zeolite-based catalysts in the PrOx-CO reaction in H2-rich streams was performed using zeolites with different cations (H+, Na+ and Cs+) prepared by ion exchange and framework type (MFI and FAU). The assessment of the catalytic performance displayed by these zeolite-based samples revealed that both parameters play an important role in the catalytic behaviour. The optimisation of both parameters led to the preparation of an optimum catalyst, which showed high CO conversion and CO selectivity during long-term stability tests.

BETA Zeolite Thin Films Supported on Honeycomb Monoliths with Tunable Properties as Hydrocarbon Traps under Cold‐Start Conditions

A high percentage of hydrocarbon (HC) emissions from gasoline vehicles occur during the cold-start period. Among the alternatives proposed to reduce these HC emissions, the use of zeolites before the three-way catalyst (TWC) is thought to be very effective. Zeolites are the preferred adsorbents for this application; however, to avoid high pressure drops, supported zeolites are needed. In this work, two coating methods (dip-coating and in situ crystallization) are optimized to prepare BETA zeolite thin films supported on honeycomb monoliths with tunable properties. The important effect of the density of the thin film in the final performance as a HC trap is demonstrated. A highly effective HC trap is prepared showing 100% toluene retention, accomplishing the desired performance as a HC trap, desorbing propene at temperatures close to 300 °C, and remaining stable after cycling. The use of this material before the TWC is very promising, and works towards achieving the sustainability and environmental protection goals.

Room-Temperature and Aqueous-Phase Synthesis of Plasmonic Molybdenum Oxide Nanoparticles for Visible-Light-Enhanced Hydrogen Generation.

A straightforward aqueous synthesis of MoO3-x nanoparticles at room temperature was developed by using (NH4 )6 Mo7 O24 ⋅4 H2 O and MoCl5 as precursors in the absence of reductants, inert gas, and organic solvents. SEM and TEM images indicate the as-prepared products are nanoparticles with diameters of 90-180 nm. The diffuse reflectance UV-visible-near-IR spectra of the samples indicate localized surface plasmon resonance (LSPR) properties generated by the introduction of oxygen vacancies. Owing to its strong plasmonic absorption in the visible-light and near-infrared region, such nanostructures exhibit an enhancement of activity toward visible-light catalytic hydrogen generation. MoO3-x nanoparticles synthesized with a molar ratio of Mo(VI) /Mo(V) 1:1 show the highest yield of H2 evolution. The cycling catalytic performance has been investigated to indicate the structural and chemical stability of the as-prepared plasmonic MoO3-x nanoparticles, which reveals its potential application in visible-light catalytic hydrogen production.

Recent strategies targeting efficient hydrogen production from chemical hydrogen storage materials over carbon-supported catalysts

There is an evident urgent need to find a renewable and clean energy vector to ensure the worldwide energy supply while minimizing environmental impacts, and hydrogen stands out as a promising alternative energy carrier. The social concern around its safe storage is constantly fostering the search for alternative options to conventional storage methods and, in this context, chemical hydrogen storage materials have produced abundant investigations with particular attention to the design of heterogeneous catalysts that can boost the generation of molecular hydrogen. Among the chemical hydrogen storage materials, formic acid and ammonia–borane hold tremendous promise, and some of the recent strategies considered for the preparation of high-performance carbon-supported catalysts are summarized in this review. The outstanding features of carbon materials and their versatility combined with the tunability of the metal active phase properties (e.g., morphology, composition, and electronic features) provide numerous options for the design of promising catalysts.Hydrogen storage: The importance of downsizingPrecise control over the size and composition of metal nanoparticles is critical to the safe production of hydrogen from chemical storage systems. Kohsuke Mori and Hiromi Yamashita from Osaka University in Japan and colleagues review recent progress in producing hydrogen gas for fuel cell technology from the energy-rich molecules formic acid and ammonia borane. By immobilizing nanosized metal catalysts onto carbon-based supports with shapes including ultrasmall spheres, nanotubes, and graphene oxide sheets, researchers can tune hydrogen generation rates to record-high levels while still ensuring easy recovery and reuse. Catalytic reactions with formic acid can be improved by using noble metal-based palladium catalysts. While ruthenium nanocatalysts are favored for ammonia borane reactions, less expensive metal nickel and cobalt nanoparticles are gaining attention.This review recapitulates some of the most representative studies recently reported on carbon-supported catalysts for the hydrogen production from formic acid and ammonia borane by considering both active phase features and support properties. Several synthetic strategies are herein summarized to highlight the versatility of carbon materials in affording highly-performing catalysts for the hydrogen production from hydrogen carrier molecules.

Enhanced ammonia-borane decomposition by synergistic catalysis using CoPd nanoparticles supported on titano-silicates

Pd and CoxPd1−x nanoparticles (NPs), synthesized using the reduction by solvent method, were loaded on SiO2 and Ti–SiO2 supports. The resulting catalysts were tested in the ammonia-borane decomposition reaction under dark and UV-vis conditions. The synergistic promotion by Co (in the NPs) and Ti (in the support), combined with the UV-vis light irradiation, enhanced the catalytic activity showing very promising TOFs values for this kind of catalysis, from 1.53 to 49.5 mol H2 per mol Pd per min.

Black Phosphorus-Based Compound with Few Layers for Photocatalytic Water Oxidation

Although black phosphorus (BP) is an interesting 2D nanosheet material with a high hole mobility, its application in the photocatalytic water oxidation for O2 evolution is not reported yet. Herein the use of BP coupled with a reductive hydroxide, Ni(OH)2, is reported for the first time. The developed photo‐assisted process confirms that the BP XPS measurements confirm that the oxidation state of BP is reduced through the photo‐assisted loading method. The obtained P−Ni(OH)2 samples present the steady and efficient photocatalytic water splitting for O2 generation. Under the simulated sunlight irradiation in 0.1 M Na2S2O4 solution, the O2 generation rate can reach up to 15.7 μmol/(gcatalyst*h) or 224.3 μmol/(gBP*h). The density functional theory (DFT) calculation suggests that the electrons and holes move to surface of BP and Ni(OH)2, respectively. The merit of self‐polarization of P−Ni(OH)2 ensures the stability of BP and achieves the photocatalytic O2 generation from water.