Víctor A. de la Peña O'Shea

Advances in the design of ordered mesoporous materials for low-carbon catalytic hydrogen production

It is believed that hydrogen will play a relevant role as an energy vector in the near future, but in order to fulfil these expectations the development of economically feasible routes with limited CO2 emissions is required. In this respect, catalysis is crucial in most of the possible processes for hydrogen generation and, accordingly, improvement in the catalyst properties should have a significant impact on the efficiency of the production. In particular, ordered mesoporous materials of different chemical composition (oxides and non-oxides) possess a high potential for improving a variety of catalytic routes for the production of low-carbon hydrogen. The activity of this type of catalyst is frequently enhanced due to a combination of high surface area, low diffusion restrictions, and high dispersion of the supported active phases. In this work, we review the latest advances in the use of these mesostructured catalysts in the most relevant routes for hydrogen generation with reduced greenhouse emissions: steam reforming of biomass derived feedstocks (biogas, ethanol, and glycerol), methane and ammonia decomposition and photocatalytic reduction using sacrificial electron donors.

Co-production of graphene sheets and hydrogen by decomposition of methane using cobalt based catalysts

The present study reports the simultaneous formation of graphene sheets and hydrogen by methane decomposition using cobalt catalysts. The production of graphene structures can be promoted by adjusting the method and conditions employed in the preparation of the metallic catalyst. The use of methane as a reducing agent seems to be an essential factor for the formation of graphene. The best performance in terms of graphene selectivity is shown by the catalyst obtained using Na2CO3 as a precipitating agent in ethylene glycol medium. Several characterization techniques viz.HRTEM, AFM and Raman spectroscopy have been used to identify the graphene sheets.

Mixed NaNbxTa1−xO3 perovskites as photocatalysts for H2 production

Mixed perovskites NaNbxTa1−xO3 were prepared by solid state reaction (SSR) as well as by hydrothermal (Hyd) methods, and their photocatalytic activity for hydrogen production was studied using the water–methanol system. The assessment of the NaNbxTa1−xO3 materials obtained by the SSR method reveals that the activity of the individual NaTaO3 and NaNbO3 perovskite semiconductors is largely improved in their combined form. Among several compositions employed, the 1 : 1 molar ratio (NaNb0.5Ta0.5O3 sample) shows the best performance for H2 production. On the other hand, using the Hyd method, which implies lower synthesis temperature, the photocatalytic activity of NaNb0.5Ta0.5O3 is enhanced compared to the material obtained by the high temperature SSR method. The characterization of the materials reveals that catalyst properties like high surface area, a larger proportion of the monoclinic crystalline phase and lower crystal defects for the NaNb0.5Ta0.5O3 photocatalyst synthesized by the hydrothermal route may be responsible for its superior activity. Further significant improvement in the activity of the NaNb0.5Ta0.5O3 semiconductor is achieved by the addition of Pt as the co-catalyst, showing that the loading amount has a great influence on the activity. The highest H2 production rate (37.8 μmol g−1 min−1) is obtained for the catalyst prepared by the hydrothermal method (Hyd-NaNb0.5Ta0.5O3) with 0.125 wt% of Pt loading. Moreover, the developed Hyd-NaNb0.5Ta0.5O3 sample shows a stable H2 evolution activity for several reuse cycles.

Dichromatic Photocatalytic Substitutions of Aryl Halides with a Small Organic Dye

Photocatalytic bond activations are generally limited by the photon energy and the efficiency of energy and electron transfer processes. Direct two-photon processes provide sufficient energy but the ultra-short lifetimes of the excited states prohibit chemical reactions. The commercial dye 9,10-dicyanoanthracene enabled photocatalytic aromatic substitutions of non-activated aryl halides. This reaction operates under VIS-irradiation via sequential photonic, electronic, and photonic activation of the simple organic dye. The resultant highly reducing excited photocatalyst anion readily effected C-H, C-C, C-P, C-S, and C-B bond formations. Detailed synthetic, spectroscopic, and theoretical studies support a biphotonic catalytic mechanism.