Photocatalytic Approaches to Circular Economy: CO2 Photoreduction to Regenerated Fuels and Chemicals and H2 Production from Wastewater

The photoreduction of CO2 is an unconventional process to regenerate fuels and chemicals storing solar radiation. A new photoreactor has been designed recently to achieve high productivity during the process, i.e. up to 39 mol/h kgcat of HCOOH or 1.4 mol/h kgcat of CH3OH, which are unprecedented results with respect to literature, especially with a very simple commercial TiO2 catalyst. The production of hydrogen through photoreforming of aqueous solutions of organic compounds is also considered as a way to exploit solar energy storage in the form of hydrogen. Different sugars were selected as substrates derived from the hydrolysis of biomass or from wastewater (food or paper industry). A significant amount of H2 was obtained with very simple catalyst formulations, e.g. 14 mol kgcat-1 h-1 were obtained at 4 bar, 80 \u2daC over commercial TiO2 samples, added with 0.1 mol% of Pt and using glucose as substrate. This result is very remarkable with respect to similar research in conventional photoreactors. Both the routes represent a circular way to regenerate valuable products from gaseous or liquid wastes. Our attention was predominantly focused on the development of innovative reactors, possibly operating under unconventional conditions, with fine tuning of the operation parameters. The exploitation potential of these results under solar irradiation is presented

Vorejant l'ortodoxia dins els camins del reformisme: La conversió lul·liana

Abstract not availabl

Non-affine geometrization can lead to nonphysical instabilities

Geometrization of dynamics consists of representing trajectories by geodesics on a configuration space with a suitably defined metric. Previously, efforts were made to show that the analysis of dynamical stability can also be carried out within geometrical frameworks, by measuring the broadening rate of a bundle of geodesics. Two known formalisms are via Jacobi and Eisenhart metrics. We find that this geometrical analysis measures the actual stability when the length of any geodesic is proportional to the corresponding time interval. We prove that the Jacobi metric is not always an appropriate parametrization by showing that it predicts chaotic behavior for a system of harmonic oscillators. Furthermore, we show, by explicit calculation, that the correspondence between dynamical- and geometrical-spread is ill-defined for the Jacobi metric. We find that the Eisenhart dynamics corresponds to the actual tangent dynamics and is therefore an appropriate geometrization scheme.Comment: Featured on the Cover of the Journal. 9 pages, 6 figures: http://iopscience.iop.org/1751-8121/48/7/07510