Sustainable Carbon Dioxide Photoreduction by a Cooperative Effect of Reactor Design and Titania Metal Promotion

Abstract

An effective process based on the photocatalytic reduction of CO 2 to face on the one hand, the crucial problem of environmental pollution, and, on the other hand, to propose an efficient way to product clean and sustainable energy sources has been developed in this work. Particular attention has been paid to the sustainability of the process by using a green reductant (water) and TiO 2 as a photocatalyst under very mild operative conditions (room temperature and atmospheric pressure). It was shown that the efficiency in carbon dioxide photoreduction is strictly related to the process parameters and to the catalyst features. In order to formulate a versatile and high performing catalyst, TiO 2 was modified by oxide or metal species. Copper (in the oxide CuO form) or gold (as nanoparticles) were employed as promoting metal. Both photocatalytic activity and selectivity displayed by CuO-TiO 2 and Au-TiO 2 were compared, and it was found that the nature of the promoter (either Au or CuO) shifts the selectivity of the process towards two strategic products: CH 4 or H 2 . The catalytic results were discussed in depth and correlated with the physicochemical features of the photocatalysts.

Characterization and Effect of Ag(0) vs. Ag(I) Species and Their Localized Plasmon Resonance on Photochemically Inactive TiO2

“…Therefore, much effort has been focused on enhancing the photocatalytic activity of TiO 2 , including doping with metal or non-metal species [17,18], surface sensitization [19,20], and noble metal deposition [21][22][23][24][25]. In particular, the noble metal deposition has attracted a lot of attention since it can improve e − -h + separation and enhance the semiconductor's absorption in the visible light region [26,27].…”

Solar Fuels by Heterogeneous Photocatalysis: From Understanding Chemical Bases to Process Development

“…Concerning gas phase reactions, several different reactor configurations have been reported, such as packed bed [244], plate thin-film [170] and coated honeycomb [175], although no direct comparison among them has been done. It is worth observing that reactor design, as reported in Section 2.2, has a crucial role in photocatalysis, since as we recently report for CO 2 photoreduction, a proper irradiation pattern creates higher productivity with lower amounts of catalyst [74]. Nonetheless, there is plenty of work that can be done on PR reactors' design.…”

“…On the contrary, CO 2 photoreduction can also be performed in the gas phase, feeding water as vapour, leading to slightly different results in observed mechanisms. For example, Karamian and co-workers [88] reported that in most cases, in gaseous systems CO is the first intermediate product of CO 2 photoreduction by water vapour [74].…”

“…According to their calculations, the last two configurations, which involve the weakening of C=O bond, seem to be the most likely intermediate in the reduction route. Very recently, Olivo et al, by means of CO2 adsorption studies using FTIR analyses, observed that all three species are present on metal modified TiO2, but samples with the highest photocatalytic activity proved to be characterised by the highest share of adsorbed CO2 in bidentate structures [74].…”

“…As reported by Nguyen and Ha from theoretical and spectroscopic studies, CO2 can interact with water vapour [76]; oxygen lone pairs in H2O can interact with anti-bonding 2πu at central carbon atoms in CO2, leading to the formation of van der Waals complexes [77]. Very recently, Olivo et al, by means of CO 2 adsorption studies using FTIR analyses, observed that all three species are present on metal modified TiO 2 , but samples with the highest photocatalytic activity proved to be characterised by the highest share of adsorbed CO 2 in bidentate structures [74].…”