Abstract
The CO2 photoreduction is a promising way to convert one of the most abundant greenhouse gases to valuable chemicals. The photoreduction in the liquid phase is limited by the low solubility of CO2 in water, but this point is overcome here by using an innovative photoreactor, which allows one to work up to pressures of 20 bar, improving the overall productivity. The photoreduction was performed in the presence of Na2SO3 and using in primis commercial titanium dioxide (P25) and a set of titania catalysts functionalized by surface deposition of either monometallic or bimetallic cocatalysts. The gaseous products were hydrogen and traces of CO, while, in the liquid phase, formic acid/formate, formaldehyde and methanol were quantitatively detected. The pH was observed to shift the products distribution. A neutral environment led mainly to hydrogen and methanol, while, at pH 14, formate was the most abundant compound. The trend for monometallic cocatalysts showed enhanced productivity when using noble metals (i.e., gold and platinum). In order to limit the cost of the catalytic material, bimetallic cocatalysts were explored, adding titania with Au+Ag or Au+Pt. This may open to the possibility of performing the reaction with a smaller amount of the most expensive metals. In the end, we have expressed some conclusions on the cost of the photocatalysts here employed, to support the overall feasibility assessment of the process.
Highlights
Warnings on climate change are unequivocal, and since the 1950s, many of the observed phenomena are unprecedented over decades to millennia leading to a globally averaged warming of 0.85 °C over the period 1880−2012, as explained in the fifth assessment report of IPCC.[1]
Commercial titanium dioxide (P25) and Au 0.2 wt %/P25 were widely characterized in a previous work.[16]
No peaks associated with the metallic phase appeared, which is expected since the metal represents only a small fraction of the entire particle weight and is very well dispersed over the titania surface
Summary
Warnings on climate change are unequivocal, and since the 1950s, many of the observed phenomena are unprecedented over decades to millennia leading to a globally averaged warming of 0.85 °C over the period 1880−2012, as explained in the fifth assessment report of IPCC.[1]. Unequivocal is the human contribution to the phenomenon, as a consequence of greenhouse gases emissions.[1] In particular, the atmospheric concentration of carbon dioxide, methane, and nitrous oxide has increased to levels unprecedented in at least the last 800 000 years. CO2 concentration has increased by 40% since preindustrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.[1] Limiting CO2 levels is important to reduce emissions by decreasing the use of fossil fuels, and to adopt strategies to remove CO2 using the approach of carbon capture and sequestration (CCS) from point sources.[2] CCS has some drawbacks,[3] such as the risk of leakage, energy consumption during compression and transportation, and null direct economical return
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