Which Future Route in the Methanol Synthesis? Photocatalytic Reduction of CO2, the New Challenge in the Solar Energy Exploitation

Nowadays, the practical exploitation of the sun for industrial purposes is still almost limited to the photovoltaic and the solar-thermal technologies. As an alternative route, the direct photoconversion of CO2 to methanol is potentially one of the most promising ways for a larger utilization of the solar source. Since the late 1970s, many studies have been proposed for reproducing artificially the photosynthesis process, aiming to convert CO2 into high value products. Indeed, the direct photoconversion of CO2 is energetically more effective than catalytic hydrogenation processes, although the energy density and the efficiency of the current photocatalytic systems are still far away from large scale application. Thus, advances in the photocatalytic CO2 conversion deserve systematic efforts in the fields of material science and reactor engineering. To overcome this technological gap, two feasible routes are pursued; these consist in the development of efficient photocatalytic materials at higher "quantum yield" for improving activity and selectivity, and the optimization of the photoreactor configuration enhancing the light transmission over the photocatalytic phase.