Hydrogen production by the photoreforming of methanol and the photocatalytic water–gas shift reaction

Abstract

We have examined the reforming of methanol and CO on Pd/P25 TiO2 catalysts for hydrogen production, and compared it with rates for similarly supported Au and Cu catalysts. Both reactions proceed, but the photocatalytic water–gas shift (WGS) reaction is much slower than for methanol reforming. CO2 is evolved as expected, but the yields can be much lower than for the expected stoichiometry (CH3OH + H2O → CO2 + 3H2). We show that this is due to dissolution of the carbon dioxide into the aqueous phase. We have also carried out both reactions in the gas phase. Both proceed at a higher rate in the gas phase, and for methanol reforming, there is some CO evolution. In H2 + CO2 reactions, there is little sign of the reverse WGS reaction, but some photo-methanation does occur. Of the three catalysts Pd is the best for the methanol reforming reaction, while Au is best for the water–gas shift. Nonetheless, Cu works reasonably well for methanol reforming and makes a much cheaper, earth-abundant catalyst.

The Role of Metal Nanoparticles in Promoting Photocatalysis by TiO2

“…An example of results from such a system is given below, in this case with Pd as the metal (Fig. 2 ) [ 28 ]. Here it can be seen that both hydrogen and CO 2 are evolved coincidently.…”

“…The catalyst is stirred in the liquid phase with water and methanol, with an inert atmosphere above. Note, though, that if the ratio of the gas phase volume above the liquid to the liquid volume is high, then most of the CO 2 will dissolve and will be observed to be under-stoichiometric in the gas phase [ 28 , 29 ], as can be seen in this figure. However, if the solution volume is reduced, then the reservoir for CO 2 absorption is reduced and so more CO 2 is seen (Fig.…”

“…Using a 0.5 wt% Pd loading catalyst in the liquid phase with 100 ml water and 1% vol methanol. Reprinted with permission from [ 28 ]; Copyright 2021 IOPscience

Fig. 3 The ratio of H 2 :CO 2 evolution, and H 2 : (CO 2 + CO) after 3 h photocatalysis, using different volumes of water.

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“…Using a 0.5 wt% Pd loading catalyst in the liquid phase with 100 ml water and 1% vol methanol. Reprinted with permission from [ 28 ];…”

Foto(eletro)reforma do glicerol empregando filmes de Bi2WO6 como fotoanodos seletivos

“…Os tungstatos obtidos foram avaliados frente a redução fotocatalítica do H2 a partir da reforma do metanol. Os ensaios foram realizados sem a presença de Pt como co-catalisador, e usando o metanol como reagente de sacrifício, pois o mesmo é reconhecido pela rápida transferência de elétrons para a banda de valência do semicondutor (KAWAI; SAKATA, 1980;ZHAO, J. et al, 2020;KENNEDY et al, 2021).…”