Mechanistic Considerations on the H₂ Production by Methanol Thermal‐assisted Photocatalytic Reforming over Cu/TiO₂ Catalyst

Abstract

We have studied the gas phase H 2 production by methanol thermo-photoreforming using Cu-modified TiO 2 . Metal cocatalyst has been deposited by means of photodeposition method. The concentration of methanol in the steam was also considered. It appears that H 2 production is notably higher as temperature increases. Moreover, the optimum H 2 yield is achieved using methanol concentration of 10 % v/v. CO and CO 2 were monitored as side products of the overall reaction. It has been stated that CO evolution is significant at lower temperatures. As temperature increases, CO evolution is hindered and H 2 appeared boosted. We have demonstrated that other reactions such water-gas-shift or formate dehydration would participate in the overall process. On this basis, optimal operational condition for H 2 production is attained for thermo-photocatalytic reforming of methanol solution 10 % v/v at 200°C.

Efficiency of thermo–photocatalytic production of hydrogen from biomolecules: a multifaceted perspective

“…In Figure 6 we summarize two presentative studies using Pt/CeO x /TiO 2 39 and CuO/ZnO/ZrO 2 45 systems. Relatively similar results can be encountered in works concerning Cu/TiO 2 , 59,70 PdCu/TiO 2 , 60 Ru/RuO x /TiO 2, 41 and Cu/CeO x /TiO 2 . 38 The methanol reforming reaction was the subject of analysis in all cases.…”

“…Although complex this appears a general or basic mechanism, common to all reported works. [38][39][40][41]45,59,60,70 Comparing dark and illuminated conditions, the works highlight the promotion of different intermediates under thermo-photo conditions. Specifically, under thermo-photo conditions, most of the active materials promote formate production, 38,39,45 while a few described significant promotion of formaldehyde 41 and/or the water gas shift reaction.…”

“…Although complex, this appears a general or basic mechanism, common to all reported works. 38–41,45,59,60,70…”

H2 Photoproduction Efficiency: Implications of the Reaction Mechanism as a Function of the Methanol/Water Mixture

“…As mentioned in the introduction section, CO is not detected as reaction product, which indicates, in first place, the existence of decarbonylation reactions to generate the chemical species and, also, the consumption of carbon monoxide through a water gas shift reaction, which further promotes the formation of hydrogen with the co-generation of carbon dioxide. The water gas shift efficiency to generate hydrogen depends critically on the Pt particle size and metal-support interface, as CO can act as a poison or not depending on the adsorption enthalpy, surface coverage, and degree of activation [9,26,35,37]. In our case, infrared CO signals display a marked dependence on the sample (sulfide inhibits to a significant extent the formation) and methanol content of the reaction mixture.…”

“…The alkoxy route generates carboxylate-types species, formic acid, and methyl formate. These are typical main products of Pt-TiO 2 composites [9,17,25,26]. However, the less studied, carbon-centered radical route renders a larger number of products such as ethylene glycol, acetaldehyde, acetic acid, and also C 3 products such as 2-methoxyacetaldehyde [27].…”