Bifunctional Rhodium Cocatalysts for Photocatalytic Steam Reforming of Methane over Alkaline Titanate

Abstract

Photocatalytic steam reforming of methane (PSRM; 2 H2O (g) + CH4 → 4 H2 + CO2) was examined over metal-loaded K2Ti6O13 photocatalysts. Although the production rate was improved by loading Pt cocatalyst on the K2Ti6O13 photocatalyst, unfavorable formation of CO and gradual deactivation of photocatalyst were observed. On the other hand, a Rh-loaded K2Ti6O13 sample showed two times higher activity than the Pt-loaded one did, and promoted the PSRM selectively without deactivation for many hours. In the highly active Rh-loaded photocatalyst, the Rh cocatalyst existed as a mixture of small metallic rhodium and large rhodium oxide particles. The photocatalytic activity tests for hydrogen evolution and oxygen evolution from each aqueous solution of sacrificial reagent (methanol and silver nitrate, respectively) revealed that the metallic rhodium particles and the rhodium oxide particles could function as cocatalysts preferably for reduction and oxidation, respectively. Also on a Na2Ti6O13 photocatalyst, a mixture of rhodium metal and oxide similarly enhanced the photocatalytic activity. Thus, it is suggested that the Rh cocatalyst on these alkaline titanates bifunctionally promoted the PSRM.

Influence of Rh nanoparticle size and composition on the photocatalytic water splitting performance of Rh/graphitic carbon nitride

“…The photocatalytic activity increased with decreasing particle size for three systems with average particle sizes in the 2e7 nm range. Shimura et al demonstrated that metallic Rh nanoparticles (typically around 9 nm) were preferred for the hydrogen evolution reaction, whereas larger (typically in the range of 25e50 nm) oxidic Rh particles were preferred as catalysts for the oxidative reaction (CH 4 þ 2H 2 O / CO 2 þ 8H þ ) by using Rh/K 2 Ti 6 O 13 materials prepared by photodeposition [30,31].…”

Size dependence of photocatalytic oxidation reactions of Rh nanoparticles dispersed on (Ga1-xZnx)(N1-xOx) support

“…The photogenerated electrons reduce protons at the NP metal surfaces. Shimura et al [49,50] and Maeda et al [37] suggested that electron extraction from the conduction band of ZGON by rhodium oxide is less efficient than that achieved by Rh metal. This suggests that rhodium oxide cocatalyst reduction is necessary for obtaining active photocatalysts.…”

“…It is reasonable to assume that metal NPs would also be active sites in H2 generation during photocatalytic water splitting. Shimura et al [49,50] have investigated the effects of the oxidation states of Rh NPs supported on Sr2Ti6O13 in the photocatalytic water-splitting reaction, and found that Rh metal catalyzes photocatalytic H2 production better than rhodium oxide does. Our earlier research on Rh particles supported on g-C3N4 also demonstrated that Rh metal particles are preferable for the H2 production reaction [27].…”

CHAPTER 8. Hydrogen Production from Biomass Derivatives over Heterogeneous Photocatalysts

“…The mixture of rhodium metal and oxide co-catalysts also enhanced the activity of a Na 2 Ti 6 O 13 photocatalyst. 162 …”