The reactions of H2O, H2 D2 and CO with clean and rhodium covered black titania have been investigated by TDS, AES and sensitive temperature programmed work function (TP-WF) measurements to elucidate the complex interactions with this narrow bandgap material promising for visible light energy harvesting. Water formed molecular and dissociative adsorption states with positive outward dipole moments on the reduced, r–TiO2 (110). Surface hydroxyl groups decomposed to H2 and recombined to H2O in a broad temperature range, characterized by TDS peaks at 300, 355–377 and 470 K, which has been associated with surface inhomogeneity. On a strongly reduced, sr–TiO2 (110), a part of H atoms arising from OHa species dissolved in the titania at 200–500 K, and desorbed as H2O with Tp = 570, 670 and 750 K. Sub-monolayer TiOx films produced by stepwise heating on r–TiO2 (110) supported Rh particles suppressed the adsorption of hydrogen, but allowed its spillover to the support. Co-adsorption experiments with D2, H2, H2O and CO on the Rh covered r–TiO2 (110) were also performed. Saturating the Rh by CO at 330 K blocked the uptake of hydrogen on the metal, eliminating its spillover to the support. At 270 K saturation CO exposure removed the pre-adsorbed hydrogen, while at 200 K replaced a part of it decreasing the adsorption bond energy of the rest remained adsorbed. Co-adsorption data proved that the hydrogen desorption states with Tp = 470 and 570 K belong to the decomposition of hydroxyl groups on the r–TiO2 (110) support and at the Rh–TiOx interface, respectively. It is remarkable that the latter state can evolve in the presence of adsorbed CO, which exhibits reactivity towards the same interface.
Black titania Hydrogen dissolution Hydrogen spillover Rh–TiOx interface OH decomposition CO coadsorption
This is a preview of subscription content, log in to check access.
Supports through grants of the Hungarian Scientific Research Fund (OTKA) K120115, GINOP-2.3.2-15-2016-00013 and COST Action CM1104 are gratefully acknowledged.