The Nature of Loading-Dependent Reaction Barriers over Mixed RuO₂/TiO₂ Catalysts

Abstract

Mixed-metal oxides are one of the most frequently used catalysts in chemical industry, because the superior catalytic reactivity can be achieved by taking advantage of the synergetic effects of their parent oxides. However, the interfacial electronic interactions between metal oxides remain unclear, because of their structural complexity. This paper describes the modulation of catalytic performance of mixed RuO 2 /TiO 2 catalysts via adjusting the loading amount of RuO 2 . We show that, at very low loadings, the majority of RuO 2 catalysts can be anchored at the defective sites of TiO 2 substrates. Spectroscopic studies, combined with density functional calculations, indicate that electrons transfer from defective sites of substrates to RuO 2 , causing an increase in the apparent reaction barrier of CO oxidation. As the loading of Ru increases, RuO 2 starts to appear on the terrace of TiO 2 , and the apparent reaction barrier of CO oxidation decreases. At the medium loading of ∼0.75 wt %, the lowest apparent reaction barrier is achieved. The phenomenon can be attributed to the electron transfer from RuO 2 to the terrace of TiO 2 . By further increasing the loading of Ru, the apparent reaction barrier rises again. When the loading of Ru is more than 2 wt %, the apparent reaction barrier is found to be very comparable to that over RuO 2 catalysts supported on an inert substrate, indicating that the electronic effect of TiO 2 is isolated underneath thick RuO 2 overlayers. The demonstrated loading−electron transfer−reaction barrier relationship at RuO 2 /TiO 2 catalysts provides an insight into the interfacial interaction between mixed oxides and can be readily extended to many other catalytic systems.

Controlling CO2 Hydrogenation Selectivity by Metal‐Supported Electron Transfer

“…Studies on Ru/a-TiO 2 with different Ru loadings suggest that the effect of hydrogen spillover and charge transfer is general. Consistent with the catalytic performance (selectivity to CH 4 ), the hydrogen spillover and electron transfer, detected by operando DRIFT spectra (Figure 4c), NAP-XPS analysis (Table 1a nd Figure S15) and in situ PL measurements ( Figure S14c), decreased greatly on 5Ru/a-TiO 2 .T he weaker spillover should be related to adecrease in exposed a-TiO 2 surface Os ites with Ru loading increase, [44] which lowers the possibility of forming Ti-O(H)-Tibyhydrogen spillover.Furthermore,the study combining synchrotronradiation photoelectron spectroscopy,s canning tunneling microscopy and density functional calculations indicated that the charge transfer across metal/support interface was associated with metal particle size. [45] Ther elatively larger particles may limit the charge transfer as well.…”

Coverage‐Dependent Behaviors of Vanadium Oxides for Chemical Looping Oxidative Dehydrogenation

“…TheBET surface areas of TiO 2 supports are about 21 m 2 ,t herefore the Vd ensity of 1V/TiO 2 was determined to be 0.89 mmol Vp er 100 m 2 of titanium oxide (namely,0 .081 wt %v anadium oxide per m 2 of titanium oxide), which is close to the previous reported theoretical monolayer (a value of 0.1 wt %v anadium oxide per m 2 of titanium oxide surface area). [17] So we suggest that the VO x with 1wt% Vl oadings completely encapsulate the TiO 2 substrate and reach to the monolayer dispersion capacity. TEM and HRTEM images showed that the particle size of TiO 2 supports is about 50 nm with ad -spacing of 0.325 nm, which is ascribed to TiO 2 (110) (Supporting Information, Figure S1C,D).…”

Modulating the surface defects of titanium oxides and consequent reactivity of Pt catalysts

“…Previously, extensive studies showed that metal nanoparticles and single atom catalysts exhibit variable catalytic reactivity when they are deposited on different supports, such as SiO 2 , Al 2 O 3 , CeO 2 , TiO 2 , FeO x and many others. [6][7][8][9][10][11][12] Surprisingly, the inuence of different surface states of oxide supports on the structure and catalytic performance of metal catalysts has only been studied using model surface science systems while little is known about this factor in real supported catalysts. [13][14][15][16] Recently, several related studies on this issue have been published.…”