Computational Screening and Experimental Synthesis of Doped TiO₂ for Propane Dehydrogenation

Abstract

Low-cost, environmentally friendly, and highly efficient catalysts are urgently needed for the direct propane dehydrogenation (PDH) to propylene. Studies have shown that defective TiO2 obtained by in situ reduction shows excellent catalytic PDH performance. Doping metals in the lattice of TiO2 is a plausible method for tuning the vacancy content and electronic property. In this paper, doping with fifth period transition metals was screened using a computational method, followed by experimental synthesis to further improve the PDH activity of TiO2-based catalysts. The TiO2 (101) surface with doping metals was first studied to determine the positive effect on the vacancy formation. Then, the two disputed reaction paths, that is, the concerted and stepwise path, were compared extensively on all of the doping models. Step one is found to be more preferable for all. The microkinetic modeling was employed to obtain the turnover frequency (TOF), based on which the linear relationship is found for TOF and binding energy of dissociated H2 or co-adsorption energy of 2-propyl&H. The abovementioned screening process shows Ru-doped TiO2, which shows the highest PDH activity and is justified by experimental results.

Structure–Activity Relationships in Lewis Acid–Base Heterogeneous Catalysis

“…Vanadium-doped TiO 2 was further identified as an effective PDH catalyst (with a C–H activation energy barrier of 0.93 eV) through a computational screening of TiO 2 doped with fourth-period TMs . A similar BEP relationship was obtained for PDH on oxygen-deficient TM–TiO 2– x where Ru–TiO 2– x exhibited the highest PDH activity . Additionally, a linear relationship was identified between the d-band center of the TM dopant on TiO 2 -based catalysts and the adsorption energy of (i) 2-propyl and (ii) 2-propyl&H in the TS, which in turn affect the activation barrier of the first C–H bond activation on propane .…”

“…However, under dry conditions, the strong affinity of undercoordinated Ga III for hydride resulted in (i) substantial site blocking with hydride species, especially at high conversions of ethane where a considerable amount of H 2 forms, and (ii) low partial reaction order with respect to ethane (0.40 vs 1.00 in case of pristine γ-Al 2 O 3 ). Song et al performed both experimental and computational studies on PDH using TiO 2 doped with fifth-period TMs and found a linear relationship between PDH TOFs and BE H 2 , where the dissociated hydrogens were both bounded to the dopant TM (Lewis acid site) of the oxygen-deficient TM–TiO 2–x . The more exothermic the BE H 2 , the lower the barrier for the first C–H bond activation and the higher the PDH rate.…”

“…Chang et al identified the coadsorption energy of 2-propyl and H ( E 2‑propyl&H ) as an activity descriptor for PDH on reducible and nonreducible MOs . Although the E 2‑propyl&H descriptor is based on BEP relationships where the intermediate reaction energy correlates with the catalytic activity, one would expect ( E 2‑propyl&H ) to correlate with the aforementioned BE H 2 . Similarly, Xiao et al obtained a linear relationship between PDH TOF and E 2‑propyl&H on TiO 2 -based catalysts .…”

Advanced design and development of catalysts in propane dehydrogenation

“…12f). 135 Moreover, based on the DFT calculations, Xiao et al pointed out that V-modified TiO 2 also presented higher PDH activity owing to the increased oxygen vacancy content. 138…”

“…12f ). 135 Moreover, based on the DFT calculations, Xiao et al pointed out that V-modified TiO 2 also presented higher PDH activity owing to the increased oxygen vacancy content. 138 In general, numerous efforts have been devoted to the development of non-precious metal-based catalysts to substitute the commercial Pt-based and toxic Cr-based catalysts, while it is difficult to meet the requirements of the practical application.…”