Bismuth‐Doped Ceria, Ce_0.90Bi_0.10O₂: A Selective and Stable Catalyst for Clean Hydrogen Combustion

Abstract

Bismuth-doped cerias are successfully applied as solid "oxygen reservoirs" in the oxidative dehydrogenation of propane. The lattice oxygen of the ceria is used to selectively combust hydrogen from the dehydrogenation mixture at 550 8C. This process has three key advantages: it shifts the dehydrogenation equilibrium to the desired products side, generates heat, aiding the endothermic dehydrogenation, and simplifies product separation (water vs. hydrogen). Furthermore, the process is safer, since it uses the catalysts lattice oxygen instead of gaseous oxygen. We show here that bismuth-doped cerias are highly active and stable towards hydrogen combustion, and explore four different approaches for optimising their application in the oxidative dehydrogenation of propane: first, the addition of extra hydrogen which lowers hydrocarbon conversion by suppressing both combustion and coking; second, the addition of tin which completely inhibits coking; third, the addition of platinum which increases selectivity, but at the expense of lower activity. The best results are obtained through tuning the reaction temperature. At 400 8C, high activity and selectivity were obtained for the bismuth-doped ceria Ce 0.90 Bi 0.10 O 2 . Here, 90% of the hydrogen feed is converted at 98% selectivity. This optimal reaction temperature can be rationalised from the hydrogen and propene temperature-programmed reduction (TPR) profiles: 400 8C lies above the reduction maximum of hydrogen, yet below that of propene. That is, this temperature is sufficiently high to facilitate rapid hydrogen combustion, but low enough to prevent hydrocarbon conversion.

Chemical looping beyond combustion – a perspective

“…Ceria doped with W, Bi, Cr or Pb, were found to be stable in the temperature range 500-600 1C with selectivities of up to 98% for hydrogen combustion in the presence of C 2 and C 3 hydrocarbons and oxygen storage capacities as high as 2 wt%. 273,[278][279][280][281][282] Mn-and La-containing perovskites also showed a high SHC selectivity and stability in the presence of C 3 hydrocarbons at 550 1C. 84 It is noted, however, that the SHC selectivity tends to decrease with increasing temperature due to the lower activation energy for hydrogen combustion compared to hydrocarbon oxidation.…”

Hydrothermal Synthesis and in Situ Powder X-ray Diffraction Study of Bismuth-Substituted Ceria Nanoparticles

“…[1][2][3][4][5][6][7][8][9] CeO 2 is part of this family of compounds and doped ceria is being investigated as an 3 alternative to yttria-stabilized zirconia, which is one of the most used solid electrolytes in solid oxide fuel cells (SOFCs). It is well established that aliovalent metal substitution with ions of lower valence commonly leads to increased ionic conductivity in compounds such as yttria.…”

“…The technology is, at the present, at a state where various start-up companies are trying to commercialize it, and thus upscale production volumes to 1000 tons per annum. 23 Sub-and supercritical flow synthesis has been used to produce a wide variety of inorganic materials including CeO 2 , ZrO 2 , TiO 2 , α-Fe 2 O 3 , Fe 3 O 4 , AlOOH, Al 5 (Y+Yb) 3 [24][25][26][27][28][29] Conducting flow synthesis at supercritical conditions has proven as a viable method for producing inorganic materials with very narrow crystallite size distributions due to the instantaneous nucleation of nanoparticles upon the dramatic changes observed in the solvent properties of water at supercritical conditions. 25 The number of adjustable parameters in the hydrothermal synthesis method is vast.…”

Enhancing the capacity of oxygen carriers for selective oxidations through phase cooperation: bismuth oxide and ceria–zirconia

“…A possible candidate active support is ceria, which is stable and conducts oxide ions but needs to be doped to be selective. These dopants could be Bi or W. 23,25 Zirconia is often mixed with ceria to increase its stability and oxygen-carrying capacity at a given temperature. 26,27 A combination of bismuth oxide supported on ceria-zirconia has been shown to be active, selective and stable, 6 but the effect of the support on the innate selectivity of bismuth has not been established.…”

“…This reaction has had some historical interest in the context of the oxidative dehydrogenation of light alkanes. 5,23 This reaction was chosen because it is possible to analyse rapidly and quantitatively the gaseous products H 2 O and CO 2 . Accordingly, the reactions during the reduction step in the chemical looping cycle are reactions (1) and (2), with reoxidation described by reaction (3) (applicable for a Bi-based oxygen carrier):…”