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

Abstract

Oxygen carriers are a class of materials, typically solid oxides, that can reversibly store and release oxygen for a variety of applications in energy and chemical processes, e.g. chemical looping combustion (CLC) and chemical looping air separation (CLAS). In recent years, growing interest in these materials have been focused on their use in chemical looping selective oxidations. A method for enhancing the oxygencarrying capacity of oxygen carriers for use in selective oxidations is presented. In this approach, one material that is selective and active in the reaction is deposited on the surface of a second material acting as a reservoir of oxygen and as a support. Here, the approach has been investigated using the selective combustion of hydrogen in the presence of ethylene, an important step in the oxidative dehydrogenation of ethane. Bismuth oxides, supported on a range of ceria-zirconia materials, were made into particulate oxygen carriers and studied for their activity, selectivity and oxygen-storage capacity. STEM-EDS imaging showed that the bismuth phase was spread uniformly over the surface of the nanocrystalline particles. XPS measurements indicated that the surface was enriched with bismuth oxide. It was found that the presence of ceria in the support supplied lattice oxygen additional to that provided by the bismuth oxide, without affecting the selectivity of bismuth oxide towards the combustion of H 2 . In other words, the surface chemistry was decoupled from the bulk properties of the support, thus simplifying the design and formulation of selective oxygen carriers. This demonstrates a readily-applicable generic approach for the design of oxygen carriers for selective oxidations.

Chemical looping beyond combustion – a perspective

“…Representative materials showing high (490%) SHC selectivities, defined as the conversion of the hydrogen divided by the conversion of all combustible species, include Sb 2 O 4 , In 2 O 3 , WO 3 , Bi 2 O 3 , PbCrO 4 , doped ceria, ion-exchanged ZSM-5, etc. 268,269,[272][273][274][275][276][277] Bi, In, Pb, and Sb oxides often suffer from a poor redox stability owing to relatively low melting temperatures of their reduced states. 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%.…”

Bi-Doped Ceria as a Highly Efficient Catalyst for Soot Combustion: Improved Mobility of Lattice Oxygen in CexBi1–xOy Catalysts

“…Bismuth could be used as the dopant for ceria-based catalysts because of the following reasons: (i) Bi 2 O 3 has a high anion conductivity − and reducibility; , (ii) Bi 3+ has lower valence than Ce 4+ , which may promote formation of oxygen vacancies and thus accelerate the transfer of active oxygen via doping. , Shang et al reported that Bi-doped Co 3 O 4 catalysts prepared by the sol–gel method exhibited excellent activity for soot oxidation, the mobility of active oxygen species was accelerated, and the strength of the metal–O bond was weakened with the doping of Bi . Ishihara et al reported that CeO 2 -promoted Pr 4.8 Bi 1.2 O 11 was highly active for soot combustion in DPF used for diesel engine exhaust gas .…”

Oxygen Activation through β-Bi2O3 and Ultrafine CeO2 Interactions to Promote Catalytic Soot Combustion

“…The reduction peaks located from 200 to 400 °C are referred to surface-adsorbed oxygen, and the reduction peaks in the range of 400−550 °C are ascribed to surface lattice oxygen. Moreover, the reduction peaks above 800 °C, near the melting point of Bi 2 O 3 (825 °C), 46 represent bulk lattice oxygen. 47 Compared with Bi 2 O 3 -P, the intensity of the reduction peaks over CeO 2 -P500 and CeO 2 -R500 is basically negligible, and the reduction peaks shift to lower temperatures over the Bi x Ce 10−x catalysts because of the formation of the Bi−O−Ce interface.…”