Sustainable selective oxidations using ceria-based materials

Abstract

This Perspective covers sustainable oxidation processes using doped cerias, ceria-supported catalysts and ceria-based mixed oxides. Firstly, we consider the general properties of ceria-based catalysts. We outline the advantages of the ceria redox cycle, and explain the dynamic behaviour of these catalysts in the presence of metal additives and dopants. We then review three types of catalytic oxidation processes: preferential CO oxidation (PROX), oxidative dehydrogenation and the selective oxidations of hydrocarbons and inorganics. The preferential oxidation of CO from hydrogen-rich mixtures is interesting for fuel cell applications. Copper-ceria catalysts, where the copper species are well dispersed and interact strongly with the ceria surface, show good selectivity and activity. The oxidative dehydrogenation of small alkanes is another important potential application. To avoid mixing oxygen and hydrocarbons at high temperatures, one can run the dehydrogenation over a conventional Pt/Sn catalyst while burning the hydrogen formed using the ceria lattice oxygen. This safer redox process allows separate tuning of the dehydrogenation and hydrogen combustion stages. A combinatorial screening showed good results for ceria doped with Pb, Cr or Bi, amongst others. Finally, we also discuss the catalytic selective oxidation of various hydrocarbons, oxygenates and inorganic molecules (H 2 S, H 2 and NH 3). The goal here is either product valorisation or waste stream purification. Ceria-based materials show promise in a variety of such selective oxidations.

Selective Hydrogenation of Phenol Catalyzed by Palladium on High-Surface-Area Ceria at Room Temperature and Ambient Pressure

“…19,21 Recently, ceria-based materials have been investigated for use in soot removal from diesel engine exhausts, 22 volatile organic compound (VOC) degradation, 23 fuel cell technology, 24 water-gas shift reaction, 25,26 preferential CO oxidation (PROX), 27 oxidative dehydrogenation, 28 and selective hydrocarbon oxidations. 29,30 The success of ceria and ceria-based materials in catalysis is oftentimes due to facile Ce 4+ /Ce 3+ redox cycling without disruption of the fluorite lattice structure. 20 Furthermore, the redox properties of ceriabased materials can be tuned by incorporation of dopants or deposition of metals, which offer significant opportunities for modifying their activity and improving their performance.…”

Catalysing Sustainable Fuel and Chemical Synthesis

“…Supports employing porous architectures, acid/base character and/or surface redox chemistry e.g. strong metal support interaction (SMSI), afford further opportunities to influence catalyst reactivity [170][171][172][173]. Mesoporous silicas are widely used to disperse metal nanoparticles [135,136,171,174,175].…”

“…$Ce 4? redox chemistry [173,[184][185][186][187][188]. Sacrificial reduction of the ceria supports by reactively formed hydrogen liberated during the oxidative dehydrogenation of alcohols could mitigate in situ reduction of oxidised palladium, and hence maintain selox activity and catalyst lifetime, with Ce 4?…”

Honeycomb nano cerium oxide fabricated by vacuum drying process with sodium alginate

“…[1][2][3][4][5] The different application properties of nano CeO2 are directly related to its structure and morphology. So the study on the structure and morphology of nano CeO2 attracts so much attention.…”