Transition-Metal Doped Ceria Microspheres with Nanoporous Structures for CO Oxidation

Catalytic oxidation of carbon monoxide (CO) is of great importance in many different fields of industry. Until now it still remains challenging to use non-noble metal based catalysts to oxidize CO at low temperature. Herein, we report a new class of nanoporous, uniform, and transition metal-doped cerium (IV) oxide (ceria, CeO2) microsphere for CO oxidation catalysis. The porous and uniform microsphere is generated by sacrificed polymer template. Transition-metals, like Cu, Co, Ni, Mn and Fe, were doped into CeO2 microspheres. The combination of hierarchical structure and metal doping afford superior catalytic activities of the doped ceria microspheres, which could pave a new way to advanced non-precious metal based catalysts for CO oxidation.


Sulfonation of porous polymer microspheres
To obtain sulfonated polymer microspheres, 2.0 g of Poly (GMA-co-EGDMA) microspheres was dispersed in 50 mL deionized water, followed by the addition of 9 g of Na 2 SO 3 in 10 mL deionized water. The resulting transparent solution was stirred in oil bath at 70 o C for 24 hours. The white microspheres with sulfonated groups on the surface were obtained by filtration and then washed repeatedly with deionized water and ethanol. After that, the microspheres were dried in the oven at 60 o C overnight, which were denoted as sulfonated polymer microspheres.

Preparation of Monodisperse Porous Ceria Microspheres
To a suspension of 1g of the sulfonated polymer microspheres in 5 mL of water, 2 g of Ce(NO 3 ) 3 · 6H 2 O were added. The mixture was transferred to oven set and then heated at 60 o C for 6 h. Then, the poly(GMA-co-EGDMA)/cerium microspheres were calcined at 600 o C for 12 h. Finally, monodisperse porous ceria microspheres were obtained.

Preparation of Monodisperse Porous Ceria Microspheres Substituted with Cu
To a suspension of 1g ofthe sulfonated microspheres in 5 mL water, 2 g of Ce(NO 3 ) 3 · 6H 2 O was added into the mixture. At the same time, 64.3 mg of CuSO 4 . 5H 2 O were added.The mixed solution was transferred to oven set at 60 o C and then heat-treated for 6 h. Finally, the obtained poly (GMA-co-EGDMA)/cerium microspheres with Cu 2+ were calcined at 600 o C for 12 h. After that, Cu x CeO 2-X microspheres were obtained. The microspheres were then further activated at 330 o C for 3 h in flowing H 2 /N 2 (0.5/99.5 v/v) at a heating rate of 10 o C/min.

Preparation of Monodisperse Porous Ceria Microspheres Substituted with Co
To a suspension of 1g of the sulfonated microspheres in 5 mL water, 2 g of Ce(NO 3 ) 3 · 6H 2 O and 68.0 mg of Co(OAc) 2 . 4H 2 O were added. The mixed suspension was transferred to oven and then heat-treated at 60 o C for 6 h. The obtained polymer/cerium microspheres susbstituted with Co 2+ were calcined at 600 o C for 12 h.
After that, the Co x CeO 2-X microspheres were treated at 330 o C for 3 h in flowing H 2 /N 2 (0.5/99.5 v/v) at a heating rate of 10 o C /min.

Preparation of Monodisperse Porous Ceria Microspheres Substituted with Ni
1g of the sulfonated microspheres in 5 mL water was mixed with 2 g of Ce(NO 3 ) 3 · 6H 2 O, followed by the addition of 65.6 mg of Ni(OAc) 2 . 4H 2 O. The mixture was heat treated in the oven at 60 o C for 6 h. After calcination at 600 o C for 12 h, Ni x CeO 2-X microspheres were obtained. Further activation was conductedat 330 o C for 3 h under the same reaction condition as Cu x CeO 2-X .

Preparation of Monodisperse Porous Ceria Microspheres Substituted with Fe
In the sol-gel process, 1g of the sulfonated microspheres, 2 g of Ce (

Preparation of Monodisperse Porous Ceria Microspheres Substituted with Mn
1g of the sulfonated microspheres and 2 g of Ce(NO 3 ) 3 · 6H 2 O were dispersed in 5 mL water. Also, 59.8 mg of MnCl 2 . 4H 2 O was mixed with the above suspension. The mixture was put in the oven set at 60 o C for 6 h. After calcination at 600 o C for 12 h,  MnxCeO2-X ---10 13 Supplementary Figure S3.DFTIR spectra of Cu x CeO 2-X microspheres before and after H 2 reduction.
Supplementary Figure S4. XPS of Cu 2p region in Cu x CeO 2-X microspheres.
Supplementary Figure S5. SEM of an individual Cu x CeO 2-X microspheres.
Supplementary Figure S6. XRD patterns of M x CeO 2-X microspheres: Fe x CeO 2-X , Ni x CeO 2-X , Co x CeO 2-X and Mn x CeO 2-X microspheres. a Cu x CeO 2-X without Cu doping was CeO 2 microsphere.

Supplementary
b Cu x CeO 2-X without template was Cu x CeO 2-X composite.
Supplementary Figure S10. Cycling CO conversion of Cu x CeO 2-X microspheres.