Defect-Induced Efficient Partial Oxidation of Methane over Nonstoichiometric Ni/CeO₂ Nanocrystals

Abstract

We report the development of a highly crystalline Ni/CeO 2 catalyst with varying amounts of Ni content using ammonium carbonate complex solution of cerium(IV) at a low temperature. The catalyst was characterized by XRD, XPS, BET-surface area, TEM, and H 2 -TPR analysis. We have observed that the maximum incorporation of Ni in CeO 2 crystal system as the substitution point defect took place up to impregnation of 2.5% Ni, and an almost maximum reduction of unit cell parameter was observed. Further increase in the amount of Ni, the additional Ni may create interstitial point defects with surface defects. The synthesized catalysts showed defect-dependent catalytic activity for low temperature (∼450°C ) methane activation to form synthesis gas. The 7.5 wt % Ni/CeO 2 catalyst showed 98% conversion of methane with 73 and 71% selectivity of CO and H 2 , respectively, at 800°C without any deactivation until 50 h on time on stream. We also believe that with enhancement of Ni loading, the interstitial point defects and the surface defects due to the formation of the Ce−O−Ni−O− layer, with under-coordinated oxygen atom, on the surface may be the possible reason for the high activity of the catalyst with Ni loading between 5 and 7.5 wt %. With further increase of Ni loading, the Ni nanoparticles were formed with the expense of the Ce−O−Ni−O− layer and in-turn decreased the catalytic activity.

Promoting Effect of CeO2and MgO for CO2Reforming of Methane over Ni-ZnO Catalyst

“…Calculated lattice parameter of CeO 2 crystal (a=b=c= 0.54105 nm) was little bit less from the value (0.5412) obtained from JCPDS 81–0792. Lowering of lattice parameter was due to the incorporation of smaller nickel ions into the CeO 2 unit cell and the formation of Ni‐CeO 2 mixed oxide . The OSC of the CeO 2 particles of NiCeZn‐f catalyst enhanced the re‐oxidation of the nickel particles but the absence of such property of NiMgZn‐f catalyst helped to be more stable during catalysis.…”

Synthesis of core-shell structured CdS@CeO 2 and CdS@TiO 2 composites and comparison of their photocatalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde

“…As shown in Fig. 1e, after hydrothermal treatment, CeO 2 displays four peaks at 2 = 28.5 • , 33.1 • , 47.5 • , and 56.3 • , corresponding to the (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes, respectively (JCPDS: 43-1002) [34,35]. CdS@CeO 2 -180 also appears two new peaks at 2 = 33.1 • and 56.3 • compared with pure CdS, indicating the successful loading of CeO 2 shell layer.…”

Pretreatment Effect on Ceria‐Supported Gold Nanocatalysts for CO Oxidation: Importance of the Gold–Ceria Interaction

“…The N 2 adsorption–desorption isotherms, pore size distributions, and cumulative pore volumes of S, S1, and S3 are shown in Figure a–c. The isotherms present type IV hysteresis loops, which reveals that the samples are mesoporous materials as reported previously . The specific surface area and cumulative pore volume decreased clearly after the Au NPs were loaded [S3 (205 m 2 g −1 , 0.286 cm 3 g −1 )<S1 (210 m 2 g −1 , 0.365 cm 3 g −1 )<S (229 m 2 g −1 , 0.400 cm 3 g −1 ); Figure a, c], which confirms that Au NPs were embedded in the pores of CeO 2 .…”

“…This suggests that the Au NPs supported on variousA u/CeO 2 samples were not crystalline.TheN 2 adsorption-desorption isotherms,p ore size distributions,a nd cumulative pore volumes of S, S1, and S3 are shown in Figure 2a-c. Thei sotherms present type IV hysteresis loops,w hich reveals that the samples are mesoporous materials as reported previously. [26,28] Thes pecific surface area and cumulative pore volume decreased clearly after the Au NPs were loaded [S3 (205 m 2 g À1 ,0 .286 cm 3 g À1 ) < S1 (210 m 2 g À1 ,0 .365 cm 3 g À1 ) < S( 229 m 2 g À1 ,0 .400 cm 3 g À1 ); Figure 2a,c], which confirms that Au NPs were embedded in the pores of CeO 2 .T he pore size distributions (Figure 2b)o f Sn are similar, and the pore diameters are approximately 4nm. However, for S, the pore diameters( 4-8 nm) are biggert han that of Sn,w hich further demonstrates that some Au NPs were loaded in the pores of CeO 2 .H ence, the Au depositionm echanism can be deduced as follows:H AuCl 4 was first adsorbed on the surface of CeO 2 after standing overnight, then Au NPs were formed by using NaBH 4 as a reducinga gent, and some of the Au NPs were embedded in the pores of CeO 2 (Figure S4 a, Supporting Information).…”