Effects of extrinsic defects originating from the interfacial reaction of CeO2-x-nickel silicate on catalytic performance in methane dry reforming

Effect of Ce doping on the catalytic performance of xNiCeOy@SiO2 catalysts for dry reforming of methane

“…The peak at 615 cm −1 is derived from the vibration of oxygen vacancies caused by the transformation between Ce 4+ and Ce 3+ and is also called an intrinsic defect mode (D i mode), 31 and the peak at 547 cm −1 is attributed to the vibration of oxygen vacancies caused by the substitution of Ce 4+ by Ni 2+ or Si δ+ (δ = 4, 3, or 2) in the ceria lattice, which is called extrinsic defect mode (D e mode) 32 . The appearance of D e mode indicates that Ni 2+ and/or Si δ+ (δ = 4,3 or 2) are incorporated into the cerium oxide lattice and the formation of Ce–Si–O or Ce–Ni–O bonds, which is consistent with the XPS results 12 . As can be seen from Figure 11, 10NiCeO y @SiO 2 catalyst with the best stability shows the highest proportion of extrinsic defects.…”

“…XPS measurement was carried out to study the changes in the electronic states of various elements (Figure 10). As can be seen from the O 1s XPS spectra (Figure 10a), for Ni@SiO 2 , the peak appears at 533 eV, which is attributed to the O species in the Si–O–Si group, while for the most stable catalyst 10NiCeO y @SiO 2 , a new peak at 530.5 eV may be attributed to the O species in the Ce–O–Si group, 12 which is consistent with the attribution of peak C in the H 2 ‐TPR results. In the Ce 3d XPS spectra (Figure 10b), “u” and “v” correspond to spin–orbit coupling of 3d 5/2 and 3d 3/2 , respectively.…”

“…Raman spectroscopy was further applied to identify the various states of Ce species in fresh x NiCeO y @SiO 2 catalysts. As shown in Figure 11, there is a sharp peak at 450 cm −1 , which is attributed to the symmetrical stretching mode of the eight oxygen atoms coordinated with cerium atoms in the cubic fluorite lattice of cerium oxide (F 2g mode) 30 ; the broad shoulder peak at 600 cm −1 is associated with the longitudinal optical mode, which is widely reported to be attributed to the symmetry reduction of the ceria cubic lattice due to the existence of oxygen vacancies 12 . This is also consistent with the appearance of large number of Ce 3+ species in the XPS results.…”

“…The proportion of surface Ce 3+ species is shown in Table 6. It is well‐known that the Ce 3+ concentration is directly proportional to the amount of oxygen vacancies or defect sites in the catalyst, which can transfer adsorbed O * species to Ni active components to oxidize CH x * species so as to further enhance the rate of carbon gasification reaction to improve the stability of the catalysts 12,28,29 . Therefore, the most stable catalyst 10NiCeO y @SiO 2 with the highest Ce 3+ proportion of 45.2% has more oxygen vacancies on the catalyst surface to help eliminate the carbon deposits, thereby improving the stability of the catalyst.…”

“…To improve the stability and the reaction activity of the catalyst, many solutions have been proposed, including addition of second metal as a promoter, 10,11 introduction of defects on the surface of the metal catalyst, 12 and encapsulation of metal nanoparticles into porous supports with core–shell structure. Zhang et al 13 prepared a series of Ni@SiO 2 catalysts calcined at different temperatures using the microemulsion method, and through precisely adjusting the size of the nickel particles and optimizing the interaction strength between the active species and the support, the DRM performance and stability of the catalysts were significantly improved.…”