Ni/CeO₂ Nanocatalysts with Optimized CeO₂ Support Morphologies for CH₄ Oxidation

Abstract

Catalytic oxidation of CH4 over nonprecious Ni/CeO2 catalysts has attracted wide attention. Controlling the morphology of a CeO2 support can enhance the CH4 oxidation activity without changing the catalyst composition. Herein, a series of 2 wt % Ni/CeO2 nanocatalysts with different CeO2 support morphologies (nanoparticles (P), rods (R), cubes (C)) and synthetic procedures (precipitation, sol-gel (SG)) were evaluated for their CH4 oxidation performance. The redox properties of CeO2 supports and corresponding Ni loaded catalysts were characterized by H2-temperature-programmed reduction and oxygen storage capacity (OSC) measurements. The relationship among the CeO2 morphologies, surface areas, redox properties, and CH4 oxidation activity for both CeO2 supports and Ni/CeO2 catalysts was established. The findings suggest that CeO2-R has a greater amount of surface oxygen vacancies as well as an improved OSC and CH4 oxidation activity compared to CeO2-P and CeO2-C supports. The same CH4 oxidation activity pattern was observed for the Ni containing catalysts (Ni/CeO2-R > Ni/CeO2-P > Ni/CeO2-C). Increasing the CeO2 surface area by using a sol-gel synthesis method (CeO2-SG) improved the amount of surface oxygen vacancies and CH4 oxidation performance of CeO2-SG and Ni/CeO2-SG compared to CeO2-R and Ni/CeO2-R, respectively. Finally, all studied Ni/CeO2 nanocatalysts showed improved hydrothermal stability compared to conventional Pd/Al2O3.

A Novel Molten Salt Mediated Synthesis of Mesoporous Metal Oxides with High Crystallization

“… The higher oxygen defect concentrations are also reflected in the Fourier Transform infrared spectroscopy (FTIR) and Raman spectra. In the Raman spectrum of CeO 2 , the oxygen vacancies on the surface can be compared by the intensity ratio of the D-band and F2g peaks ( I D / I F2g ), and one can see from Figure S4a that the concentration of oxygen vacancies in CeO 2 is higher compared to that of commercial CeO 2 . Due to the higher concentration of oxygen vacancies, a higher concentration of water molecules is adsorbed on its surface, which leads to the appearance of obvious O–H vibrational peaks in the infrared spectra of mCeO 2 (Figure S4b).…”

“…In the Raman spectrum of CeO 2 , the oxygen vacancies on the surface can be compared by the intensity ratio of the D-band and F2g peaks (I D /I F2g ), and one can see from Figure S4a that the concentration of oxygen vacancies in CeO 2 is higher compared to that of commercial CeO 2 . 34 Due to the higher concentration of oxygen vacancies, a higher concentration of water molecules is adsorbed on its surface, which leads to the appearance of obvious O−H vibrational peaks in the infrared spectra of mCeO 2 35 (Figure S4b). The oxygen vacancies mainly come from the insufficient oxidation from an oxygen-deficient environment in the molten salt.…”

Synergistic effects of Fe-substitutional-doping and a surface close-contact Fe2O3/CeO2 heterojunction in Fe/CeO2 for enhanced CH4 photocatalytic conversion

“…49,50 The inuences of the heterojunction on CH 4 conversion include not only modied electron/hole separation efficiency resulting from charge transfer, but also changed CH 4 C-H breaking energy induced by Fe 2 O 3 /CeO 2 interfacial sites. 41 As it is difficult to establish a heterojunction model consistent with the experiments (especially the spatial distribution and relative space position relations of the two phases, which are crucial for the calculation of reaction energy), the inuence of the rst aspect was mainly studied experimentally from the perspective of the band structure (Fig. 7).…”

“…S7, † the H 2 -TPR prole of CeO 2 -900/6 (red line) exhibits only one reduction peak at around 790 °C, which was derived from the reduction of bulk CeO 2 to CeO x . 40,41 Three reduction peaks were detected for Fe 2 O 3 -900/6 (blue line), with reduction peaks at around 450, 580 and 737 °C assigned to the reduction process of Fe 2 O 3 / Fe 3 O 4 , Fe 3 O 4 / FeO and FeO / Fe respectively. However, all these peaks have shied to the much lower temperature side for 1 : 3 Fe 2 O 3 /CeO 2 -900/6 (black line), indicating signicantly improved low temperature reducibility of Fe 2 O 3 and CeO 2 in 1 : 3 Fe 2 O 3 / CeO 2 -900/6 as a result of their strong interactions.…”

Construction of cerium-based oxide catalysts with abundant defects/vacancies and their application to catalytic elimination of air pollutants

“…This CH 4 activation leads to the reduction of surface nickel oxides and the formation of oxygen vacancies in the CeO 2 support, while gas-phase oxygen is activated over the oxygen vacancies. Chen et al 231 synthesized a series of Ni/CeO 2 nanocatalysts with different morphologies of CeO 2 (nanoparticles, rods, cubes). Among the above catalysts, the Ni/CeO 2 nanorod catalyst has the most amount of surface oxygen vacancies and exhibits the highest activity for CH 4 oxidation.…”