Complete Oxidation of Methane on NiO Nanoclusters Supported on CeO₂ Nanorods through Synergistic Effect

Abstract

Catalytic complete oxidation of CH4 at relatively low temperatures is significant for removing unburned CH4 from the exhaust of combustion engines fueled with natural gas or liquefied petroleum gas. Here a nanocomposite catalyst (NiO/CeO2) consisting of CeO2 nanorods and supported NiO nanoclusters was prepared by a two-step wet-chemistry method. This nanocomposite catalyst exhibits high catalytic activity for the complete oxidation of CH4 in the temperature range of 350–600 °C. A CH3-like intermediate bound to Ni cations was observed at a relatively low temperature by ambient pressure X-ray photoelectron spectroscopy under catalytic conditions. Parallel kinetic studies of NiO/SiO2, CeO2 and NiO/CeO2 catalysts show that the apparent barrier for complete oxidation of CH4 on NiO/CeO2 (69.4 ± 4 kJ/mol) is much lower than the 95.1 ± 5 kJ/mol of pure CeO2 and 98.4 ± 5 kJ/mol of NiO/SiO2, supported by the turnover frequency of NiO/CeO2 being significantly higher than NiO/SiO2 and CeO2. These differences indicate a synergistic effect between the CeO2 nanorods and the supported NiO nanoclusters. This synergistic effect occurs at the interface of NiO and CeO2, observed in TEM. The lattice oxygen atoms at the interface exhibit high activity based on the lower reduction temperature uncovered in studies of the temperature-programmed reduction of H2.

Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

“…As for NAP-XPS studies, C 1s spectra allowed the identification of a stable intermediate methyl species formed on the surface of Co 3 O 4 /CeO 2 during catalysis, which could be generated through dissociation of C−H of methane on Ce 4+ , Co 3+ or Co 2+ sites, since no oxygen vacancies were formed and detected on the cerium oxide support. Very similar results were obtained by Zhang and co-workers [141], who prepared CeO 2 nanorods with supported NiO nanoclusters of 10-12 nm average size and studied them under the same methane complete oxidation conditions as the work of Dou and colleagues [140]. Tracking the evolution of C 1s NAP-XPS features with increasing temperature under reaction conditions, they deduced the formation of a stable CH 3 -like intermediate bound to the Ni cation at 423−473 K. The generated surface CH 3 could be further activated to form CH 2 or even CH species, which in turn could combine with surface lattice oxygen atoms to form CO 2 and H 2 .…”

Integral structured Co–Mn composite oxides grown on interconnected Ni foam for catalytic toluene oxidation

“…6d shows four peaks at the binding energy of 856.4, 861.5, 873.1 and 880.2 eV attributed to Ni 2p 3/2 , satellite peak of Ni 2p 3/2 , Ni 2p 1/2 and the satellite peak of Ni 2p 1/2 , respectively. 35,36 The Ni a The specic toluene reaction rates over all the catalysts were calculated at 270 C. 2p XPS spectra primarily come from Ni foams. As for Co 2p XPS spectra (Fig.…”

Methane Combustion Over Ni/CexZr1–xO2 Catalysts: Impact of Ceria/Zirconia Ratio

“…Deactivation of Ni/CeO 2 has been previously observed after CH 4 combustion reaction [26a,b] . For example, Zhang et al [26a] . showed that CeO 2 nanorods in Ni/CeO 2 catalysts significantly sintered after reacting at 600 °C, which was attributed to the low thermal stability of the CeO 2 nanorods.…”

“…Another challenge for CH 4 combustion reactions is catalyst deactivation via coke formation or metal sintering due to exposure to high temperatures (∼400‐700 °C) [26] . Deactivation of Ni/CeO 2 has been previously observed after CH 4 combustion reaction [26a,b] . For example, Zhang et al [26a] .…”