Penta‐coordinated Al³⁺ Stabilized Defect‐Rich Ceria on Al₂O₃ Supported Palladium Catalysts for Lean Methane Oxidation

Abstract

In heterogeneous catalysis, the strong interaction between metal and support can significantly modulate the electronic properties of the metals and play a crucial role in metal particle dispersion and morphology. Herein, a facile strategy was utilized to fabricate highly dispersive palladium catalysts supported on defective Al2O3−CeO2 for lean methane oxidation. Ceria was immobilized on the coordinatively unsaturated Al3+penta sites of γ‐alumina activated by pre‐reduction to fabricate hybrid‐oxide support (abbreviated as RAl2O3−CeO2), and then Pd precursor was uniformly deposited on the defective surface. Such a RAl2O3−CeO2 interface can effectively upgrade the dispersion of deposited palladium species and improve the concentration of reactive oxygen species owing to strong electronic interactions, invoking a superior catalytic activity for lean methane oxidation. After loading 1.0 wt% palladium, Pd/RAl2O3−CeO2 exhibited a 90 % methane conversion at 328 °C under the space velocity of 60,000 mL g−1 h−1, far lower than that of bare 1.0 wt% Pd/RAl2O3 (400 °C). In addition, Pd/RAl2O3−CeO2 catalyst showed an excellent hydrothermal stability under the harsh conditions (600 °C, water vapor)for 120 h without obvious deactivation. The reaction pathway of total methane combustion was elucidated by in situ DRIFTS. The crucial intermediate compositions (carbon oxygenates and carbonate)on Pd/RAl2O3−CeO2 surface are more readily oxidized into CO2 and H2O. This work provides an effective interface‐promoted strategy to develop efficient and durable palladium catalysts for many challenging reactions.

Single‐Step Oxidation of Low‐Concentration Methane to Methanol in the Gaseous Phase Using Ceria‐Based Iridium‐Copper Catalysts

“…The O 1s XPS spectra was further analyzed in Figure 7b, in which three obvious characteristic peaks were observed. Regarding previous research, [5] the peak located at 529.3 eV can be identified as the lattice oxygen (O α , e.g, O 2− ), the binding energy situated at 531.1 eV can be attributed to the adsorbed oxygen components (O β , e.g, O 2 2− , O 2 − or O − ), and the binding energy at 533–534 eV can be caused by the weak‐bonded oxygen species (O γ ) [2b] . As compiled in Table 2, the O β /(O α +O β ) ratio is a measurement to appraise the ratio of reactive oxygen components [40] .…”

“…41.28 m 2 /g), likely due to the structure reengineering, which is conducive to the oxidation of methane. All catalysts exhibit a microporous structure based on the BJH model [5] . Generally, the intrinsic activity of heterogeneous catalysis rests with the nanostructure, particularly the specific surface area and porous structure of the catalysts, which guarantee sufficient exposure of active site.…”

“…Accordingly, one‐step conversion of methane to methanol is considered to be a promising approach to achieve the lucrative utilization of methane because of low consumption and high conversion efficiency. Unfortunately, on the one hand, the breaking energy of first C−H chemical bond in methane molecule need higher activation energies (104 kcal/mol) because it's symmetrical regular tetrahedral structure with sp 3 orbital hybridization [5] . On the other hand, how to prevent the excessive oxidation of methyl intermediates and methanol is another difficult problem to efficiently synthesize methanol from methane [6] .…”

Direct Catalytic Oxidation of Low-Concentration Methane to Methanol in One Step on Ni-Promoted BiOCl Catalysts

“…The gradual disappearance of the hydroxyl peak indicates that the hydroxyl group plays a role in oxidizing methane and adsorbing species during the whole reaction. In addition, the strong band at around 1589, 2357, and 3070 cm –1 are assigned to bidentate formate (υ as (OCO)), − adsorption of carbon dioxide, , and vibration of the methyl (−CH 3 ) group, respectively. The peak of bidentate formate first appeared and then disappeared with the increase of temperature.…”

Atmospheric- and Low-Level Methane Abatement via an Earth-Abundant Catalyst

“…While the high end of observed activation temperatures and durations are within the range of previous studies (at or above 450 °C 15 , 16 , 18 , 20 and with durations at or above 1 h 18 , 20 ), use of ambient levels of oxygen has not been demonstrated previously for copper zeolites. 17 Some novel “lean methane” catalysts based on cobalt, 30 nickel mixtures, 31 , 32 or platinum group metal (PGM) 33 − 38 structures have been shown to work at or below 10% oxygen, 30 , 33 , 34 , 36 , 38 but these require both high temperatures, expensive or complex synthetic processes, applied voltage, and/or a combination of activation gases far from ambient.…”