Preparation of Pd/SiO2 Catalysts by a Simple Dry Ball-Milling Method for Lean Methane Oxidation and Probe of the State of Active Pd Species

Abstract

A series of Pd/SiO2 catalysts were prepared with different Pd precursors by a dry ball-milling method and used in the catalytic oxidation of lean methane at low temperature. The effect of Pd precursors on the catalytic performance was investigated and the state of the most active Pd species was probed. The results indicate that dry ball-milling is a simple but rather effective method to prepare the Pd/SiO2 catalysts for lean methane oxidation, and palladium acetylacetonate is an ideal precursor to obtain a highly active Pd/SiO2-Acac catalyst with well- and stably dispersed Pd species, owing to the tight contact between acetylacetonate and Si–OH on the SiO2 support. Besides the size and dispersion of Pd particles, the oxidation state of Pd species also plays a crucial role in determining the catalytic activity of Pd/SiO2 in lean methane oxidation at low temperature. A non-monotonic dependence of the catalytic activity on the Pd oxidation state is observed. The activity of various Pd species follows the order of PdOx >> Pd > PdO; the PdOx/SiO2-Acac catalysts (in particular for PdO0.82/SiO2-Acac when x = 0.82) exhibit much higher activity in lean methane oxidation at low temperature than Pd/SiO2-Acac and PdO/SiO2-Acac. The catalytic activity of PdOx/SiO2 may degrade during the methane oxidation due to the gradual transformation of PdOx to PdO in the oxygen-rich ambiance; however, such degradation is reversible and the activity of a degraded Pd/SiO2 catalyst can be recovered through a redox treatment to regain the PdOx species. This work helps to foster a better understanding of the relationship between the structure and performance of supported Pd catalysts by clarifying the state of active Pd species, which should be beneficial to the design of an active catalyst in lean methane oxidation at low temperature.

One-pot mechanochemical hydrogenation and acetylation of 4-nitrophenol to 4-aminophenol and paracetamol

“…Indeed, the possibility of activity loss of Pd based catalysts from sintering is well described in the literature. 36,37…”

“…Indeed, the possibility of activity loss of Pd based catalysts from sintering is well described in the literature. 36,37 To address these issues, the recycle procedure was modified to avoid oxygen exposure as well as use more mild milling conditions. To eliminate the possibility of oxidation, the outlet gas port of the ball mill vessel was opened, and the additional 4-NP was fed into the port while hydrogen flowed through the vessel.…”

Advancement of modification engineering in lean methane combustion catalysts based on defect chemistry

“…Researchers have also used ball milling to modify catalysts. 178–181 Shu et al mechanically mixed NaCl and metal salts by ball milling and washed with deionised water to remove NaCl-crystal support to obtain porous metal oxides Co 3 O 4 (ref. 182) (Fig.…”

“…Researchers have also used ball milling to modify catalysts. [178][179][180][181] 10A) and NiO (ref. 183) (Fig.…”

Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures

“…For example, Pd/Co 3 O 4 nanosheets, Pd/ γ ‐Al 2 O 3, and Pd/SiO 2 ‐Acac synthesized through hydrothermal/Incipient wetness impregnation, Impregnation‐vortexing, and dry ball‐milling demonstrated T 90 of 248, 275, and 288 °C, respectively, in the dry conditions. [ 52 , 84 , 152 ] While Pd/NAAl 2 O 3 , [ 33 ] Pd/SnO 2 , [ 102 ] and Pd/ α ‐Al 2 O 3 demonstrated T 90 of 350, 420, and 450 °C in the presence of water, respectively.…”