Synthesis, Characterization and Activity of Palladium Catalysts on the Dual Support of Cerium and Aluminum Oxides
The effects of sequence of impregnation (Pd on cerium oxides -alumina and cerium oxides on Pd-alumina) and calcination temperature (500 ℃ and 850 ℃) on the catalytic oxidation of methane under lean conditions were investigated. The catalysts were prepared by a combination of impregnation, slurry and vortexing methods. The catalysts had 4.7 wt.% Pd and 10.7 wt.% Ce based on inductively coupled plasma optical emission spectrometry (ICP-OES) analysis. The catalysts were characterized by pulse chemisorption, temperature programmed reduction (TPD), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). The activity of the catalysts for methane combustion was measured in a fixed-bed flow reactor by flowing a gas mix (0.98 vol % methane, 4.01 vol % and balance nitrogen) through a catalytic bed. The temperature of the catalytic bed was controlled by a temperature -controlled tube furnace. The % methane in the effluent gas mix was measured by a gas chromatograph fitted with a flame ionization detector and a ‘Carbon Plot’ column. Palladium was present as PdO and PdOx x>2+ and cerium as CeOx (+3 and +4 oxidation states) as per XPS analysis. The activity of the Pd/cerium oxides-alumina500C catalyst was higher than the cerium oxides/Pd-alumina500C catalyst at 250-500 ℃. Similar trends in the activity were seen for the two catalysts calcined at 850 ℃. Higher dispersion and lower particle size, and the presence of small Pd particles on alumina accounted for the higher catalytic activities of the Pd/cerium oxides-alumina500C and 850C catalysts. The lower activities of cerium oxides/Pd-alumina500C and 850C were primarily due to the embedment of Pd onto ceria due to strong PdO-CeOx interactions. This research implies that the sequence of impregnation and calcination temperature could alter catalytic properties and activity for methane combustion through PdO/PdOx -support interactions.
Impregnation Sequence, Catalyst Preparation Methods, Methane Combustion, Characterization, Metal-Support Interactions, Chemistry, Inorganic Chemistry
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