Abstract
5 wt% Pd/γ-Al2O3 catalysts were prepared by a modified Vortex Method (5-Pd-VM) and Incipient Wetness Method (5-Pd-IWM), and characterized by various techniques (Inductively coupled plasma atomic emission spectroscopy (ICP-AES), N2-physisorption, pulse CO chemisorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD)) under identical conditions. Both catalysts had similar particle sizes and dispersions; the 5-Pd-VM catalyst had 0.5 wt% more Pd loading (4.6 wt%). The surfaces of both catalysts contained PdO and PdOx with about 7% more PdOx in 5-Pd-VM. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscope (SEM) images indicated presence of PdO/PdOx nanocrystals (8–10 nm) on the surface of the support. Size distribution by STEM showed presence of smaller nanoparticles (2–5 nm) in 5-Pd-VM. This catalyst was more active in the lower temperature range of 275–325 °C and converted 90% methane at 325 °C. The 5-Pd-VM catalyst was also very stable after 72-hour stability test at 350 °C showing 100% methane conversion, and was relatively resistant to steam deactivation. Hydrogen TPR of 5-Pd-VM gave a reduction peak at 325 °C indicating weaker interactions of the oxidized Pd species with the support. It is hypothesized that smaller particle sizes, uniform particle distribution, and weaker PdO/PdOx interactions with the support may contribute to the higher activity in 5-Pd-VM.
Highlights
Catalytic combustion of methane at low temperatures has been a challenging issue both academically and industrially
Pd/Al2 O3 catalysts have been deactivation by water and long-term stability [7,12,22] We previously reported the development of a PdO-PdOx /γ-Al2 O3 catalyst by vortex method [4] and the catalyst showed low-temperature activity for methane combustion
Catalysts were prepared by a modified Vortex Method (VM) [4] and Incipient Wetness Method (IWM) [5,23] assuming a 5.0 wt% Pd loading on γ-Al2 O3 support
Summary
Catalytic combustion of methane at low temperatures has been a challenging issue both academically and industrially. Banerjee et al [4] developed a PdO-PdOx /γ-Al2 O3 catalyst by a novel Vortex Method which showed high activity with methane conversion of 90–94% at 300–320 ◦ C. Liu et al [10] developed a rice husk derived porous silica support for a Pd-CeO2 catalyst for low temperature combustion of methane with 90% conversion at 325 ◦ C. Reported the development of a Pd/Co3 O4 catalyst with 100% methane conversion at 360 ◦ C in a gas feed of 1% CH4 , 18% O2 , and balance N2. Pd/Al2 O3 catalysts have been deactivation by water and long-term stability [7,12,22] We previously reported the development of a PdO-PdOx /γ-Al2 O3 catalyst by vortex method [4] and the catalyst showed low-temperature activity for methane combustion. We conducted long-term stability tests and effect of water and nitrogen in the gas feed with both catalysts to test their performance
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