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

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Summary

Introduction

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

Catalyst Preparation
Pulse CO Chemisorption
Size distribution of metal
Temperature Programmed Reduction
O3 catalyst and the peak temperature was more reactive on the Alto
X-Ray Diffraction
Activity Studies
Activities
Oactivities
20 Conversion min at 275–325
Long-Term Stability Test of the Catalysts
Effect of Steam
Active Phases and Tentative Mechanism
Catalyst Synthesis
ICP-AES
Chemisorption and Physisorption
Activity Measurements
Stability Test of the Catalysts
Conclusions

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