Comparative Study of the Characteristics and Activities of Pd/γ-Al2O3 Catalysts Prepared by Vortex and Incipient Wetness Methods

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.

Pd4S/SiO2: A Sulfur-Tolerant Palladium Catalyst for Catalytic Complete Oxidation of Methane

“…It has therefore found great applications in modern industry, such as catalytic exhaust converters aimed to reduce methane emission and catalytic gas turbine combustors designed to combust fuel under mild conditions [9,10]. Supported PdO catalysts have shown excellent catalytic property in methane oxidation, and currently are under extensive study [11][12][13][14][15][16][17][18]. However, once sulfur species (e.g., H 2 S or SO 2 ) are present in the reaction atmosphere, the poisoning of PdO catalyst which would lead to inactive PdO-SO x is irreversible and the activity of the catalyst cannot be recovered at relatively low temperature [19][20][21][22][23][24][25].…”

Sustainable Production of High-Value Chemicals from Selective Hydrogenolysis of Lignin Catalyzed by Co–Pd Bimetallic Supported on Nitrogen-Doped Carbon Spheres

“…The negative peaks between 70 and 80 °C are due to the desorption of hydrogen adsorbed on the Pd metal surface during pretreatment or decomposition of palladium hydride (PdHx) formed by Pd chemisorption of H 2 . A broad peak was observed between 400 and 500 °C at 1% Pd@NDCS, which was attributed to PdO species that strongly interact with the carrier . In the catalysts 1%Co@NDCS and 1%Co-1%Pd@NDCS, the peaks between 450 and 500 °C were attributed to the reduction of Co 2+ to Co 0 .…”

“…47 A broad peak was observed between 400 and 500 °C at 1% Pd@NDCS, which was attributed to PdO species that strongly interact with the carrier. 48 In the catalysts 1%Co@ NDCS and 1%Co-1%Pd@NDCS, the peaks between 450 and 500 °C were attributed to the reduction of Co 2+ to Co 0 . 49 Compared to 1%Co@NDCS, the reduction peak of Co 2+ on 1%Co-1%Pd@NDCS shifted toward higher temperatures.…”

Catalytic Oxidation of Methane

“…A PdO-PdO x /γAl 2 O 3 catalyst synthesized by a vortex-assisted incipient wetness method exhibited exceptional low-temperature activities, with 90-94% methane conversion at 300-320 • C. X-ray photoelectron spectroscopy established that the active phase, PdO x , originated from the interaction of PdO with the alumina support during the calcination process [14]. Banerjee et al [15] compared the relative efficiencies of Pd/alumina catalysts prepared by the vortex and incipient wetness methods. The catalyst synthesized by the vortex method produced smaller PdO/PdOx nanoparticles (2-5 nm) and converted 90% methane at 325 • C. Li et al [16] reported nitrogen-modified perovskite type composite catalysts prepared by a hydrothermal method for catalytic oxidation of methane.…”