Sulfur Poisoning and Regeneration of Pd Catalyst under Simulated Emission Conditions of Natural Gas Engine

Abstract

Palladium-based catalyst can be employed for natural gas exhaust clean up due to its high activity for light hydrocarbon oxidation. Unfortunately, trace amounts of sulfur in the natural gas feed severely deactivate the catalyst. In this paper, SO 2 adsorption over a monolithic Pd/Al 2 O 3 oxidation catalyst is monitored in a time-resolved manner in the presence of 100 ppm SO 2 under simulated aging conditions of a natural gas engine, which is correlated with the oxidation activity for CO and hydrocarbons such as CH 4 , C 2 H 6 and C 3 H 8. The SO 2 adsorption is saturated in 0.5 h at 400°C and 100,000 h-1. The molar ratio of adsorbed SO 2 and Pd is about 2/1, indicating SO 2 molecules adsorbed, or transferred to the Al 2 O 3 support. The oxidation activity gets stabilized upon saturation of sulfur adsorption, and the hydrocarbon oxidation activity cannot recover even when 100 ppm SO 2 is completely removed from the stream. The light-off temperatures (T 50) of hydrocarbons shift 50-100°C higher after SO 2 poisoning. When the gas stream was switched to the fuel-rich mode, 15% of the adsorbed SO 2 molecules were released from the poisoned catalyst at 400°C. No H 2 S was detected in the outlet stream in the reducing atmosphere. Only traces of SO 2 molecules were detected when the regenerating temperature increased to 550°C. The poisoned Pd catalyst was reactivated to some degree, but suffered from a significant deactivation in 30 min even in the absence of SO 2 , regardless of regenerating temperature. The results revealed the existence of reversible and irreversible sulfur in the reducing atmosphere. A mechanism of sulfur poisoning and regeneration is proposed.

Regeneration of Sulfur-Poisoned Pd-Based Three-Way Catalysts for Stoichiometric Natural Gas Vehicles

“…However, the sulfates produced on the alumina support would migrate to PdO x particles and cause another deactivation. It is just the migration of sulfates between PdO x and the alumina support that leads to catalysts only partial regeneration, as reported. , This migration explains the reappearance of alumina diffraction in the XRD pattern on the Reg.1 sample.…”

“…In other words, sulfur species can make the phase of α-Al 2 O 3 disappear and only rich-burn regeneration ( Reg.1 ) makes it reproduce. According to Hu et al, the maximum S/Pd atom ratio over unsupported PdO x is much smaller than the ratio of accumulated SO 2 and palladium observed over supported ones. They have concluded that SO 2 oxidation is catalyzed by PdO x , forming sulfate species selectively on the surface of PdO x particles, and the excess sulfates are believed to be transported to alumina sites.…”

“…It is just the migration of sulfates between PdO x and the alumina support that leads to catalysts only partial regeneration, as reported. 10,29 This migration explains the reappearance of alumina diffraction in the XRD pattern on the Reg.1 sample.…”

SO2 Capture and Oxidation in a Pd6L8 Metal–Organic Cage

“…These results are in good agreement with those calculated by Wang et al, where a chemisorption process was predicted for a series of electron-rich transition metals (Pd, Pt, Ag, and Au) doped in a MoSe 2 monolayer. One of the few studies addressing the SO 2 adsorption performances was reported by Hu and Williams . In this work, small Pd/PdO particles doped in an Al 2 O 3 matrix were experimentally studied as a natural gas cleaner.…”

“…One of the few studies addressing the SO 2 adsorption performances was reported by Hu and Williams. 36 In this work, small Pd/PdO particles doped in an Al 2 O 3 matrix were experimentally studied as a natural gas cleaner. This palladium-aluminum-based matrix showed a nonreversible early saturation (30 min) in the presence of 100 ppm of SO 2 at 550 °C.…”