Low temperature NH3 regeneration of a sulfur poisoned Pt/Al2O3 monolith catalyst

Sulfur poisoning is a ubiquitous challenge in diesel emission control. This study examines the potential for in situ, reactive regeneration of a SOx (x = 2, 3) poisoned, low loading Pt/Al2O3 (0.1 wt%) washcoated monolith, representative of the catalytic oxidation function of the ammonia slip catalyst (ASC). A combination of light-off, temperature-programmed reaction, and DRIFTS experiments are conducted to characterize and understand NH3 regeneration of the poisoned Pt catalyst. Systematic variation in the temperature ramp rate and reactive feed composition (NH3, O-2, SO2) for fresh and poisoned catalysts reveals significant deactivation from sulfur exposure as well as the viability of NH3 as a regenerant. DRIFTS measurements show the accumulation of surface ammonium sulfates and bisulfates during exposure to NH3 at 200 degrees C. During an ensuing temperature ramp mimicking engine warmup, the presence of NH3 serves to regenerate the S-poisoned catalyst in a unique way. A mechanism is proposed that explains the restoration of the poisoned catalytic activity. Al-2(SO4)(3) formed during SOx exposure is converted to (NH4)(2)(SO4) in the presence of NH3 and decomposes by 350 degrees C during a subsequent temperature ramp, releasing NH3 and SO2. During a cofeed of SO2 and NH3 on the fresh catalyst only ammonium sulfate or bisulfate is detected. The findings suggest that NH3 is a formidable reagent to enable conversion of thermodynamically stable aluminum sulfate to less stable ammonium sulfate, offering a potentially practical method for low temperature in situ regeneration of Pt-containing catalysts in the diesel emission control system.

Automated summary

This study investigates the in situ regeneration of sulfur-poisoned Pt catalysts in diesel emission control. The results show that NH3 can effectively regenerate the poisoned catalysts at elevated temperatures, and propose a possible mechanism for the restoration of catalytic activity.