Efficient In-Situ Regeneration Method of the Catalytic Activity of Aged TWC

Abstract

The expansion of durability of deactivated ''three-way'' catalysts (TWCs) used in gasoline-driven cars by applying efficient, economically viable and environmentally friendly methods for the in situ regeneration of their performance to acceptable levels was investigated. New experimental results on the use of a weak oxalic acid washing solution as a means of an efficient regeneration method of a severely aged (83,000 km mileage) commercial TWC are presented. Oxalic acid is shown to be the most efficient extracting agent of phosphorus, a severe poison of TWCs, among acetic acid, citric acid, NTA and EDTA investigated. X-ray diffraction studies provided strong evidence that washing of the aged TWC results in the removal of CePO 4 , AlPO 4 and (Mg,Ca,Zn) 3 (PO 4 ) 2 type phosphates leading to a significant increase of BET area and pore volume, as well as of CO and NO conversions (catalytic activity tests). The latter is strongly related with the increase in the number of active catalytic sites, as illustrated by in situ DRIFTS studies, after opening closed pores and uncovering additional catalyst surface.

The nature of oxygen states on the surfaces of CeO2 and La-doped CeO2

“…CeO 2 is a valuable material for a range of catalytic applications, such as threeway-catalysts (TWC) for automotive emissions, [1] water-gas-shift reactions, [2][3][4] and soot oxidation. [5,6] The effectiveness of CeO 2 as a catalyst is associated with its high oxygen storage capacity (OSC), i.e.…”

Effects of diffusion and particle size in a kinetic model of catalyzed reactions

“…As noted above, the broader use of these terms follows a trend of some recent works [2,21,22,23,29,32].…”

“…The simplest models are based on rate equations (mean-field models) that do not account for the spatial heterogeneity of the media where reactions take place [20,21,22,23], or that use some type of approximation to represent that heterogeneity [24,25]. Other models represent it through distributions of catalytic sites in lattices.…”

Regeneration of Aged Commercial Three-Way Catalytic Converters

“…Expanding the durability of deactivated automobile TWCs by applying efficient as well as environmentally friendly techniques for the regeneration of their catalytic performance has attracted some scientific attention in the past few years, although TWC technology has been emerged in the mid-1970s. Scientific efforts spent so far in terms of regeneration and reutilization of severely aged TWCs might be classified in the following two main categories: (a) methods that apply thermo-chemical treatments using oxygen, hydrogen, and/ or chlorine-containing gas mixtures [3][4][5], or other chlorine-containing reagents [6][7][8], and (b) methods that involve washing of the catalyst by the use of liquid solvents, such as organic acids [9][10][11][12][13][14][15] or other chelating agents [16,17].…”

“…acetic, citric and oxalic acids) and chelating agents (e.g. EDTA, NTA), which dissolve the contaminant compounds and sequester the contaminant metal ions [9][10][11][12][13][14][15][16][17]. Thus, regeneration of deactivated TWCs is the result of the removal of contaminants, inhibitors and fouling agents accumulated in the aged TWC.…”