Activity and thermal stability of Rh-based catalytic system for an advanced modern TWC

Kinetic model for modern double-layered Pd/Rh TWC as a function of metal loadings and mileage

“…2. The decreasing rate of the TWC activity slows with the increasing catalyst mileage; the TWC activity decreases rapidly during the early stage of the catalyst mileage from 4 k to 20 k, while decreasing rather gradually in the higher catalyst mileage from 50 k to 100 k. Consequently, the LOTs of CO, C 3 H 6 , H 2 and NO conversions over the Rh10 catalyst shift to a higher temperature region from 216, 261, 235 and 222°C (at 4 k) to 243, 290, 263 and 244°C (at 20 k), respectively, while a gradual increase of the LOTs of CO, C 3 H 6 , H 2 and NO conversions is observed with the increase of the catalyst mileage from 50 k to 100 k. The decline of the TWC activity over the Rh-based TWC upon the thermal aging has been reported to be mainly attributable to the loss of the active surface area of Rh [12,13].…”

“…Details of the reactor system are described elsewhere [16,17]. After pre-calcination of the catalyst sample in a stoichiometric feed condition (S = 1) at 450°C for 2 h, the TWC performance was examined with the ''full feed'' gas stream containing 1% CO, 500 ppm C 3 H 6 , 0.3% H 2 , 500 ppm NO, 1% O 2 , 10% CO 2 and 10% H 2 O in Ar balance (S = 1.17) [3,12,15]. The concentrations of CO, C 3 H 6 , H 2 and O 2 were monitored by GC equipped with a TCD and an FID (6890 N, Agilent), while those of NO and products including NH 3 and N 2 O were by FT-IR (Nicolet 6700, Thermo Electrons Co.).…”

Inhibition of Rh sintering and improved reducibility of Rh on ZrO2 nanocomposite with an Al2O3 diffusion barrier

“…Those studies suggested that the lower temperature reduction peak could be assigned to the reduction of three-dimensional Rh 2 O 3 particles, which had little interaction with the support, and the higher temperature peak was identified as due to the reduction of twodimensional Rh 2 O 3 that interacted with the support oxides. Heo et al [6] investigated the interaction of Rh and ZrO 2 with different crystallite phases. In their report, Rh had a stronger interaction with tetragonal ZrO 2 than with the monoclinic form.…”

“…These results indicate that the Al 2 O 3 diffusion barrier suppresses the sintering of ZrO 2 particles after not only the final calcination at 900 • C but also higher temperature durability test (1000 • C) and the barrier in A80ZL most effectively inhibit the crystallite growth of ZrO 2 . Since pure ZrO 2 prepared by the conventional precipitation method generally forms a monoclinic crystal phase after thermal aging [6], rare earth elements have been added to improve the thermal stability of the crystallite itself [26]. In the case of a solid solution formed with these additives, the ZrO 2 crystal phase changes from monoclinic to cubic or tetragonal, hence improving its thermal stability.…”

“…The principal factors contributing to reduced Rh dispersion are Rh sintering and the solid phase reaction between Rh and the inorganic oxide support after thermal aging [5]. Studies have found that Rh sintering is promoted by the reduction of the specific surface area (SSA) of the oxide support due to poor thermal stability [5][6][7][8][9]. Most of these studies investigated Rh/Al 2 O 3 catalysts after high-temperature aging under oxidizing conditions [10][11][12].…”