Smart Pd TWC technology to meet stringent standards

Heterogeneous Catalyst Deactivation and Regeneration: A Review

“…For example, the loss of Rh due to solid-state reaction with alumina in the automotive three-way catalyst can be prevented by supporting Rh on ZrO2 in a separate layer from Pt and/or Pd on alumina [215][216][217][218][219][220][221][222] In Fischer-Tropsch synthesis, the oxidation of the active cobalt phase in supported cobalt catalysts to inactive oxides, aluminates, and silicates can be minimized by employing a two-or three-stage process in which product steam is moderated in the first stage by limiting conversion and in subsequent states by interstage removal of water [223] It can also be moderated by addition of noble metal promoters that facilitate and maintain high reducibility of the cobalt and by coating the alumina or silica support with materials such as ZrO2 that are less likely to react with cobalt to form inactive phases.…”

“…The development of thermally stable automotive catalysts has received considerable attention, thus providing a wealth of scientific and technological information on catalyst design (e.g., Refs. [8,[215][216][217][218][219][220][221][222]). The basic design principles are relatively simple: (1) utilize thermally and hydrothermally stable supports, e.g., high-temperature δ-or θ-aluminas or alkaline-earth or rare-earth oxides that form ultrastable spinels with γ-alumina; (2) use PdO rather than Pt or Pt-Rh for high temperature converters, since PdO is considerably more thermally stable in an oxidizing atmosphere because of its strong interaction with oxide supports; and (3) use multilayer strategies and/or diffusion barriers to prevent thermally induced solid-state reactions (e.g., formation of Rh aluminate) and to moderate the rate of highly exothermic CO and hydrocarbon oxidations.…”

Advances in Catalyst Deactivation

“…The most serious problems of oxidation of metal catalysts, overreduction of oxide catalysts, and reaction of the active catalytic phase with carrier or promoter, can be minimized or prevented by careful catalyst and process design (as enumerated in Table 18 and illustrated in Table 19). For example, the loss of Rh due to solid-state reaction with alumina in the automotive three-way catalyst can be prevented by supporting Rh on ZrO2 in a separate layer from Pt and/or Pd on alumina [215][216][217][218][219][220][221][222] In Fischer-Tropsch synthesis, the oxidation of the active cobalt phase in supported cobalt catalysts to inactive oxides, aluminates, and silicates can be minimized by employing a two-or three-stage process in which product steam is moderated in the first stage by limiting conversion and in subsequent states by interstage removal of water [223] It can also be moderated by addition of noble metal promoters that facilitate and maintain high reducibility of the cobalt and by coating the alumina or silica support with materials such as ZrO2 that are less likely to react with cobalt to form inactive phases.…”

NO Heterogeneous Catalysis Viewed from the Angle of Nanoparticles

“…Considering the light -off issue fi rst, research on Pd as an alternative to Pt/Rh for NOx control showed that excellent NOx reduction could be achieved with Pd formulations when suitably promoted (as noted above) and at loadings higher than those for Pt/Rh [58,59] . Simultaneously, segregating some of the Pd from ceria was recognized to yield a better low -temperature performance (including light -off) [60] . All major catalyst suppliers then used noble metals in different layers or on different support particles within a single washcoat layer.…”