Close-coupled or manifold catalysts have been extensively employed to reduce emissions during cold start by achieving quick catalyst light-off. These catalysts must have good thermal durability, high intrinsic light-off activity and high HC/CO/NOx conversions at high temperature and flow conditions. A number of studies have been dedicated to engine control, manifold design and converter optimization to reduce cold start emissions. The current paper focuses on the effect of catalyst design parameters and their performance response to different engine operating conditions. Key design parameters such as catalyst formulation (CeO 2 vs. non CeO 2 ), precious metal loading and composition (Pd vs. Pd/Rh), washcoat loading, catalyst thermal mass, substrate properties and key application (in use) parameters such as catalyst aging, exhaust A/F ratio, A/F ratio modulation, exhaust temperature, temperature rise rate and exhaust flow rate were studied on engine dynamometers in a systematic manner. Optimized Pd light-off catalysts on 400cpsi/6.5, 600cpsi/3 and 900cpsi/2mil cordierite substrates were further examined at the manifold location for FTP-75 emission performance as a function of cold start A/F ratio to achieve the best emission results on a 1997 Nissan Altima.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

X-ray Absorption Near Edge Spectroscopy (XANES) shows that Pt in Pt nitrate solutions has +4 oxidation state. Extended X-ray absorption fine structure (EXAFS) reveals each Pt is coordinated to an average of 5.4(+/-0.5) oxygen atoms with a Pt-O bond distance of 1.99(5) Angstrom. Each Pt center has an average of 2.9 neighboring Pt atoms with a Pt...Pt non-bonding distance of 3.08(3) Angstrom. A Pt[mu -O(H)](2)Pt ring with two Pt atoms linked by two O or OH ligands is;proposed to be the primary structure moiety and building blocks fur more complex oligomeric structures.Pt(IV) nitrate solution is prone to hydrolysis upon dilution forming an amorphous reddish-brown precipitate PtO2. xH(2)O. Pt nitrate has more complete adsorption on alumina than H2PtCl6 with no significant change of Pt coordination and oxidation state observed upon adsorption. Upon calcination to 500 degreesC, Pt complexes undergo structural changes but remain as Pt(IV). H-2 TPR of Pt nitrate on alumina is consistent with Pt(IV) to Pt metal reduction.The rapid and strong adsorption of Pt nitrate results in Pt depositing only at the outer surface of catalyst washcoats, in sharp contrast to uniform distribution from H2PtCl6. Pt/Rh three-way catalysts made from Pt nitrate/Rh nitrate have equivalent light-off but better hydrocarbon, CO and NOx conversions than those made from H2PtCl6/RhCl3 solutions. (C) 2001 Elsevier Science B.V. All rights reserved.