Lambda dynamics sampling

Catalysts were characterized by means of X-ray diffraction (Phillips diffractometer PW3710, with CuKa as radiation source), UV-Vis-DR spectroscopy (Perkin-Elmer Lambda 19) and chemical analysis. Measurements of surface acidity were carried out by recording transmission FT-IR spectra of samples pressed into self-supported disks, after adsorption of pyridine at room temperature, followed by stepwise desorption under dynamic vacuum at increasing temperature (Perkin-Elmer mod 1700 instrument). The procedure for chemical analysis is described in detail in ref. (13). 

Figure 67. Influence of the washcoat formulation on the conversion of CO, HC and NO , reached over various engine aged three-way catalysts as a function of the exhaust gas lambda value (monolith catalyst with 62cells cm three-way formulation with Pt 1.16gC, Rh 0.23gl" engine bench test A/F scan at a space velocity of 60000 Nl 1 h exhaust gas temperature 723 K dynamic frequency 1 Hz amplitude 1 A/F engine bench high temperature aging cycle for lOOh). Sample A baseline formulation, samples B-D increasing amounts of stabilizers.

A KrF excimer laser (Lambda Physik LEXTRA 200, 248 nm, 30 ns fwhm) or a XeF excimer laser (ibid., 351 nm, 30 ns fwhm) was used as an excitation pulse for inducing expansion/contraction dynamics. The fluence was adjusted with partially transmitting laser mirrors, and was monitored shot-by-shot by a photodiode whose output was corrected with a joulemeter (Gentec, ED-200) with an oscilloscope (Hewlett-Packard, HP54522A). A c tral area of the excimer laser pattern with a homogeneous intensity distribution was chosen with an appropriate aperture and then focused onto the sample surface by using a quartz lens (f = 200 mm). Fresh surface of the sample film was used in every measurement. Etch depth was measured by a surface depth profiler (Sloan, Dektak 3). All experiments were done in air at room temperature. 

UV-VIS extinction spectra were measitred with a Lambda 35 spectrophotometer (Perkin Elmer, USA). Particle size distribution, based on hydrodynamic diameter, was evaluated by Nano S (Malvern, UK), a dynamic light scattering analyzer (DLS). Urueacted metal cations, extracted from the sample by a semi-permeable osmotic membrane (Visking tube), were detected by ICP-AES qirantitative analysis (Liberty 200, Varian, Austraha) in order to determine the reaction yield. Suspensiorts were dropped and dried on a copper grid, then observed by high resolution transmission electron microscopy (HRTEM) (Tecnai F20) and by the STEM mode with microanalysis EDX. 

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