Kucherov, M. Shelef

Ford Research Laboratory, Ford Motor Company, MD3179/SRL, POBox 2053, Dearborn, MI 48121 USA 

Permanent Addresses Karpov Institute of Physical Chemistry, Moscow, Russia Zelinsky Institute of Organic Chemistry, Moscow, Russia 

Rhodium supported on y-ALOs is an important component of 3-way automotive catalysts and has been studied by a wide variety of methods [1-5] including ESR. In the last 15 years Rh-species introduced into zeolites of different types (Y, X, L, A, SAPO) have also been examined by several techniques [6-9]. However, most of these methods were applied after the specimens were removed from actual reaction conditions and transferred into the respective characterization instruments and the state or behavior of the catalyst in-situ was arrived at indirectly by inference. Also the deactivation processes or the effect of modifiers is seldom, if ever, determined by direct in-situ observations. We have previously devised a method for high-temperature measurement of ESR-active ions under flow conditions and applied it to characterize specimens containing Cu [10] or Cr [11]. We have extended this method now to specimens containing Rh. Here, we summarize the results of a study of the interaction of Rh/y-ALOB and Rh/ZSM-5 with different gases and gas mixtures (NO, NO2, CO, propene, O2, H2O) at 120-573 °K. The amount of Rh present in the samples is evaluated quantitatively. The effect of copper and lanthanide addition on the stabilization of by the zeolitic matrix was also investigated. 

Two Rh/ZSM-5 samples, with 1.0 and 0.25 wt% Rh, were prepared by incipient wetness impregnation of (NH4)ZSM-5 (Si/Al = 25) by water solutions of [Rh(NH3)6](N03)3 (0.8 cm3 per 1 g of dried zeolite). A different 0.25%Rh/ZSM-5 sample was also prepared by the same method starting from HZSM-5 with a Si/Al ratio of 40. A Rh/y-ALOa catalyst with 2.2 wt% Rh was prepared by impregnation of y-Al203 precalcined at 600°C and having a surface area of 130 m /g by a solution of the same complex. The samples were pressed without binder, crushed into 0.1-0.2 mm particles and placed in a quartz cell for ESR measurements. Dried samples were precalcined at 500-800 C in an [He+10%O2] stream for 2-5 h. 

For the study of the effect of a second cation on Rh distribution in the ZSM-5 matrix, copper (1.5 wt%) and gadolinium (up to 4 wt%) were introduced into the catalyst by incipient wetness impregnation of precalcined l%Rh/ZSM-5 using a solution of Cu(N03)2 or Gd(N03)3. 

---