Distinct roles of copper in bimetallic copper-rhodium three-way catalysts deposited on redox supports

Copper (4.7%)-rhodium (0-2000 ppm) catalysts deposited on three supports with different oxygen storage capacity (OSC) were tested under three-way catalytic cycling conditions using a low frequency and large composition fluctuations. The reducibility by hydrogen was also studied for all the catalysts in order to assess their OSC. Alumina (Al), ceria-alumina (CeAl) and ceria-zirconia (CeZr) were selected as supports. Both copper and rhodium metals favour the reduction of CeAl and CeZr at low temperature. The catalytic activity of rhodium in CO, NO and C3H6 conversion in presence of oxygen is less influenced by the oxygen mobility of the support. However the OSC of the supports allow to attenuate or even suppress the effects of the composition fluctuations and thus improves the conversion at high temperatures. For monometallic copper catalysts, copper participates in the regulation of the oxidant/reducer ratio and is determinant if the support OSC is insufficient. Moreover, the interaction between copper and the mobile oxygen of the support greatly favours the CO oxidation at low temperature, whereas it has less influence on C3H6 oxidation and disfavours the NO reduction at low temperature. No synergetic effect was observed for the bimetallic CuRh catalysts. In this case, the activity is ruled by the metal or the association metal-support, which is the most active in each temperature range. The association “copper-support exhibiting mobile oxygen” is the most active for CO conversion. NO reduction depends mainly on the rhodium content, especially at low temperature, and C3H6 conversion is a little improved by rhodium addition.