TPR investigations on the reducibility of Cu supported on Al2O3, zeolite Y and SAPO-5

Reducibility of Cu supported on Al2O3, zeolite Y and silicoaluminophosphate SAPO-5 has been investigated in dependence on the Cu content using a method combining conventional temperature programmed reduction (TPR) by hydrogen with reoxidation in N2O followed by a second the so-called surface-TPR (s-TPR). The method enables discrimination and a quantitative estimation of the Cu oxidation states +2, +1 and 0. The quantitative results show that the initial oxidation state of Cu after calcination in air at 400 °C, independent on the nature of the support, is predominantly +2. Cu2+ supported on Al2O3 is quantitatively reduced by hydrogen to metallic Cu0. Comparing the TPR of the samples calcined in air and that of samples additionally pre-treated in argon reveals that in zeolite Y and SAPO-5 Cu2+ cations are stabilized as weakly and strongly forms. In both systems, strongly stabilized Cu2+ ions are not auto-reduced by pre-treatment in argon at 650 °C, but are reduced in hydrogen to form Cu+. The weakly stabilized Cu2+ ions, in contrast, may be auto-reduced by pre-treatment in argon at 650 °C forming Cu+ but are reduced in hydrogen to metallic Cu0.