PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion: Further insights by spectroscopic characterization

The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT, Pd carbonyl IR band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2. The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd2+/Zn2+ carbonyls appear due to ion exchange into SAPO-34 framework.