Effect of A-site substitution in perovskites: Catalytic properties of PrMnO3 and Ba/K/Ce substituted PrMnO3 for CO and PM oxidation

Abstract

ABO3 type perovskite based catalysts with PrMnO3 composition and its A site substituted variants Pr0.8A0.2MnO3+δ/−δ (A=Ba or K or Ce) have been synthesized by sol–gel method. A systematic study has been carried out to understand the change in physicochemical properties, catalytic properties and related mechanistic aspects of the A site substituted ABO3 type perovskite materials with the help of XRD, BET-SA, SEM, XPS and H2-TPR techniques. These studies have inferred the altered oxidation states of B site cation Mn, as well as change in overall redox properties of PrMnO3, as a function of A site substitution. On the other hand, to study the impact on catalytic properties, these catalysts have been evaluated for two different reactions namely, CO and PM oxidation. The substitution/promotion of alkali metal (K) at A site of the PrMnO3 decreases its catalytic activity towards CO oxidation. However, Ba and Ce substitution in PrMnO3 enhanced the CO oxidation activity. The catalytic activity for PM oxidation was prominently enhanced with the substitution of K at the A site of PrMnO3 as well as with that of Ba and Ce substitutions. XRD, BET-SA, XPS and TPR data enabled to correlate the material properties with the catalytic activity, pointing out the role of substitution element with different valence state. The structure–property correlation for these two different reactions therefore, brings out certain findings about the role of substituted cation in PrMnO3 perovskite type catalysts.