Noble metal ionic catalysts: correlation of increase in CO oxidation activity with increasing effective charge on Pd ion in Pd ion substituted Ce_1−xM_xO_2−δ(M = Ti, Zr and Hf)

Abstract

Pd ion substituted Ce1-xMxO2-delta (M = Ti, Zr, Hf) have been prepared by a single step solution combustion method. Two atom% Pd ion substitution in the title compounds is confirmed by X-ray diffraction (XRD) and Pd ion charge state and redox properties have been determined by X-ray photoelectron spectroscopy (XPS) and H2/TPR studies. While Pd ion in CeO2 (Ce0.98Pd0.02O2-delta) showed higher catalytic activity for CO oxidation than Pd metal impregnated over CeO2, further increase in the catalytic activity is observed with Pd ion in Ce1-xTi(Hf)xO2 and a decrease in the activity with Pd ion in Ce1-xZrxO2. Effective charge on Pd ion could be varied by its substitution in these solid solutions Ce1-xMxO2 (M = Ti, Zr & Hf) and also in TiO2 compared to Pd ion in PdO. Effective positive charge on Pd ion is determined from the core level binding energy shift of Pd(3d5/2) peak with respect to Pd metal. Rate of CO oxidation increased and activation energy decreased with increase in effective charge on the Pd ion in the Pd ion substituted fluorites.

Noble metal ion substituted CeO2 catalysts: Electronic interaction between noble metal ions and CeO2 lattice

“…It has been found that activation energy decreases with increase in the effective charge on Pd ion in these oxides [74]. There are also points to note that in general, CO oxidation rates with metal ionic catalysts are higher by 20-30 times compared with the same amount of metal impregnated catalysts.…”

“…Noble as well as transition metal ion substituted CeO 2 catalysts such as Ce 0.67 Cr 0.33 O 2+ı , Ce 1−x Ru x O 2−ı , Ce 1−x Fe x O 2−ı and Ce 1−x Pt x O 2−ı have been synthesized by hydrothermal and sonochemical methods, respectively [60][61][62][63]. Table 1 compiles metal ion substituted CeO 2 materials prepared by solution combustion, hydrothermal and sonochemical methods [33,[50][51][52][53][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74].…”

Metal–support interaction in Pd/CeO2 model catalysts for CO oxidation: from pulsed laser-ablated nanoparticles to highly active state of the catalyst

“…The remarkably high performance of Pd/CeO 2 catalysts in oxidation reactions is caused by the strong interaction between palladium and cerium oxide 8,21 . The metal-support interaction in Pd/CeO 2 catalysts has been studied in many works 4,9,23,[28][29][30][31][32][33][34][35][36][37][38][39] . The metal-support interaction in Pd/CeO 2 catalysts has been studied in many works 4,9,23,[28][29][30][31][32][33][34][35][36][37][38][39] .…”

Support‐dependent activity of noble metal substituted oxide catalysts for the water gas shift reaction

“…Dissociative adsorption of H 2 O and CO 2 resulted in the release of H 2 and CO while the surface reactions between the adsorbed species resulted in release of CO 2 and H 2 O. Substitution of Zr and Ti is beneficial as the bulk substitution of these elements results in an enhanced oxygen storage capacity 30,31 and, hence, enhanced redox couples are expected.…”