Pd and Pt ions as highly active sites for the water–gas shift reaction over combustion synthesized zirconia and zirconia-modified ceria

Noble metal substituted ionic catalysts were synthesized by solution combustion technique. The compounds were characterized by X-ray diffraction, FT-Raman spectroscopy, and X-ray photoelectron spectroscopy. Zirconia supported compounds crystallized in tetragonal phase. The solid solutions of ceria with zirconia crystallized in fluorite structure. The noble metals were substituted in ionic form. The water–gas shift reaction was carried out over the catalysts. Negligible conversions were observed with unsubstituted compounds. The substitution of a noble metal ion was found to enhance the reaction rate. Equilibrium conversion was obtained below 250 °C in the presence of Pt ion substituted compounds. The formation of Bronsted acid–Bronsted base pairs was proposed to explain the activity of zirconia catalysts. The effect of oxide ion vacancies on the reactions over substituted ceria–zirconia solid solutions was established.