High rates of catalytic hydrogen combustion with air over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ Ti 0.97 Pd 0.03 O 2 - δ coated cordierite monolith

Abstract

$$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta }$$ was coated on $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ -coated honeycomb structured cordierite monolith (AHCM) by solution combustion method using dip-dry-heat process. This is a modified conventional method to coat the catalysts on honeycomb structured cordierite monolith (HCM). Formation of $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ on AHCM was confirmed by XRD. The XPS spectra of Pd(3d) core level confirmed Pd ion in $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ is in the form of +2 state. The surface morphology of coated catalyst was unchanged by long time exposure to hydrogen combustion reaction; i.e., $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination reaction which indicated the stability of coating on monolith. $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ showed high rates of $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination compared to 2 atom% Pd(metal)/ $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ , $$\hbox {Ce}_{0.98}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta } $$ , $$\hbox {Ce}_{0.98}\hbox {Pt}_{0.02}\hbox {O}_{2-\updelta } $$ , $$\hbox {Ce}_{0.73}\hbox {Zr}_{0.25}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta }$$ , $$\hbox {Ti}_{0.99}\hbox {Pd}_{0.01}\hbox {O}_{2-\updelta } $$ and $$\hbox {Ti}_{0.98}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta } $$ . The activation energy of $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ is 7.8 kcal/mol. The rates of reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ at 60 $$^{\circ }\hbox {C}$$ are in the range between 10 and 20 $$\upmu \hbox {mol/g/s}$$ . The rate of reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ increased with increase in the concentration of $$\hbox {H}_{2}$$ . For 50 mL of $$\hbox {H}_{2}$$ , it showed rates of the reaction around 36.45 $$\upmu \hbox {mol/g/s}$$ at room temperature and 230 $$\upmu \hbox {mol/g/s}$$ at 60 $$^{\circ }\hbox {C}$$ . It was found that the rate of reaction due was lower due to hindering effect by adsorption of other gas molecules on the catalytic site. Finally, we propose a mechanism of hydrogen and oxygen recombination reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ . $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ catalysts were coated by solution combustion method on $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ coated honeycomb structured cordierite monolith. Among the catalysts, $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ coated monolith showed high catalytic activity for hydrogen combustion with air. The proposed mechanism of $$\hbox {H}_{2} + \hbox {O}_{2}$$ reaction clarified that $$\hbox {Pd}^{+2}$$ ion state is unaltered in $$\hbox {Ti}\hbox {O}_{2}$$ lattice.