Improving anti-coking and sulfur-resisting performance of Rh-based lanthanum zirconate pyrochlore catalysts for diesel reforming through partial substitution with alkali earth metals

Abstract

This work studied the effect of partial substitution of La by alkali earth metals (Mg, Ca, and Ba) on the catalytic performance of steam reforming of diesel over pyrochlore type catalysts with n-hexadecane as surrogate fuel. The experimental results indicated that LaBaZrRh catalyst exhibited a superb catalytic activity and sulfur tolerance with ∼100% fuel conversion and ∼65.8% H2 concentration in the reformate for a runtime over 30 h in the presence of 50 ppm sulfur. The introduction of Ba was found to greatly inhibit the coke formation and sulfur poisoning to catalysts. The H2-TPR and H2 pulse chemisorption tests further revealed that it is the partial substitution of La by Ba that enhances the interaction between the active metal Rh and La2Zr2O7 support, thus significantly improving the dispersion of Rh active component and decreasing the size of Rh particles. The XPS results showed that the electron-deficient Rh was formed in LaBaZrRh catalyst. The weaker interaction between sulfur and electron-deficient metals led to the easy breaking of the sulfur-metal bond in LaBaZrRh catalyst, thus resulting in good sulfur tolerance. Additionally, the La substitution by Ba also enhanced the concentration of oxygen vacancies, which improved the coking resistance.