Titanium modified Ru/CeO2 catalysts for ammonia synthesis

Abstract

In catalytic reaction that involves hydrogen species, the adsorption/desorption property of hydrogen species would greatly affect the catalytic performance. In this work, we introduce titanium into ceria to tune the properties of ceria-supported Ru catalysts for ammonia synthesis, and the result shows that the ammonia synthesis rate of Ru catalysts exhibits a volcanic trend with an increase of titanium content. XRD and Raman results reveal that an appropriate amount of Ti addition would be incorporated into CeO2 lattice to form CeTiO2-x solid solution, while the presence of excess TiO2 leads to the formation of TiO2 particles. Raman and UV-vis results of Ru catalysts confirm that CeTiO2-x serves as preferential platform for the dispersion of Ru species. Moreover, the O 1s spectra, CO-TPR and 1H NMR indicate that the introduction of titanium decreases the number of the active oxygen species. As a result, the introduction of an appropriate amount of Ti species in Ru/CeO2 catalysts leads to enhancement of the hydrogen species desorbed at low temperature, contributing to N2 dissociation or ammonia synthesis as well as the alleviation of hydrogen poisoning. The sample with 3 mL titanium butoxide (19.4 wt% of TiO2) exhibits the optimal ammonia synthesis rates. This work demonstrates a general approach of the decoration of oxide supports to tune the adsorption property and the catalytic activity for the catalytic reaction that involves hydrogen species.