Engineering of Ce3+-O-Ni structures enriched with oxygen vacancies via Zr doping for effective generation of hydrogen from ammonia

Abstract

In heterogeneous catalysis that involves metal oxides, the performance of catalysts is usually determined by the presence and nature of oxygen vacancies. In this article, we report the synthesis of Ni/Ce1−xZrxO2 catalysts for ammonia (NH3) decomposition with their properties tuned by controlling the level of Zr doping. In situ and ex situ spectroscopic investigations confirm the formation of Ce1−xZrxO2 solid solutions, and with Zr doping there is an increase of Ce3+ and oxygen vacancy concentration. At 600 °C and 30 000 mL gcat−1h−1, the Ni/Ce0.85Zr0.15O2 catalyst exhibits an NH3 conversion of ~90% with superior stability in a test period of 80 h. Characterizations of the reduced (in situ) and used catalysts confirm the integrity of the catalyst. The results of temperature-programmed surface reaction reveal that the enhanced catalytic performance can be ascribed to the associative desorption of N2 at a relatively low temperature. This work demonstrates a general approach of isovalent ion doping to engineer metal oxide heterogeneous catalysts with properties tuned for a target process.