Ammonia (NH) is one of the basic chemicals in artificial fertilizers and a promising carbon-free energy storage carrier. Its industrial synthesis is typically realized the Haber-Bosch process using traditional iron-based catalysts. Developing advanced catalysts that can reduce the N activation barrier and make NH synthesis more efficient is a long-term goal in the field. Most heterogeneous catalysts for N-to-NH conversion are multicomponent systems with singly dispersed metal clusters on supporting materials to activate N and H molecules. Herein, we report single-component heterogeneous catalysts based on 5 actinide dioxide surfaces (ThO and UO) with oxygen vacancies for N-to-NH conversion. The reaction cycle we propose is enabled by a dual-site mechanism, where N and H can be activated at different vacancy sites on the same surface; NH is subsequently formed by H migration on the surface associative pathways. Oxygen vacancies recover to their initial states after the release of two molecules of NH, making it possible for the catalytic cycle to continue. Our work demonstrates the catalytic activities of oxygen vacancies on 5 actinide dioxide surfaces for N activation, which may inspire the search for highly efficient, single-component catalysts that are easy to synthesize and control for NH conversion.