Nanoporous gold (NPG) catalysts with different types of oxide residues are fabricated by a simple electrochemical dealloying method with the aim of exploring the origin of high catalytic activity on unsupported gold catalyst systems. By leaching out the reactive components from AuCu and AuAl alloys, unsupported NPG with so-called active CuO and inert Al2O3 residues were generated, characterized by an open interconnected network architecture with a narrow ligament size distribution. The NPG catalyst with inert Al2O3 residues shows a CO reaction rate and turnover frequency similar to those on NPG with active CuO residues under the same measurement conditions. In comparison, NPG((Cu)) with active CuO residues exhibits better catalytic durability for CO oxidation than NPG((Al)) catalyst, possibly because of its stabilization for nanoporous architecture. Experimental observations suggest that the so-called active or inert oxide residues in the as-made NPG catalysts have almost no effect on the intrinsic catalytic activity of gold, whereas metallic gold plays the catalytic role in this unsupported NPG system. (C) 2015 Elsevier Inc. All rights reserved.