The present study focuses on a new technique for the prevention of metal dusting in carbonaceous gas environments at intermediate temperature. Preliminary laboratory metal dusting test was conducted for Ni-x%Cu binary alloys and Ni-Cr alloys with various Si and Cu content in a simulated 60%CO-26%H(2)-11.5%CO(2)-2.5%H(2)O (in vol.%) gas mixture at 650 degrees C. Specimens of the binary alloys containing low Cu were entirely covered with coke and showed rough metal surfaces due to the degradation of metal. Alloys of 20% and more Cu, on the contrary, had no coke deposition and smooth metal surfaces, suggesting alloys with an adequate Cu do not react with CO in the syngas mixture without an oxide scale barrier. Based on these results, we conclude that Cu does not protect by formation of the oxide scale but has a "Surfactant-Mediated Suppression" against metal dusting. This effect can be explained in terms of atomistic interaction of CO with transition-metal surfaces by electronic structure analyses. For the Ni-Cr alloy, both addition of Si and Cu played a role of preventing pit formation in the simulated syngas atmosphere. The concept can be also useful for the practical material design of Ni-Cr-Si-Cu alloy with excellent metal dusting resistance.