The extinction characteristics of particle clouds of NiO, CuO, and Fe2O3 metal oxides undergoing synthesis gas (syngas) reduction in chemical looping reactors were theoretically investigated using an adaptation of Semenov's theory. The extinction was characterised in terms of a critical particle radius and a minimum percentage of the cloud mass loss (%CML). The critical sizes of metal oxide particles in the cloud were found to be strongly affected by the particle size, shape, and reactivity as well as solid volume fraction and type and concentration of the reducing gas. Our analyses indicate that blending of a base metal oxide with another metal oxide species with different reactivity may lower the extinction potential of the cloud (i.e. likelihood of extinction). (C) 2012 Elsevier Ltd. All rights reserved.