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tungstated zirconia is a robust solid acid catalyst for light alkane (c-4-c-8) isomerization. several structural models for catalytically active sites have been proposed, but the topic remains controversial, partly because of the absence of direct structural imaging information on the various supported wo x species. high-angle annular dark-field imaging of wo3/zro2 catalysts in an aberration-corrected analytical electron microscope allows, for the first time, direct imaging of the various species present. comparison of the relative distribution of these wo x species in materials showing low and high catalytic activities has allowed the deduction of the likely identity of the catalytic active site-namely, subnanometre zr-wox clusters. this information has subsequently been used in the design of new catalysts, in which the activity of a poor catalyst has been increased by two orders of magnitude using a synthesis procedure that deliberately increases the number density of catalytically relevant active species.