The bulk and surface structure of gamma-alumina

Despite its widespread use, the composition and structure of gamma-alumina have been the subject of controversy for decades. In this article we review the historical attempts to resolve two principal questions that have each been extensively debated, but in independent communities: (1) What is the d istribution of vacancies over the two cation sublattices in the nominal spi nel structure, and (2) what is the hydrogen content of gamma-alumina, if an y? We then review how recent investigations have shown that these two quest ions are, in fact, related, and have a single resolution. The experimental study of gamma-alumina surfaces has long been dominated by IR spectroscopy of the hydroxylated surfaces, and Al-27 NMR. Both techniques have produced perplexing results. Here we review the development of these surface studies and parallel computational studies. Finally, we review recent computationa l results that explain the puzzling experimental findings.