Paper #6 is the work of Wayne Goodman and Mingshu Chen of Texas A&M University and describes the remarkable catalytic power of gold atoms supported on titanium dioxide (TiO₂). An earlier and much-cited paper of Goodman’s (M. Valden, et al., Science, 281[5383]: 1647-50, 1998) reported on the excellent catalytic properties of gold clusters on TiO₂, and the current work is a major step forward in understanding them. Moreover, it is the first example of complete "wetting" of an oxide surface by gold atoms and proves that such an ultra-thin gold film can act as a catalyst for CO oxidation and that gold nanoparticles as such are not essential for catalytic activity, as originally speculated.

The new catalyst was made by building a layer of TiO₂ on a molybdenum substrate and then depositing a layer of gold, only one or two atoms thick, on top. This was annealed at 900 K to form a well-ordered layer of gold atoms which was shown to be bonded directly to titanium atoms and not to oxygens. Goodman and Chen then tested the catalytic efficiency of the gold films by their abilities to oxidize CO at room temperature, which was up to 45 times better than the most reactive gold/TiO₂ surface previously reported.

Currently Goodman’s group is studying these gold layers and related materials as potential catalysts. They are also synthesizing functional oxide supports for stabilizing thin gold films, and in related work they have addressed the promotional effect of the gold in palladium-gold catalysts for the synthesis of vinyl acetate (see M.S. Chen, et al., Science, 310[5746]: 291-3, 2005). Speaking to Science Watch, Goodman commented: "We are hopeful and very optimistic that the methodologies used to synthesize highly active model gold catalysts can be utilized to prepare vastly superior high-surface-area catalysts for a variety of industrial applications." A golden age of catalysis may well be dawning.

Paper #7 also involves palladium as a catalyst, in this case for the Suzuki-Miyaura coupling reaction, in which two benzene rings join together by the reaction of a boronic acid group on one molecule with a chlorine atom on the other, the result being a biaryl. The work was done by Stephen Buchwald’s group at MIT, and what is particularly striking is the way the catalyst was designed rather than being discovered by accident or by testing possible candidates.

Making a hindered biaryl is what the Suzuki-Miyaura process is all about. If the benzene-ring carbons adjacent to the boronic acid group and the chlorine carry other substituents, and especially bulky substituents, then making the biaryl becomes somewhat problematical, as the region of space surrounding the bond to be formed is highly congested. Palladium complexes can, however, catalyze the process, and in paper #7 a new "universal" catalyst is reported.

The new catalyst is a biaryl phosphorus compound which can complete a Suzuki-Miyaura reaction in a couple of hours, with yields in excess of 90%, catalyst concentrations of 0.2% Pd or less, and at room temperature. Even with only 0.02% of catalyst present in the reaction it is still possible to obtain comparable yields, although these require heat and take much longer. In one reaction, and using only 30 ppm (0.003%) of catalyst, Buchwald was able to calculate that each Pd participated in 31,000 individual reactions. He was even able to report that at a mere 10 ppm there was still significant catalytic activity.