Heterogeneous catalysts based on nano- and sub-nano clusters, whose properties can be superb and highly tunable, provide the opportunity for a “greener” chemistry, reducing the amount of precious metals in use. The most important problem of industrial hetereogeneous catalysis, however, is the catalyst loss of activity with time-on-stream, i.e. “deactivation”, which leads to a decrease in catalyst lifetime and performance. Two main processes cause the deactivation of the catalysts. On the one hand, the formation and build-up of coke deposits on the catalysts surface leads to poisoning of the active sites. On the other hand, nanoclusters tend to sinter into bigger particles, with the subsequent loss of active sites. Our work shows that boron can be a promising candidate to mitigate the deactivation of metallic nano-catalysts via coking and sintering. Specifically, we have focused on supported patinum nanoclusters, used to catalyze dehydrogenation reactions of alkanes. On the one hand, our recent study shows that adding B to MgO-supported Pt4 clusters could be a “magic bullet” against both sintering and coke deposition. Indeed, boron doped clusters were found to anchor to the support via a covalent B-O bond, and the cluster-surface binding was much stronger than in the pure Pt clusters. B introduces covalency to the intra-cluster bonding, leading to structural distortion and stabilization and reduced propensity to sinter. Moreover, it is shown that the affinity to C drops dramatically for borated clusters, discouraging coking and increasing the selectivity of cluster catalysts. On the other hand, pure and boron doped platinum nanoclusters were deposited on alpha-alumina, which is durable at high temperatures. In this case bigger clusters were considered, namely, Pt7B and Pt8.

Improvement of platinum nanocatalysts via boron doping

251st National Meeting (2016)

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