Grinding Out Reactions Boosts Catalytic Rate

Heterogeneous catalytic reactions, which involve solid catalysts and liquid or gaseous reagents, are nearly always driven by thermal energy—heat. A few solid-state reactions are driven by mechanical energy, as provided, for example, by grinding solid reagents in a ball mill. The enhancing effect of mechanical energy on solid-state reactions led Sarah Immohr, Ferdi Schüth, and coworkers at the Max Planck Institute for Coal Research, in Germany, to consider whether ball milling would accelerate heterogeneously catalyzed gas-phase reactions. For one reaction, they found that indeed it does. By comparing results obtained from a specially designed ball-mill reactor to those from a conventional reactor, the team found that the rate of CO oxidation by O₂ in the presence of solid Cr₂O₃ catalyst is 1,000 times as high at room temperature and 10 times as high at 100 °C (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201305992). Schüth and coworkers suggest that this finding, which they do not fully understand even after having conducted a series of control tests, could lead to new process options in the chemical industry.