Lawrence Berkeley National Laboratory

Propylene hydrogenation over Pt nanoparticles supported on mesoporous silica type SBA-15 was monitored by time-resolved FT-IR spectroscopy at 23 ms resolution using short propylene gas pulses that joined a continuous flow of hydrogen in N2 (1 atm total pressure). Experiments were conducted in the temperature range 323-413 K. Propane was formed within 100 milliseconds or faster. The CH stretching region revealed distinct bands for propane molecules emerging inside the nanoscale channels of the silica support. Spectral analysis gave the distribution of the propane product between support and surrounding gas phase as function of time. Kinetic analysis showed that the escape of propane molecules from the channels occurred within hundreds of milliseconds (3.1 + 0.4 s-1 at 383 K). A steady state distribution of propane between gas phase and mesoporous support is established as the product is swept from the catalyst zone by the continuous flow of hydrogen co-reactant. This is the first direct spectroscopic observation of emerging products of heterogeneous catalysis on nanoporous supports under reaction conditions.