Needle in a haystack catalysis

A new configuration of catalyst loading in the Temporal Analysis of Products (TAP) reactor is presented. It is a single Pt particle packed in a bed with approximately 100,000 inert quartz particles. In TAP studies, the single particle configuration was proven to be sensitive enough to monitor and compare kinetic characteristics of the same catalyst particle at both high vacuum and atmospheric pressures. Catalytic CO oxidation reaction over platinum was used to illustrate these new possibilities. In the TAP single particle experiments under high vacuum conditions, a single particle provides high conversion (up to a total conversion of 95%) despite the catalyst particle occupies less than 0.1% of the total reactor volume. This phenomenon was proven in a variety of pulse response experiments. A mathematical probabilistic theory of this counterintuitive phenomenon will be published in the next paper. Also, an interesting similarity was found from both TAP vacuum and atmospheric pressure data, i.e. both sets of data are characterized by a “turning point” at the same temperature of 170 °C indicating a transition from an O2 dominated regime to a CO dominated regime. This observation of pressure independent characteristic of the Pt particle creates a new possibility for bridging across the pressure gap.

Comparison of CO2 produced during TAP vacuum pump-probe experiments and atmospheric flow experiments for CO oxidation over single Pt particle with the same composition of reactants. (A) A typical set of pump-probe CO2 responses (m/e = 44) for reaction at 140, 170, and 350 °C. There is a shift in the amount of CO2 produced during both CO and oxygen pulses as temperature increases. (B) CO2 production observed from atmospheric flow experiment. The CO2 produced while increasing reactor temperature is less than the CO2 produced during reactor temperature decrease as shown by the counter-clockwise hysteresis loop. (C) CO2 production observed from vacuum pump-probe experiment. The black line represents the total CO2 yield. The red and blue lines represent the CO2 yield on the oxygen pulse and CO pulse, respectively.Figure optionsDownload as PowerPoint slide