Novel recirculating loop reactor for studies on model catalysts: CO oxidation on Pt/TiO2(110)

Abstract

A novel recirculating loop microreactor coupled to an ultrahigh vacuum (UHV) chamber has been constructed for the kinetic evaluation of model catalysts, which can be fully characterized by UHV surface science techniques. The challenge for this reactor design is to attain sufficient sensitivity to detect reactions on model single-crystal surfaces, which have a low number of active sites compared to conventional catalysts of equivalent mass. To this end, the total dead volume of the reactor system is minimized (32 cm(3)), and the system is operated in recirculation mode so that product concentrations build up to detectable levels over time. The injection of gas samples into the gas chromatography column and the refilling of the recirculation loop with fresh feed gas are achieved with computer-controlled, automated switching valves. In this manner, product concentrations can be followed over short time intervals (15 min) for extended periods of time (24 h). A proof of principle study in this reactor for CO oxidation at 145-165 °C on Pt clusters supported on a rutile TiO2(110) single crystal yields kinetic parameters that are comparable to those reported in the literature for CO oxidation on Pt clusters on powdered oxide supports, as well as on Pt(100). The calculated activation energy is 16.4 ± 0.7 kcal/mol, the turnover frequency is 0.03-0.06 molecules/(site·s) over the entire temperature range, and the reaction orders in O2 and CO at 160 °C are 0.9 ± 0.2 and -0.82 ± 0.03, respectively.

Understanding Active Sites in the Water–Gas Shift Reaction for Pt–Re Catalysts on Titania

“…Experiments were conducted in two ultrahigh vacuum chambers which have been described in detail elsewhere. The first chamber ( P < 3 × 10 –10 Torr) is coupled to a custom-made microreactor and is equipped with a residual gas analyzer (Stanford Research Systems, RGA 300), a hemispherical analyzer (SPECS, EA10) and Mg/Al Kα X-ray source (Leybold Heraeus, RQ 20/63) for XPS, and an infrared reflection absorption spectroscopy (IRAS) system (Bruker, Tensor 27). The second chamber − ( P ≤ 1 × 10 –10 Torr) houses a quadrupole mass spectrometer (Hiden HAL 301/3F) for temperature programmed desorption studies (TPD), a cylindrical mirror analyzer (Omicron CMA 150) for Auger electron spectroscopy, and low energy electron diffraction optics (Omicron SPECTALEED).…”

“…Activity measurements were performed in recirculation mode, 44 in which the reactant gases recirculate over the catalyst surface once every 2 min, and the concentration of CO 2 is increased to a detectable level during the recirculation period. An in-line gas sample (∼1.096 cm 3 ) was injected into the gas chromatograph (HP 5890A) equipped with a PoraPLOT Q capillary column and thermal conductivity detector (TCD).…”