Design and operating characteristics of a transient kinetic analysis catalysis reactor system employing in situ transmission Fourier transform infrared

A novel apparatus for gas phase heterogeneous catalysis kinetics is described. The apparatus enables fast isotopic transient kinetic analysis (ITKA) to be performed in which both the gaseous and adsorbed species inside the catalytic reactor are monitored simultaneously with rapid-scan transmission Fourier transform infrared (FTIR), and its gaseous effluent can be monitored by mass spectroscopy during rapid switching of reagent gas streams. This enables a more powerful version of the well-known steady-state isotopic transient kinetic analysis (SSITKA) technique in which the vibrational spectra of the gas phase and adsorbed species are also probed: FTIR-SSITKA. Unique reactor characteristics include tungsten construction, liquid nitrogen cooling or heating (∼200-770 K), pressures of 1.0-2.5 atm, fast reactor disassembly and reassembly, and catalyst loading in a common volume. The FTIR data acquisition rate of this apparatus (3 Hz) is tenfold faster than previously reported instruments. A 95% signal decay time of ∼3 s for gas switching was measured. Very good temperature reproducibility and uniformity (<±3 K) were observed by in situ rotational temperature analysis, which allows accurate calibration of the reactor thermocouple to the reactor gas temperature. Finally, FTIR-SSITKA capabilities are demonstrated for CO2 isotope switching over a γ-alumina sample at 75 deg. C, which reveal an adsorbed carbonate species with an average surface residence time of τ=148±5 s and a coverage of ∼2.5x1015 molecules cm-2