(511a) Transient Pseudo-Random Binary Sequence (PRBS) Gas Injections for the Determination of Elementary Rate Constants

Transient experiments yield richer data streams than steady-state experiments to inform microkinetic models. Current transient methods can be improved through the use of pseudo random binary sequence (PRBS) perturbations. PRBS differs from other pulsed-based transient techniques due to the random actuation of the valve introducing reactant gases to the catalyst. Repeated pulses at a single frequency lead to redundant measurements. Confidence in fitted parameters may be higher, but the model may still be misinformed or biased. PRBS leads to enhanced system state sampling in a shorter time while eliminating bias.

An in-house reactor designed for transient PRBS experiments is used for experimental data collection. The main components of the reactor are a fast-acting solenoid valve capable of time-scales ranging from milliseconds to minutes, an interchangeable furnace or differentially scanning calorimeter (DSC), and a Hiden HPR-20 mass spectrometer. For initial experiments, CO oxidation on Pd/SiO₂ is studied. Helium and oxygen are continuously fed into a plug-flow reactor. Carbon monoxide gas (50% CO/5% Ar/He) is pulsed into the reactor. An argon tracer is used to correct for system dynamics and reconstruct the reactor inlet profile. During experiments, CO (m/z = 28), O2 (m/z = 16), CO2 (m/z = 44), Ar (m/z = 40), and pressure are followed.

Simulated kinetic modeling indicates elementary rate constants are determined with higher confidence and accuracy when a transient PRBS inlet is used compared to steady-state or a single pulse. Experimental PRBS data has been collected and modeled for CO oxidation on Pd/SiO₂ catalysts. Sequences are conducted at different temperatures and modeled to predict elementary rate constants as a function of temperature. Assuming an Arrhenius dependence for all elementary reactions allows for the calculation of activation energy for each elementary step. PRBS methodology aims to improve catalytic mechanism understanding and the speed at which it is done.