Optical Diagnostics of Plasma Assisted Chemical Looping Reactions

Abstract

Here, we study time- and spatially resolved heterogeneous plasma catalysis chemical looping reactions using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> laser diagnostics in a novel parallel plate dielectric barrier discharge (DBD) plasma reactor at atmospheric pressure and temperatures: 473 and 673 K. A chemical looping material, 50:50 by mass mixture of lanthanum–nickel-based perovskite (La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Ce <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> NiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , was placed directly in non-equilibrium DBD plasma. Optical diagnostic techniques used include high-speed imaging (i.e., ns gate width), N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> optical emission spectroscopy (OES) at 337 nm, and Rayleigh scattering (RS). During the reduction step, a mixture of CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flow was used, and during the oxidation step, the airflow was used. During the reduction step, the average temperatures measured at the furnace setpoint temperature of 473 and 673 K were 580 and 800 K, respectively. For the oxidation step, the average temperatures measured were 520 and 830 K, respectively. There was good agreement in average temperatures measured by RS and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> OES. The 2-D RS imaging showed lower temperatures near the catalyst during the reduction step and higher temperatures during the oxidation step. Although corona discharges were observed over chemical looping materials in high-speed images, RS temperature measurements showed non-equilibrium plasma chemistry over the materials.