Electrical and reaction performances of packed‐bed plasma reactors moderated with ferroelectric or dielectric materials

Abstract

The operational behavior of packed‐bed plasma reactors depends on the dimension, shape, and chemical properties of the pellets used as moderators, but little information exists about the influence of their specific dielectric properties. Herein, we comparatively study the electrical behavior of a packed‐bed reactor filled with pellets of either dielectric (Al2O3 and glass) or ferroelectric (BaTiO3 and lead zirconate titanate) materials. We found that plasma current was higher for ferroelectrics and presented a nonlineal dependence on voltage. Moreover, for BaTiO3, we found a drastic decrease at around its relatively low Curie temperature. Differences in electrical behavior have a direct effect on the reactor performance, as illustrated for the ammonia synthesis, demonstrating the importance of moderator material dielectric properties and their dependence on temperature.

Incorporation of a Metal Catalyst for the Ammonia Synthesis in a Ferroelectric Packed-Bed Plasma Reactor: Does It Really Matter?

“…According to Rouwenhorst et al, this temperature is a kind of threshold for the catalytic promotion of the ammonia synthesis in plasma reactors incorporating a Ru-based catalyst . Owing to the specific conditions of our experiment, it is expected that the temperature inside the packed-bed zone may be higher that this nominal value at the reactor wall …”

“…The differences in electric field distribution in the interpellet space for the PZT and PZT-Al 2 O 3 /PZT configurations respond to the distinct dielectric constants of the ferroelectric PZT and dielectric Al 2 O 3 materials . Interestingly, the electric field intensity appears enhanced at locations where either the Al 2 O 3 or the PZT surfaces present irregularities.…”

“…PZT was chosen as ferroelectric barrier material because it has demonstrated a better performance for the ammonia synthesis than the more widely utilized BaTiO 3 ferroelectric . Moreover, Curie temperatures of 332 °C for the former vs 120 °C for the latter ensure that PZT ferroelectric properties are preserved at high operating temperatures . The bottom electrode was grounded, and the upper one was connected to a high voltage power amplifier (Trek Inc., Model PD05034), coupled to an AC function generator (Stanford Research Systems, Model DS345).…”

“…The differences in electric field distribution in the interpellet space for the PZT and PZT-Al 2 O 3 /PZT configurations respond to the distinct dielectric constants of the ferroelectric PZT and dielectric Al 2 O 3 materials. 37 Interestingly, the electric field intensity appears enhanced at locations where either the Al 2 O 3 or the PZT surfaces present irregularities. The influence of asperities and irregularities is usually overlooked for similar simulations in the literature, where perfectly spherical interelectrode pellets are usually considered for the calculations.…”

“…36 Owing to the specific conditions of our experiment, it is expected that the temperature inside the packed-bed zone may be higher that this nominal value at the reactor wall. 37 Since an applied voltage of 2.5 kV provided the highest energy efficiency at ambient temperature (c.f., Figure 5), the 190 °C experiments were carried out at this voltage, varying the frequency between 1 and 3 kHz. The electrical characterization of the reactor under these operating conditions reported in Figure 4b,d, and in the Supporting Information shows that, at high temperature, current and power values increase with the frequency for all the configurations, although this increase is slightly less pronounced for the Al 2 O 3 /PZT configuration.…”