Effect of Porous Catalyst Support on Plasma-Assisted Catalysis for Ammonia Synthesis

Area of Science:

• Plasma Chemistry
• Catalysis
• Chemical Engineering

Background:

• Ammonia (NH3) synthesis is crucial for agriculture and industry.
• Dielectric barrier discharge (DBD) plasma reactors offer a promising alternative for NH3 synthesis.
• Catalyst support properties significantly influence plasma-assisted chemical reactions.

Purpose of the Study:

• To investigate the impact of catalyst support particle porosity on NH3 synthesis efficiency in a DBD plasma reactor.
• To compare the performance of porous silica (SiO2) beads versus nonporous glass beads as catalyst supports.
• To understand the underlying mechanisms of how support porosity affects plasma-chemical processes.

Main Methods:

• Utilized a coaxial DBD plasma reactor operating at room temperature and near atmospheric pressure (550 Torr).
• Employed AC applied voltage and compared porous SiO2 beads (8 nm average pore size) with nonporous glass beads.
• Analyzed discharge and plasma properties using Lissajous plots, BOLSIG+ software, and high-resolution optical emission spectroscopy.

Main Results:

• NH3 conversion and energy yield increased with applied voltage for both support types.
• Porous SiO2 beads consistently yielded higher NH3 conversion and energy efficiency compared to glass beads.
• Plasma properties and discharge characteristics were largely unaffected by support porosity.
• Lower concentrations of key plasma species (N2+, atomic N, atomic H) were observed with SiO2 supports, indicating their consumption in surface reactions.

Conclusions:

• The increased surface area of porous SiO2 supports enhances heterogeneous reactions involving plasma-generated species.
• Porous catalyst supports significantly improve ammonia synthesis rates and energy efficiency in DBD plasma reactors.
• Optimizing support porosity is a viable strategy for advancing plasma-based chemical synthesis.