02/15/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation defense by Visal Veng on "Catalytic Membrane Dielectric-Barrier Discharge Reactor for Ammonia Synthesis."

Candidate Name: Visal Veng
Degree: Doctoral
Defense Date: Feb. 27, 2024
Time: 1 to 3 p.m.
Location: Southwick Hall 302 (SOU-302)

Committee:

  • Advisor Juan Pablo Trelles, Professor, Department of Mechanical and Industrial Engineering, UMass Lowell
  • Fanglin Che, Assistant Professor, Chemical Engineering, UMass Lowell
  • Fuqiang Liu, Associate Professor, Mechanical and Industrial Engineering, UMass Lowell
  • John Hunter Mack, Associate Professor, Mechanical and Industrial Engineering, UMass Lowell

Brief Abstract:
Ammonia synthesis via non-thermal plasma presents advantages over the currently-dominant Haber-Bosch process, particularly for small-scale and distributed operations powered by intermittent electricity from renewable energy sources. This doctoral dissertation research focuses on the design, characterization, and assessment of a catalytic membrane Dielectric-Barrier Discharge (mDBD) reactor for ammonia synthesis from nitrogen and hydrogen. The research first addressed the design and evaluation of the mDBD reactor without catalyst. The reactor used a porous alumina membrane as dielectric barrier and as distributor of H2. This arrangement enabled greater residence time for N2 decomposition together with greater H2 availability in the reaction zone, as assessed by a computational thermal-fluid model. The reactor's operation was evaluated with membranes with pore size between 0.1 and 2.0 µm and porosities between 25% and 51%, and also in conventional DBD mode using a non-porous dielectric. The experimental characterization of the reactor encompassed electrical, optical, and spectroscopic diagnostics, as well as Fourier-Transform Infrared Spectroscopy (FTIR) to analyze gas products, as function of driving voltage. The results showed that both, ammonia production and power consumption, vary inversely with the product of membrane pore size and porosity, with the highest energy yield of 0.25 g-NH3/kWh obtained with the 1.0 µm pore membrane, whereas the maximum yield under conventional DBD operation was three-times lower. The findings demonstrate that the use of a membrane dielectric can enhance the performance of DBD-based ammonia synthesis. Building on this foundation, the subsequent study focused on the incorporation of metal catalyst within the mDBD reactor. The integration is based on filling the membrane-ground electrode gap with catalyst powder embedded in porous dielectric support (glass wool). Three different metal catalysts were evaluated: nickel (Ni), cobalt (Co), and bi-metallic nickel-cobalt (Ni-Co), all loaded at 5% by weight on alumina powder (surface area ~ 200 m2/g). The expected catalyst performance was assessed through Density Functional Theory (DFT) calculations, revealing their predicted activation energy under non-thermal plasma conditions. The results showed that Ni-Co/Al2O3 catalyst emerged as the most effective, achieving an energy yield of 0.87 g-NH3/kWh, compared to a maximum of 0.82 and 0.78 g-NH3/kWh for the Co/Al2O3 and Ni/Al2O3 catalysts, respectively, corroborating theoretical predictions. The utilization of metal catalysts resulted in an ammonia yield approximately 4 times greater than that achieved with Al2O3, and approximately 8 times higher than the yield obtained without either metal catalyst or a porous dielectric support. Additionally, the Ni-Co catalyst configuration led to the highest NH3 synthesis rate of 1.4 mmol/h/g-cat. These findings underscore the pronounced enhancement in DBD plasma-based ammonia production achievable through the incorporation of a porous membrane, metal catalyst, and porous dielectric support.