Structure Sensitivity of Ammonia Synthesis on Cobalt: Effect of the Cobalt Particle Size on the Activity of Promoted Cobalt Catalysts Supported on Carbon.

Zybert, Magdalena; Tarka, Aleksandra; Patkowski, Wojciech; Ronduda, Hubert; Mierzwa, Bogusław; Kępiński, Leszek; Raróg-Pilecka, Wioletta

This work presents a size effect, i.e., catalyst surface activity, as a function of active phase particle size in a cobalt catalyst for ammonia synthesis. A series of cobalt catalysts supported on carbon and doped with barium was prepared, characterized (TEM, XRPD, and H2 chemisorption), and tested in ammonia synthesis (9.0 MPa, 400 °C, H2/N2 = 3, 8.5 mol% of NH3). The active phase particle size was varied from 3 to 45 nm by changing the metal loading in the range of 4.9–67.7 wt%. The dependence of the reaction rate expressed as TOF on the active phase particle size revealed an optimal size of cobalt particles (20–30 nm), ensuring the highest activity of the cobalt catalyst in the ammonia synthesis reaction. This indicated that the ammonia synthesis reaction on cobalt is a structure-sensitive reaction. The observed effect may be attributed to changes in the crystalline structure, i.e., the appearance of the hcp Co phase for the particles with a diameter of 20–30 nm.

COBALT catalysts; CATALYST supports; COBALT; DOPING agents (Chemistry); CATALYST synthesis; CRYSTAL structure; AMMONIA

Catalysts (2073-4344), 2022, Vol 12, Issue 10, p1285

2073-4344

Academic Journal

10.3390/catal12101285