Promotional effect of Cu, Fe and Pt on the performance of Ni/Al₂O₃ in the deoxygenation of used cooking oil to fuel-like hydrocarbons

Inexpensive Ni-based catalysts can afford comparable performance to costly precious metal formulations in the conversion of fat, oil, or greases (FOG) to fuel-like hydrocarbons via decarboxylation/decarbonylation (deCO_x). While the addition of certain metals has been observed to promote Ni-based deCO_x catalysts, the steady-state performance of bimetallic formulations must be ascertained using industrially relevant feeds and reaction conditions in order to make meaningful comparisons. In the present work, used cooking oil (UCO) was upgraded to renewable diesel via deCO_x over Ni/Al₂O₃ promoted with Cu, Fe, or Pt in a fixed-bed reactor at 375^◦C using a weight hourly space velocity (WHSV) of 1 h⁻¹. Although all catalysts fully deoxygenated the feed to hydrocarbons throughout the entire 76 h duration of these experiments, the cracking activity (and the evolution thereof) was distinct for each formulation. Indeed, that of the Ni-Cu catalyst was low and relatively stable, that of the Ni-Fe formulation was initially high but progressively dropped to become negligible, and that of the Ni-Pt catalyst started as moderate, varied considerably, and finished high. Analysis of the spent catalysts suggests that the evolution of the cracking activity can be mainly ascribed to changes in the composition of the metal particles.