High-grade diesel production by hydrodeoxygenation of palm oil over a hierarchically structured Ni/HBEA catalyst

Abstract

A highly active catalyst, hierarchical nano-sized Ni/HBEA, is developed for stearic acid and palm oil hydrodeoxygenation (HDO) in dodecane. The TPAOH/NaOH treated hierarchical HBEA sample (crystal size: 15–20 nm) affords more homogeneously dispersed open inter-mesopores (main pore diameter: 25 nm) via controllable base leaching, as evidenced by various microscopy and spectroscopy techniques. By the formation of an aluminum complex on the crystal surface, TPA⁺ prevents the specific external structure from deep corrosion. After loading Ni nanoclusters, the modified Ni/HBEA was supported with more loadable and dispersive Ni nanoclusters (d = 7.7 ± 1.5 nm) in the newly formed inter-crystalline mesopores, which provide higher accessibility towards heavy molecules, as well as restrict the Ni particle growth. This novel catalyst shows a significantly high initial rate of 67 mmol g⁻¹ h⁻¹ (equivalent to 19 g g⁻¹ h⁻¹) for producing 85% n-C₁₇/C₁₈ and 11% iso-C₁₇/C₁₈ alkanes by stearic acid conversion at 260 °C and 4 MPa H₂, and the efficiency of this method is far beyond the current techniques using sulfur-metal and reduced-metal catalysts. The HDO route follows the major pathway of sequential hydrogenation and dehydration steps, affording a highly atom-economical process and a suitable diesel oil ingredient (with certain branched alkanes). In addition, high activities are achieved with the improved catalyst after treatment with high concentration stearic acid in dodecane (up to 0.5 g mL⁻¹), and the catalyst remains highly active and stable in the four recycling runs of palm oil HDO.