Hydrodeoxygenation of palm oil to green diesel products on mixed-phase nickel phosphides

Abstract

This work aims to investigate the catalytic hydrodeoxygenation (HDO) of palm oil to produce green diesel (GD) on phosphides of nickel (Ni), cobalt (Co), and copper (Cu) without support materials. The metal phosphides were obtained by co-precipitation of metal precursors and phosphoric acid followed by calcination and reduction with hydrogen. The as-synthesized, calcined and reduced samples were characterized by various modes of X-ray absorption spectroscopy (XAS) including time-resolved X-ray absorption (TR-XAS), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and X-ray diffraction (XRD). The phosphide phases of Ni, Co and Cu after reduction were mixed-phase Ni2P and Ni12P5 (denoted as NixPy), Co2P and Cu3P, respectively. Their catalytic performance was determined in a continuous fixed-bed flow reactor under H2 atmosphere at 300, 350 and 400 °C for 6 h. The best catalyst was NixPy providing the highest GD yields. The main catalytic route was decarbonylation (DCO) yielding C15 + C17. The minor routes were decarboxylation (DCO2) and HDO. Moreover, NixPy provided better yields of all products than the commercial single-phase Ni2P.