Enhanced synergistic effect of acidity and active phase for Ni-Co@NHZ-5-AT on hydroconversion of benzyoxybenzene to polycyclic alkanes

Abstract

Improving polycyclic alkanes (PCAs) selectivity by controlling the functional active sites of metal-acid at nanoscale for catalyzing hydroconversion of biomass is of great important in sustainable chemical industry. Herein, 10Ni-4Co@NHZ-5-AT with synergistic metal centers and Lewis acidic sites (LASs) was successfully prepared by a simple two-stage strategy. The characterization results indicated that removal Al or/and Si atoms of nano-HZSM-5 crystals through alkali-treatment could obtain the NHZ-5-AT with rough surface, more crystal defects, and strong LASs, which can improve the dispersion of Ni-Co active phases to enhance the catalytic hydroconversion performance. As a demonstration, the yields of derived PCAs (all dimers and trimers) from benzyoxybenzene (BOB) are as high as 85.2 mol% at 200 °C under 5 MPa initial H₂ pressure (IHP) for 100 min. Correspondingly, the electrostatic potential distribution of BOB and derived monomers through DFT calculation indicates that > C_ar-OH in aromatic intermediates with multiple accessible sites is prone to bind with benzylium or benzyl radical fragments, which speculated that PACs are mainly produced from C-C coupling by inducing cation/radical fragments to activate aromatic α-C over Ni-Co@NHZ-5-AT. Especially, Ni-Co@NHZ-5-AT catalyst with synergistic Ni-Co centers and LASs can activate H₂ to H^…H, ^δ+H^…H^δ−, H⁺, and H· to facilitate the catalytic hydroconversion of BOB to obtain PACs via multiple cascade reaction steps. These findings inspired the exploration the metal-acid bifunctional catalysts for conversion of biomass to high-density liquid fuels.