Surfactant-confined synthesis of novel W-precursor and its application in the preparation of efficient hydrotreating catalysts

Abstract

This article presents a surfactant-dispersed W precursor to prepare highly active hydrotreating (HDT) Al2O3-supported NiW catalyst. The proposed strategy converts polytungstate anions into surfactant-dispersed decatungstate precursor with a core–shell structure, which is then successfully deposited onto the pore channels of γ-alumina under moderate hydrothermal conditions. A variety of characterization methods, including X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), N2 adsorption–desorption, fourier transform infrared (FT-IR), ultraviolet–visible spectroscopy (UV–Vis), Raman spectroscopy, and H2 temperature programmed reduction (H2-TPR) were employed to identify the structure and composition of synthesized W precursor, as well as its states on the catalyst surface after drying and after calcination. After sulfidation, slab morphology and proportion of WS2 and NiWS phases on the as-obtained sulfide catalysts were determined by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Results show that the hydrothermal deposition method ensures the the uniform distribution of the W species. Moreover, the long-chain quaternary ammonium cation shell of as-prepared W-precursor not only weakens the metal-support interaction, but also acts as a dispersant to prevent the aggregation of W species after decomposition. The multiple effects facilitate the formation of highly dispersed WS2 slabs with enhanced stacking, and therefore yield a larger number of accessible NiWS edge sites after Ni incorporation. The resulted W/Al2O3 and NiW/Al2O3 catalysts exhibits higher HDT activity for dibenzothiophene (DBT) and quinoline (Q) removal in comparison with that of reference catalysts prepared from conventional precursor. The present work explores the essential role of surfactants in adjusting metal-support interaction and controlling the morphology of active phases, and reveals the directing effects of W-precursors on the size and morphology of active phases, thereby further shedding light on the rational design and controllable fabrication of supported WS2 for efficient HDT.