NiMo-MMO catalyst derived from LDHs precursors toward the deep hydrogenation of pyrene

Abstract

A series of Ni-based catalysts were prepared via structural topological transformation from the Ni@Al2O3 layered double hydroxides (LDHs) precursors, and applied for the deep catalytic hydrogenation saturation of pyrene in a high-pressure reactor. The pore structures, active species dispersion, surface morphology, amount and type of acid of the prepared catalysts were characterized by BET, XRD, SEM, TEM, XPS, SEM, NH3-TPD and Py-IR. We studied the influence of physicochemical properties of Ni-based catalysts on the regularity and mechanism of deep hydrogenation of pyrene. Meanwhile, the synergy between Ni and Mo, and the interaction between active metals and support were discussed to further reveal the constitutive relationship during the hydrogenation reaction of pyrene. The results of the evaluation of the catalytic hydrogenation of pyrene show that the as-prepared NiMo mixed metal oxide (MMO) catalyst showed excellent catalytic activity: ~95% pyrene conversion, 90.12% for the selectivity of deep hydrogenation products (hexahydropyrene, decahydropyrene and hexadecahydropyrene). It was expected that the successfully preparation and utilization of NiMo-MMO catalyst could provide a theoretical basis for the design of this kind of catalysts for deep catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs).

1. Introduction

Coal is an important energy resource in the world, particularly in China, where coal production and consumption exceed 50% of the world's total [1]. As a by-product of coal carbonization, high-temperature coal tar (HTCT) has a high annual output. In recent years, China's annual off-take potential of HTCT has reached approximately 26 Mt, which consists of 95% PAHs [2]. PAHs are important raw materials for preparing medicines, hydrogen donors, dyes, and pesticides [3]. Therefore, the processing and utilization of PAHs has received increasing attention in the past few years, particularly the hydrogenation of PAHs [4]. The deep hydrogenation of PAHs is a clean and efficient process that is important for the value-added application of HTCT [5].

In reactions of hydrogenation and dehydrogenation, low molecular weight PAHs (mainly naphthalene, anthracene, and phenanthrene) have been extensively investigated [6,7]. However, the intrinsic properties of highly condensed PAHs make their hydrogenation susceptible to thermodynamic and kinetic constraints, as well as strong effects of resonance, steric hindrance, and competitive adsorption [8]. Thus, choosing suitable high molecular weight dense ring aromatic hydrocarbons as a model compound allows for a better understanding of the hydrogenation mechanism of PAHs. Pyrene (PY) is a complex tetracyclic aromatic hydrocarbon, and the hydrogenation products of PY are high value-added materials in the petroleum and pharmaceutical industry [9], which could be regarded as a model for studying the hydrogenation of PAHs.