Effect of β-zeolite nanoclusters on the acidity and hydrodesulfurization activity of an unsupported Ni Mo catalyst

The Influence of Pore Structure and Acidity on the Hydrodesulfurization of Dibenzothiophene over NiMo-Supported Catalysts

A series of mesoporous materials of SBA-16 were in situ incorporated into ZSM-5 crystallites via a two-step self-assemble method, and hydrodesulfurization (HDS) catalysts were prepared on the corresponding ZSM-5/SBA-16 (ZS) composites. The characterization results indicated that ZSM-5 nanoseeds were fabricated into the silica framework of the ZS composites, and the three-dimensional Im3m cubic structure of SBA-16 was retained simultaneously. In addition, the ZS series materials possessed open pores and large surfaces, which would facilitate the diffusion of reactants in the mesoporous channels. Moreover, the introduction of ZSM-5 seeds into composites could enhance the acidities of supports. As a result, the NiMo/ZS series catalysts exhibited high activities for DBT HDS processes. The NiMo/ZS-160 catalyst exhibited the highest catalytic efficiency (96.5%), which was apparently attributed to the synergistic contributions of the physicochemical properties of ZS supports and the dispersion states of active metals. Correspondingly, DBT HDS reactions over the NiMo/ZS series catalysts mainly proceeded via a hydrogenation desulfurization route that benefitted from the enhanced acidities especially the total Brønsted acid.

Multishell Hollow Metal/Nitrogen/Carbon Dodecahedrons with Precisely Controlled Architectures and Synergistically Enhanced Catalytic Properties

Multishell hollow nanoarchitectures are one of the most important branches in the nanomaterial field due to their enormous potential in many fields, but synthesizing them in a well-controlled manner remains challenging. Herein, we present a general strategy for the construction of multishell hollow metal/nitrogen/carbon dodecahedrons (metal@NC) with well-defined and precisely controlled architectures. This strategy is based on the pyrolysis of multilayer solid ZIFs prepared by a step-by-step crystal growth approach, which enables precise control over the shell number and composition of the resultant hollow metal@NC. Impressively, our strategy can be further extended to the synthesis of yolk@multishell hollow structures or multishell hollow structures that are assembled by carbon nanotubes. The multishell hollow structures can efficiently facilitate the mass diffusion, which together with the high dispersity and increased surface area are responsible for their significantly enhanced catalytic performances for the selective hydrogenation of biomass-derived furfural to cyclopentanol when compared with their solid and single-shell counterparts. We anticipate that our general strategy would shed light on the rational design and accurate construction of other complex multishell hollow materials for various important yet challenging applications.

Acid Modification of the Unsupported NiMo Catalysts by Y-Zeolite Nanoclusters

Unsupported NiMo catalyst has high hydrogenation activity due to its high active site distribution. However, low specific surface area and pore distribution greatly limit the efficient utilization of the active components. The Y-zeolite nanoclusters were hydrothermally synthesized and introduced into the unsupported NiMo catalysts from a layered nickel molybdate complex oxide. The XRD, N2 adsorption-desorption, FT-IR, Py-IR, SEM, NH3-TPD, and TEM were used to characterize all catalysts. The dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction was performed in a continuous high pressure microreactor. The results showed that the specific surface area, pore volume, and average pore size of the unsupported NiMo catalysts were greatly increased by the Y-zeolite nanoclusters, and a more dispersed structure was produced. Furthermore, the Lewis acid and total acid content of the unsupported NiMo catalysts were greatly improved by the Y-zeolite nanoclusters. The HDS results showed that the unsupported NiMo catalysts modified by the nanoclusters had the same high desulfurization efficiency as the unmodified catalyst, but had more proportion of direct desulfurization (DDS) products. The results offer an alternative to reducing hydrogen consumption and save cost in the production of ultra clean diesel.