Top1. Supported 2D Layer Mo(W)S2 Catalysts
Supporting the Mo(W)S2 nanosheeets on a high surface area material is beneficial to increases the number of active sites via enhanced dispersion and distribution of active phases. Meanwhile cheaper support decreases the cost of industry catalysts.
In petroleum and chemical industry, conventionally, the Mo(W)S2 nanosheets is supported on the alumina support and promoted by Co or Ni co-catalysts. In the sulfiding process before usage, the Mo(W)S2 active phases are yielded in situ by the sulfidation of the oxidic precursors, which are in advance prepared through three steps, i.e., impregnation, drying and calcination. The almost exclusive use of alumina as support is due to its outstanding textural and mechanical properties and the relatively low cost. However, the undesirable very strong metal-support interaction has urged to introduce new supports.
Recently, ordered mesoporous materials with high surface area, large pore volume, ordered pore structure, and good thermal and mechanical stabilities have been studies as the support of Mo(W)S2 based nanosheets. They act as host to support the active species and/or behave as a nanoreactor to provide a space for the catalytic reactions. According to the pore symmetry, these meso materials can be classified as 2D (e.g. HMS, SBA-15 and MCM-41) and 3D (e.g. MCM-48, SBA-16, KIT-6, and FDU-12) architectures (Fan et al. 1998). When incorporated into the pores of the support, the active phases will be confined by the pore size and pore structure, evoking interesting modulation of the structural and electronic properties.
When MoS2 nanosheets were supported on the FDU-12 mesoporous material, with the increasing of Mo loading, the layer structure of MoS2 active phase transforms from straight to slightly curved then to ring-like and finally to spherical like morphology in the pores due to the restriction of the cage-like pores of FDU-12. And catalyst with 10 wt% MoO3 loading shown the hydrodesulfurizaiton (HDS) performance of dibenzothiophens (DBT) superior to those supported on commercial 𝛾-Al2O3 and SBA-15 (Liu et al 2016a).
SBA-16-supported ternary CoMoW catalysts were demonstrated to be more active in HDS of DBT reaction than their SBA-15-supported counterparts (Huirache-Acuña et al. 2009). It was attributed to that SBA-16 substrate possesses super large cage-like mesoporous structure with a high surface area and high thermal stability, thus providing favorable mass transfer kinetics.
For supported Co(Ni)MoW catalysts, Huirache-Acuña et al. (2012) compared the effects of the support (HMS versus SBA-16), promoter (Co vs. Ni) and modification of support with Al on the HDS of DBT. The results revealed that NiMoW/Al-HMS catalyst was more active than all Co-promoted catalysts (including a commercial CoMo/Al2O3 catalyst). The HDS activity was markedly influenced by the textural properties of support and the dispersion of the active phases. After Al doping, the presence of extra framework AlNO3 phases on the surface of CoMoW/Al-SBA16 suppressed its HDS activity by formation of a less active “onion-type” Mo(W)S2 structure.
Mendoza-Nieto et al. (2012) compared the HDS activities of NiMo catalysts supported on different types of silica supports (nanostructured supports of MCM-41 and SBA-15 types and commercial amorphous silica) and the same ones modified by TiO2 grafting. Titania addition to all silica supports resulted in an increase in the HDS activity. However, this increase was smaller for the MCM-41 support than for the SBA-15 and amorphous silica supports. The NiMo/Ti-SBA-15 catalyst was found significantly more active (~40%) than the reference NiMo/γ-Al2O3 catalyst for HDS of 4,6-DMDBT. It revealed that the increased metal-support interaction after titania grafting improved the dispersion of Mo oxide species on Ti-SBA-15 support.