Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Filters applied. Clear all
. 2019 Nov 12;12(22):3727.
doi: 10.3390/ma12223727.

Bimetallic Nanoparticles as a Model System for an Industrial NiMo Catalyst

Affiliations
Free PMC article

Bimetallic Nanoparticles as a Model System for an Industrial NiMo Catalyst

Sara Blomberg et al. Materials (Basel). .
Free PMC article

Abstract

An in-depth understanding of the reaction mechanism is required for the further development of Mo-based catalysts for biobased feedstocks. However, fundamental studies of industrial catalysts are challenging, and simplified systems are often used without direct comparison to their industrial counterparts. Here, we report on size-selected bimetallic NiMo nanoparticles as a candidate for a model catalyst that is directly compared to the industrial system to evaluate their industrial relevance. Both the nanoparticles and industrial supported NiMo catalysts were characterized using surface- and bulk-sensitive techniques. We found that the active Ni and Mo metals in the industrial catalyst are well dispersed and well mixed on the support, and that the interaction between Ni and Mo promotes the reduction of the Mo oxide. We successfully produced 25 nm NiMo alloyed nanoparticles with a narrow size distribution. Characterization of the nanoparticles showed that they have a metallic core with a native oxide shell with a high potential for use as a model system for fundamental studies of hydrotreating catalysts for biobased feedstocks.

Keywords: NiMo catalyst; alloyed nanoparticles; industrial catalysts; lignin; model catalyst.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM image of the nanoparticles with the graph showing the size distribution. (a) The SEM image, showing nanoparticles evenly dispersed on the SiOx substrate; (b) The size distribution of the particles selected by the DMA. Singly charged particles that pass through the DMA have a diameter of 25 nm, while a small fraction of doubly charged particles has a diameter of 35 nm.
Figure 2
Figure 2
(a) Typical STEM HAADF image of three nanoparticles. An example of STEM XEDS mapping of Mo (b) and Ni (c) indicating that the Ni and Mo are homogeneously mixed in all three nanoparticles. The scale is the same in (ac). (d) The high-resolution TEM image of one nanoparticle shows that the nanoparticles have a crystalline structure with a lattice distance of 2.5 Å.
Figure 3
Figure 3
XPS spectra of Ni 2p3/2, O1s, and Mo 3d. The fits indicate that Ni and Mo are mixed, forming an alloy. (a) The Mo 3d spectrum is complex and the fitted components are color-coded to account for the spin-orbit splitting, and only the binding energy of the 3d5/2 component is indicated. The peaks at 228.44 eV and 231.57 eV (blue) originate from metallic Mo. The peaks at 229.51 eV and 232.62 eV (yellow) are interpreted as originating from Mo4+. The most shifted component in binding energy at 232.71 eV and 235.81 eV (green) is assigned to Mo6+. (b) The O1s spectrum has two clear components assigned to the SiOx in the substrate and the oxide in the particles. (c) The Ni 2p3/2 spectrum is fitted with three components, where the peak at 853.2 eV originates from metallic Ni, while the component at 856 eV is assigned to the oxide in the NiMoO4 alloy.
Figure 4
Figure 4
STEM HAADF and XEDS mapping of the industrial NiMo/δ-Al2O3 catalyst. (a) STEM HAADF image at one edge of the catalyst. The blue squares indicate the region in which elemental analysis was performed. The scale is the same for all images. Strong Al (b) and O signals (c) were observed in the XEDS mapping image, originating largely from the alumina support. The much weaker signals from Mo (d) and Ni (e) are due to the low concentrations of these metals in the catalyst, but XEDS mapping indicates that the catalytically active Ni and Mo are well-dispersed over the support. The loading of Ni and Mo is estimated to be submonolayer on the δ-Al2O3 surface, based on the measured wt % of the Ni and Mo and the surface area of the support.
Figure 5
Figure 5
PXRD diffraction pattern obtained from the industrial NiMo/δ-Al2O3 catalyst where the majority of the peaks originate from planes of the δ-Al2O3 support (indicated by hkl indices). A broad, weak diffraction peak is, however, also visible at 26.7° which corresponds to the NiMoO4 structure.
Figure 6
Figure 6
Chemical analysis of the NiMo/δ-Al2O3 sample was performed using XPS and H2-TPR. (a) XPS spectra of the Ni 2p3/2 and (b) Mo 3d regions. Fitting the spectra indicates a strong interaction between Ni and Mo. (c) H2-TPR spectra from the Mo/δ-Al2O3, Ni/δ-Al2O3, and NiMo/δ-Al2O3 catalysts. The results show that Ni promotes the reduction of the Mo oxide.
Figure 7
Figure 7
A schematic of the NiMo nanoparticle produced, where the high energy of the electrons in TEM-XEDS probe a cross-section of the particle, while XPS provides information of the surface. The XPS results indicate oxide formation on the outer atomic layers with a higher Ni content than in the core of the particles.

Similar articles

See all similar articles

References

    1. Gnansounou E., Pandey A. Life-Cycle Assessment of Biorefineries. Elsevier; Amsterdam, The Netherlands: 2017. p. 312.
    1. Abhilash P., Thomas D. Biopolymer Composites in Electronics-Biopolymers for Biocomposites and Chemical Sensor Applications. Elsevier; Amsterdam, The Netherlands: 2017.
    1. Mortensen P.M., Grunwaldt J.D., Jensen P.A., Knudsen K.G., Jensen A.D. A review of catalytic upgrading of bio-oil to engine fuels. Appl. Catal. Gen. 2011;407:1–19. doi: 10.1016/j.apcata.2011.08.046. - DOI
    1. Abdelaziz O.Y., Meier S., Prothmann J., Turner C., Riisager A., Hulteberg C.P. Oxidative Depolymerisation of Lignosulphonate Lignin into Low-Molecular-Weight Products with Cu–Mn/δ-Al2O3. Top. Catal. 2019;62:639–648. doi: 10.1007/s11244-019-01146-5. - DOI
    1. Dupont C., Lemeur R., Daudin A., Raybaud P. Hydrodeoxygenation pathways catalyzed by MoS2 and NiMoS active phases: A DFT study. J. Catal. 2011;279:276–286. doi: 10.1016/j.jcat.2011.01.025. - DOI
Feedback