Structure and Quantification of Edge Sites of WS₂/Al₂O₃ Catalysts Coupling IR/CO Spectroscopy and DFT Calculations

Abstract

IR spectroscopy of CO adsorption (IR/CO) and Density Functional Theory (DFT) calculations on sulfide W/Al2O3 catalyst were investigated for an insight into the sulfide edge sites. Parallel between experimental and theoretical results allow to assign the ν(CO) bands at 2121 and 2066 cm−1 to CO adsorption on M‐ and S‐edge sites of WS2 phase, respectively. Through a careful analysis of CO spectra on well‐selected W catalysts, the molar attenuation coefficients for CO adsorbed on the two exposed edges could be determined. This allowed the morphology of WS2 slabs to be calculated. This work shows that increasing the W loading (6–20 wt% W) changes the slab morphology from an almost pure triangle exhibiting mostly M‐edge to a truncated triangle. On W as well as on Mo sulfide catalysts, IR spectroscopy and DFT calculation show that CO adsorption allows to account for M‐ and S‐edge sites, and thus of the morphology of sulfide slabs. It was shown that increasing the W loading shifts the slab morphology from a triangle exposing predominantly M‐edge towards a more hexagonal shape. For close to monolayer coverage of alumina, Mo and W sulfide slabs present similar shape i. e. truncated triangle. However, edge sites of WS2 slabs clearly exhibit greater stability under H2 atmosphere than Mo sulfided ones.

Effect of sulfidation pressure on the structure and activity of Ni(CyDTA)W/γ-Al2O3 hydrodesulfurization catalysts

“…From these IR spectra, it is observed that the addition of Ni to W brings three new bands at 2127, 2093 and 2079 cm −1 . These wavenumbers are very close to those reported by Duchet et al [31], Zuo et al [15], Travert et al [33] and more recently by Zavala-Sanchez [28,29]. These authors proposed that these three bands characterize interaction between Ni and W but with different environments.…”

“…Infrared spectroscopy of adsorbed CO provides interesting information for investigation of the surface species of sulfide catalysts like the NiW ones. In particular, IR signal of CO (IR/CO) allows discriminating unpromoted W phase from NiWS one [15,28,29]. Figures 5,6 and 7 show the IR spectra of CO adsorbed on sulfided W, NiW and NiW(4.0), respectively.…”

“…Note that their frequencies can be shifted according to the support nature [15,30,31]. Recent parallel between IR/CO spectroscopy and DFT calculations allow assigning these two bands to CO adsorbed on M-and S-edge sites of the WS2 slab, respectively [28]. It should be mentioned that, on Mo sulfided catalysts, IR/CO spectroscopy also allows to distinguish Mo sites located on M-edge from Mo sites located on S-edge [17].…”

Biofuel purification: Coupling experimental and theoretical investigations for efficient separation of phenol from aromatics by zeolites

“…In that sense, in-situ IR spectroscopy is a powerful technique for investigating the interaction modes of adsorbates on zeolite active sites. [39,40] The combination of experiments and predictive calculations for IR spectra can be critical for the allocation of the spectra related to the adsorption modes of the different adsorbate/adsorbent systems. [39][40][41][42] In the present work, in-situ IR spectroscopy experiments have been combined with periodic DFT in order to assign the vibrational frequencies of the different adsorption modes of phenol and toluene over proton and sodium exchanged zeolites.…”

“…[39,40] The combination of experiments and predictive calculations for IR spectra can be critical for the allocation of the spectra related to the adsorption modes of the different adsorbate/adsorbent systems. [39][40][41][42] In the present work, in-situ IR spectroscopy experiments have been combined with periodic DFT in order to assign the vibrational frequencies of the different adsorption modes of phenol and toluene over proton and sodium exchanged zeolites. The interaction energy of the most stable adsorbed configuration of phenol and toluene have been compared for the two zeolites with the purpose to select the most suitable cation-type for achieving the selective removal of phenol from synthetic biofuel feed (isooctane + 1 wt.% phenol + 1 wt.% n-nonane + 40 wt.% toluene).…”