The purification of biofuels becomes a challenging issue because of the harmfulness of remaining phenolic molecules for human health and engines. To this end, protonic Y zeolites with different Si/Al ...ratios were explored as effective adsorbent materials to remove phenol from isooctane solution by using a dual experimental/computational strategy. Phenol was selectively removed from isooctane over HY and USY zeolites with a maximal adsorption capacity of 2.2 mmol·g–1, which corresponds to 3–4 phenol molecules per zeolitic supercage. The adsorption equilibrium was reached faster over dealuminated zeolites, due to the presence of large pores at the expense of microporosity as well as a low density of acidic sites. We further evidence that the presence of acid sites limits the regeneration capacity since phenol was strongly adsorbed on both Brønsted and Lewis acid sites. USY zeolite with the highest Si/Al ratio presents the best regeneration capacity since it has the lower aluminum loading. A fundamental understanding of these performances was obtained by coupling characterization (infrared spectroscopy, breakthrough curves, and desorption experiments) and modeling tools (Grand Canonical Monte Carlo and Density Functional Theory).
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•Phenol condensed in Y zeolite supercages but adsorbed on external silanol groups.•HY selectively adsorbed phenol in presence of toluene and linear hydrocarbon.•Easy regeneration ...requires low amount of acidic sites.
This paper investigates the parameters that influence the selective adsorption of phenol, toxic molecule, from a semi-model biofuel mixture containing alkanes and different proportions of aromatic compounds. The adsorption capacity, selectivity and regeneration ability of different adsorbents, i.e. zeolites, silica-based solids, alumina and activated carbon, were related to their textural properties and the nature, strength or location of their acidic sites. This work demonstrates that phenol differently adsorbs in the micropores and mesopores. In the micropores of faujasites, phenol is condensed into the supercages. Otherwise, in the mesopores of the zeolite, phenol interacts with the silanol groups. On purely siliceous adsorbents, a ratio of one phenol adsorbed on one silanol group could be established. As for selectivity, the strong acidic sites of the faujasites are necessary to favor phenol adsorption compared to toluene. By contrast, the amount of strong Brønsted and Lewis acid sites limits regeneration. Hence, a compromise has to be found and the best performances were obtained using a slightly dealuminated zeolitic adsorbent presenting both micro and mesopores.
A fine tuning of the Brønsted acidity of the hydrotreatment catalyst (by boron addition) leads to progressive changes of the electronic properties of the Mo and Co–Mo sulfided phases. This change ...markedly improved the hydrogenation activity in HDN test as well as in HDS of refractory molecules for Mo catalysts.
•Support Brønsted acidity monitoring.•Control of the sulfide site electronic properties.•Fit of the hydrogenation activity.
Aluminas with different boron loadings were prepared by impregnation with H3BO3 solutions and then used to prepare pure Mo and CoMo catalysts. According to infrared (IR) spectroscopy of 2,6-dimethylpyridine, the acid properties of the alumina have been finely tuned by boron addition. The effect of alumina acidity change on the properties of sulfided Mo and CoMo has been characterized using transmission electron microscope, X-ray photoelectron spectroscopy, and IR spectroscopy of CO-adsorption as well as model compound reactions as thiophene hydrodesulfurization (HDS), 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS and 2,6-dimethylaniline (DMA) hydrodenitrogenation (HDN). The acidity change of alumina has a direct influence on the electronic properties of MoS2 and CoMoS sites but not substantially modifies the morphology and dispersion of the sulfide phase. The results point out a relationship between the Brønsted acidity of the support and the electronic properties of the MoS2 and CoMoS phase. The change of the electronic properties of the active sites has a marked positive influence on the hydrogenation activity of the active phase. The performances of the Mo and CoMo catalysts in the reactions of HDS of thiophene and 4,6-DMDBT and HDN of DMA have been related to the variations of the structural and electronic properties resulted from boron addition.
In this work, the effect of citric acid (CA) on the structure and activity of Ni-promoted WS2 particles supported on γ-Al2O3 were investigated by HRTEM (high resolution transmission electron ...microscopy), HR STEM-HAADF (high resolution scanning transmission electron microscopy equipped with high angular annular dark field detector), CO adsorption followed by infrared (IR) spectroscopy, and thiophene hydrodesulfurization (HDS) test. It is shown that CA addition increases the thiophene HDS activity. This may be directly ascribed to the increase in NiWS site concentration detected by IR spectroscopy. HRTEM emphasizes that the addition of CA to NiW catalysts decreases the average size of the particles. This is confirmed by HR STEM-HAADF that even evidences the presence of nanoclusters on NiW catalysts prepared with CA. Hence, local and global analysis of the NiW samples are in good agreement to account for the increase of NiWS site concentration by CA addition. Then the contrast and interatomic distances were analyzed in the atomic-scale images obtained by HR STEM-HAADF. These measurements allow identification of the nature of the atoms in the core and edge of the sulfided particles. The metal atoms of particle core are only W ones, whereas the edges of the particles could be either fully promoted with detection of only Ni atoms or partially promoted with detection of both Ni and W atoms. Accordingly, IR spectroscopy evidenced edge sites with different promotion degrees.
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•Modification of MoS2 slab morphology (S-edge/M-edge ratio) by citric acid addition.•Differentiation of M-edge and S-edge reactivity on real-like catalysts.•Formation of sulfur ...vacancy easier on M-edge.•Preferential thiophene adsorption on S-edge.•S-edge is intrinsically more active than M-edge for thiophene HDS.
Citric acid was used as chelating agent to prepare a series of MoS2/Al2O3 catalysts. CO adsorption followed by infrared spectroscopy characterization (IR/CO) was employed to probe the M-edge and S-edge of MoS2 slabs on these catalysts. Addition of citric acid promotes the growth of S-edge, whereas it inhibits that of M-edge: The morphology of MoS2 is progressively modified from a slightly truncated triangle with predominately M-edge to a hexagon with both M-edge and S-edge with increasing citric acid amount. Such morphology change is of great importance to the catalytic performance as M-edge and S-edge demonstrate different reactivity in hydrodesulfurization (HDS) reactions. Indeed, IR/CO data reveal that sulfur vacancy creation occurs more easily on M-edge, whereas at room temperature, thiophene tends to adsorb more strongly on S-edge. Moreover, parallel between IR/CO study and HDS test shows that S-edge has a higher intrinsic activity than M-edge in thiophene HDS reaction.
Low temperature CO adsorption followed by IR spectroscopy (IR/CO) characterization was used to depict the MoS2 morphology change with sulfidation temperature on MoS2/Al2O3 catalyst. It is found that ...the morphology of MoS2 slabs on MoS2/Al2O3 catalyst under typical sulfidation temperature range (573 to 723 K) is a truncated triangle exposing both the M-edge and S-edge. Moreover, the IR/CO data indicate that the truncation degree (ratio of S-edge/M-edge) of MoS2 slabs gradually increases with increasing sulfidation temperature. This finding is in line with density functional theory calculation on model catalysts, providing IR evidence of MoS2 morphology change with sulfidation temperature on an Al2O3-supported catalyst. As a further step, it is also found that the MoS2 morphology is strongly influenced by MoS2–Al2O3 interactions under the same sulfidation temperature.
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•Mg addition decreases the weak Brønsted acidity of alumina.•Decrease of Brønsted acidity affects the electronic properties of the MoS2 phase.•Hydrogenation activity of MoS2 is ...balanced by electronic properties and Mg element.•O2− sites on the support may be beneficial for hydrogenation activity by spillover effects.
The effect of Mg addition on alumina on the properties of sulfided Mo/Al2O3Mg(x) (x=0–3.2wt.% Mg) catalysts has been investigated using various characterization techniques (transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy) and catalytic tests (hydrodesulfurization of 4,6-dimethyldibenzothiophene and hydrodenitrogenation of 2,6-dimethylaniline). It is observed that Mg addition decreases the weak Brønsted acidity and increases the basicity of the alumina support. Mg addition also increases the electronic density of the MoS2 slabs, as revealed by the shift of the frequency of CO adsorbed on the sulfide Mo phase. A parallel between the increase of the electronic density of the sulfide slabs and the decrease of the Brønsted acidity of the support is evidenced. The addition of Mg does not lead to significant changes of dispersion of the MoS2 phase but tends to decrease its stacking. The addition of a small amount of Mg increases the hydrogenation activity of the Mo catalysts for hydrodesulfurization and hydrodenitrogenation. This beneficial effect is more marked in case of co-addition of Mg and B. These data show that the addition of Mg, through the modification of the electronic properties of the sulfide sites and by the presence of Mg, leads to improvement of the intrinsic hydrogenation activity of Mo catalyst supported on alumina.
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•The rational design of phosphated-zirconia leads to a highly active and selective catalyst for propanol dehydration to propene.•At low loading, the phosphate species form a monolayer ...of pyrophosphate on zirconia, while they develop as 3D blocks of orthophosphate at high loading.•The strong Brønsted acidic sites present on orthophosphate supported on zirconia are active for propanol dehydration.
High surface area phosphated-modified zirconia was prepared by adding phosphoric acid to zirconium hydroxide (0–3.8P atoms nm−2). Up to 0.8P atoms nm−2, phosphate species are present mainly as monolayer of pyrophosphate (P2O74−) whereas for larger loading of phosphorus, 3D blocks of orthophosphate HPO42− are formed. The formation of these phosphate species leads to marked changes in the acid-base and catalytic properties of the oxides. When major POx species are pyrophosphate (0–0.8P atoms nm−2), basicity and Lewis acidity of zirconia decreased. In parallel, Brønsted acidic sites with weak (bidentate zirconia OH in the vicinity of P atom) and moderate (OH associated with pyrophosphate species) acidic strength are created. By contrast, orthophosphate species that mostly devellopps when larger amount of phosphate is introduced (>0.8P atoms nm−2), generates stronger Brønsted acid sites (OH associated with orthophosphate phase). The correlation between the amount of these Brønsted acid sites and the rate of propene formation points out that the development of orthophosphate species on zirconia is a key factor to make this catalyst very active for propanol dehydration into propene.
The review focuses on presenting recent findings on CO2 methanation plasma-catalytic process. In order to understand the background of the research, firstly a summary of thermal catalytic CO2 ...methanation is presented. Secondly, discussion on plasma CO2 hydrogenation including various plasma types and process parameters is addressed. Catalytic CO2 methanation is already an industrial process achieving high conversions of CO2 and CH4 yield. However, the need to optimize this process (decrease reaction temperature, increase catalyst activity, selectivity and stability) resulted in the development of plasma technology. It was proven that plasma can actively convert CO2. The main product of plasma CO2 hydrogenation is, however, carbon monoxide. Therefore, a plasma process is not selective for CH4 production and the presence of a catalyst is necessary to effectively convert CO2 to CH4 under plasma conditions. The study of plasma-catalytic CO2 methanation is quite a new topic focused mainly on the application of dielectric barrier discharge plasma and Ni-based catalyst. This review summarizes recent advantages of the plasma catalytic process and discusses possible directions of catalyst development.
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•Plasma-catalytic CO2 methanation may become an important technology for H2 storage and CO2 valorisation.•CO2 activation in plasma requires catalyst to produce CH4.•Catalyst for plasma process should be active in thermal catalysis.•Beneficial effect of plasma-catalysis may be enhanced via adjustment of catalyst properties and plasma operating conditions.
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