A synthesis strategy combining an impregnation approach with a self-combustion process to develop Ni-based catalysts (5–15 wt% of Ni) supported on mesoporous CeO2 is proposed. This strategy favors an intimate Ni–CeO2 coupling enabling a fine NiO dispersion in form of ultrasmall particles/clusters on CeO2. Comprehensive characterization, including XRD, Raman, N2-physisorption, HRTEM, STEM-EDXS/EELS, H2-TPR, CO2-TPD, and H2-TPD, revealed a strong metal–support interaction and promotion of oxygen vacancy formation. CO2 methanation testing under atmospheric pressure demonstrated high CO2 conversion and near-complete CH4 selectivity. At lower reaction temperatures, CO₂ conversion increased with Ni loading, which can be reasonably attributed to the higher concentration of oxygen vacancies. However, above 325 °C, the catalyst with the lowest Ni content exhibited performances comparable to the other samples, likely due to its very high Ni dispersion. Notably, a critical comparison with state-of-the-art systems, despite differences in operating conditions, highlighted the outstanding performance of the catalysts, particularly in terms of methane productivity (256-486 ), CO2 conversion (68-85 mol%) and CH4 selectivity (close to 100%) under mild conditions. The results place the obtained Ni–CeO2 catalysts among the most effective systems reported to date for CO2 methanation with strong potential for integration in sustainable catalytic technologies.

The catalytic performance in the direct CO2 methanation of a model biogas is investigated on NiO-CeO2 nanostructured mixed oxides synthesized by the soft-template procedure with different Ni/Ce molar ratios. The samples are thoroughly characterized by means of ICP-AES, XRD, TEM and HR-TEM, N2 physisorption at -196 & DEG;C, and H2-TPR. They result to be constituted of CeO2 rounded nanocrystals and of polycrystalline needle-like NiO particles. After a H2-treatment at 400 & DEG;C for 1 h, the surface basic properties and the metal surface area are also assessed using CO2 adsorption microcalorimetry and H2-pulse chemisorption measurements, respectively. At increasing Ni content the Ni0 surface area increases, while the opposite occurs for the number of basic sites. Using a CO2/CH4/H2 feed, at 11,000 cm3 h-1 gcat-1, CO2 conversions in the 83-89 mol% range and methane selectivities >99.5 mol% are reached at 275 & DEG;C and atmospheric pressure, highlighting the very good performances of the investigated catalysts.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [CnMIM][NTf2] n = {2, 10}, + ethanol or + N-methyl-2-pyrrolidone have been investigated to determine excess molar enthalpies, HE, and excess partial molar enthalpies of components, $$H_{1}^{{\text{E}}}$$ and $$H_{2}^{{\text{E}}}$$ , over the entire mole fraction, x1, range, at 298.15 K and 0.10 MPa. Ionic liquids, ILs, were pre-treated by heating and by using activated molecular sieves. Both mixtures in ethanol are endothermic and the $$H_{{\text{i}}}^{{\text{E}}}$$ of the components are always positive while those in NMP are exothermic and the corresponding values of $$H_{{\text{i}}}^{{\text{E}}}$$ are negative, in the whole x1 range. The deviations from ideality are quite significant, being the HE values at equimolar composition, $$H_{{{\text{eq}}}}^{{\text{E}}} \pm u$$ ; (+ 1800 ± 40 and + 2110 ± 10) J mol−1 for ethanol-containing mixtures and (− 1410 ± 10 and − 1980 ± 20) J mol−1 for NMP-containing mixtures ( $$u$$ is the standard uncertainty). The values of the excess partial molar enthalpies at infinite dilution of the components, $$H_{\rm i}^{{{\text{E,}}\infty }}$$ , show regular trends. The $$H_{1}^{{{\text{E,}}\infty }}$$ are always greater than the $$H_{2}^{{{\text{E,}}\infty }}$$ ; their ratio is about 1.8 for mixtures in EtOH and 2.5 for NMP-containing mixtures. The greatest thermal effects are found when the molecular compound acts as a solvent in the dissolution of one mole of IL, under extreme dilution condition.

In this study, CeO2, La2O3, and CeO2-La2O3 mixed oxide catalysts with different Ce/La molar ratios were prepared by the soft template method and characterized by different techniques, including inductively coupled plasma atomic emission spectrometry, X-ray diffraction, N2 physisorption, thermogravimetric analysis, and Raman and Fourier transform infrared spectroscopies. NH3 and CO2 adsorption microcalorimetry was also used for assessing the acid and base surface properties, respectively. The behavior of the oxides as catalysts for the dimethyl carbonate synthesis by the transesterification of propylene carbonate with methanol, at 160 °C under autogenic pressure, was studied in a stainless-steel batch reactor. The activity of the catalysts was found to increase with an increase in the basic sites density. The formation of dimethyl carbonate was favored on medium-strength and weak basic sites, while it underwent decomposition on the strong ones. Several parasitic reactions occurred during the transformation of propylene carbonate, depending on the basic and acidic features of the catalysts. A reaction pathway has been proposed on the basis of the components identified in the reaction mixture.

Nanosized NiO, CeO2 and NiO-CeO2 mixed oxides with different Ni/Ce molar ratios were prepared by the soft template method. All the samples were characterized by different techniques as to their chemical composition, structure, morphology and texture. On the catalysts submitted to the same reduction pretreatment adopted for the activity tests the surface basic properties and specific metal surface area were also determined. NiO and CeO2 nanocrystals of about 4 nm in size were obtained, regardless of the Ni/Ce molar ratio. The Raman and X-ray photoelectron spectroscopy results proved the formation of defective sites at the NiO-CeO2 interface, where Ni species are in strong interaction with the support. The microcalorimetric and Fourier transform infrared analyses of the reduced samples highlighted that, unlike metallic nickel, CeO2 is able to effectively adsorb CO2, forming carbonates and hydrogen carbonates. After reduction in H2 at 400 °C for 1 h, the catalytic performance was studied in the CO and CO2 co-methanation reaction. Catalytic tests were performed at atmospheric pressure and 300 °C, using CO/CO2/H2 molar compositions of 1/1/7 or 1/1/5, and space velocities equal to 72000 or 450000 cm3·h−1·gcat−1. Whereas CO was almost completely hydrogenated in any investigated experimental conditions, CO2 conversion was strongly affected by both the CO/CO2/H2 ratio and the space velocity. The faster and definitely preferred CO hydrogenation was explained in the light of the different mechanisms of CO and CO2 methanation. On a selected sample, the influence of the reaction temperature and of a higher number of space velocity values, as well as the stability, were also studied. Provided that the Ni content is optimized, the NiCe system investigated was very promising, being highly active for the COx co-methanation reaction in a wide range of operating conditions and stable (up to 50 h) also when submitted to thermal stress.

NiO–CeO2–ZrO2 mixed oxides, with Ni/(Ce + Zr) = 1 mol/mol and different Ce/Zr molar ratios, were prepared by the soft-template method. The chemical composition, texture, structure, and redox features of the synthesized systems were investigated by different techniques. All samples were nanocrystalline (NiO nanocrystal average size 4 nm) and had high surface area and quite an ordered mesoporous system. The catalytic performances in the CO2 conversion into methane were studied at atmospheric pressure, 300 °C, and stoichiometric H2/CO2 molar ratio. Prior to reaction the catalysts were submitted to a mild reduction pretreatment (H2 at 400 °C for 1 h). XRD analysis of the samples after pretreatment showed the presence of small Ni crystals (4–7 nm) on all the samples as well as of some unreduced NiO nanocrystals on the systems with high Zr content, in accordance with H2-TPR experiments, which indicated that NiO reduction is promoted by CeO2 but hindered by ZrO2. The catalytic tests were performed at two different space velocities (72000 and 900000 cm3 h−1 g−1cat) on a series of Ni-based catalysts supported on CeO2–ZrO2 systems with different Ce/Zr ratios, including the two pure oxides. CO2 conversion and selectivity to CH4 (which was always close to 100 mol%) were constant throughout the 6-hour runs. CO2 conversion resulted to increase with CeO2 content in the catalyst, thus indicating the role of the CeO2 component of the support in activating CO2, whereas H2 is activated on the Ni nanoparticles.

Supported nickel catalysts were synthesized, characterized, and employed in the carbon oxides co-methanation process. Five NiO/CeO2-ZrO2 mixed oxides, with the same Ni content and different Ce/Zr molar ratios, were prepared by the soft-template method. They were characterized through ICP-AES, N2 adsorption, XRD, and TPR. Reduced Ni/CeO2-ZrO2 catalysts were obtained by submitting the oxide systems to reduction treatment in H2 at 400 °C. They were characterized by XRD, H2-TPD, and CO2 adsorption microcalorimetry and their catalytic performances in the carbon oxides co-methanation were investigated. Catalytic tests were performed in a fixed-bed continuous-flow microreactor at atmospheric pressure. The effect of experimental conditions (reaction temperature, space velocity, reactants molar ratio) was also studied. Almost complete CO conversion was obtained on any catalyst, whereas CO2 conversion was much lower and increased with Ce content, at least up to Ce/Zr = 1. The beneficial effect of the Ce content could be related to the increased NiO reducibility and to the higher ability to adsorb and activate CO2. However, at high Ce/Zr ratios, it is probably counterbalanced by an interplay of reactions involving CO and CO2.

NiO-CeO₂-ZrO₂ mixed oxides, with Ni/(Ce + Zr) = 1 mol/mol and different Ce/Zr molar ratios, were prepared by the soft-template method. The chemical composition, texture, structure, and redox features of the synthesized systems were investigated by different techniques. All samples were nanocrystalline (NiO nanocrystal average size 4 nm) and had high surface area and quite an ordered mesoporous system. The catalytic performances in the CO₂ conversion into methane were studied at atmospheric pressure, 300 °C, and stoichiometric H₂/CO₂ molar ratio. Prior to reaction the catalysts were submitted to a mild reduction pretreatment (H₂ at 400 °C for 1 h). XRD analysis of the samples after pretreatment showed the presence of small Ni crystals (4-7 nm) on all the samples as well as of some unreduced NiO nanocrystals on the systems with high Zr content, in accordance with H₂-TPR experiments, which indicated that NiO reduction is promoted by CeO₂ but hindered by ZrO₂. The catalytic tests were performed at two different space velocities (72000 and 900000 cm³ h-1 g-1cat) on a series of Ni-based catalysts supported on CeO₂-ZrO₂ systems with different Ce/Zr ratios, including the two pure oxides. CO₂ conversion and selectivity to CH₄ (which was always close to 100 mol%) were constant throughout the 6-hour runs. CO₂ conversion resulted to increase with CeO₂ content in the catalyst, thus indicating the role of the CeO₂ component of the support in activating CO₂, whereas H₂ is activated on the Ni nanoparticles.

Mesostructured NiO-CeO2 mixed oxides, with Ni loadings in the range 5-35 wt% (g(Ni)/g(ceo2)); were synthesized by the hard template procedure using SBA-15 as the template. A hard-templated CeO2 was also prepared and used as the support for depositing Ni (5-35 wt%) by impregnation. Two NiO-Al2O3 catalysts were synthesized for comparison, by impregnating nickel on a commercial gamma -alumina. All the samples were characterized by different techniques as to their chemical composition, structure, morphology, texture, and redox features. The catalytic performance was investigated in the CO2 methanation reaction after mild reduction pretreatment (H-2 at 400 degrees C for 1 h). Catalytic testing was performed under atmospheric pressure, 300 degrees C, 72,000 cm(3)h(-1) g(cat)(-1) and stoichiometric H-2/CO2 molar ratio. High catalytic activity, with CH4 selectivity values >= 93 mol%, was obtained with the NiO-CeO2 mixed oxides (CO2 conversions up to 76 mol%). When gamma-Al2O3 was used as the support, catalysts with low activity (CO2 conversion <= 20 mol%) were obtained. On selected samples, additional catalytic runs were also performed for reaction times up to 30 h or with a higher space velocity value. The catalytic results were explained by taking into account the role of the nickel-ceria interactions both during the reduction of NiO and in the reactants activation. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

NiO-CeO2 mixed oxides were prepared by the soft-template method with nominal Ni/Ce molar ratios between 0.3 and 4.0. NiO and CeO2 pure oxides were also prepared through the same procedure. A second series of NiO-CeO2 mixed oxides (nominal Ni/Ce values = 0.3-1.5 mol mol(-1)) was synthesized by using the soft-templated ceria as the support and depositing Ni through incipient wetness impregnation. All samples were characterized by different techniques as to their chemical composition, structure, morphology, texture, and redox features. NiO nanocrystals of about 4 nm in size were obtained in the case of the soft-templated samples, regardless of the Ni loading. Larger NiO nanocrystals (up to 20 nm in size) were formed by depositing Ni through the impregnation procedure. The catalytic performance was investigated in the CO2 methanation reaction after mild reduction pretreatment (H-2 at 400 degrees C for 1 h). Catalytic testing was performed under atmospheric pressure, 300 degrees C, 72,000 cm(3) h(-1) g(cat)(-1), and stoichiometric H-2/CO2 molar ratio. Pure NiO as well as the two NiO-CeO2 mixed oxides series showed high CO2 conversions (up to 87 mol%) together with CH4 selectivity values close to 100 mol%. Despite the significantly different size (6-8 and 15-35 nm, respectively) of the Ni-0 nanocrystals originated by NiO reduction, comparable CO2 conversion values were observed for the soft-templated and impregnated catalysts. The catalyst stability as well as the effect of reaction temperature, space velocity, and H-2/CO2 molar ratio were investigated on selected samples. The catalytic results were explained by taking into account that CO2 and H-2 are activated on different phases.

The combined influence of the catalyst acidity and porosity features on the transesterification of soybean oil with methanol was investigated over micro/mesoporous hierarchical Beta (Si/Al = 18 and 30), conventional microporous Beta (Si/Al = 23 and 43) and MCM-22 (Si/Al = 40) zeolites. All the catalysts were characterized as to their structure and texture by X-ray diffraction and N2 physisorption, respectively. Their acid features were assessed by adsorption microcalorimetry, using NH3 as probe molecule. Catalytic testing was carried out in batch at 453 K and 4 MPa. The nature of the organic material adsorbed/trapped in the catalyst during reaction (“coke”) was determined by GC/MS after solvent extraction. Fatty acid methyl esters (FAMEs) yields of 22–40 mol% were attained with a reaction time of 24 h over the conventional Beta and MCM-22 samples, whereas remarkably higher values (50–70 mol%) were observed over the hierarchical Beta zeolites. For both the hierarchical and conventional zeolites, the initial FAMEs yield was found to increase with the concentration of the acid sites able to adsorb ammonia with strength higher than ca. 100 kJ mol−1. In comparison with the conventional zeolites of similar acidity, the methyl esters yield over the hierarchical zeolites was twice to three times higher, as a consequence of the enhanced reactants diffusion in their secondary mesoporous system. The presence of free fatty acids in the reaction mixture and the nature of the coke revealed that several acid-catalyzed reactions and thermal degradation processes can occur simultaneously with transesterification. A general scheme for the different reaction pathways for the oil transformation was outlined.

Al-SBA-15 samples with molar Si/Al ratios of 3, 22 and 73 were synthesized and tested for the acid catalyzed transesterification of Jatropha curcas oil with methanol. Being non-edible, low-cost and acidic, Jatropha oil is an interesting feed for biodiesel production, as its use would not entrain competition between food and fuel markets. For fundamental reasons, soybean oil, a typical high quality feed, was also investigated, as its negligible free fatty acids content would not mask the extent of transesterification by the simultaneous occurrence esterification. All the catalysts were characterized as to their composition, structure and texture by ICP-AES, Al-27 MAS NMR, X-ray diffraction and nitrogen physisorption. Surface acidity was assessed by ammonia adsorption microcalorimetry. The nature of the organic material adsorbed/trapped on the catalyst during reaction was determined by GC-MS after solvent extraction. The possibility of recovering the activity of the catalayst after a reaction cycle was also checked. In the case of soybean oil, the best-performing catalyst was that with Si/Al = 3 (90 mol% fatty acids methyl esters yield at 180 degrees C, reaction time 24h, methanol/oil ratio 12). In the case of Jatropha oil, the three catalysts showed a virtually identical performance (ca. 100 mol% methyl esters yield at 180 degrees C, reaction time 24 h, methanol/oil ratio 12), in spite of their remarkable differences in terms of both concentration and strength distribution of the acid sites. Esterification of the free fatty acids present in the feed occurred in parallel to triglycerides transesterification, both reactions being catalysed by the acid sites of the catalyst, as well as by the acids present in the feed. Several secondary reactions occurred during the transformation of both soybean oil and Jatropha oil. The corresponding reaction pathways were outlined. (C) 2015 Elsevier B.V. All rights reserved.

Layered double hydroxides were prepared by pH-controlled co-precipitation method with a Mg/Al molar ratio between 1.5 and 4.0 and used as precursors for obtaining, through calcination, a series of MgAl mixed oxides, which were used as catalysts for soybean oil transesterification with methanol. The mixed oxide with the highest Mg/Al ratio was doped with potassium for obtaining highly basic catalysts. Three different potassium salts (K2CO3, KNO3, CH3COOK) were used for loading potassium on the support (K loading ca. 3 mass%) by two different techniques, namely conventional incipient wetness impregnation and innovative mechanical milling. All the catalysts were characterized as to their chemical composition, structure and texture by inductively coupled plasma atomic emission spectroscopy, X-ray diffraction and N-2 physisorption, respectively. Their basic and acid features were assessed by adsorption microcalorimetry, using CO2 and NH3 as probe molecules, respectively. Catalytic testing was carried out in a slurry batch reactor operated at 343 K and atmospheric pressure. The occurrence of potassium leaching into the liquid phase was checked for the K-doped catalysts. The initial activity of the heterogeneous catalysts was interpreted in terms of surface basicity, by taking into account a possible role of acidity in determining the mechanism.

•Two sulfonic acid-functionalized-SBA-15 samples were prepared by co-condensation.•The two samples were characterized through SAXS, N2-isotherms and FTIR spectroscopy.•The acidity of the samples was characterized through adsorption microcalorimetry.•Phenyl-sulfonic acid functionalized SBA-15 is active toward biodiesel synthesis.

Using a post-synthetic grafting method, mesoporous SBA-15 was functionalized first with aminopropyl silane reagents such as (3-aminopropyl)trimethoxysilane (APTMS) or bis[3-(trimethoxysilyl)propyl]amine (BTMSPA) and then with chlorinated ligands such as 4-(2-chloroacetyl)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (H-AP) or 5-chloromethyl-8-quinolinol hydrochloride (H-HQ). Vanadyl cations [(VO)(2+)] were then immobilized over functionalized silica samples in order to prepare new oxovanadium(IV) based "quasi-homogeneous" catalysts, namely Ia (Ia'), Ib (Ib'), and IIa. Alternatively, a preformed oxovanadium(IV) complex such as [VO(AP)(2)(H2O)] has been immobilized over a previously functionalized SBA-15-NH2 silica support, affording catalyst Ic. Elemental analysis (C, H, N), N-2 adsorption-desorption isotherms, FT-IR, Si-29 and C-13 CP-MAS NMR, XPS, ICP-AES, SEM-EDX and TG-DTG techniques have been used for the full characterization of these materials. Their catalytic properties in the H2O2 promoted oxidation of conjugated olefins like styrene, alpha-methyl and beta-methylstyrene were investigated, in terms of activity, selectivity and recyclability, and compared with that shown by more simple systems prepared by the direct grafting of the vanadyl cation onto SBA-15 (catalyst A) or SBA-15-NH2 (catalyst B). Generally, high activity, selectivity and recyclability (over the first three runs) were shown by all anchored catalysts, with the only exception of A and B systems. A full account of the obtained results, along with insights into the effects due to the different strategies employed for the functionalization of SBA-15 on the properties of final anchored catalysts, are reported.

In this study, MgNiAl mixed oxides derived from layered double hydroxide precursors were prepared by pH-controlled co-precipitation. Three samples were prepared with a (Mg2+ + Ni2+)/Al3+ ratio of 2 and a Ni2+/Mg2+ with ratios of 0.22, 0.47, and 4.05. The structural, textural and redox features of the oxides were investigated by a variety of techniques, including X-ray diffraction, transmission electron microscopy, N2 physisorption, and temperature-programmed reduction. The acid and base properties were assessed by NH3 and CO2 adsorption microcalorimetry, respectively. The acid–base features were also investigated by testing the catalytic behaviors of the oxides for the conversion of 4-methylpentan-2-ol under both mild and stressed conditions. The reactant alcohol can undergo dehydration into 4-methylpent-1-ene, 4-methylpent-2-ene, and skeletal isomers of C6-alkenes, as well as dehydrogenation to 4-methylpentan-2-one and higher ketones, the product selectivity being governed by the concentration and strength of the acid and base sites. Comparison between the calorimetric and test reaction results is discussed.

A series of Al-SBA-15 catalysts in a wide compositional range (Si/Al=130-5.2) was prepared by “pH-adjusting” aiming to evaluate the effect of aluminium incorporation on their structural, acidic and catalytic properties. The calcined materials were characterized by ICP, XRD, N2 adsorption/desorption, TEM, 27Al MAS NMR, microcalorimetry of ammonia adsorption and FTIR of adsorbed pyridine. It was found that the progressive incorporation of aluminium in SBA-15 has a positive effect on the structural and textural characteristics of catalysts as well as on the number of Brönsted and Lewis acid sites, whereas no net effect was observed on the relative distribution of acid sites according to their nature or strength. The catalytic properties of mesoporous SBA-15 aluminosilicates were finally evaluated by test-reactions in the liquid phase tert-butylation of phenol and isomerization of styrene oxide, under mild conditions. The catalytic results showed that the progressive incorporation of aluminium results in higher reaction rates in the O- and C-alkylation of phenol as well as isomerization of styrene oxide, providing evidence that the number of acid sites controls the catalytic activity of Al-SBA-15. On the other hand, the incorporation of aluminium had no effect on the selectivity to the reaction products, indicating that selectivity levels are controlled by the relative distribution of acid sites. It was also reported that Al-SBA-15 prepared by “pH-adjusting” are highly active catalysts in the isomerization of styrene oxide and very selective to phenylacetaldehyde.

CuNiAl and MgCuNiAl mixed oxides (Cu2+/Ni2+ = 0.29 and 0.32 mol/mol) were obtained from layered double hydroxide precursors (M2+/Al3+ = 2 mol/mol) synthesized by pH-controlled co-precipitation. After structural and textural characterization (by X-ray diffraction and N2 physisorption, respectively), the acid and basic features of the mixed oxides were investigated by adsorption microcalorimetry. NH3 and CO2 were used for probing the acid and basic features, respectively. By the use of temperature-programmed technique, the redox features of the oxides were investigated as well. The behaviour of the oxides as catalysts for the conversion of 4-methylpentan-2-ol at 448, 473, and 523 K under atmospheric pressure was studied in a fixed-bed reactor. The dehydration products distribution and the relative extents of the dehydration and dehydrogenation reactions are discussed in terms of the possible occurrence, depending on the lack or presence of Mg in the oxide and the reaction temperature, of either acid–base-governed E1 and E2 mechanisms or Cu-promoted reaction pathways.