Biodiesel produced through catalytic transesterification of triglycerides from edible and non-edible oils and alcohol is considered an alternative to traditional petro-diesel. The interest in the use of alkaline earth metal oxides as heterogeneous basic catalysts has increased due to their availability, non-toxicity, the capacity to be reused, low cost, and high concentration of surface basic sites that provide the activity. This work is a compilation of the strategies to understand the effect of the source, synthesis, and thermal treatment of MgO, CaO, SrO, and BaO on the improvement of the surface basic sites density and strength, the morphology of the solid structure, stability during reaction and reusability. These parameters are commonly modified or enhanced by mixing these oxides or with alkaline metals. Also, the improvement of the acid-base properties and to avoid the lixiviation of catalysts can be achieved by supporting the alkaline earth metal oxides on another oxide. Additionally, the effect of the most relevant operation conditions in oil transesterification reactions such as methanol to oil ratio, temperature, agitation method, pressure, and catalysts concentration are reviewed. This review attempts to elucidate the optimum parameters of reaction and their application in different oils.
Catalytic propane dehydrogenation is an attractive method to produce propylene while avoiding the issues of its traditional synthesis via naphtha steam cracking of naphtha. In this contribution, a series of Pt-Sn/SBA-16 catalysts were synthesized and evaluated for this purpose. Bimetallic Pt-Sn catalysts were more active than catalysts containing only Pt. The catalyst with the best performance was assessed at different reaction times of 0, 60, 180, and 300 min. The evolution of coke deposits was also studied. Thermogravimetric analysis demonstrated the presence of two types of coke on the catalyst surface at low and high temperature, respectively. Raman results showed an increased coke’s crystal size from 60 to 180 min on stream, and from 180 to 300 min under reaction, Raman suggested a reduction in the crystal size of coke. Also transmission electron microscopy confirmed a more evident agglomeration of metallic particles with reaction times higher than 180 min. These results are consistent with the phenomena called “coke migration” and the cause is often explained by coke movement near the particle to the support; it can also be explained due to sintering of the metallic particle, which we propose as a more suitable explanation.
Catalytic hydrodeoxygenation (HDO) has been considered as a promising route for biomass revalorization. The development of active and stable materials has been undertaken over the past decade, and precious metals have displayed high activities. Ru has exhibited an outstanding performance due to its high hydrogenation capacity, among other properties. Rational development of these catalysts requires understanding the contribution of properties like acidity, oxophilicity, reducibility, and capacity to generate oxygen vacancies. However, the fundamental basis for effective C–O cleavage is not well understood, to our knowledge. Therefore, this work aimed to evaluate the effect of support in HDO of ethanol, cyclohexanol, and phenol as oxygenated model molecules for bio-oil on Ru catalysts. A series of 0.6 wt % Ru catalysts were prepared by wet impregnation with Ru(NO)(NO3)3 solutions. A strong influence of support in HDO activity of different molecules with the Ru catalyst was evidenced. Differences in activity on the catalyst with comparable particle size indicated that reactions involving the C–O cleavage by hydrogenation did not occur only on metallic sites. Rather, the activity took place by a cooperative action between the metallic phase and the support. For the HDO reaction of the studied molecules, Ru/TiO2 and Ru/ZrO2 were the most active solids as compared with Ru/SiO2 and Ru/Al2O3. Ethanol and cyclohexanol dehydration-reformation reactions showed that catalytic functionalities could be tuned with the reaction temperature. It was found that acid properties were more relevant when the temperature was increased (formation of ethylene and diethyl ether). At the same time, the metallic (dehydrogenation) function decreased (formation of acetaldehyde and its reformation to methane and CO). The usage of oxyphilic supports with oxygen vacancies, moderate acid site density, and redox properties in combination with high hydrogenating capacity metals like Ru may be the clue to developing highly active materials for alternative fuel production.
The doping reactions of graphite oxide (GO) with 3-3′-diaminobenzidine (DAB) were studied using N, N′-dicyclohexylcarbodiimide (DCC), cyanuric chloride (CC) and hexafluorophosphate (HATU) as coupling agents. The bifunctionality of the coupling agents aid to interact GO functional groups with amino groups of DAB without being part of the final product. The doped materials (d-GO) and GO were characterized by thermogravimetric analysis, x-ray diffraction, FTIR/Raman spectroscopy, x-ray photoelectron, high-resolution electron microscopy and cyclic voltammetry. The GO-HATU material was more thermally stable than other graphitic material, with at 10% weight loss at 300°C, this thermal stability is related to a more difficult intramolecular physisorbed water removal process than the other d-GO materials. GO-CC and GO-HATU materials presented 8.2 and 8.0 Å of interlayer spacing, which was associated with a good oxidation-doping process. Besides, these two materials showed modifications in the vibrations by FTIR technique, corresponding to epoxy and hydroxyl groups of the GO being more susceptible to react with the amino groups. Moreover, I D /I G ratio calculated by Raman Spectroscopy presents the following trend 0.70, 0.94, 0.97 and 1.04 for GO, GO-CC, GO-DCC and GO-HATU, respectively, this increase is related with a major disorder during the doping process. XPS analysis shows C-N and N=C bands for high resolution of C 1s and N 1s, respectively, for d-GO materials. This possibly suggests the formation of benzimidazoles during the oxidation-doping process, this generates a similar -non-lattice and -lattice oxygen amount for O 1s related to crosslinking between the functional groups of GO and DAB which improve the electronic mobility between the surface and the bulk of the final graphitic material. Finally, the obtained d-GO materials were investigated as a working electrode for electrochemical capacitors and all of them showed typical capacitive behaviour. applications, including conductive polymer composites [2] supercapacitors [3], molecular, electrochemical, or biochemical sensors [4], antigen biosensors [5], lithium storage materials [6], amongst others.GO's diverse physicochemical properties are due to the synthesis method and the degree of oxidation generating disorganization of the structure. The oxidation exhibits lamellar structure with randomly distributed unoxidized aromatic regions (sp 2 -carbon atoms), six-membered aliphatic regions (sp 3 -carbon atoms), GO's interlayer spacing is about two times larger at ∼0.7 nm than that of graphite [7]. The space between layers results in different hydration capacities with intermolecular attraction type Van der Waals forces. The interlayer spacing caused by the oxidation process generates ortho-quinone, ketone, para-quinone, carboxyl, hydroxyl and epoxy functional groups, which are capable of facilitating a broad range of synthetic transformations. Popular synthesis methods are Brodie, Staudenmaier, Staudenmaier-Hofmann-Hamdi and Hummer, this last method being one of th...
During several reactions, similar to dehydrogenation of propane to propylene, coke is one of the main reasons for the catalyst deactivation. The coke formation and further deactivation of the catalyst are strongly dependent to the active site in the catalyst and/or the properties of the support. KIT-6 with interconnected porous and high surface area can handle with the coke formation, and can disperse easily the deposited Pt nanoparticles. In this sense, a series of Pt-Sn/KIT-6 catalysts were synthesized with distinct Sn loadings and used in the dehydrogenation of propane. The performance of these catalysts during reaction varied with the Sn loading. The specific activities for propylene formation obtained with the catalysts were comparable to the best result reported in the literature. The nanoparticles present in the catalyst through pretreatment and reaction condition was the Pt-Sn alloy (1:1 atomic ratio), and that alloy is suggested to be the active phase. This Pt-Sn alloy was stable during the entire reaction time, that even in two catalysts containing a considerable amount of coke, deactivation was not observed. Also, the support (KIT-6) with high connectivity helped to avoid deactivation by coke.
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