Regular ArticleActivity and Selectivity in the Reactions of Substituted α,β-Unsaturated Aldehydes
Abstract
The effect of substitution of α,β-unsaturated aldehydes on the activity and selectivity of a series of platinum catalysts was investigated for the hydrogenation of these compounds. The silica-supported platinum catalysts were promoted by a selected group of additives: compounds of Na (alkali metal), V, Ti, Fe (transition metals), Ga, Sn, and Ge (nontransition elements). For all catalysts the selectivity to unsaturated alcohol (UOL) increased with increasing substitution on the terminal olefinic carbon atom (crotonaldehyde and methyl-crotonaldehyde, respectively). This indicates that the adsorption modes are related to selectivity and the selectivity is influenced by the competition of the CO and CC group for the same sites on the promoter. In the hydrogenation of methacrolein, wherein the methyl substituent is located on the internal olefinic carbon atom, and in the hydrogenation of methyl vinyl ketone, very pronounced differences in the selectivity to UOL were observed. The trends in activity and selectivity indicate that the substitutional effects are mainly steric in origin. In general, the activity of a specific group decreases with substitution on that group.
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Selective hydrogenation of carbon–carbon double bond catalyzed by FLP-MOFs
2023, Microporous and Mesoporous MaterialsSelective hydrogenation of CC double bond in α, β-unsaturated carbonyl compounds is of great significance in the production of fine chemicals, and the design and preparation of hydrogenation catalysts with high selectivity is the key to realize the industrialization of this reaction. Controlling and adjusting the steric hindrance between substrate molecules and active center of catalysts is an effective strategy to achieve high selectivity. In this work, the spatially hindered “Frustrated Lewis pairs” (FLPs) was used as the active component and metal-organic frameworks (MOFs) materials with a certain window size were used as the catalyst support. We designed and synthesized a heterogeneous hydrogenation catalyst B(C6F5)3/DO-MIL-101 by immobilizing FLP onto metal-organic frameworks (MIL-101). Characterizations and catalytic performance tests revealed that the catalytically active species B(C6F5)3/DO was confined in MIL-101 nanocavities via Cr–O coordination bond. The resulting B(C6F5)3/DO-MIL-101 catalyst not only realized the recycling of FLP, but also showed excellent catalytic activity and high selectivity in the selective hydrogenation of CC double bond in α, β-unsaturated carbonyl ketones. It should be noted that the steric hindrance between FLP and substrate molecules, as well as the shape selectivity of MOFs nanocages, are the principal factors for the high selectivity of the catalyst.
Regulating the catalytic activities of Ni and Pd through doping on Fe<inf>2</inf>O<inf>3</inf><sup>HT</sup> for selective hydrogenation of conjugated aldehyde (citral) in lemongrass essential oil to organoleptically superior monoterpene alcohols (geraniol/nerol)
2023, Applied Catalysis A: GeneralFe2O3 was modified by doping Ni and Pd to obtain 3%Ni-1.5%Pd/Fe2O3HT catalyst via the hydrothermal process for selective hydrogenation of citral to nerol and geraniol. This catalyst was prepared by different techniques like co-precipitation, wet impregnation, and hydrothermal process, and their activity towards citral hydrogenation was thoroughly studied. The prepared catalysts were thoroughly characterized. Various parameters such as pressure, temperature, reaction time, and metal weight (%) have been optimized through the RSM-BBD module to attain high selectivity towards nerol and geraniol. The optimal reaction conditions of 6.45 bar pressure, 3%Ni-1.5%Pd loading at 72.1 °C for 84 min, the citral (>99%) was converted to nerol/geraniol with 97.2% of selectivity. The modified catalyst activated the oxygen species of the carbonyl atom and thus favours the selective hydrogenation of the CO bond without reducing the CC bond. This process is very effective for the selective transformation of citral (75%) in lemongrass essential oil to organoleptically superior nerol/geraniol-rich oil using 3%Ni-1.5%Pd/Fe2O3HT catalyst.
Efficient transformation of hemicellulosic biomass into sugar alcohols with non-precious and stable bimetallic support catalyst
2023, Industrial Crops and ProductsThe conversion of hemicellulosic biomass to sugar alcohols commonly applies homogeneous acids and noble metals as catalysts, which is neither economical nor environmentally friendly. In order to overcome the deficiencies of the reports, a series of non-precious catalysts were synthesized through the co-precipitation method and incipient wetness impregnation (IWI) method in converting hemicellulosic biomass, i.e., hemicellulose and xylose into sugar alcohols (i.e., xylitol and arabitol). Reaction experiments showed that the Ni8.98Fe1 @ 1.54SiO2 catalyst prepared by the IWI method has excellent catalytic performance for converting xylose to sugar alcohols in the neutral aqueous solution, and can be applied to the direct conversion of hemicellulose as well. Specifically, the optimum yield of xylitol and arabitol could obtain 99.48 mol% and 26.01 mol% for xylose as the substrate and 88.16 mol% and 20.55 mol% for hemicellulose as the substrate, respectively. Characterization techniques such as X-ray diffraction (XRD), N2 adsorption-desorption isotherm, transmission electron microscopy (TEM), scanning electron microscope (SEM), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy of pyridine (Py-FTIR), and SQUID vibrating sample magnetometry (SQUID -VSM) were performed to study physicochemical properties of the catalyst. N2 adsorption-desorption isotherm and NH3-TPD characterizations indicated that the catalyst with mesoporous properties and proper acidic sites is vital for hydrolyzing hemicellulose to pentose (i.e., xylose and arabinose). TEM, H2-TPR, and XPS techniques revealed that the (111) plane of metallic Ni is the main active phase for the hydrogenation of pentose into sugar alcohols, and Fe2+ and Fe3+ species act as effective promoters to enhance the pentose hydrogenation. Py-FTIR characterization and reaction conditions indicated that the appropriate ratio of Brønsted to Lewis acidic sites could facilitate the conversion of xylose to arabitol. The reaction mechanisms for converting hemicellulosic biomass to sugar alcohols were proposed based on the systematic study of reaction conditions and characterizations. N2 adsorption-desorption, H2-TPR, and XPS indicated that the catalyst with strong metal-support interaction, large specific surface area and pore volume could be beneficial for catalytic stability, which is verified in leaching and reusability tests. The catalyst has superparamagnetic, which can be quickly separated from the reaction system under the external magnetic field, facilitating the recovery and utilization of the catalyst.
Effect of precipitating agents on activity of co-precipitated Cu–MgO catalysts towards selective furfural hydrogenation and cyclohexanol dehydrogenation reactions
2023, Results in EngineeringThe major industrial application and study of hydrogenation of furfural-to-furfural alcohol and dehydrogenation of cyclohexanol to cyclohexanone, over different precipitating agents namely K2CO3, Na2CO3, KOH, NH3 and (COOH)2.2H2O was carried out in vapour phase reactor. Efforts were made to study the effect of these different precipitating agents on Cu–MgO catalyst and its activity towards the hydrogenation and dehydrogenation reactions due to its industrial applications. The prepared co-precipitated Cu–MgO catalysts were characterized by using various modern analytical and spectroscopic techniques which include FE-SEM, BET, XRD, XPS, TPR and DTA. The characterization data revealed that different precipitating agents strongly influenced the physiochemical properties of the developed heterogeneous catalysts. Additionally, FE-SEM images revealed that employing different precipitating agents resulted in various morphologies for the final catalysts. The hydrogenation and dehydrogenation reactions over the Cu–MgO catalyst revealed that the catalyst prepared by K2CO3 as precipitating agent exhibited high catalytic activity. Meanwhile, The presence of more Cuo/Cu+ species on this catalyst with smaller Cu crystallite size as evidenced by XPS and XRD results seems to be accountable for its high activity towards the formation of furfural alcohol and cyclohexanone compared to the other catalysts with different precipitating agents. Additionally, the time on stream (T.O.S) studies performed and it revealed that the catalyst was fairly stable for 300 min showing consistency in its activity towards both reactions. The yield obtained for furfural alcohol and cyclohexanone was 97% and 64%, respectively.
Selective electrocatalytic hydrogenation of α,β-unsaturated ketone on (111)-oriented Pd and Pt electrodes
2022, Electrochimica ActaIn this paper, we study the electrocatalytic reduction of methyl vinyl ketone on Pt(111) and Pd-modified Pt(111) electrodes, as well as some of its expected hydrogenation derivatives and isolated functional moieties. The selectivity and Faraday efficiency have been calculated via sampling the catholyte solution after two hours of electrolysis. Furthermore, the adsorbates involved in the deactivation process on both surfaces were studied by means of potential opening experiments and in situ infrared spectroscopy. The Pd-modified Pt(111) electrode is very active (even mass transport limited) for the selective electrochemical hydrogenation of the C=C to 2-butanone, in the hydrogen underpotential deposition potential window (between 0 and 0.2 VRHE), with limited poisoning. Pt(111) is much less active, and poisons rapidly with adsorbed CO. The poison is formed from the C=C bond, not from the C=O moiety, as evidenced by the same poisoning occurring for ethylene. Further hydrogenation to the saturated alcohol happens at more negative potentials, but with 2-butenol as intermediate, not 2-butanone, as the latter species interacts too weakly with the (111) surface.
Kinetic study of selective hydrogenation of crotonaldehyde over Fe-promoted Ir/BN catalysts
2019, Applied Surface ScienceA series of FeOx-promoted Ir/BN catalysts were tested for gas phase selective hydrogenation of crotonaldehyde. The addition of FeOx in the catalyst greatly improves the performance, up to a 5-fold enhanced steady state crotyl alcohol yield (46.9%) compared to that of the bare Ir/BN (7.2%). The characterization results reveal that the Ir-FeOx interaction results in the generation of new active sites at the interface, which are responsible for the enhanced performance. The kinetic study showed that the Ir-FeOx interfacial active site has much higher turnover frequency (82.9 × 10−3 s−1) than the Ir0-Irδ+ site in the Ir/BN catalyst (3.10 × 10−3 s−1), due to the promotion of FeOx leads to a higher intrinsic rate constant (12.1 × 10−7 v.s. 1.19 × 10−7 mol g−1 s−1) and a higher adsorption equilibrium constant of crotonaldehyde (3.49 v.s. 0.62 kPa−1).