查看更多>>摘要：? 2022 Elsevier B.V.The feasibility of using a series of Zn-Zr mixed oxides for the gas-phase production of light olefins from butyric acid, a platform molecule derived from biomass processing, was investigated. These materials with Zn/Zr molar ratios of 0.11–0.66 were prepared by incipient wetness impregnation of Zn on Zr(OH)4 and characterized by BET, XRD and CO2 and NH3 TPD. At full butyric acid conversion conditions, a range of C2-C7 olefins was obtained. The molecular weight of the olefin pool as well as the total olefin yield depend on the catalyst composition and experimental conditions. The catalyst acid-base properties can be tuned for optimal olefin yield by generating a high number of Zn-O-Zr species and oxygen vacancies resulting from incorporation of Zn2+ to the ZrO2 lattice. The best olefin yield coincides with the catalyst showing the highest acid site number and moderate basic properties. Also, the reaction temperature and reactor contact time were varied to improve the olefin yield. A total olefin yield of 60.7% was obtained with a catalyst having 11.1 wt% Zn (Zn/Zr=0.25) at 723 K and 835 h g cat./mol. Ethylene (52%) and isobutene (33%) were the main components of the olefin fraction, the other 15% being pentene, isohexene and heptene. The olefin yield can be further improved to 65.8% by increasing the contact time to 1500 h g cat./mol. Butyric acid transformation proceeds with the intermediate formation of different ketones (heptanone, pentanone and acetone), each of which gives rise to a particular olefin. Isobutene forms through tandem butyric acid ketonization/C-C bond rupture by McLafferty rearrangement/aldol condensation/breaking of the aldol adduct reactions. Ethylene is generated during the McLafferty step. The pathways toward other olefins may involve deoxygenation steps such as reduction of unsaturated bonds by in-situ generated hydrogen species, followed by dehydration. Acetic and propionic acids, formed in minor amounts, participate in further tandem sequences. No catalyst deactivation was observed during standard and extended catalytic tests because water co-feeding and hydrogen generation prevent heavy product formation and active site loss.
查看更多>>摘要：? 2022 Elsevier B.V.MgAl hydrotalcites (HTCs) are widely used as basic heterogenous catalysts. Their calcination followed by rehydration enhances their basicity and catalytic activity. The effect of repetitive “calcination-rehydration” treatments on their properties and catalytic performance needs to be established to understand regeneration and reusability of HTCs. Therefore, we investigated the properties of MgAl HTCs in dependence on the rehydration conditions and the number of repeated calcination-rehydration cycles. We found that regardless of the rehydration conditions, all catalysts after the first rehydration recovered their properties and furfural conversion was > 80%. After successive treatments at 25 °C, the HTCs properties deteriorated significantly and furfural conversion dropped < 5%. When rehydrating at 75 °C for 120 min the characteristics and performance of the rehydrated HTCs were maintained near the original values. We concluded that complete rehydration needed to maximize the catalytic activity was associated with the efficient reincorporation of Al species into the HTC framework.
查看更多>>摘要：? 2022 Elsevier B.V.Mechanochemical bead-milling is a promising post-synthetic way to generate nanocrystalline zeotype materials with promoted catalytic performance. Post-milling recrystallization is often entailed to remedy the damaged framework but leads to crystal growth. Herein, using SAPO-34 (ca. 20 μm) derived from inexpensive morpholine as an example, we showcase that secondary growth can be suppressed by porogen-assisted recrystallization, resulting in formation of tiny crystals (100–200 nm) with better mass transport property. The presence of porogen (polydiallyldimethylammonium chloride) also induced a reduction of acid site density owing to a re-distribution of Si across the crystal, which alleviated zoning of Si at the external surface. The catalytic advantages, with respect to a control sample recrystallized in the absence of porogen, have been experimentally verified in dimethyl ether-to-olefin conversion, exhibiting an exaggerated light olefin selectivity and prolonged catalyst lifetime. This advancement of mechanochemical synthesis opens an avenue to better tailor crystal size for zeotype materials.
查看更多>>摘要：? 2022 Elsevier B.V.Carbon xerogels were synthesised and used as support of ruthenium-based catalysts for the ammonia decomposition reaction. To improve their physical-chemical properties, carbon xerogels were either activated in carbon dioxide atmosphere (for 1 and 5 h), or doped with nitrogen via co-precursor method, using urea as nitrogen source. Un-promoted and sodium-promoted ruthenium catalysts were prepared by incipient wetness impregnation. All catalysts were tested during the ammonia decomposition reaction (1 atm, 100–600 °C), showing high catalytic activity. The 5 h carbon dioxide activation treatment resulted in a decrease in oxygen surface groups (i.e. by 11 wt%) on carbon xerogels surface, and in an increase in the structure crystallinity (i.e. by 15% in the TBurn) of carbon xerogels, resulting in a higher ammonia decomposition reaction rate (i.e. 3.5-fold at 450 °C). Similarly, nitrogen addition to carbon xerogels had a positive effect on the catalysts basicity, enhancing their catalytic performance (i.e. triple reaction rate at 450 °C). The addition of sodium conferred an enhancement in the performance of each catalyst (i.e. reaction rate up to 9 times higher at 450 °C). Two ammonia decomposition reaction runs were performed for all catalysts, to test the performance reproducibility of the catalysts. It was found that un-promoted catalysts exhibited higher reaction rates (i.e. up to 3.5 times at 450 °C) during the second run of reaction due to the larger ruthenium particle size, whereas sodium-promoted catalysts exhibited similar catalytic activity in both reaction runs due to the presence of sodium oxide avoiding the sintering of ruthenium particles.
查看更多>>摘要：? 2022 The AuthorsThe catalytic co-conversion of glycerol and oleic acid (45/55 wt%) to bio-based aromatics (benzene, toluene, and xylenes, bio-BTX) over a technical H-ZSM-5/Al2O3 catalyst in a fixed-bed reactor was investigated with special attention to catalyst deactivation phenomena. The spent catalysts after a time on stream (TOS) of 12 h were regenerated by an ex-situ oxidative treatment to remove coke and reused for another run. In total, 5 reaction-regeneration cycles were performed. The performance and characteristics of the fresh and regenerated catalysts were determined to identify and quantify the effects of co-feeding on catalyst stability and regenerability. The performance of the catalyst changes upon the number of reaction-regeneration cycles. Despite a negative effect on the peak BTX yield, a remarkable improvement in catalyst stability was found, leading to higher BTX productivity (1260–1505 gBTX gcat-1 for the regenerated catalysts during a TOS of 12 h vs. 834 gBTX gcat-1 for the fresh one during a life-time of 11 h). Detailed catalyst characterization studies show irreversible changes in the catalyst structure after reaction-regeneration cycle(s), such as textural property, crystal structure, framework, and acidity, which impact catalyst performance.
查看更多>>摘要：? 2022The rational design of efficient polar heterogeneous catalysts for oxidation adsorption desulfurization (OADS) is still a challenge. Herein, we fabricated a novel polar fingerprint-like heterogeneous catalyst (HPW-NH2-CPRNSs) by immobilizing phosphotungstic acid on amino grafted phenolic resin nanospheres prepared through gradient temperature hydrothermal method, which exhibits highly effective oxidative-adsorptive desulfurization (OADS) performance. The fingerprint-like nanospheres catalysts were formed when the F127 exposed on the surface of PRNSs was dissolved during the refluxing. Moreover, the polarity of the HPW-NH2-CPRNSs catalysts can be well adjusted by controlling the amount of amino grafting and calcination temperature, which plays an important role in OADS. The removal rate of DBT on optimal polar catalyst reached the highest 98.9% in 90 min. It is the first time that this work involving the phenolic resin polymers have been used as the carrier of desulfurization catalyst and the polarity of the catalyst has been artificially controlled for OADS.
查看更多>>摘要：? 2022 Elsevier B.V.Structural origins of the promotional effects of the La or Si doping of alumina supported Ir catalysts in anaerobic ammonium dinitramide decomposition were investigated. Our findings reveal that Ir/Al2O3 and Ir/La-Al2O3 favorably lower the onset temperature of the ADN decomposition reaction, whereas Si doping boosts the pressure generation during the reaction. Formation of mostly metallic Ir nanoparticles for Ir/Al2O3 and Ir/La-Al2O3 enables the lowering of the activation energy of the reaction. On the other hand, enhancement due to Si promotion is associated to the generation of small oxidic Irnx+ clusters which are strongly interacting with the SiOx-AlOx surface domains of the support material. Fundamental structure-functionality relationships unraveled in the current work may allow design of novel catalytic systems for aerospace monopropellant propulsion systems with higher performance by simultaneous exploitation of Ir active sites with different electronic properties.
查看更多>>摘要：? 2022Glucose isomerization into fructose is the dominant reaction path for biomass conversion. Lewis acidic aluminum or tin were firstly impregnated in microporous UiO-66 for remarkably enhanced glucose isomerization. Al@UiO-66 achieved 37.5% fructose yield with a 63.9% selectivity with no obvious leaching of aluminum while Sn@UiO-66 failed the leaching test. The 27Al NMR and XPS spectra of Al@UiO-66 demonstrated the complex environment of aluminum in UiO-66 involving the chains of aluminum octahedra and the Al–O–C structure, which contributed to the enhanced Lewis acidity and promoted performance of the catalyst.
查看更多>>摘要：? 2022 Elsevier B.V.Conversion of ethanol to higher alcohols was studied over MgO/KNaX, prepared by ion exchange with Mg(OAc)2, followed by KOH washing. The catalysts were characterized by XRF, XRD, SEM, BET, 27Al MAS NMR, EXAFS, NH3- and CO2-TPD. All catalysts showing MgO nanopetals and aggregates on the external surface, contained occluded [Mg4(OH)4]4+ clusters in the zeolite cavities, providing medium basic (Mb) and acid (Ma) sites. Ethanol conversion and higher alcohols selectivity (up to 78%) increased with Mb/Ma ratio due to the increase in both MgO (4–6 wt%) and K (14.7–17.3 wt%) loadings. Decreasing occluded [Mg4(OH)4]4+ clusters and/or increasing MgO aggregates led to the lower conversion and yields of higher alcohols. The essential role of the occluded [Mg4(OH)4]4+ clusters in producing higher alcohols was verified by the reactions using various control catalysts. The MgO/KNaX showed high stability even after steaming at 380 °C, as well as being regenerated by calcination (450 °C in air).
查看更多>>摘要：? 2022 Elsevier B.V.Herein, we developed a one-pot tandem catalytic process for the hydrogenation of dimethyl terephthalate (DMT) to 1,4-cyclohexanedimethanol (CHDM) with physically mixed 5 Pd/CMK-3 and Cu-600 catalysts in a batch reactor. The reaction process was systematically studied in order to improve the yield of CHDM. The hydrogenation of the phenyl group of DMT was preferential to the ester groups, mainly owing to strong adsorption of DMT and the high activity of the 5 Pd/CMK-3 catalyst, as confirmed by UV–visible spectra and kinetic studies. Up to 82% yield of CHDM can be achieved under the optimized reaction conditions. The possible reaction pathways were proposed based on the detailed investigations with different reactants and catalysts. Promisingly, the developed method may lay a solid foundation for the one-pot synthesis of CHDM via the hydrogenation of DMT.
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