查看更多>>摘要：Catalytic fast pyrolysis of polyolefinic waste streams was investigated to recover valuable base chemicals at high selectivity. HZSM-5 zeolite with different properties, affected by Si/Al, mesoporosity, phosphorus stabilization, and steaming, were tested and thoroughly characterized. Different feeds, catalyst/feed ratios and reaction temperatures were evaluated in a micropyrolysis reactor coupled to two-dimensional gas chromatography. While unmodified HZSM-5 rapidly deactivated, phosphorus-modified and steamtreated HZSM-5 showed almost no deactivation due to its lower coking propensity during 130 runs with stable conversion towards C5+ aliphatics and high C-2-C-4 olefins selectivity (-75%) using post-consumer mixed polyolefins. The performance of this direct olefins production route with unprecedented high olefin selectivity was further evaluated in a plantwide context. It was found that it requires-37% lower energy input than the plastics pyrolysis followed by pyrolytic oil steam cracking, while it results to at least a one order of magnitude lower environmental burden as compared to waste incineration.
查看更多>>摘要：A novel heterogeneous and porous FeSe2_x @C-5 with abundant Se vacancies (V-se) was facilely synthesized via one-step carbonization-selenization approach from Fe-MOFs (metal-organic frameworks) and firstly applied in activating peroxymonosulfate (PMS) for iohexol (IOH) removal, exhibiting extraordinary catalytic performance with superior stability and adaptability. The roles and functions of V-se in the reaction system are deeply elucidated. Strikingly, systematic characterization and theoretical calculations revealed that V-se can modulate the surface electronic structure and accelerate Fe3+/Fe2+ cycle, leading to the strengthened binding energy and accelerated charge deliver for PMS activation. Accordingly, Iohexol (15 mg/L) can be eliminated within 30 min in FeSe2_x @C-5/PMS system, with apparent reaction rate constant (k(app)) 23.7 times higher than that in FeSe2/ PMS system. This study not only contributes to a tutorial guideline for designing high-performance catalysts by virtue of structural control and V-se engineering, but also extends its potential application in low-strength wastewater treatment.
Bi, QingyuanSong, ErhongChen, JiachengRiaz, Muhammad Sohail...
11页
查看更多>>摘要：A nanocomposite design is proven for achieving efficient, selective, and robust alkyne semi-hydrogenation through photocatalytic process, which avoids the use of additional heat sources and traditional toxic Pb additives. The gold nanoparticles (Au NPs) coupled crystalline-core@amorphous-shell structured and wide-spectrum responsive black titania (BT) with enhanced surface plasma properties holds the key to attaining high activity and selectivity. The hot electron injection from conductive BT to the surface of plasmonic Au NPs stimulated by solar light activates the alkynes and directly participates in the selective conversion to overcome the energy barriers. The engineered Au/BT gives a record turnover frequency of 1012 h(-1) and excellent stability for phenylacetylene semi-hydrogenation under solar light irradiation and shows broad scope toward selective hydrogenation of alkynes containing various substituent groups of -CH3, -OH, and -Cl. The kinetic isotope effects and in situ infrared spectroscopy analysis for structure-activity relationship and reaction mechanism of phenyl acetylene reduction were also demonstrated.
查看更多>>摘要：Gas adsorption/desorption process and conversion efficiency of solar energy are crucial to photocatalytic CO2 conversion. Here, we report the synthesis of a metal-organic-framework based monolithic NF@ZnO/Au@ZIF-8 photocatalyst that can simulate the respiratory process to accelerate adsorption of CO2 and desorption of CH4 during the photocatalytic reaction. Particularly, this selective-breathing monolithic photocatalyst could coupling external magnetic field into the photocatalytic process, achieving photo-thermal-magnetic field synergy in the reaction system. Upon this photo-thermal-magnetic coupling, the temperature of surface reaction could be elevated to about 180 degrees C, leading to a drastically improved charge transfer behavior and the significantly increased breathing efficiency. The yield of CH4 over the selective-breathing monolithic NF@ZnO/Au@ZIF-8 photocatalyst reaches 270.02 mu mol/g with a high stability and a high selectivity up to 89.72%. This study provides an ideal approach for the design of monolithic catalysts not only with balanced gas adsorption desorption property, but also endowed with multi-field coupling ability.
查看更多>>摘要：Mn2O3 is an exceptional earth-abundant mineral that has been extensively applied in catalytic oxidation because of the strong redox couples like Mn3+/Mn2+ and Mn4+/Mn3+ exposed on Mn2O3 surface. Herein, the catalytic activity of Mn2O3 in photothermal degradation of toluene was regulated by halogens including F-, Cl-, and Br-. As the electronegativity ordered in F (3.98) > O (3.44) > Cl (3.16) > Br (2.96), F- doped Mn2O3 overperforms Cl- doped and Br- doped Mn2O3 in decomposing toluene. DFT theoretical calculation illustrates that F- attracts the shared electrons from Mn to itself, the deviated charge center stretches the adjacent Mn-O bonds and boosts the generation of abundant oxygen vacancies, helping to strengthen the catalytic activity of Mn2O3. Conversely, MnO bonds are shortened by Cl- and Br- that have lower electronegativity than O. The multiple electrons circling Cl- and Br- push Mn towards O and squeeze Mn-O bonds, resulting in the formation of passivated Mn2O3. In conjunction with Mn redox couples and oxygen vacancies, 99% of 400 ppm toluene can be eliminated by F doped Mn2O3, corresponding mineralization rate is high up to 95.8%.
查看更多>>摘要：Cross coupling of aniline and alcohol for the synthesis of imine and secondary amines represents a highly atom efficient processes, yet achieving high selectivity requires specialized catalysts and harsh reaction conditions to avoid over-hydrogenation of as-produced imines and dehydrogenation of secondary amines. Here we employ metal cocatalysts to mediate photocatalytic activation of alcohols, thus separating the stepwise dehydrogenative-condensation process to imine and the direct condensation process to secondary amine. The Rh/TiO2 promotes the photocatalytic dehydrogenation of alcohol into aldehyde and molecular hydrogen, resulting in rapid condensation of aldehyde with aniline to yield imine. In contrast, Fe/TiO2 activates the alcohol mildly without forming aldehyde and hydrogen atoms under irradiation, allowing a direct dehydrative coupling of the activated alcohol with aniline to produce secondary amine. Both Rh/TiO2 and Fe/TiO2 photocatalysts show high performance in terms of conversion, selectivity, stability and a wide substrate scope, rendering the strategy promising for applications.
查看更多>>摘要：Transforming glycerol to value-added chemicals by mild electrochemical oxidation on earth-abundant, low-cost transition metal electrocatalysts is both environmentally and economically beneficial. Herein, substoichiometric cobalt (oxy)hydroxide CoOxHy has been demonstrated as an effective electrocatalyst for selective glycerol oxidation to hydroxypyruvic acid (HPA), an important chemical intermediate with three carbon atoms bearing three different functional groups. The Faradaic efficiency for HPA production can reach 43.2%, with an average production rate of 679.2 mu mol min(-1) m(geo)(-2). Through systematic investigation using cyclic voltammetry, step potential electrochemical spectroscopy, and in situ Raman spectroscopy characterizations, we have revealed that the high-valent cobalt center is responsible for the enhanced activity and selectivity, where electrochemically more stable CoOx exhibits much lower activity and Faradaic efficiency in comparison. This redox-mediated glycerol oxidation mechanism offers a new perspective for future electrocatalyst development toward selective glycerol valorizations.
查看更多>>摘要：CeO2 catalysts with four different morphologies (sphere, rod, octahedral and cube) were successfully synthesized under hydrothermal conditions and showed quite different thermocatalytic activities for gaseous styrene degradation. Unexpectedly, even though its main exposed lattice plane was (111), spherical CeO2 (CeO2-S), presented the highest styrene catalytic degradation activity (T-90 =184 degrees C) with a styrene degradation rate of 1.36 x 10(-3) molstyrene g(-1) h(-1) at 200 degrees C that was approximately 12 times higher than that of cubic CeO2. A comprehensive structural characterization and mechanistic study found that the four CeO2 samples exhibit different degrees of lattice distortion and different oxygen vacancy concentrations. CeO2-S has the greatest lattice distortion, resulting in abundant oxygen vacancies. Oxygen vacancies were identified to be the main active sites through increasing reactive oxygen generation. Meanwhile, styrene was activated by adsorption of oxygen vacancies. Based on the results of in-situ DRIFTS and XPS measurements, O-18(2) isotope tracing experiment and DFT theoretical calculations, the superior thermocatalytic performance of CeO2-S can be attributed to the lesser accumulation of intermediates on its surface, which follows the Langmuir-Hinshelwood (L-H) mechanism (low temperature) and the Mars-van Krevelen (MVK) mechanism (high temperature). In addition, no obvious decrease was observed in the activity of the CeO2-S catalyst for styrene degradation at 210 degrees C in the presence of water vapor, which is beneficial for the actual industrial application.
查看更多>>摘要：Formic acid (FA), a major product formed in biomass processing and CO2 reduction, has attracted considerable attention as a promising renewable liquid-phase hydrogen carrier. Designing highly efficient catalysts for FA dehydrogenation is a key challenge for fuel cell-based hydrogen economy. Herein, Pd-WOx nano-heterostructures (2.9 nm in diameter) anchored on ZIF-8 @ZIF-67 core-hell MOFs-derived nitrogen-doped porous carbon cage (NPCC) are fabricated for the first time through a phosphate mediation approach. Strong adsorption and dispersion of Pd2+ in the phosphate-modified NPCC are essential for the synthesis of highly dispersed ultrafine Pd nanoparticles. The alkaline solution produced during the subsequent reduction process of metal ions can remove the phosphate. The obtained Pd-WOx/(P)NPCC catalyst presents an extraordinarily catalytic performance (TOF, 2877 h(-1) at 303 K and 6135 h(-1) at 323 K) with a 100% H-2 selectivity and conversion toward FA dehydrogenation. The superior performance of Pd-WOx/(P)NPCC is likely due to the strong interaction effect between Pd-WOx and NPCC; unique structures of Pd-WOx nano-heterostructures; and NPCC with hollow and large surface area and abundant surface defects. Kinetic isotope effect (KIE) measurements demonstrated that cleavage of C-H bond is the rate-determining step for HCOOH dehydrogenation. This study provides new insights into a facile and controllable synthesis strategy of inexpensive and efficient catalysts for high-efficiency dehydrogenation of liquid-phase hydrogen carrier.
Lee, JuyeonBack, SeoinJang, HongjeSa, Young Jin...
8页
查看更多>>摘要：An efficient approach to shift the reaction pathway from the 4-electron oxygen reduction reaction (4e(-) ORR) to the 2e(-) ORR is by fabricating precious metal compounds. The selectivity of the latter reaction is critical for the efficiency of H2O2 electrosynthesis technology. Herein, we demonstrate the high 2e(-) ORR activity and selectivity of a nanocoral-shaped Pd-based compound comprising Pd17Se15 and Pd3B mixed phases (Pd-Se-B NC). In contrast, metallic Pd exhibited nearly 100% 4e- ORR selectivity. The mass activity of Pd-Se-B NC for H2O2 generation was similar to 37-fold higher than that of the Pd black catalyst. Importantly, Pd-Se-B NC exhibited one of the highest H2O2 electrosynthesis activities in neutral media reported to date. The chemical states and composition of the Pd-Se-B NC remained almost intact even after sustained electrocatalysis.
NSTL
Elsevier