Ruiz-Zamora, Evelinde la Rosa, Javier RiveraMaldonado, Carolina SolisLucio-Ortiz, Carlos J....
14页
查看更多>>摘要：Siliceous self-pillared pentasi l (SPP) zeolite catalysts with incorporated phosphorus groups were synthesized using four different percentages of P, obtaining a network of nanosheets in a house-of-cards arrangement. The catalysts were used in the dehydra-decyclization of tetrahydrofuran (THF) as biomass-derived molecule to obtain 1,3-butadiene. The presence and stability of phosphate (PO43-) and phosphite (PO33-) groups incorporated in the SPP zeolite framework was evidenced. The analysis of fresh and used catalysts by nuclear magnetic resonance (NMR) tests showed that 95% phosphorus in zeolite catalysts is present as orthophosphate groups and less than 5% as pyrophosphate or other polyphosphate groups. The P bonded to Si (Si-O-P, corresponding to orthophos-phate groups), identified by 31 P-{29Si}-Rotational Echo Double Resonance (REDOR)-NM R analysis, are proposed as the active sites responsible for the dehydra-decyclization of T H F to obtain 1,3-butadiene. The P-SPP zeolite catalyst with 0.2 ratio of precursors P and Si in the synthesis, presented the best performance.
查看更多>>摘要：Imines are important N-containing intermediates in organic synthesis. The photocatalytic production of specific imines through direct coupling of alcohols and amines under mild conditions has been widely explored. However, the reported processes are not practical due to negative factors such as low photocatalytic efficiency, involvement of non-stoichiometric raw materials, limited scope of substrates, and the need of additives that are not environmentally friendly. Herein, we report the synthesis of CdS-SnS2 photocatalysts with compact heterojunctions by a one-step hydrothermal method. Using air as oxidant and without the need of additive, the prepared CdS-SnS2 composites display good to excellent activity (conversion of amines up to 98% and selectivity to the corresponding imines 99.9%) for imines generation from primary amines and alcohols with different functional groups under visible light irradiation. Unlike most of the reported methods, equivalent amounts of alcohol and amine are involved in the present protocol. A reaction mechanism based on the quenching of active species is proposed. The present work offers an effective, versatile and atom-economic approach for the synthesis of imines by cross-coupling of alcohols and amines under mild conditions.
Deka, Dhruba J.Daya, RohilJoshi, Saurabh Y.Partridge, William P....
12页
查看更多>>摘要：The Standard SCR reaction on Cu-SSZ-13 is a complex redox process facilitated by a reduction half cycle (RHC) and an oxidation half cycle (OHC). It is generally accepted that RHC requires the simultaneous presence of NO and NH3, while OHC requires both NO and O2; however understanding of how these individual reactants impact the Cu redox cycle is limited. In this study, we provide experimental investigation of NO-only, NH3-only and NO+NH3 RHC, and their relative rates. Simple kinetic models were developed to understand the dependance of NO-only and NH3-only RHC on Cu speciation. Various OHC routes including NO+O2 and O2-only OHC, and a previously unreported H2O-mediated OHC pathway were also investigated. Detailed NH3 temperatureprogrammed desorption studies showed that RHC selectively consumes NH3 adsorbed on Lewis-acid sites, and that part of the remaining Bronsted-bound NH3 moves to the Lewis-acid sites during subsequent OHC, thereby resulting in a repartitioning of adsorbed NH3.
Schjodt, Niels C.Jorgensen, Susanne L.Lundegaard, Lars F.Beato, Pablo...
10页
查看更多>>摘要：A new kind of high-temperature water gas shift catalyst based on K-promoted ZnO/ZnAl2O4, introduced by Haldor Topsoe as SK-501 Flex (TM), has begun to replace the well-known Fe/Cr oxide catalysts in the industry. In this research article, we focus on optimization of the catalyst system, especially on promotion with alkali metals and on structural characterization using X-ray diffraction. The promotional effect of the alkali metals increases in the order Li < < Na < < Cs < Rb < K. With K, a 20-fold increase of the mass-based intrinsic rate constant compared to an un-promoted sample is observed. The optimum in the K-content, 2.1 wt%, corresponds to a surface concentration of 0.0057 mmol/m2 or 0.0059 mmol/m(2) if K only decorates the ZnAl2O4 spinel surface. This coverage coincides with the surface concentration of Al vacancies on the dominating spinel (111) facet, the so-called kagome layer, with a coverage of 0.00586 mmol/m(2). Potassium decoration of the spinel surface is corroborated by FTIR studies of promoted and un-promoted samples in a CO atmosphere. The promotion by potassium is both structural, inhibiting growth of the spinel crystals as evidenced by XRD and BET surface area measurements, but also electronic since the activity per surface area strongly increases on K-promotion. Finally, our studies include long term tests of thermal stability and tolerance towards H2S.
查看更多>>摘要：Surface defects have a significant effect on the photocatalytic reaction of Bi4Ti3O12, but the mechanism is unclear. In addition, when surface defects and highly exposed facets exist at the same time, which factor plays the main role in photocatalytic activity is also controversial. Herein, it is found that Bi4Ti3O12 with adjustable concentrations of surface defects and percentage of exposed {001} facets can be prepared by using titania of different crystal types and sizes as raw materials, which is extremely beneficial for exploring the above problems. The photocatalytic activity of Bi4Ti3O12 nanosheets with surface defects and exposed {001} facets was the same as that of Bi(4)Ti(3)O(12 )nanosheets with surface defects alone (about 72.5% of photodegradation levofloxacin under 10 min of simulated sunlight irradiation). Based on the experimental results and density functional theory calculations, the influence mechanism of surface defects was deeply studied. The surface defects resulting from partial exfoliation of the external (Bi2O2)(2+) layers changed band structure of Bi4Ti3O12. More importantly, surface defects with high concentration became hole trapping sites, which was conducive to the faster participation of holes in the photocatalytic oxidation process.
查看更多>>摘要：The well-dispersed Ni-LTA-derived catalysts with high-density Ni sites were fabricated by the ion-exchanged method, where the degraded LTA structure as a sacrificial component promoted the dispersion of Ni sites. As Ni content reached 11.6 wt%, an excellent catalyst efficiency (0.075 molC3/(gcat center dot h)) and an outstanding propylene consumption rate on a per Ni basis (38.3 molC3/(molNi center dot h)) with ~100% selectivity to oligomers containing 75.1% of C6 were obtained for propylene dimerization under mild conditions (70 degrees C, 2.5 MPa and WHSV = 3.6 h-1). Moreover, it has been proposed that the three-coordinated Ni2+ ion in a trigonal structure is the active site. The uniform coordinatively unsaturated Ni2+ ion in the ion-exchanged Ni-LTA catalysts, presenting a strong Lewis acid concentration, boosts the catalytic activity for the propylene dimerization, whereas NiO nanoparticles are confirmed to be spectators for the reaction. The understanding of Ni active sites promotes the rational design of improved catalysts for the dimerization of light olefins.
查看更多>>摘要：Mn-based catalysts modified by copper, alumina and/or rGOs were synthesized by a simple coprecipitation method to decompose ozone under high humidity conditions, and their intrinsic mechanisms of ozone decomposition were investigated deeply. Hereinto, Mn-based catalysts doped by Cu-Al and Cu-Al-rGOs exhibited excellent activity and durability, maintaining above 94% and 98% ozone conversion for nearly 40 h under 85% RH and GHSV of 300 L.g(-1).h(-1) at 25 degrees C. The characterization results showed that the Cu dopants enhance the reducibility and regeneration speed owing to the formation of CuMn2O4 solid solutions, and the additions of Al and rGO significantly increase the amount of surface and sub-surface lattice oxygen, promoting effectually catalytic performances. XPS results revealed that the abundant surface oxygen species with high reactivity and stability were generated from the sites associated with Cu-O, Al-O bonds, and large amounts of Mn2+/Mn3+ in Mn-based catalysts modified by Cu, Al and GOs.
查看更多>>摘要：The N-alkylation of amines with tetrahydrofuran (THF) to synthesize pyrrolidine compounds is an economic and environmental benign route. However, current catalytic system often suffered from harsh reaction condition and hazardous reagents. In this work, we developed an alumina nanosheet catalyst with a large amount of medium acid sites for synthesis of N-arylpyrrolidines. Nearly 100% target product yield could be obtained at 190 ?, and this catalyst could be reused at least 5 times without obvious deactivation. NH3-temperature programmed desorption (TPD) and pyridine-infrared (py-IR) revealed that the catalytic performance is positively correlated with the content of medium acid sites. In-situ IR spectrum proved that the reaction follows the carbocation mechanism. This work affords a competitive system for green sustainable chemistry.
查看更多>>摘要：Upgrading biomass platform molecules, e.g. furfural, to value-added fine chemicals has been intensively studied due to its promising potential to substitute the traditional petroleum route producing downstream chemicals. This study presents a high performance K-Cu#SiO2 catalyst derived from the hybrid of copper-based metalorganic-frameworks (Cu-BTC) and silica, for hydrogenation of furfural. The obtained K-Cu#SiO2 having uniformly dispersed copper nanoparticles (-5 nm), achieved a high furfuryl alcohol (FOL) yield (-33 molFOL/molCu h-1), as well as robust recycle utility (trace activity loss after 5 times recycle) at 140 degrees C and 2.0 MPa. The improved copper metal dispersion and abundant active sites dominating as Cu+/Cu0 species were responsible for the enhanced activity, both of which were closely associated with the functional role of potassium acetate (KAc) serving in the synthesized route. In one respect, the introduced KAc facilitated the Cu-BTC and silica to hybrid a uniform gel by balancing their hydrolysis or crystal growth rates, enabling strengthened copper-silica interactions to yield highly dispersed copper nanoparticles; furthermore, the KAc acted as an electronic regulator to tune the reducibility of copper species on K-Cu#SiO2 catalyst during subsequent N2-calcination. This work could shed a light on the synthesis of high-performance and robust silica-supported copper catalysts for biomass valorization.
NSTL
Elsevier