Leaching Stability and Redox Activity of Copper-MFI Zeolites Prepared by Solid-State Transformations: Comparison with Ion-Exchanged and Impregnated Samples

The catalyst preparation route is well known to affect the copper loading and its electronic state, which influence the properties of the resulting catalyst. Electronic states of copper ions in copper-containing silicalites with the MFI-framework topology obtained by a solid-state transformation S (SST) were studied with using EPR, UV-Vis DR, XRD, H2-TPR and chemical differentiating dissolution. They were compared with Cu-ZSM-5 and Cu-MFI (silicalite) prepared via the ion-exchange and incipient wetness impregnation. SST route was shown to provide the formation of MFI structure and favor clustering of Cu-ions near surface and subsurface of zeolite crystals. The square-planar oxide clusters of Cu2+-ions and the finely dispersed CuO nanoparticles with the size down to 20 nm were revealed in Cu-MFI-SST samples with low (0.5–1.0 wt.%) and high (16 wt.%) Cu-content. The CuO nanoparticles were characterized by energy band gap 1–1.16 eV. The CuO-like clusters were characterized by ligand-to-metal charge transfer band (CTB L → M) at 32,000 cm−1 and contain EPR-visible surface Cu2+-ions. The low Cu-loaded SST-samples had poor redox properties and activity towards different solvents due to decoration of copper-species by silica; whereas CuO nanoparticles were easily removed from the catalyst by HCl. In the ion-exchanged samples over MFI-silicalite and ZSM-5, Cu2+-ions were mainly CuO-like clusters and isolated Cu2+ ions inside MFI channels. Their redox properties and tendency to dissolve in acidic solutions differed from the behavior of SST-series samples

Nature of the Surface Intermediates Formed from Methane on Cu-ZSM-5 Zeolite: A Combined Solid-State Nuclear Magnetic Resonance and Density Functional Theory Study

The intermediates formed upon the interaction of methane with Cu-modified ZSM-5 zeolites (Cu/H-ZSM-5) have been analyzed with solid-state NMR spectroscopy and DFT methods. Methane activation by Cu/H-ZSM-5 zeolites gives rise to three distinct surface methoxy-like species (-O-CH3) detected by 13C MAS NMR spectroscopy with specific chemical shifts in the range of 53-63 ppm. DFT calculations on representative cluster models of different sites potentially present in Cu/H-ZSM-5 have been used to assign these signals to (i) methanol adsorbed on two neighboring Cu sites (Cu-(HOCH3)-Cu, 62.6 ppm), (ii) methanol adsorbed on zeolite Brønsted acid sites (52.9 ppm), and (iii) lattice-bound methoxy groups (Si-O(CH3)-Al, 58.6). The formation of these methoxy-like intermediates depends on the Cu loading and, accordingly, the type of Cu species in the Cu/H-ZSM-5 zeolite. For the sample with low (0.1 wt %) Cu loading containing exclusively mononuclear isolated Cu species, only the intermediates ii and iii have been detected. The Cu-bound intermediate (i) is formed upon methane activation by multinuclear Cu sites featuring Cu-O-Cu bridging moieties present in the materials with relatively higher Cu loading (1.38 wt %). The presented results indicate that methane activation by Cu/H-ZSM-5 can be promoted by both mono- and multinuclear Cu species confined in the zeolite matrix.Accepted Author ManuscriptChemE/Inorganic Systems EngineeringChemE/Algemee

Atomic Structure of Pd-, Pt-, and PdPt-Based Catalysts of Total Oxidation of Methane: In Situ EXAFS Study

In this study, 3%Pd/Al2O3, 3%Pt/Al2O3 and bimetallic (1%Pd + 2%Pt)/Al2O3 catalysts were examined in the total oxidation of methane in a temperature range of 150–400 °C. The evolution of the active component under the reaction conditions was studied by transmission electron microscopy and in situ extended X-ray absorption fine structure (EXAFS) spectroscopy. It was found that the platinum and bimetallic palladium-platinum catalysts are more stable against sintering than the palladium catalysts. For all the catalysts, the active component forms a “core-shell” structure in which the metallic core is covered by an oxide shell. The “core-shell” structure for the platinum and bimetallic palladium-platinum catalysts is stable in the temperature range of 150–400 °C. However, in the case of the palladium catalysts the metallic core undergoes the reversible oxidation at temperatures above 300 °C and reduced to the metallic state with the decrease in the reaction temperature. The scheme of the active component evolution during the oxidation of methane is proposed and discussed

Methane Catalytic Peroxide Oxidation Over Fe-Containing Zeolite

Изучена селективность Fe-MFI-катализаторов в парциальном пероксидном окислении метана до метанола и муравьиной кислоты в зависимости от их топологии (нанокристаллы, микрокристаллы и массивный коммерческий) и активации щавелевой кислотой. Катализаторы изучены методами РФА, ИСП-ОЭС, СЭМ, ЭСДО, ТПД- NH3, адсорбции N2. TOF окисления метана увеличивается в ряду: нанокристаллы < микрокристаллы << коммерческий. Селективность по метанолу зависит главным образом от размера кристаллитов и увеличивается в том же ряду. Увеличение TOF и селективности по муравьиной кислоте, а также резкое снижение селективности по CO2 на всех активированных катализаторах были объяснены увеличением общей кислотности катализаторов и количества олигомерных оксокластеров железа. Высказано предположение о различных путях образования метанола/ CO2 (по свободнорадикальному маршруту) и муравьиной кислоты (по гетерогенному маршруту) на катализаторах Fe-MFIThe selectivity of Fe-MFI catalysts to partial peroxide oxidation of methane to methanol and formic acid was studied depending on their topology (Nanocrystals, Microcrystals, and bulk Commercial) and activation with oxalic acid. The catalysts were characterized by XRD, ICP-OES, SEM, UV-vis DR, NH3-TPD, N2 adsorption. TOF of methane oxidation increased in the series: Nanocrystals < Microcrystals << Commercial. The selectivity to methanol depended mainly on the crystallite size and increased in the same series. The increase in TOF and selectivity to formic acid, as well as a sharp decrease in the selectivity to CO2 over all the activated catalysts were accounted for by an increase in the total acidity of the catalysts and the number of oligomeric Fe oxo-clusters. Different pathways to the formation of methanol/CO2 (via free radical mechanism) and formic acid (via heterogeneous route) over Fe-MFI catalysts were suggeste

Hydrogen production by autothermal reforming of methane: Effect of promoters (Pt, Pd, Re, Mo, Sn) on the performance of Ni/La2O3 catalysts

We developed bimetallic catalysts Ni–Me/La2O3 (Me = Pt, Pd, Re, Mo, Sn) for hydrogen production by autothermal reforming of methane (ATR of CH4). The preparation procedure was based on the reduction of an appropriate LaNi1 − xMexO3 (x = 0.01–0.05) perovskite precursor obtained by the citrate sol–gel method. We investigated the effects of promoter type and molar ratio Me/Ni (Me = Pt, Pd, Re, Mo, Sn; Me/Ni = 0.01–0.05) on the structural, reducing and catalytic properties of Ni–Me/La2O3 samples in the ATR of CH4 and systematically studied the genesis of catalysts by means of X-ray diffraction, thermogravimetric and differential thermal analysis, Ar adsorption, H2 temperature-programmed reduction, high-resolution transmission electron microscopy with energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy techniques. The genesis of the active phase is shown to be strongly affected by the promoter type. The Pt, Re, Mo or Sn promoters in contrast to Pd impede the destruction of LaNiO3 structure and formation of Ni0 phase. The catalytic performance of Ni–Me/La2O3 samples in the ATR of CH4 can be regulated by the type and content of the promoter. At low reaction temperatures (700–800 °C) and at the molar ratio Me/Ni = 0.01 the conversion of methane and product (H2, CO) yields increases in the following order of promoters: Pt < Sn < Mo < Re < Pd, which correlates with the increase of reducibility of Ni species as a result of promoter addition. At 850 °C the LaNi0.99Pd0.01O3 catalyst provided the yields of ∼41% H2 and ∼57% CO at CH4 conversion ∼100% during a stability test that lasted 24 h.The presented research has received funding from the European Union 7th Framework Programme (FP7/2007–2013) under Grant Agreement No. 262840 (Project DEMCAMER).Peer Reviewe

Non-agglomerated silicon–organic nanoparticles and their nanocomplexes with oligonucleotides: synthesis and properties

The development of efficient and convenient systems for the delivery of nucleic-acid-based drugs into cells is an urgent task. А promising approach is the use of various nanoparticles. Silica nanoparticles can be used as vehicles to deliver nucleic acid fragments into cells. In this work, we developed a method for the synthesis of silicon–organic (Si–NH2) non-agglomerated nanoparticles by the hydrolysis of aminopropyltriethoxysilane (APTES). The resulting product forms a clear solution containing nanoparticles in the form of low molecular weight polymer chains with [─Si(OH)(C3H6NH2)O─] monomer units. Oligonucleotides (ODN) were conjugated to the prepared Si–NH2 nanoparticles using the electrostatic interaction between positively charged amino groups of nanoparticles and negatively charged internucleotide phosphate groups in oligonucleotides. The Si–NH2 nanoparticles and Si–NH2·ODN nanocomplexes were characterized by transmission electron microscopy, atomic force microscopy and IR and electron spectroscopy. The size and zeta potential values of the prepared nanoparticles and nanocomplexes were evaluated. Oligonucleotides in Si–NH2·ODN complexes retain their ability to form complementary duplexes. The Si–NH2Flu nanoparticles and Si–NH2·ODNFlu nanocomplexes were shown by fluorescence microscopy to penetrate into human cells. The Si–NH2Flu nanoparticles predominantly accumulated in the cytoplasm whereas ODNFlu complexes were predominantly detected in the cellular nuclei. The Si–NH2·ODN nanocomplexes demonstrated a high antisense activity against the influenza A virus in a cell culture at a concentration that was lower than their 50% toxic concentration by three orders of magnitude

Hydrogen production by autothermal reforming of methane over NiPd catalysts: Effect of support composition and preparation mode

NiPd/Ce0.5Zr0.5O2/Al2O3 and NiPd/La2O3/Ce0.5Zr0.5O2/Al2O3 catalysts were prepared by incipient wetness co-impregnation method or sequential impregnation method for autothermal reforming of methane (ATR of CH4). The influence of the preparation mode, Ce0.5Zr0.5O2 and La2O3 additives on the physicochemical properties of NiPd supported catalysts and the effect on their activity to produce hydrogen by ATR of CH4 were investigated. Characterization of fresh and spent Ni-based catalysts by X-ray fluorescence spectroscopy, N2 adsorption, X-ray diffraction, H2 temperature-programmed reduction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were performed. It was demonstrated that support composition determines NiO dispersion as well as reducibility of Ni species through different strength of Ni-support interaction. The preparation method modifies the phase composition and catalyst ability for reduction. The catalyst evolution under reaction conditions was studied. The NiO (∼15 nm) and NiPd alloy (∼18 nm) phases were observed in the spent catalysts. It was found that the Nio/NiO ratio can be regulated by support composition and preparation mode of catalysts. It is demonstrated that studied catalysts provide high methane conversion of 90–100%, CO yield of 55–85% and H2 yield of 55–75% in ATR of CH4 at 750–950 °C. The optimal composition and preparation method of catalyst were selected. The best ATR of CH4 performance is provided by 10 Ni0.5Pd/10Ce0.5Zr0.5O2/Al2O3 catalyst prepared by Pd/Ni sequential impregnation method that can be associated with peculiarity of NiPd particles structure and the optimal ratio between NiO species with different ability for reduction.The presented research has received funding from the European Union 7th Framework Programme (FP7/2007–2013) under grant agreement No. 262840.Peer Reviewe

Methane Catalytic Peroxide Oxidation Over Fe-Containing Zeolite

Изучена селективность Fe-MFI-катализаторов в парциальном пероксидном окислении метана до метанола и муравьиной кислоты в зависимости от их топологии (нанокристаллы, микрокристаллы и массивный коммерческий) и активации щавелевой кислотой. Катализаторы изучены методами РФА, ИСП-ОЭС, СЭМ, ЭСДО, ТПД- NH3, адсорбции N2. TOF окисления метана увеличивается в ряду: нанокристаллы < микрокристаллы << коммерческий. Селективность по метанолу зависит главным образом от размера кристаллитов и увеличивается в том же ряду. Увеличение TOF и селективности по муравьиной кислоте, а также резкое снижение селективности по CO2 на всех активированных катализаторах были объяснены увеличением общей кислотности катализаторов и количества олигомерных оксокластеров железа. Высказано предположение о различных путях образования метанола/ CO2 (по свободнорадикальному маршруту) и муравьиной кислоты (по гетерогенному маршруту) на катализаторах Fe-MFIThe selectivity of Fe-MFI catalysts to partial peroxide oxidation of methane to methanol and formic acid was studied depending on their topology (Nanocrystals, Microcrystals, and bulk Commercial) and activation with oxalic acid. The catalysts were characterized by XRD, ICP-OES, SEM, UV-vis DR, NH3-TPD, N2 adsorption. TOF of methane oxidation increased in the series: Nanocrystals < Microcrystals << Commercial. The selectivity to methanol depended mainly on the crystallite size and increased in the same series. The increase in TOF and selectivity to formic acid, as well as a sharp decrease in the selectivity to CO2 over all the activated catalysts were accounted for by an increase in the total acidity of the catalysts and the number of oligomeric Fe oxo-clusters. Different pathways to the formation of methanol/CO2 (via free radical mechanism) and formic acid (via heterogeneous route) over Fe-MFI catalysts were suggeste