1,721,060 research outputs found
A Raman lens on the active sites in the oxygenation of cyclohexene catalyzed by a Cu-bipyridine homoleptic complex
No full textIn [Cu(6,6’-dimethyl-2,2’-bipyridine)2](PF6) (hereafter coded as CuBPA) the presence of methyl moieties allows a stabilization of Cu(I) form, enabling an easier switching between Cu(I) and Cu(II) that is of particular interest in catalysis. In this contribution, resonant Raman spectroscopy (with simultaneous UV-Vis acquisition) supported by DFT calculations is employed as a lens to precisely monitor the metal organic complex throughout its redox cycle and to identify its active species. As a model reaction, the CuBPA-mediated oxygenation of cyclohexene (as the reductant/substrate) by means of tert-Butyl hydroperoxide (as the oxidant) is selected. In this context, 266 nm laser turns out to be quintessential for the characterization of the oxidized form (Ox-CuBPA) and to follow the system evolution throughout the redox cycle, although it fails in giving an unambiguous identification and quantification of reaction products. Aiming at this, catalytic tests are performed under conditions that replicate the spectroscopic experiments. 2-cyclohexene-1-ol and 2-cyclohexene-1-one are identified as the dominant products, proving a promising catalytic activity of CuBPA in partial oxidation reactions
Functionalizing the Defects: Postsynthetic Ligand Exchange in the Metal Organic Framework UiO-66
Full text linkFunctionalizing the Defects: Postsynthetic Ligand
Exchange in the Metal Organic Framework UiO-6
Process
Full text linkThe invention provides a process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I): Μ(ΙΙ)χΑl11-χΡO4 (I), wherein M(II) is a divalent metal ion; and x = 0.002 to 0.5</p
MAPO-18 Catalysts for the Methanol to Olefins Process: Influence of Catalyst Acidity in a High-Pressure Syngas (CO and H2) Environment
Full text linkThe transition from integrated petrochemical complexes toward decentralized chemical plants utilizing distributed feedstocks calls for simpler downstream unit operations. Less separation steps are attractive for future scenarios and provide an opportunity to design the next-generation catalysts, which function efficiently with effluent reactant mixtures. The methanol to olefins (MTO) reaction constitutes the second step in the conversion of CO2, CO, and H2 to light olefins. We present a series of isomorphically substituted zeotype catalysts with the AEI topology (MAPO-18s, M = Si, Mg, Co, or Zn) and demonstrate the superior performance of the M(II)-substituted MAPO-18s in the conversion of MTO when tested at 350 °C and 20 bar with reactive feed mixtures consisting of CH3OH/CO/CO2/H2. Co-feeding high pressure H2 with methanol improved the catalyst activity over time, but simultaneously led to the hydrogenation of olefins (olefin/paraffin ratio < 0.5). Co-feeding H2/CO/CO2/N2 mixtures with methanol revealed an important, hitherto undisclosed effect of CO in hindering the hydrogenation of olefins over the Brønsted acid sites (BAS). This effect was confirmed by dedicated ethene hydrogenation studies in the absence and presence of CO co-feed. Assisted by spectroscopic investigations, we ascribe the favorable performance of M(II)APO-18 under co-feed conditions to the importance of the M(II) heteroatom in altering the polarity of the M–O bond, leading to stronger BAS. Comparing SAPO-18 and MgAPO-18 with BAS concentrations ranging between 0.2 and 0.4 mmol/gcat, the strength of the acidic site and not the density was found to be the main activity descriptor. MgAPO-18 yielded the highest activity and stability upon syngas co-feeding with methanol, demonstrating its potential to be a next-generation MTO catalyst
Process
Full text linkThe invention provides a process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I): Μ(ΙΙ)χΑl11-χΡO4 (I), wherein M(II) is a divalent metal ion; and x = 0.002 to 0.5</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Process
Full text linkThe invention provides a process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I): Μ(ΙΙ)χΑl11-χΡO4 (I), wherein M(II) is a divalent metal ion; and x = 0.002 to 0.5</p
Process
Full text linkThe invention provides a process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I): Μ(ΙΙ)χΑl11-χΡO4 (I), wherein M(II) is a divalent metal ion; and x = 0.002 to 0.5</p
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