scholarly journals Comparing the Nature of Active Sites in Cu-loaded SAPO-34 and SSZ-13 for the Direct Conversion of Methane to Methanol

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 191 ◽  
Author(s):  
Karoline Kvande ◽  
Dimitrios K. Pappas ◽  
Michael Dyballa ◽  
Carlo Buono ◽  
Matteo Signorile ◽  
...  
Keyword(s):  
Active Sites ◽  
Co Adsorption ◽  
Direct Conversion ◽  
Active Species ◽  
Ch4 Oxidation ◽  
Structure Activity ◽  
Conversion Of Methane ◽  
Higher Temperature ◽  
X Ray Absorption ◽  
Better Than

On our route towards a more sustainable future, the use of stranded and underutilized natural gas to produce chemicals would be a great aid in mitigating climate change, due to the reduced CO2 emissions in comparison to using petroleum. In this study, we investigate the performance of Cu-exchanged SSZ-13 and SAPO-34 microporous materials in the stepwise, direct conversion of methane to methanol. With the use of X-ray absorption spectroscopy, infrared (in combination with CO adsorption) and Raman spectroscopy, we compared the structure–activity relationships for the two materials. We found that SSZ-13 performed significantly better than SAPO-34 at the standard conditions. From CH4-TPR, it is evident that SAPO-34 requires a higher temperature for CH4 oxidation, and by changing the CH4 loading temperature from 200 to 300 °C, the yield (μmol/g) of SAPO-34 was increased tenfold. As observed from spectroscopy, both three- and four-fold coordinated Cu-species were formed after O2-activation; among them, the active species for methane activation. The Cu speciation in SAPO-34 is distinct from that in SSZ-13. These deviations can be attributed to several factors, including the different framework polarities, and the amount and distribution of ion exchange sites.

scholarly journals Photocatalytic degradation of trace CHCl3 in drinking water by nano TiO2

2020 ◽  
Author(s):  
T.-L. Hsiung ◽  
L.-W. Wei ◽  
H.-L. Huang ◽  
H. Paul Wang
Keyword(s):  
Drinking Water ◽  
Photocatalytic Degradation ◽  
Active Sites ◽  
Disinfection Byproducts ◽  
Active Species ◽  
Nano Tio2 ◽  
Edge Structure ◽  
Tio2 Photocatalysts ◽  
X Ray Absorption

Abstract Toxic disinfection byproducts such as trihalomethanes (CHCl3) are frequently found after chlorination for drinking water. Nano TiO2 which has been widely used for photocatalytic degradation of organic pollutants in wastewater, however, has relatively low effectiveness in the treatments of trace CHCl3. To engineer capable TiO2 photocatalysts, an understanding of their photoactive sites is of great importance and interest. By in situ X-ray absorption near edge structure (XANES) spectroscopy, photoactive sites such as A1 (4969 eV), A2 (4971 eV) and A3 (4972 eV) can be distinguished asfour-, five-, and six- coordinated Ti species, respectively in the nano-TiO2 (8.5 and 4.6 nm for TiO2 on SBA-15), TiO2 clusters (TiO2-SiO2), and highly atomic dispersed Ti (Ti-MCM-41) photocatalysts. It appears that the reactivity for the photocatalytic degradation of trace CHCl3 in drinking water lacks an expected relationship with the crystalline phase, band gap absorption edge, nor the particle size of the TiO2-based photocatalysts. Notably, the A2 sites being the main photocatalytic active species of the TiO2 may be accountable for the main (about 95%) photocatalytic degradation of trace CHCl3 in drinking water (7.2 ppm CHCl3/gTiO2∙hr). This work reveals that the A2 active sites of a TiO2-based photocatalyst are responsible for the photocatalytic reactivity, especially in photocatalytic degradation of CHCl3 in drinking water.

Prediction of anti-tuberculosis activity of 3-phenyl-2H-1,3-benzoxazine-2,4(3H)-dione derivatives

2013 ◽  
Vol 67 (3) ◽  
Author(s):  
Peter Nemeček ◽  
Ján Mocák ◽  
Jozef Lehotay ◽  
Karel Waisser
Keyword(s):  
Chemical Shifts ◽  
Quantitative Structure Activity Relationship ◽  
Active Species ◽  
1H And 13C Nmr ◽  
Nmr Data ◽  
Structure Activity ◽  
Best Value ◽  
Successful Prediction ◽  
Tuberculosis Activity ◽  
Better Than

AbstractCorrelation analysis and, in particular, artificial neural networks (ANN) were used to predict the anti-mycobacterial activity of substituted 3-phenyl-2H-1,3-benzoxazine-2,4(3H)-diones (PBODs) by quantitative structure — activity relationship (QSAR) calculations. Initially, sixty-four derivatives were synthesised and biologically tested; ten further derivatives were proposed for future synthesis on the basis of the prediction results. The biological activity was originally expressed by minimum inhibitory concentration (MIC) against Mycobacterium tuberculosis; however, its transformed pMIC form was found to be more informative. Theoretical molecular descriptors of several types were selected to establish a primary drug model of the species which was expected to exhibit a substantial anti-mycobacterial effect. Lipophilicity and solubility indices, several basic molecular properties, quantum chemistry quantities as well as 1H and 13C NMR chemical shifts, were employed as the descriptors, enabling a very successful prediction of the pMIC values. The utilisation of in silico variables and simulated NMR data is highly advantageous in the first phase of the drug design, as they permit prediction of the compounds with a high expected activity, minimising the risk of synthesising less active species. The MIC values predicted at less than 4 μmol L−1 for six of the ten compounds suggested for further synthesis are better than the best value for the original set of compounds.

Effects of single and double active sites of Cu oxide clusters over MFI zeolite for direct conversion of methane to methanol: DFT calculations

2021 ◽  
Author(s):  
Watinee Nunthakitgoson ◽  
Anawat Thivasasith ◽  
Thana Maihom ◽  
Chularat Wattanakit
Keyword(s):  
Dft Calculations ◽  
Active Sites ◽  
Direct Conversion ◽  
Mfi Zeolite ◽  
Zeolite Framework ◽  
Conversion Of Methane

In this context, we investigate the effect of the single and double active sites of Cu oxide clusters over the MFI zeolite framework for direct conversion of methane to methanol....

scholarly journals Active sites and mechanism of the direct conversion of methane and carbon dioxide to acetic acid over the zinc-modified H-ZSM-5 zeolite

2019 ◽  
Vol 9 (22) ◽  
pp. 6297-6307 ◽  
Author(s):  
Peng Zhang ◽  
Xuejing Yang ◽  
Xiuli Hou ◽  
Jianli Mi ◽  
Zhizhong Yuan ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Acetic Acid ◽  
Catalytic Activity ◽  
Active Sites ◽  
Direct Conversion ◽  
Conversion Of Methane ◽  
Zeolite P

The catalytic activity of the conversion of CH4 and CO2 on zinc modified H-ZSM-5 is strongly dependent on the structure of the active sites.

scholarly journals Active sites and mechanisms in the direct conversion of methane to methanol using Cu in zeolitic hosts: a critical examination

2020 ◽  
Vol 49 (5) ◽  
pp. 1449-1486 ◽  
Author(s):  
Mark A. Newton ◽  
Amy J. Knorpp ◽  
Vitaly L. Sushkevich ◽  
Dennis Palagin ◽  
Jeroen A. van Bokhoven
Keyword(s):  
Critical Review ◽  
Active Sites ◽  
Direct Conversion ◽  
Critical Examination ◽  
Selective Conversion ◽  
Current State ◽  
Conversion Of Methane

In this critical review we examine the current state of our knowledge in respect of the nature of the active sites in copper containing zeolites for the selective conversion of methane to methanol.

scholarly journals Copper-Modified Zeolites and Silica for Conversion of Methane to Methanol

Catalysts ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 545 ◽  
Author(s):  
Xueting Wang ◽  
Natalia Martin ◽  
Johan Nilsson ◽  
Stefan Carlson ◽  
Johan Gustafson ◽  
...  
Keyword(s):  
Active Sites ◽  
Copper Ions ◽  
Ambient Pressure ◽  
Direct Conversion ◽  
Minor Amount ◽  
Powder Materials ◽  
Methanol Production ◽  
Conversion Of Methane ◽  
First Time

Powder materials containing copper ions supported on ZSM-5 (Cu-Zeolite Socony Mobil-5) and SSZ-13 (Cu-Standard Oil synthesised zeolite-13), and predominantly CuO nanoparticles on amorphous SiO 2 were synthesised, characterised, wash-coated onto ceramic monoliths and, for the first time, compared as catalysts for direct conversion of methane to methanol (DCMM) at ambient pressure (1 atm) using O 2 , N 2 O and NO as oxidants. Methanol production was monitored and quantified using Fourier transform infrared spectroscopy. Methanol is formed over all monolith samples, though the formation is considerably higher for the copper-exchanged zeolites. Hence, copper ions are the main active sites for DCMM. The minor amount of methanol produced over the Cu/SiO 2 sample, however, suggests that zeolites are not the sole substrate that can host those active copper sites but also silica. Further, we present the first ambient pressure in situ infrared spectroscopic measurements revealing the formation and consumption of surface methoxy species, which are considered to be key intermediates in the DCMM reaction.

Application of In Situ X-ray Absorption Spectroscopy to Study Dilute Chromium Ions in a Molten Chloride Salt

2019 ◽  
Author(s):  
Jisue Moon ◽  
Carter Abney ◽  
Dmitriy Dolzhnikov ◽  
James M. Kurley ◽  
Kevin A. Beyer ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Local Structure ◽  
Chloride Salt ◽  
X Ray ◽  
Molten Chloride ◽  
Stable Species ◽  
Higher Temperature ◽  
Cr Concentration ◽  
X Ray Absorption

The local structure of dilute CrCl<sub>3</sub> in a molten MgCl<sub>2</sub>:KCl salt was investigated by <i>in situ</i> x-ray absorption spectroscopy (XAS) at temperatures from room temperature to 800<sup>o</sup>C. This constitutes the first experiment where dilute Cr speciation is explored in a molten chloride salt, ostensibly due to the compounding challenges arising from a low Cr concentration in a matrix of heavy absorbers at extreme temperatures. CrCl<sub>3</sub> was confirmed to be the stable species between 200 and 500<sup>o</sup>C, while mobility of metal ions at higher temperature (>700<sup>o</sup>C) prevented confirmation of the local structure.

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